1 | NAME |
1 | NAME |
2 | AnyEvent - provide framework for multiple event loops |
2 | AnyEvent - provide framework for multiple event loops |
3 | |
3 | |
4 | Event, Coro, Glib, Tk - various supported event loops |
4 | EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported |
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5 | event loops. |
5 | |
6 | |
6 | SYNOPSIS |
7 | SYNOPSIS |
7 | use AnyEvent; |
8 | use AnyEvent; |
8 | |
9 | |
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10 | # file descriptor readable |
9 | my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub { |
11 | my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... }); |
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12 | |
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13 | # one-shot or repeating timers |
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14 | my $w = AnyEvent->timer (after => $seconds, cb => sub { ... }); |
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15 | my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ... |
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16 | |
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17 | print AnyEvent->now; # prints current event loop time |
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18 | print AnyEvent->time; # think Time::HiRes::time or simply CORE::time. |
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19 | |
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20 | # POSIX signal |
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21 | my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... }); |
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22 | |
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23 | # child process exit |
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24 | my $w = AnyEvent->child (pid => $pid, cb => sub { |
10 | my ($poll_got) = @_; |
25 | my ($pid, $status) = @_; |
11 | ... |
26 | ... |
12 | }); |
27 | }); |
13 | |
28 | |
14 | * only one io watcher per $fh and $poll type is allowed (i.e. on a |
29 | # called when event loop idle (if applicable) |
15 | socket you can have one r + one w or one rw watcher, not any more |
30 | my $w = AnyEvent->idle (cb => sub { ... }); |
16 | (limitation by Tk). |
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17 | |
31 | |
18 | * the $poll_got passed to the handler needs to be checked by looking for |
32 | my $w = AnyEvent->condvar; # stores whether a condition was flagged |
19 | single characters (e.g. with a regex), as it can contain more event |
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20 | types than were requested (e.g. a 'w' watcher might generate 'rw' |
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21 | events, limitation by Glib). |
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22 | |
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23 | * AnyEvent will keep filehandles alive, so as long as the watcher |
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24 | exists, the filehandle exists. |
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25 | |
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26 | my $w = AnyEvent->timer (after => $seconds, cb => sub { |
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27 | ... |
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28 | }); |
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29 | |
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30 | * io and time watchers get canceled whenever $w is destroyed, so keep a |
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31 | copy |
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32 | |
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33 | * timers can only be used once and must be recreated for repeated |
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34 | operation (limitation by Glib and Tk). |
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35 | |
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36 | my $w = AnyEvent->condvar; # kind of main loop replacement |
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37 | $w->wait; # enters main loop till $condvar gets ->broadcast |
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38 | $w->broadcast; # wake up current and all future wait's |
33 | $w->send; # wake up current and all future recv's |
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34 | $w->recv; # enters "main loop" till $condvar gets ->send |
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35 | # use a condvar in callback mode: |
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36 | $w->cb (sub { $_[0]->recv }); |
39 | |
37 | |
40 | * condvars are used to give blocking behaviour when neccessary. Create a |
38 | INTRODUCTION/TUTORIAL |
41 | condvar for any "request" or "event" your module might create, |
39 | This manpage is mainly a reference manual. If you are interested in a |
42 | "->broadcast" it when the event happens and provide a function that |
40 | tutorial or some gentle introduction, have a look at the AnyEvent::Intro |
43 | calls "->wait" for it. See the examples below. |
41 | manpage. |
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42 | |
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43 | WHY YOU SHOULD USE THIS MODULE (OR NOT) |
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44 | Glib, POE, IO::Async, Event... CPAN offers event models by the dozen |
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45 | nowadays. So what is different about AnyEvent? |
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46 | |
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47 | Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of |
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48 | policy* and AnyEvent is *small and efficient*. |
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49 | |
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50 | First and foremost, *AnyEvent is not an event model* itself, it only |
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51 | interfaces to whatever event model the main program happens to use, in a |
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52 | pragmatic way. For event models and certain classes of immortals alike, |
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53 | the statement "there can only be one" is a bitter reality: In general, |
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54 | only one event loop can be active at the same time in a process. |
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55 | AnyEvent cannot change this, but it can hide the differences between |
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56 | those event loops. |
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57 | |
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58 | The goal of AnyEvent is to offer module authors the ability to do event |
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59 | programming (waiting for I/O or timer events) without subscribing to a |
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60 | religion, a way of living, and most importantly: without forcing your |
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61 | module users into the same thing by forcing them to use the same event |
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62 | model you use. |
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63 | |
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64 | For modules like POE or IO::Async (which is a total misnomer as it is |
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65 | actually doing all I/O *synchronously*...), using them in your module is |
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66 | like joining a cult: After you joined, you are dependent on them and you |
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67 | cannot use anything else, as they are simply incompatible to everything |
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68 | that isn't them. What's worse, all the potential users of your module |
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69 | are *also* forced to use the same event loop you use. |
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70 | |
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71 | AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works |
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72 | fine. AnyEvent + Tk works fine etc. etc. but none of these work together |
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73 | with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your |
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74 | module uses one of those, every user of your module has to use it, too. |
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75 | But if your module uses AnyEvent, it works transparently with all event |
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76 | models it supports (including stuff like IO::Async, as long as those use |
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77 | one of the supported event loops. It is trivial to add new event loops |
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78 | to AnyEvent, too, so it is future-proof). |
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79 | |
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80 | In addition to being free of having to use *the one and only true event |
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81 | model*, AnyEvent also is free of bloat and policy: with POE or similar |
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82 | modules, you get an enormous amount of code and strict rules you have to |
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83 | follow. AnyEvent, on the other hand, is lean and up to the point, by |
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84 | only offering the functionality that is necessary, in as thin as a |
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85 | wrapper as technically possible. |
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86 | |
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87 | Of course, AnyEvent comes with a big (and fully optional!) toolbox of |
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88 | useful functionality, such as an asynchronous DNS resolver, 100% |
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89 | non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms |
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90 | such as Windows) and lots of real-world knowledge and workarounds for |
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91 | platform bugs and differences. |
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92 | |
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93 | Now, if you *do want* lots of policy (this can arguably be somewhat |
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94 | useful) and you want to force your users to use the one and only event |
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95 | model, you should *not* use this module. |
44 | |
96 | |
45 | DESCRIPTION |
97 | DESCRIPTION |
46 | AnyEvent provides an identical interface to multiple event loops. This |
98 | AnyEvent provides an identical interface to multiple event loops. This |
47 | allows module authors to utilizy an event loop without forcing module |
99 | allows module authors to utilise an event loop without forcing module |
48 | users to use the same event loop (as only a single event loop can |
100 | users to use the same event loop (as only a single event loop can |
49 | coexist peacefully at any one time). |
101 | coexist peacefully at any one time). |
50 | |
102 | |
51 | The interface itself is vaguely similar but not identical to the Event |
103 | The interface itself is vaguely similar, but not identical to the Event |
52 | module. |
104 | module. |
53 | |
105 | |
54 | On the first call of any method, the module tries to detect the |
106 | During the first call of any watcher-creation method, the module tries |
55 | currently loaded event loop by probing wether any of the following |
107 | to detect the currently loaded event loop by probing whether one of the |
56 | modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is |
108 | following modules is already loaded: EV, Event, Glib, |
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109 | AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is |
57 | used. If none is found, the module tries to load these modules in the |
110 | used. If none are found, the module tries to load these modules |
58 | order given. The first one that could be successfully loaded will be |
111 | (excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should |
59 | used. If still none could be found, it will issue an error. |
112 | always succeed) in the order given. The first one that can be |
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113 | successfully loaded will be used. If, after this, still none could be |
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114 | found, AnyEvent will fall back to a pure-perl event loop, which is not |
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115 | very efficient, but should work everywhere. |
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116 | |
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117 | Because AnyEvent first checks for modules that are already loaded, |
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118 | loading an event model explicitly before first using AnyEvent will |
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119 | likely make that model the default. For example: |
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120 | |
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121 | use Tk; |
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122 | use AnyEvent; |
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123 | |
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124 | # .. AnyEvent will likely default to Tk |
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125 | |
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126 | The *likely* means that, if any module loads another event model and |
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127 | starts using it, all bets are off. Maybe you should tell their authors |
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128 | to use AnyEvent so their modules work together with others seamlessly... |
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129 | |
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130 | The pure-perl implementation of AnyEvent is called |
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131 | "AnyEvent::Impl::Perl". Like other event modules you can load it |
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132 | explicitly and enjoy the high availability of that event loop :) |
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133 | |
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134 | WATCHERS |
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135 | AnyEvent has the central concept of a *watcher*, which is an object that |
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136 | stores relevant data for each kind of event you are waiting for, such as |
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137 | the callback to call, the file handle to watch, etc. |
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138 | |
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139 | These watchers are normal Perl objects with normal Perl lifetime. After |
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140 | creating a watcher it will immediately "watch" for events and invoke the |
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141 | callback when the event occurs (of course, only when the event model is |
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142 | in control). |
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143 | |
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144 | Note that callbacks must not permanently change global variables |
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145 | potentially in use by the event loop (such as $_ or $[) and that |
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146 | callbacks must not "die". The former is good programming practise in |
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147 | Perl and the latter stems from the fact that exception handling differs |
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148 | widely between event loops. |
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149 | |
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150 | To disable the watcher you have to destroy it (e.g. by setting the |
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151 | variable you store it in to "undef" or otherwise deleting all references |
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152 | to it). |
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153 | |
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154 | All watchers are created by calling a method on the "AnyEvent" class. |
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155 | |
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156 | Many watchers either are used with "recursion" (repeating timers for |
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157 | example), or need to refer to their watcher object in other ways. |
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158 | |
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159 | An any way to achieve that is this pattern: |
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160 | |
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161 | my $w; $w = AnyEvent->type (arg => value ..., cb => sub { |
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162 | # you can use $w here, for example to undef it |
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163 | undef $w; |
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164 | }); |
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165 | |
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166 | Note that "my $w; $w =" combination. This is necessary because in Perl, |
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167 | my variables are only visible after the statement in which they are |
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168 | declared. |
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169 | |
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170 | I/O WATCHERS |
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171 | You can create an I/O watcher by calling the "AnyEvent->io" method with |
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172 | the following mandatory key-value pairs as arguments: |
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173 | |
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174 | "fh" is the Perl *file handle* (or a naked file descriptor) to watch for |
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175 | events (AnyEvent might or might not keep a reference to this file |
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176 | handle). Note that only file handles pointing to things for which |
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177 | non-blocking operation makes sense are allowed. This includes sockets, |
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178 | most character devices, pipes, fifos and so on, but not for example |
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179 | files or block devices. |
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180 | |
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181 | "poll" must be a string that is either "r" or "w", which creates a |
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182 | watcher waiting for "r"eadable or "w"ritable events, respectively. |
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183 | |
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184 | "cb" is the callback to invoke each time the file handle becomes ready. |
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185 | |
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186 | Although the callback might get passed parameters, their value and |
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187 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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188 | callbacks cannot use arguments passed to I/O watcher callbacks. |
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189 | |
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190 | The I/O watcher might use the underlying file descriptor or a copy of |
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191 | it. You must not close a file handle as long as any watcher is active on |
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192 | the underlying file descriptor. |
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193 | |
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194 | Some event loops issue spurious readyness notifications, so you should |
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195 | always use non-blocking calls when reading/writing from/to your file |
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196 | handles. |
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197 | |
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198 | Example: wait for readability of STDIN, then read a line and disable the |
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199 | watcher. |
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200 | |
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201 | my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
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202 | chomp (my $input = <STDIN>); |
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203 | warn "read: $input\n"; |
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204 | undef $w; |
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205 | }); |
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206 | |
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207 | TIME WATCHERS |
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208 | You can create a time watcher by calling the "AnyEvent->timer" method |
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209 | with the following mandatory arguments: |
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210 | |
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211 | "after" specifies after how many seconds (fractional values are |
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212 | supported) the callback should be invoked. "cb" is the callback to |
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213 | invoke in that case. |
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214 | |
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215 | Although the callback might get passed parameters, their value and |
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216 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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217 | callbacks cannot use arguments passed to time watcher callbacks. |
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218 | |
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219 | The callback will normally be invoked once only. If you specify another |
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220 | parameter, "interval", as a strictly positive number (> 0), then the |
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221 | callback will be invoked regularly at that interval (in fractional |
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222 | seconds) after the first invocation. If "interval" is specified with a |
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223 | false value, then it is treated as if it were missing. |
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224 | |
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225 | The callback will be rescheduled before invoking the callback, but no |
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226 | attempt is done to avoid timer drift in most backends, so the interval |
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227 | is only approximate. |
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228 | |
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229 | Example: fire an event after 7.7 seconds. |
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230 | |
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231 | my $w = AnyEvent->timer (after => 7.7, cb => sub { |
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232 | warn "timeout\n"; |
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233 | }); |
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234 | |
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235 | # to cancel the timer: |
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236 | undef $w; |
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237 | |
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238 | Example 2: fire an event after 0.5 seconds, then roughly every second. |
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239 | |
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240 | my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub { |
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241 | warn "timeout\n"; |
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242 | }; |
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243 | |
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244 | TIMING ISSUES |
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245 | There are two ways to handle timers: based on real time (relative, "fire |
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246 | in 10 seconds") and based on wallclock time (absolute, "fire at 12 |
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247 | o'clock"). |
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248 | |
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249 | While most event loops expect timers to specified in a relative way, |
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250 | they use absolute time internally. This makes a difference when your |
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251 | clock "jumps", for example, when ntp decides to set your clock backwards |
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252 | from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is |
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253 | supposed to fire "after" a second might actually take six years to |
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254 | finally fire. |
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255 | |
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256 | AnyEvent cannot compensate for this. The only event loop that is |
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257 | conscious about these issues is EV, which offers both relative |
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258 | (ev_timer, based on true relative time) and absolute (ev_periodic, based |
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259 | on wallclock time) timers. |
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260 | |
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261 | AnyEvent always prefers relative timers, if available, matching the |
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262 | AnyEvent API. |
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263 | |
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264 | AnyEvent has two additional methods that return the "current time": |
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265 | |
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266 | AnyEvent->time |
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267 | This returns the "current wallclock time" as a fractional number of |
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268 | seconds since the Epoch (the same thing as "time" or |
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269 | "Time::HiRes::time" return, and the result is guaranteed to be |
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270 | compatible with those). |
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271 | |
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272 | It progresses independently of any event loop processing, i.e. each |
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273 | call will check the system clock, which usually gets updated |
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274 | frequently. |
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275 | |
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276 | AnyEvent->now |
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277 | This also returns the "current wallclock time", but unlike "time", |
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278 | above, this value might change only once per event loop iteration, |
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279 | depending on the event loop (most return the same time as "time", |
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280 | above). This is the time that AnyEvent's timers get scheduled |
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281 | against. |
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282 | |
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283 | *In almost all cases (in all cases if you don't care), this is the |
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284 | function to call when you want to know the current time.* |
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285 | |
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286 | This function is also often faster then "AnyEvent->time", and thus |
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287 | the preferred method if you want some timestamp (for example, |
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288 | AnyEvent::Handle uses this to update it's activity timeouts). |
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289 | |
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290 | The rest of this section is only of relevance if you try to be very |
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291 | exact with your timing, you can skip it without bad conscience. |
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292 | |
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293 | For a practical example of when these times differ, consider |
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294 | Event::Lib and EV and the following set-up: |
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295 | |
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296 | The event loop is running and has just invoked one of your callback |
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297 | at time=500 (assume no other callbacks delay processing). In your |
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298 | callback, you wait a second by executing "sleep 1" (blocking the |
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299 | process for a second) and then (at time=501) you create a relative |
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300 | timer that fires after three seconds. |
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301 | |
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302 | With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both |
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303 | return 501, because that is the current time, and the timer will be |
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304 | scheduled to fire at time=504 (501 + 3). |
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305 | |
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306 | With EV, "AnyEvent->time" returns 501 (as that is the current time), |
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307 | but "AnyEvent->now" returns 500, as that is the time the last event |
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308 | processing phase started. With EV, your timer gets scheduled to run |
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309 | at time=503 (500 + 3). |
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310 | |
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311 | In one sense, Event::Lib is more exact, as it uses the current time |
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312 | regardless of any delays introduced by event processing. However, |
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313 | most callbacks do not expect large delays in processing, so this |
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314 | causes a higher drift (and a lot more system calls to get the |
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315 | current time). |
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316 | |
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317 | In another sense, EV is more exact, as your timer will be scheduled |
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318 | at the same time, regardless of how long event processing actually |
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319 | took. |
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320 | |
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321 | In either case, if you care (and in most cases, you don't), then you |
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322 | can get whatever behaviour you want with any event loop, by taking |
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323 | the difference between "AnyEvent->time" and "AnyEvent->now" into |
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324 | account. |
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325 | |
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326 | AnyEvent->now_update |
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327 | Some event loops (such as EV or AnyEvent::Impl::Perl) cache the |
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328 | current time for each loop iteration (see the discussion of |
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329 | AnyEvent->now, above). |
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330 | |
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331 | When a callback runs for a long time (or when the process sleeps), |
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332 | then this "current" time will differ substantially from the real |
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333 | time, which might affect timers and time-outs. |
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334 | |
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335 | When this is the case, you can call this method, which will update |
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336 | the event loop's idea of "current time". |
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337 | |
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338 | Note that updating the time *might* cause some events to be handled. |
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339 | |
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340 | SIGNAL WATCHERS |
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341 | You can watch for signals using a signal watcher, "signal" is the signal |
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342 | *name* in uppercase and without any "SIG" prefix, "cb" is the Perl |
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343 | callback to be invoked whenever a signal occurs. |
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344 | |
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345 | Although the callback might get passed parameters, their value and |
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346 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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347 | callbacks cannot use arguments passed to signal watcher callbacks. |
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348 | |
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349 | Multiple signal occurrences can be clumped together into one callback |
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350 | invocation, and callback invocation will be synchronous. Synchronous |
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351 | means that it might take a while until the signal gets handled by the |
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352 | process, but it is guaranteed not to interrupt any other callbacks. |
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353 | |
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354 | The main advantage of using these watchers is that you can share a |
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355 | signal between multiple watchers, and AnyEvent will ensure that signals |
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356 | will not interrupt your program at bad times. |
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357 | |
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358 | This watcher might use %SIG (depending on the event loop used), so |
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359 | programs overwriting those signals directly will likely not work |
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360 | correctly. |
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361 | |
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362 | Also note that many event loops (e.g. Glib, Tk, Qt, IO::Async) do not |
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363 | support attaching callbacks to signals, which is a pity, as you cannot |
|
|
364 | do race-free signal handling in perl. AnyEvent will try to do it's best, |
|
|
365 | but in some cases, signals will be delayed. The maximum time a signal |
|
|
366 | might be delayed is specified in $AnyEvent::MAX_SIGNAL_LATENCY (default: |
|
|
367 | 10 seconds). This variable can be changed only before the first signal |
|
|
368 | watcher is created, and should be left alone otherwise. Higher values |
|
|
369 | will cause fewer spurious wake-ups, which is better for power and CPU |
|
|
370 | saving. All these problems can be avoided by installing the optional |
|
|
371 | Async::Interrupt module. |
|
|
372 | |
|
|
373 | Example: exit on SIGINT |
|
|
374 | |
|
|
375 | my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); |
|
|
376 | |
|
|
377 | CHILD PROCESS WATCHERS |
|
|
378 | You can also watch on a child process exit and catch its exit status. |
|
|
379 | |
|
|
380 | The child process is specified by the "pid" argument (if set to 0, it |
|
|
381 | watches for any child process exit). The watcher will triggered only |
|
|
382 | when the child process has finished and an exit status is available, not |
|
|
383 | on any trace events (stopped/continued). |
|
|
384 | |
|
|
385 | The callback will be called with the pid and exit status (as returned by |
|
|
386 | waitpid), so unlike other watcher types, you *can* rely on child watcher |
|
|
387 | callback arguments. |
|
|
388 | |
|
|
389 | This watcher type works by installing a signal handler for "SIGCHLD", |
|
|
390 | and since it cannot be shared, nothing else should use SIGCHLD or reap |
|
|
391 | random child processes (waiting for specific child processes, e.g. |
|
|
392 | inside "system", is just fine). |
|
|
393 | |
|
|
394 | There is a slight catch to child watchers, however: you usually start |
|
|
395 | them *after* the child process was created, and this means the process |
|
|
396 | could have exited already (and no SIGCHLD will be sent anymore). |
|
|
397 | |
|
|
398 | Not all event models handle this correctly (neither POE nor IO::Async |
|
|
399 | do, see their AnyEvent::Impl manpages for details), but even for event |
|
|
400 | models that *do* handle this correctly, they usually need to be loaded |
|
|
401 | before the process exits (i.e. before you fork in the first place). |
|
|
402 | AnyEvent's pure perl event loop handles all cases correctly regardless |
|
|
403 | of when you start the watcher. |
|
|
404 | |
|
|
405 | This means you cannot create a child watcher as the very first thing in |
|
|
406 | an AnyEvent program, you *have* to create at least one watcher before |
|
|
407 | you "fork" the child (alternatively, you can call "AnyEvent::detect"). |
|
|
408 | |
|
|
409 | As most event loops do not support waiting for child events, they will |
|
|
410 | be emulated by AnyEvent in most cases, in which the latency and race |
|
|
411 | problems mentioned in the description of signal watchers apply. |
|
|
412 | |
|
|
413 | Example: fork a process and wait for it |
|
|
414 | |
|
|
415 | my $done = AnyEvent->condvar; |
|
|
416 | |
|
|
417 | my $pid = fork or exit 5; |
|
|
418 | |
|
|
419 | my $w = AnyEvent->child ( |
|
|
420 | pid => $pid, |
|
|
421 | cb => sub { |
|
|
422 | my ($pid, $status) = @_; |
|
|
423 | warn "pid $pid exited with status $status"; |
|
|
424 | $done->send; |
|
|
425 | }, |
|
|
426 | ); |
|
|
427 | |
|
|
428 | # do something else, then wait for process exit |
|
|
429 | $done->recv; |
|
|
430 | |
|
|
431 | IDLE WATCHERS |
|
|
432 | Sometimes there is a need to do something, but it is not so important to |
|
|
433 | do it instantly, but only when there is nothing better to do. This |
|
|
434 | "nothing better to do" is usually defined to be "no other events need |
|
|
435 | attention by the event loop". |
|
|
436 | |
|
|
437 | Idle watchers ideally get invoked when the event loop has nothing better |
|
|
438 | to do, just before it would block the process to wait for new events. |
|
|
439 | Instead of blocking, the idle watcher is invoked. |
|
|
440 | |
|
|
441 | Most event loops unfortunately do not really support idle watchers (only |
|
|
442 | EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent |
|
|
443 | will simply call the callback "from time to time". |
|
|
444 | |
|
|
445 | Example: read lines from STDIN, but only process them when the program |
|
|
446 | is otherwise idle: |
|
|
447 | |
|
|
448 | my @lines; # read data |
|
|
449 | my $idle_w; |
|
|
450 | my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
|
|
451 | push @lines, scalar <STDIN>; |
|
|
452 | |
|
|
453 | # start an idle watcher, if not already done |
|
|
454 | $idle_w ||= AnyEvent->idle (cb => sub { |
|
|
455 | # handle only one line, when there are lines left |
|
|
456 | if (my $line = shift @lines) { |
|
|
457 | print "handled when idle: $line"; |
|
|
458 | } else { |
|
|
459 | # otherwise disable the idle watcher again |
|
|
460 | undef $idle_w; |
|
|
461 | } |
|
|
462 | }); |
|
|
463 | }); |
|
|
464 | |
|
|
465 | CONDITION VARIABLES |
|
|
466 | If you are familiar with some event loops you will know that all of them |
|
|
467 | require you to run some blocking "loop", "run" or similar function that |
|
|
468 | will actively watch for new events and call your callbacks. |
|
|
469 | |
|
|
470 | AnyEvent is slightly different: it expects somebody else to run the |
|
|
471 | event loop and will only block when necessary (usually when told by the |
|
|
472 | user). |
|
|
473 | |
|
|
474 | The instrument to do that is called a "condition variable", so called |
|
|
475 | because they represent a condition that must become true. |
|
|
476 | |
|
|
477 | Now is probably a good time to look at the examples further below. |
|
|
478 | |
|
|
479 | Condition variables can be created by calling the "AnyEvent->condvar" |
|
|
480 | method, usually without arguments. The only argument pair allowed is |
|
|
481 | "cb", which specifies a callback to be called when the condition |
|
|
482 | variable becomes true, with the condition variable as the first argument |
|
|
483 | (but not the results). |
|
|
484 | |
|
|
485 | After creation, the condition variable is "false" until it becomes |
|
|
486 | "true" by calling the "send" method (or calling the condition variable |
|
|
487 | as if it were a callback, read about the caveats in the description for |
|
|
488 | the "->send" method). |
|
|
489 | |
|
|
490 | Condition variables are similar to callbacks, except that you can |
|
|
491 | optionally wait for them. They can also be called merge points - points |
|
|
492 | in time where multiple outstanding events have been processed. And yet |
|
|
493 | another way to call them is transactions - each condition variable can |
|
|
494 | be used to represent a transaction, which finishes at some point and |
|
|
495 | delivers a result. |
|
|
496 | |
|
|
497 | Condition variables are very useful to signal that something has |
|
|
498 | finished, for example, if you write a module that does asynchronous http |
|
|
499 | requests, then a condition variable would be the ideal candidate to |
|
|
500 | signal the availability of results. The user can either act when the |
|
|
501 | callback is called or can synchronously "->recv" for the results. |
|
|
502 | |
|
|
503 | You can also use them to simulate traditional event loops - for example, |
|
|
504 | you can block your main program until an event occurs - for example, you |
|
|
505 | could "->recv" in your main program until the user clicks the Quit |
|
|
506 | button of your app, which would "->send" the "quit" event. |
|
|
507 | |
|
|
508 | Note that condition variables recurse into the event loop - if you have |
|
|
509 | two pieces of code that call "->recv" in a round-robin fashion, you |
|
|
510 | lose. Therefore, condition variables are good to export to your caller, |
|
|
511 | but you should avoid making a blocking wait yourself, at least in |
|
|
512 | callbacks, as this asks for trouble. |
|
|
513 | |
|
|
514 | Condition variables are represented by hash refs in perl, and the keys |
|
|
515 | used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy |
|
|
516 | (it is often useful to build your own transaction class on top of |
|
|
517 | AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call |
|
|
518 | it's "new" method in your own "new" method. |
|
|
519 | |
|
|
520 | There are two "sides" to a condition variable - the "producer side" |
|
|
521 | which eventually calls "-> send", and the "consumer side", which waits |
|
|
522 | for the send to occur. |
|
|
523 | |
|
|
524 | Example: wait for a timer. |
|
|
525 | |
|
|
526 | # wait till the result is ready |
|
|
527 | my $result_ready = AnyEvent->condvar; |
|
|
528 | |
|
|
529 | # do something such as adding a timer |
|
|
530 | # or socket watcher the calls $result_ready->send |
|
|
531 | # when the "result" is ready. |
|
|
532 | # in this case, we simply use a timer: |
|
|
533 | my $w = AnyEvent->timer ( |
|
|
534 | after => 1, |
|
|
535 | cb => sub { $result_ready->send }, |
|
|
536 | ); |
|
|
537 | |
|
|
538 | # this "blocks" (while handling events) till the callback |
|
|
539 | # calls -<send |
|
|
540 | $result_ready->recv; |
|
|
541 | |
|
|
542 | Example: wait for a timer, but take advantage of the fact that condition |
|
|
543 | variables are also callable directly. |
|
|
544 | |
|
|
545 | my $done = AnyEvent->condvar; |
|
|
546 | my $delay = AnyEvent->timer (after => 5, cb => $done); |
|
|
547 | $done->recv; |
|
|
548 | |
|
|
549 | Example: Imagine an API that returns a condvar and doesn't support |
|
|
550 | callbacks. This is how you make a synchronous call, for example from the |
|
|
551 | main program: |
|
|
552 | |
|
|
553 | use AnyEvent::CouchDB; |
|
|
554 | |
|
|
555 | ... |
|
|
556 | |
|
|
557 | my @info = $couchdb->info->recv; |
|
|
558 | |
|
|
559 | And this is how you would just set a callback to be called whenever the |
|
|
560 | results are available: |
|
|
561 | |
|
|
562 | $couchdb->info->cb (sub { |
|
|
563 | my @info = $_[0]->recv; |
|
|
564 | }); |
|
|
565 | |
|
|
566 | METHODS FOR PRODUCERS |
|
|
567 | These methods should only be used by the producing side, i.e. the |
|
|
568 | code/module that eventually sends the signal. Note that it is also the |
|
|
569 | producer side which creates the condvar in most cases, but it isn't |
|
|
570 | uncommon for the consumer to create it as well. |
|
|
571 | |
|
|
572 | $cv->send (...) |
|
|
573 | Flag the condition as ready - a running "->recv" and all further |
|
|
574 | calls to "recv" will (eventually) return after this method has been |
|
|
575 | called. If nobody is waiting the send will be remembered. |
|
|
576 | |
|
|
577 | If a callback has been set on the condition variable, it is called |
|
|
578 | immediately from within send. |
|
|
579 | |
|
|
580 | Any arguments passed to the "send" call will be returned by all |
|
|
581 | future "->recv" calls. |
|
|
582 | |
|
|
583 | Condition variables are overloaded so one can call them directly (as |
|
|
584 | if they were a code reference). Calling them directly is the same as |
|
|
585 | calling "send". |
|
|
586 | |
|
|
587 | $cv->croak ($error) |
|
|
588 | Similar to send, but causes all call's to "->recv" to invoke |
|
|
589 | "Carp::croak" with the given error message/object/scalar. |
|
|
590 | |
|
|
591 | This can be used to signal any errors to the condition variable |
|
|
592 | user/consumer. Doing it this way instead of calling "croak" directly |
|
|
593 | delays the error detetcion, but has the overwhelmign advantage that |
|
|
594 | it diagnoses the error at the place where the result is expected, |
|
|
595 | and not deep in some event clalback without connection to the actual |
|
|
596 | code causing the problem. |
|
|
597 | |
|
|
598 | $cv->begin ([group callback]) |
|
|
599 | $cv->end |
|
|
600 | These two methods can be used to combine many transactions/events |
|
|
601 | into one. For example, a function that pings many hosts in parallel |
|
|
602 | might want to use a condition variable for the whole process. |
|
|
603 | |
|
|
604 | Every call to "->begin" will increment a counter, and every call to |
|
|
605 | "->end" will decrement it. If the counter reaches 0 in "->end", the |
|
|
606 | (last) callback passed to "begin" will be executed. That callback is |
|
|
607 | *supposed* to call "->send", but that is not required. If no |
|
|
608 | callback was set, "send" will be called without any arguments. |
|
|
609 | |
|
|
610 | You can think of "$cv->send" giving you an OR condition (one call |
|
|
611 | sends), while "$cv->begin" and "$cv->end" giving you an AND |
|
|
612 | condition (all "begin" calls must be "end"'ed before the condvar |
|
|
613 | sends). |
|
|
614 | |
|
|
615 | Let's start with a simple example: you have two I/O watchers (for |
|
|
616 | example, STDOUT and STDERR for a program), and you want to wait for |
|
|
617 | both streams to close before activating a condvar: |
|
|
618 | |
|
|
619 | my $cv = AnyEvent->condvar; |
|
|
620 | |
|
|
621 | $cv->begin; # first watcher |
|
|
622 | my $w1 = AnyEvent->io (fh => $fh1, cb => sub { |
|
|
623 | defined sysread $fh1, my $buf, 4096 |
|
|
624 | or $cv->end; |
|
|
625 | }); |
|
|
626 | |
|
|
627 | $cv->begin; # second watcher |
|
|
628 | my $w2 = AnyEvent->io (fh => $fh2, cb => sub { |
|
|
629 | defined sysread $fh2, my $buf, 4096 |
|
|
630 | or $cv->end; |
|
|
631 | }); |
|
|
632 | |
|
|
633 | $cv->recv; |
|
|
634 | |
|
|
635 | This works because for every event source (EOF on file handle), |
|
|
636 | there is one call to "begin", so the condvar waits for all calls to |
|
|
637 | "end" before sending. |
|
|
638 | |
|
|
639 | The ping example mentioned above is slightly more complicated, as |
|
|
640 | the there are results to be passwd back, and the number of tasks |
|
|
641 | that are begung can potentially be zero: |
|
|
642 | |
|
|
643 | my $cv = AnyEvent->condvar; |
|
|
644 | |
|
|
645 | my %result; |
|
|
646 | $cv->begin (sub { $cv->send (\%result) }); |
|
|
647 | |
|
|
648 | for my $host (@list_of_hosts) { |
|
|
649 | $cv->begin; |
|
|
650 | ping_host_then_call_callback $host, sub { |
|
|
651 | $result{$host} = ...; |
|
|
652 | $cv->end; |
|
|
653 | }; |
|
|
654 | } |
|
|
655 | |
|
|
656 | $cv->end; |
|
|
657 | |
|
|
658 | This code fragment supposedly pings a number of hosts and calls |
|
|
659 | "send" after results for all then have have been gathered - in any |
|
|
660 | order. To achieve this, the code issues a call to "begin" when it |
|
|
661 | starts each ping request and calls "end" when it has received some |
|
|
662 | result for it. Since "begin" and "end" only maintain a counter, the |
|
|
663 | order in which results arrive is not relevant. |
|
|
664 | |
|
|
665 | There is an additional bracketing call to "begin" and "end" outside |
|
|
666 | the loop, which serves two important purposes: first, it sets the |
|
|
667 | callback to be called once the counter reaches 0, and second, it |
|
|
668 | ensures that "send" is called even when "no" hosts are being pinged |
|
|
669 | (the loop doesn't execute once). |
|
|
670 | |
|
|
671 | This is the general pattern when you "fan out" into multiple (but |
|
|
672 | potentially none) subrequests: use an outer "begin"/"end" pair to |
|
|
673 | set the callback and ensure "end" is called at least once, and then, |
|
|
674 | for each subrequest you start, call "begin" and for each subrequest |
|
|
675 | you finish, call "end". |
|
|
676 | |
|
|
677 | METHODS FOR CONSUMERS |
|
|
678 | These methods should only be used by the consuming side, i.e. the code |
|
|
679 | awaits the condition. |
|
|
680 | |
|
|
681 | $cv->recv |
|
|
682 | Wait (blocking if necessary) until the "->send" or "->croak" methods |
|
|
683 | have been called on c<$cv>, while servicing other watchers normally. |
|
|
684 | |
|
|
685 | You can only wait once on a condition - additional calls are valid |
|
|
686 | but will return immediately. |
|
|
687 | |
|
|
688 | If an error condition has been set by calling "->croak", then this |
|
|
689 | function will call "croak". |
|
|
690 | |
|
|
691 | In list context, all parameters passed to "send" will be returned, |
|
|
692 | in scalar context only the first one will be returned. |
|
|
693 | |
|
|
694 | Note that doing a blocking wait in a callback is not supported by |
|
|
695 | any event loop, that is, recursive invocation of a blocking "->recv" |
|
|
696 | is not allowed, and the "recv" call will "croak" if such a condition |
|
|
697 | is detected. This condition can be slightly loosened by using |
|
|
698 | Coro::AnyEvent, which allows you to do a blocking "->recv" from any |
|
|
699 | thread that doesn't run the event loop itself. |
|
|
700 | |
|
|
701 | Not all event models support a blocking wait - some die in that case |
|
|
702 | (programs might want to do that to stay interactive), so *if you are |
|
|
703 | using this from a module, never require a blocking wait*. Instead, |
|
|
704 | let the caller decide whether the call will block or not (for |
|
|
705 | example, by coupling condition variables with some kind of request |
|
|
706 | results and supporting callbacks so the caller knows that getting |
|
|
707 | the result will not block, while still supporting blocking waits if |
|
|
708 | the caller so desires). |
|
|
709 | |
|
|
710 | You can ensure that "-recv" never blocks by setting a callback and |
|
|
711 | only calling "->recv" from within that callback (or at a later |
|
|
712 | time). This will work even when the event loop does not support |
|
|
713 | blocking waits otherwise. |
|
|
714 | |
|
|
715 | $bool = $cv->ready |
|
|
716 | Returns true when the condition is "true", i.e. whether "send" or |
|
|
717 | "croak" have been called. |
|
|
718 | |
|
|
719 | $cb = $cv->cb ($cb->($cv)) |
|
|
720 | This is a mutator function that returns the callback set and |
|
|
721 | optionally replaces it before doing so. |
|
|
722 | |
|
|
723 | The callback will be called when the condition becomes "true", i.e. |
|
|
724 | when "send" or "croak" are called, with the only argument being the |
|
|
725 | condition variable itself. Calling "recv" inside the callback or at |
|
|
726 | any later time is guaranteed not to block. |
|
|
727 | |
|
|
728 | SUPPORTED EVENT LOOPS/BACKENDS |
|
|
729 | The available backend classes are (every class has its own manpage): |
|
|
730 | |
|
|
731 | Backends that are autoprobed when no other event loop can be found. |
|
|
732 | EV is the preferred backend when no other event loop seems to be in |
|
|
733 | use. If EV is not installed, then AnyEvent will try Event, and, |
|
|
734 | failing that, will fall back to its own pure-perl implementation, |
|
|
735 | which is available everywhere as it comes with AnyEvent itself. |
|
|
736 | |
|
|
737 | AnyEvent::Impl::EV based on EV (interface to libev, best choice). |
|
|
738 | AnyEvent::Impl::Event based on Event, very stable, few glitches. |
|
|
739 | AnyEvent::Impl::Perl pure-perl implementation, fast and portable. |
|
|
740 | |
|
|
741 | Backends that are transparently being picked up when they are used. |
|
|
742 | These will be used when they are currently loaded when the first |
|
|
743 | watcher is created, in which case it is assumed that the application |
|
|
744 | is using them. This means that AnyEvent will automatically pick the |
|
|
745 | right backend when the main program loads an event module before |
|
|
746 | anything starts to create watchers. Nothing special needs to be done |
|
|
747 | by the main program. |
|
|
748 | |
|
|
749 | AnyEvent::Impl::Glib based on Glib, slow but very stable. |
|
|
750 | AnyEvent::Impl::Tk based on Tk, very broken. |
|
|
751 | AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
|
|
752 | AnyEvent::Impl::POE based on POE, very slow, some limitations. |
|
|
753 | |
|
|
754 | Backends with special needs. |
|
|
755 | Qt requires the Qt::Application to be instantiated first, but will |
|
|
756 | otherwise be picked up automatically. As long as the main program |
|
|
757 | instantiates the application before any AnyEvent watchers are |
|
|
758 | created, everything should just work. |
|
|
759 | |
|
|
760 | AnyEvent::Impl::Qt based on Qt. |
|
|
761 | |
|
|
762 | Support for IO::Async can only be partial, as it is too broken and |
|
|
763 | architecturally limited to even support the AnyEvent API. It also is |
|
|
764 | the only event loop that needs the loop to be set explicitly, so it |
|
|
765 | can only be used by a main program knowing about AnyEvent. See |
|
|
766 | AnyEvent::Impl::Async for the gory details. |
|
|
767 | |
|
|
768 | AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed. |
|
|
769 | |
|
|
770 | Event loops that are indirectly supported via other backends. |
|
|
771 | Some event loops can be supported via other modules: |
|
|
772 | |
|
|
773 | There is no direct support for WxWidgets (Wx) or Prima. |
|
|
774 | |
|
|
775 | WxWidgets has no support for watching file handles. However, you can |
|
|
776 | use WxWidgets through the POE adaptor, as POE has a Wx backend that |
|
|
777 | simply polls 20 times per second, which was considered to be too |
|
|
778 | horrible to even consider for AnyEvent. |
|
|
779 | |
|
|
780 | Prima is not supported as nobody seems to be using it, but it has a |
|
|
781 | POE backend, so it can be supported through POE. |
|
|
782 | |
|
|
783 | AnyEvent knows about both Prima and Wx, however, and will try to |
|
|
784 | load POE when detecting them, in the hope that POE will pick them |
|
|
785 | up, in which case everything will be automatic. |
|
|
786 | |
|
|
787 | GLOBAL VARIABLES AND FUNCTIONS |
|
|
788 | These are not normally required to use AnyEvent, but can be useful to |
|
|
789 | write AnyEvent extension modules. |
|
|
790 | |
|
|
791 | $AnyEvent::MODEL |
|
|
792 | Contains "undef" until the first watcher is being created, before |
|
|
793 | the backend has been autodetected. |
|
|
794 | |
|
|
795 | Afterwards it contains the event model that is being used, which is |
|
|
796 | the name of the Perl class implementing the model. This class is |
|
|
797 | usually one of the "AnyEvent::Impl:xxx" modules, but can be any |
|
|
798 | other class in the case AnyEvent has been extended at runtime (e.g. |
|
|
799 | in *rxvt-unicode* it will be "urxvt::anyevent"). |
|
|
800 | |
|
|
801 | AnyEvent::detect |
|
|
802 | Returns $AnyEvent::MODEL, forcing autodetection of the event model |
|
|
803 | if necessary. You should only call this function right before you |
|
|
804 | would have created an AnyEvent watcher anyway, that is, as late as |
|
|
805 | possible at runtime, and not e.g. while initialising of your module. |
|
|
806 | |
|
|
807 | If you need to do some initialisation before AnyEvent watchers are |
|
|
808 | created, use "post_detect". |
|
|
809 | |
|
|
810 | $guard = AnyEvent::post_detect { BLOCK } |
|
|
811 | Arranges for the code block to be executed as soon as the event |
|
|
812 | model is autodetected (or immediately if this has already happened). |
|
|
813 | |
|
|
814 | The block will be executed *after* the actual backend has been |
|
|
815 | detected ($AnyEvent::MODEL is set), but *before* any watchers have |
|
|
816 | been created, so it is possible to e.g. patch @AnyEvent::ISA or do |
|
|
817 | other initialisations - see the sources of AnyEvent::Strict or |
|
|
818 | AnyEvent::AIO to see how this is used. |
|
|
819 | |
|
|
820 | The most common usage is to create some global watchers, without |
|
|
821 | forcing event module detection too early, for example, AnyEvent::AIO |
|
|
822 | creates and installs the global IO::AIO watcher in a "post_detect" |
|
|
823 | block to avoid autodetecting the event module at load time. |
|
|
824 | |
|
|
825 | If called in scalar or list context, then it creates and returns an |
|
|
826 | object that automatically removes the callback again when it is |
|
|
827 | destroyed. See Coro::BDB for a case where this is useful. |
|
|
828 | |
|
|
829 | @AnyEvent::post_detect |
|
|
830 | If there are any code references in this array (you can "push" to it |
|
|
831 | before or after loading AnyEvent), then they will called directly |
|
|
832 | after the event loop has been chosen. |
|
|
833 | |
|
|
834 | You should check $AnyEvent::MODEL before adding to this array, |
|
|
835 | though: if it is defined then the event loop has already been |
|
|
836 | detected, and the array will be ignored. |
|
|
837 | |
|
|
838 | Best use "AnyEvent::post_detect { BLOCK }" when your application |
|
|
839 | allows it,as it takes care of these details. |
|
|
840 | |
|
|
841 | This variable is mainly useful for modules that can do something |
|
|
842 | useful when AnyEvent is used and thus want to know when it is |
|
|
843 | initialised, but do not need to even load it by default. This array |
|
|
844 | provides the means to hook into AnyEvent passively, without loading |
|
|
845 | it. |
|
|
846 | |
|
|
847 | WHAT TO DO IN A MODULE |
|
|
848 | As a module author, you should "use AnyEvent" and call AnyEvent methods |
|
|
849 | freely, but you should not load a specific event module or rely on it. |
|
|
850 | |
|
|
851 | Be careful when you create watchers in the module body - AnyEvent will |
|
|
852 | decide which event module to use as soon as the first method is called, |
|
|
853 | so by calling AnyEvent in your module body you force the user of your |
|
|
854 | module to load the event module first. |
|
|
855 | |
|
|
856 | Never call "->recv" on a condition variable unless you *know* that the |
|
|
857 | "->send" method has been called on it already. This is because it will |
|
|
858 | stall the whole program, and the whole point of using events is to stay |
|
|
859 | interactive. |
|
|
860 | |
|
|
861 | It is fine, however, to call "->recv" when the user of your module |
|
|
862 | requests it (i.e. if you create a http request object ad have a method |
|
|
863 | called "results" that returns the results, it should call "->recv" |
|
|
864 | freely, as the user of your module knows what she is doing. always). |
|
|
865 | |
|
|
866 | WHAT TO DO IN THE MAIN PROGRAM |
|
|
867 | There will always be a single main program - the only place that should |
|
|
868 | dictate which event model to use. |
|
|
869 | |
|
|
870 | If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
|
|
871 | do anything special (it does not need to be event-based) and let |
|
|
872 | AnyEvent decide which implementation to chose if some module relies on |
|
|
873 | it. |
|
|
874 | |
|
|
875 | If the main program relies on a specific event model - for example, in |
|
|
876 | Gtk2 programs you have to rely on the Glib module - you should load the |
|
|
877 | event module before loading AnyEvent or any module that uses it: |
|
|
878 | generally speaking, you should load it as early as possible. The reason |
|
|
879 | is that modules might create watchers when they are loaded, and AnyEvent |
|
|
880 | will decide on the event model to use as soon as it creates watchers, |
|
|
881 | and it might chose the wrong one unless you load the correct one |
|
|
882 | yourself. |
|
|
883 | |
|
|
884 | You can chose to use a pure-perl implementation by loading the |
|
|
885 | "AnyEvent::Impl::Perl" module, which gives you similar behaviour |
|
|
886 | everywhere, but letting AnyEvent chose the model is generally better. |
|
|
887 | |
|
|
888 | MAINLOOP EMULATION |
|
|
889 | Sometimes (often for short test scripts, or even standalone programs who |
|
|
890 | only want to use AnyEvent), you do not want to run a specific event |
|
|
891 | loop. |
|
|
892 | |
|
|
893 | In that case, you can use a condition variable like this: |
|
|
894 | |
|
|
895 | AnyEvent->condvar->recv; |
|
|
896 | |
|
|
897 | This has the effect of entering the event loop and looping forever. |
|
|
898 | |
|
|
899 | Note that usually your program has some exit condition, in which case it |
|
|
900 | is better to use the "traditional" approach of storing a condition |
|
|
901 | variable somewhere, waiting for it, and sending it when the program |
|
|
902 | should exit cleanly. |
|
|
903 | |
|
|
904 | OTHER MODULES |
|
|
905 | The following is a non-exhaustive list of additional modules that use |
|
|
906 | AnyEvent as a client and can therefore be mixed easily with other |
|
|
907 | AnyEvent modules and other event loops in the same program. Some of the |
|
|
908 | modules come with AnyEvent, most are available via CPAN. |
|
|
909 | |
|
|
910 | AnyEvent::Util |
|
|
911 | Contains various utility functions that replace often-used but |
|
|
912 | blocking functions such as "inet_aton" by event-/callback-based |
|
|
913 | versions. |
|
|
914 | |
|
|
915 | AnyEvent::Socket |
|
|
916 | Provides various utility functions for (internet protocol) sockets, |
|
|
917 | addresses and name resolution. Also functions to create non-blocking |
|
|
918 | tcp connections or tcp servers, with IPv6 and SRV record support and |
|
|
919 | more. |
|
|
920 | |
|
|
921 | AnyEvent::Handle |
|
|
922 | Provide read and write buffers, manages watchers for reads and |
|
|
923 | writes, supports raw and formatted I/O, I/O queued and fully |
|
|
924 | transparent and non-blocking SSL/TLS (via AnyEvent::TLS. |
|
|
925 | |
|
|
926 | AnyEvent::DNS |
|
|
927 | Provides rich asynchronous DNS resolver capabilities. |
|
|
928 | |
|
|
929 | AnyEvent::HTTP |
|
|
930 | A simple-to-use HTTP library that is capable of making a lot of |
|
|
931 | concurrent HTTP requests. |
|
|
932 | |
|
|
933 | AnyEvent::HTTPD |
|
|
934 | Provides a simple web application server framework. |
|
|
935 | |
|
|
936 | AnyEvent::FastPing |
|
|
937 | The fastest ping in the west. |
|
|
938 | |
|
|
939 | AnyEvent::DBI |
|
|
940 | Executes DBI requests asynchronously in a proxy process. |
|
|
941 | |
|
|
942 | AnyEvent::AIO |
|
|
943 | Truly asynchronous I/O, should be in the toolbox of every event |
|
|
944 | programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent |
|
|
945 | together. |
|
|
946 | |
|
|
947 | AnyEvent::BDB |
|
|
948 | Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently |
|
|
949 | fuses BDB and AnyEvent together. |
|
|
950 | |
|
|
951 | AnyEvent::GPSD |
|
|
952 | A non-blocking interface to gpsd, a daemon delivering GPS |
|
|
953 | information. |
|
|
954 | |
|
|
955 | AnyEvent::IRC |
|
|
956 | AnyEvent based IRC client module family (replacing the older |
|
|
957 | Net::IRC3). |
|
|
958 | |
|
|
959 | AnyEvent::XMPP |
|
|
960 | AnyEvent based XMPP (Jabber protocol) module family (replacing the |
|
|
961 | older Net::XMPP2>. |
|
|
962 | |
|
|
963 | AnyEvent::IGS |
|
|
964 | A non-blocking interface to the Internet Go Server protocol (used by |
|
|
965 | App::IGS). |
|
|
966 | |
|
|
967 | Net::FCP |
|
|
968 | AnyEvent-based implementation of the Freenet Client Protocol, |
|
|
969 | birthplace of AnyEvent. |
|
|
970 | |
|
|
971 | Event::ExecFlow |
|
|
972 | High level API for event-based execution flow control. |
|
|
973 | |
|
|
974 | Coro |
|
|
975 | Has special support for AnyEvent via Coro::AnyEvent. |
|
|
976 | |
|
|
977 | ERROR AND EXCEPTION HANDLING |
|
|
978 | In general, AnyEvent does not do any error handling - it relies on the |
|
|
979 | caller to do that if required. The AnyEvent::Strict module (see also the |
|
|
980 | "PERL_ANYEVENT_STRICT" environment variable, below) provides strict |
|
|
981 | checking of all AnyEvent methods, however, which is highly useful during |
|
|
982 | development. |
|
|
983 | |
|
|
984 | As for exception handling (i.e. runtime errors and exceptions thrown |
|
|
985 | while executing a callback), this is not only highly event-loop |
|
|
986 | specific, but also not in any way wrapped by this module, as this is the |
|
|
987 | job of the main program. |
|
|
988 | |
|
|
989 | The pure perl event loop simply re-throws the exception (usually within |
|
|
990 | "condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()", |
|
|
991 | Glib uses "install_exception_handler" and so on. |
60 | |
992 | |
61 | ENVIRONMENT VARIABLES |
993 | ENVIRONMENT VARIABLES |
62 | The following environment variables are used by this module: |
994 | The following environment variables are used by this module or its |
|
|
995 | submodules. |
63 | |
996 | |
64 | "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event |
997 | Note that AnyEvent will remove *all* environment variables starting with |
65 | model gets used. |
998 | "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is |
|
|
999 | enabled. |
66 | |
1000 | |
67 | EXAMPLE |
1001 | "PERL_ANYEVENT_VERBOSE" |
|
|
1002 | By default, AnyEvent will be completely silent except in fatal |
|
|
1003 | conditions. You can set this environment variable to make AnyEvent |
|
|
1004 | more talkative. |
|
|
1005 | |
|
|
1006 | When set to 1 or higher, causes AnyEvent to warn about unexpected |
|
|
1007 | conditions, such as not being able to load the event model specified |
|
|
1008 | by "PERL_ANYEVENT_MODEL". |
|
|
1009 | |
|
|
1010 | When set to 2 or higher, cause AnyEvent to report to STDERR which |
|
|
1011 | event model it chooses. |
|
|
1012 | |
|
|
1013 | When set to 8 or higher, then AnyEvent will report extra information |
|
|
1014 | on which optional modules it loads and how it implements certain |
|
|
1015 | features. |
|
|
1016 | |
|
|
1017 | "PERL_ANYEVENT_STRICT" |
|
|
1018 | AnyEvent does not do much argument checking by default, as thorough |
|
|
1019 | argument checking is very costly. Setting this variable to a true |
|
|
1020 | value will cause AnyEvent to load "AnyEvent::Strict" and then to |
|
|
1021 | thoroughly check the arguments passed to most method calls. If it |
|
|
1022 | finds any problems, it will croak. |
|
|
1023 | |
|
|
1024 | In other words, enables "strict" mode. |
|
|
1025 | |
|
|
1026 | Unlike "use strict" (or it's modern cousin, "use common::sense", it |
|
|
1027 | is definitely recommended to keep it off in production. Keeping |
|
|
1028 | "PERL_ANYEVENT_STRICT=1" in your environment while developing |
|
|
1029 | programs can be very useful, however. |
|
|
1030 | |
|
|
1031 | "PERL_ANYEVENT_MODEL" |
|
|
1032 | This can be used to specify the event model to be used by AnyEvent, |
|
|
1033 | before auto detection and -probing kicks in. It must be a string |
|
|
1034 | consisting entirely of ASCII letters. The string "AnyEvent::Impl::" |
|
|
1035 | gets prepended and the resulting module name is loaded and if the |
|
|
1036 | load was successful, used as event model. If it fails to load |
|
|
1037 | AnyEvent will proceed with auto detection and -probing. |
|
|
1038 | |
|
|
1039 | This functionality might change in future versions. |
|
|
1040 | |
|
|
1041 | For example, to force the pure perl model (AnyEvent::Impl::Perl) you |
|
|
1042 | could start your program like this: |
|
|
1043 | |
|
|
1044 | PERL_ANYEVENT_MODEL=Perl perl ... |
|
|
1045 | |
|
|
1046 | "PERL_ANYEVENT_PROTOCOLS" |
|
|
1047 | Used by both AnyEvent::DNS and AnyEvent::Socket to determine |
|
|
1048 | preferences for IPv4 or IPv6. The default is unspecified (and might |
|
|
1049 | change, or be the result of auto probing). |
|
|
1050 | |
|
|
1051 | Must be set to a comma-separated list of protocols or address |
|
|
1052 | families, current supported: "ipv4" and "ipv6". Only protocols |
|
|
1053 | mentioned will be used, and preference will be given to protocols |
|
|
1054 | mentioned earlier in the list. |
|
|
1055 | |
|
|
1056 | This variable can effectively be used for denial-of-service attacks |
|
|
1057 | against local programs (e.g. when setuid), although the impact is |
|
|
1058 | likely small, as the program has to handle conenction and other |
|
|
1059 | failures anyways. |
|
|
1060 | |
|
|
1061 | Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over |
|
|
1062 | IPv6, but support both and try to use both. |
|
|
1063 | "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to |
|
|
1064 | resolve or contact IPv6 addresses. |
|
|
1065 | "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but |
|
|
1066 | prefer IPv6 over IPv4. |
|
|
1067 | |
|
|
1068 | "PERL_ANYEVENT_EDNS0" |
|
|
1069 | Used by AnyEvent::DNS to decide whether to use the EDNS0 extension |
|
|
1070 | for DNS. This extension is generally useful to reduce DNS traffic, |
|
|
1071 | but some (broken) firewalls drop such DNS packets, which is why it |
|
|
1072 | is off by default. |
|
|
1073 | |
|
|
1074 | Setting this variable to 1 will cause AnyEvent::DNS to announce |
|
|
1075 | EDNS0 in its DNS requests. |
|
|
1076 | |
|
|
1077 | "PERL_ANYEVENT_MAX_FORKS" |
|
|
1078 | The maximum number of child processes that |
|
|
1079 | "AnyEvent::Util::fork_call" will create in parallel. |
|
|
1080 | |
|
|
1081 | "PERL_ANYEVENT_MAX_OUTSTANDING_DNS" |
|
|
1082 | The default value for the "max_outstanding" parameter for the |
|
|
1083 | default DNS resolver - this is the maximum number of parallel DNS |
|
|
1084 | requests that are sent to the DNS server. |
|
|
1085 | |
|
|
1086 | "PERL_ANYEVENT_RESOLV_CONF" |
|
|
1087 | The file to use instead of /etc/resolv.conf (or OS-specific |
|
|
1088 | configuration) in the default resolver. When set to the empty |
|
|
1089 | string, no default config will be used. |
|
|
1090 | |
|
|
1091 | "PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH". |
|
|
1092 | When neither "ca_file" nor "ca_path" was specified during |
|
|
1093 | AnyEvent::TLS context creation, and either of these environment |
|
|
1094 | variables exist, they will be used to specify CA certificate |
|
|
1095 | locations instead of a system-dependent default. |
|
|
1096 | |
|
|
1097 | "PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT" |
|
|
1098 | When these are set to 1, then the respective modules are not loaded. |
|
|
1099 | Mostly good for testing AnyEvent itself. |
|
|
1100 | |
|
|
1101 | SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
|
|
1102 | This is an advanced topic that you do not normally need to use AnyEvent |
|
|
1103 | in a module. This section is only of use to event loop authors who want |
|
|
1104 | to provide AnyEvent compatibility. |
|
|
1105 | |
|
|
1106 | If you need to support another event library which isn't directly |
|
|
1107 | supported by AnyEvent, you can supply your own interface to it by |
|
|
1108 | pushing, before the first watcher gets created, the package name of the |
|
|
1109 | event module and the package name of the interface to use onto |
|
|
1110 | @AnyEvent::REGISTRY. You can do that before and even without loading |
|
|
1111 | AnyEvent, so it is reasonably cheap. |
|
|
1112 | |
|
|
1113 | Example: |
|
|
1114 | |
|
|
1115 | push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
|
|
1116 | |
|
|
1117 | This tells AnyEvent to (literally) use the "urxvt::anyevent::" |
|
|
1118 | package/class when it finds the "urxvt" package/module is already |
|
|
1119 | loaded. |
|
|
1120 | |
|
|
1121 | When AnyEvent is loaded and asked to find a suitable event model, it |
|
|
1122 | will first check for the presence of urxvt by trying to "use" the |
|
|
1123 | "urxvt::anyevent" module. |
|
|
1124 | |
|
|
1125 | The class should provide implementations for all watcher types. See |
|
|
1126 | AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and |
|
|
1127 | so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see |
|
|
1128 | the sources. |
|
|
1129 | |
|
|
1130 | If you don't provide "signal" and "child" watchers than AnyEvent will |
|
|
1131 | provide suitable (hopefully) replacements. |
|
|
1132 | |
|
|
1133 | The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) |
|
|
1134 | terminal emulator uses the above line as-is. An interface isn't included |
|
|
1135 | in AnyEvent because it doesn't make sense outside the embedded |
|
|
1136 | interpreter inside *rxvt-unicode*, and it is updated and maintained as |
|
|
1137 | part of the *rxvt-unicode* distribution. |
|
|
1138 | |
|
|
1139 | *rxvt-unicode* also cheats a bit by not providing blocking access to |
|
|
1140 | condition variables: code blocking while waiting for a condition will |
|
|
1141 | "die". This still works with most modules/usages, and blocking calls |
|
|
1142 | must not be done in an interactive application, so it makes sense. |
|
|
1143 | |
|
|
1144 | EXAMPLE PROGRAM |
68 | The following program uses an io watcher to read data from stdin, a |
1145 | The following program uses an I/O watcher to read data from STDIN, a |
69 | timer to display a message once per second, and a condvar to exit the |
1146 | timer to display a message once per second, and a condition variable to |
70 | program when the user enters quit: |
1147 | quit the program when the user enters quit: |
71 | |
1148 | |
72 | use AnyEvent; |
1149 | use AnyEvent; |
73 | |
1150 | |
74 | my $cv = AnyEvent->condvar; |
1151 | my $cv = AnyEvent->condvar; |
75 | |
1152 | |
76 | my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
1153 | my $io_watcher = AnyEvent->io ( |
|
|
1154 | fh => \*STDIN, |
|
|
1155 | poll => 'r', |
|
|
1156 | cb => sub { |
77 | warn "io event <$_[0]>\n"; # will always output <r> |
1157 | warn "io event <$_[0]>\n"; # will always output <r> |
78 | chomp (my $input = <STDIN>); # read a line |
1158 | chomp (my $input = <STDIN>); # read a line |
79 | warn "read: $input\n"; # output what has been read |
1159 | warn "read: $input\n"; # output what has been read |
80 | $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
1160 | $cv->send if $input =~ /^q/i; # quit program if /^q/i |
|
|
1161 | }, |
81 | }); |
1162 | ); |
82 | |
1163 | |
83 | my $time_watcher; # can only be used once |
1164 | my $time_watcher; # can only be used once |
84 | |
1165 | |
85 | sub new_timer { |
1166 | sub new_timer { |
86 | $timer = AnyEvent->timer (after => 1, cb => sub { |
1167 | $timer = AnyEvent->timer (after => 1, cb => sub { |
… | |
… | |
89 | }); |
1170 | }); |
90 | } |
1171 | } |
91 | |
1172 | |
92 | new_timer; # create first timer |
1173 | new_timer; # create first timer |
93 | |
1174 | |
94 | $cv->wait; # wait until user enters /^q/i |
1175 | $cv->recv; # wait until user enters /^q/i |
95 | |
1176 | |
96 | REAL-WORLD EXAMPLE |
1177 | REAL-WORLD EXAMPLE |
97 | Consider the Net::FCP module. It features (among others) the following |
1178 | Consider the Net::FCP module. It features (among others) the following |
98 | API calls, which are to freenet what HTTP GET requests are to http: |
1179 | API calls, which are to freenet what HTTP GET requests are to http: |
99 | |
1180 | |
… | |
… | |
148 | syswrite $txn->{fh}, $txn->{request} |
1229 | syswrite $txn->{fh}, $txn->{request} |
149 | or die "connection or write error"; |
1230 | or die "connection or write error"; |
150 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
1231 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
151 | |
1232 | |
152 | Again, "fh_ready_r" waits till all data has arrived, and then stores the |
1233 | Again, "fh_ready_r" waits till all data has arrived, and then stores the |
153 | result and signals any possible waiters that the request ahs finished: |
1234 | result and signals any possible waiters that the request has finished: |
154 | |
1235 | |
155 | sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
1236 | sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
156 | |
1237 | |
157 | if (end-of-file or data complete) { |
1238 | if (end-of-file or data complete) { |
158 | $txn->{result} = $txn->{buf}; |
1239 | $txn->{result} = $txn->{buf}; |
159 | $txn->{finished}->broadcast; |
1240 | $txn->{finished}->send; |
160 | $txb->{cb}->($txn) of $txn->{cb}; # also call callback |
1241 | $txb->{cb}->($txn) of $txn->{cb}; # also call callback |
161 | } |
1242 | } |
162 | |
1243 | |
163 | The "result" method, finally, just waits for the finished signal (if the |
1244 | The "result" method, finally, just waits for the finished signal (if the |
164 | request was already finished, it doesn't wait, of course, and returns |
1245 | request was already finished, it doesn't wait, of course, and returns |
165 | the data: |
1246 | the data: |
166 | |
1247 | |
167 | $txn->{finished}->wait; |
1248 | $txn->{finished}->recv; |
168 | return $txn->{result}; |
1249 | return $txn->{result}; |
169 | |
1250 | |
170 | The actual code goes further and collects all errors ("die"s, |
1251 | The actual code goes further and collects all errors ("die"s, |
171 | exceptions) that occured during request processing. The "result" method |
1252 | exceptions) that occurred during request processing. The "result" method |
172 | detects wether an exception as thrown (it is stored inside the $txn |
1253 | detects whether an exception as thrown (it is stored inside the $txn |
173 | object) and just throws the exception, which means connection errors and |
1254 | object) and just throws the exception, which means connection errors and |
174 | other problems get reported tot he code that tries to use the result, |
1255 | other problems get reported tot he code that tries to use the result, |
175 | not in a random callback. |
1256 | not in a random callback. |
176 | |
1257 | |
177 | All of this enables the following usage styles: |
1258 | All of this enables the following usage styles: |
178 | |
1259 | |
179 | 1. Blocking: |
1260 | 1. Blocking: |
180 | |
1261 | |
181 | my $data = $fcp->client_get ($url); |
1262 | my $data = $fcp->client_get ($url); |
182 | |
1263 | |
183 | 2. Blocking, but parallelizing: |
1264 | 2. Blocking, but running in parallel: |
184 | |
1265 | |
185 | my @datas = map $_->result, |
1266 | my @datas = map $_->result, |
186 | map $fcp->txn_client_get ($_), |
1267 | map $fcp->txn_client_get ($_), |
187 | @urls; |
1268 | @urls; |
188 | |
1269 | |
189 | Both blocking examples work without the module user having to know |
1270 | Both blocking examples work without the module user having to know |
190 | anything about events. |
1271 | anything about events. |
191 | |
1272 | |
192 | 3a. Event-based in a main program, using any support Event module: |
1273 | 3a. Event-based in a main program, using any supported event module: |
193 | |
1274 | |
194 | use Event; |
1275 | use EV; |
195 | |
1276 | |
196 | $fcp->txn_client_get ($url)->cb (sub { |
1277 | $fcp->txn_client_get ($url)->cb (sub { |
197 | my $txn = shift; |
1278 | my $txn = shift; |
198 | my $data = $txn->result; |
1279 | my $data = $txn->result; |
199 | ... |
1280 | ... |
200 | }); |
1281 | }); |
201 | |
1282 | |
202 | Event::loop; |
1283 | EV::loop; |
203 | |
1284 | |
204 | 3b. The module user could use AnyEvent, too: |
1285 | 3b. The module user could use AnyEvent, too: |
205 | |
1286 | |
206 | use AnyEvent; |
1287 | use AnyEvent; |
207 | |
1288 | |
208 | my $quit = AnyEvent->condvar; |
1289 | my $quit = AnyEvent->condvar; |
209 | |
1290 | |
210 | $fcp->txn_client_get ($url)->cb (sub { |
1291 | $fcp->txn_client_get ($url)->cb (sub { |
211 | ... |
1292 | ... |
212 | $quit->broadcast; |
1293 | $quit->send; |
213 | }); |
1294 | }); |
214 | |
1295 | |
215 | $quit->wait; |
1296 | $quit->recv; |
|
|
1297 | |
|
|
1298 | BENCHMARKS |
|
|
1299 | To give you an idea of the performance and overheads that AnyEvent adds |
|
|
1300 | over the event loops themselves and to give you an impression of the |
|
|
1301 | speed of various event loops I prepared some benchmarks. |
|
|
1302 | |
|
|
1303 | BENCHMARKING ANYEVENT OVERHEAD |
|
|
1304 | Here is a benchmark of various supported event models used natively and |
|
|
1305 | through AnyEvent. The benchmark creates a lot of timers (with a zero |
|
|
1306 | timeout) and I/O watchers (watching STDOUT, a pty, to become writable, |
|
|
1307 | which it is), lets them fire exactly once and destroys them again. |
|
|
1308 | |
|
|
1309 | Source code for this benchmark is found as eg/bench in the AnyEvent |
|
|
1310 | distribution. |
|
|
1311 | |
|
|
1312 | Explanation of the columns |
|
|
1313 | *watcher* is the number of event watchers created/destroyed. Since |
|
|
1314 | different event models feature vastly different performances, each event |
|
|
1315 | loop was given a number of watchers so that overall runtime is |
|
|
1316 | acceptable and similar between tested event loop (and keep them from |
|
|
1317 | crashing): Glib would probably take thousands of years if asked to |
|
|
1318 | process the same number of watchers as EV in this benchmark. |
|
|
1319 | |
|
|
1320 | *bytes* is the number of bytes (as measured by the resident set size, |
|
|
1321 | RSS) consumed by each watcher. This method of measuring captures both C |
|
|
1322 | and Perl-based overheads. |
|
|
1323 | |
|
|
1324 | *create* is the time, in microseconds (millionths of seconds), that it |
|
|
1325 | takes to create a single watcher. The callback is a closure shared |
|
|
1326 | between all watchers, to avoid adding memory overhead. That means |
|
|
1327 | closure creation and memory usage is not included in the figures. |
|
|
1328 | |
|
|
1329 | *invoke* is the time, in microseconds, used to invoke a simple callback. |
|
|
1330 | The callback simply counts down a Perl variable and after it was invoked |
|
|
1331 | "watcher" times, it would "->send" a condvar once to signal the end of |
|
|
1332 | this phase. |
|
|
1333 | |
|
|
1334 | *destroy* is the time, in microseconds, that it takes to destroy a |
|
|
1335 | single watcher. |
|
|
1336 | |
|
|
1337 | Results |
|
|
1338 | name watchers bytes create invoke destroy comment |
|
|
1339 | EV/EV 400000 224 0.47 0.35 0.27 EV native interface |
|
|
1340 | EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers |
|
|
1341 | CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal |
|
|
1342 | Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation |
|
|
1343 | Event/Event 16000 517 32.20 31.80 0.81 Event native interface |
|
|
1344 | Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers |
|
|
1345 | IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll |
|
|
1346 | IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll |
|
|
1347 | Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour |
|
|
1348 | Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers |
|
|
1349 | POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event |
|
|
1350 | POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select |
|
|
1351 | |
|
|
1352 | Discussion |
|
|
1353 | The benchmark does *not* measure scalability of the event loop very |
|
|
1354 | well. For example, a select-based event loop (such as the pure perl one) |
|
|
1355 | can never compete with an event loop that uses epoll when the number of |
|
|
1356 | file descriptors grows high. In this benchmark, all events become ready |
|
|
1357 | at the same time, so select/poll-based implementations get an unnatural |
|
|
1358 | speed boost. |
|
|
1359 | |
|
|
1360 | Also, note that the number of watchers usually has a nonlinear effect on |
|
|
1361 | overall speed, that is, creating twice as many watchers doesn't take |
|
|
1362 | twice the time - usually it takes longer. This puts event loops tested |
|
|
1363 | with a higher number of watchers at a disadvantage. |
|
|
1364 | |
|
|
1365 | To put the range of results into perspective, consider that on the |
|
|
1366 | benchmark machine, handling an event takes roughly 1600 CPU cycles with |
|
|
1367 | EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 |
|
|
1368 | CPU cycles with POE. |
|
|
1369 | |
|
|
1370 | "EV" is the sole leader regarding speed and memory use, which are both |
|
|
1371 | maximal/minimal, respectively. Even when going through AnyEvent, it uses |
|
|
1372 | far less memory than any other event loop and is still faster than Event |
|
|
1373 | natively. |
|
|
1374 | |
|
|
1375 | The pure perl implementation is hit in a few sweet spots (both the |
|
|
1376 | constant timeout and the use of a single fd hit optimisations in the |
|
|
1377 | perl interpreter and the backend itself). Nevertheless this shows that |
|
|
1378 | it adds very little overhead in itself. Like any select-based backend |
|
|
1379 | its performance becomes really bad with lots of file descriptors (and |
|
|
1380 | few of them active), of course, but this was not subject of this |
|
|
1381 | benchmark. |
|
|
1382 | |
|
|
1383 | The "Event" module has a relatively high setup and callback invocation |
|
|
1384 | cost, but overall scores in on the third place. |
|
|
1385 | |
|
|
1386 | "IO::Async" performs admirably well, about on par with "Event", even |
|
|
1387 | when using its pure perl backend. |
|
|
1388 | |
|
|
1389 | "Glib"'s memory usage is quite a bit higher, but it features a faster |
|
|
1390 | callback invocation and overall ends up in the same class as "Event". |
|
|
1391 | However, Glib scales extremely badly, doubling the number of watchers |
|
|
1392 | increases the processing time by more than a factor of four, making it |
|
|
1393 | completely unusable when using larger numbers of watchers (note that |
|
|
1394 | only a single file descriptor was used in the benchmark, so |
|
|
1395 | inefficiencies of "poll" do not account for this). |
|
|
1396 | |
|
|
1397 | The "Tk" adaptor works relatively well. The fact that it crashes with |
|
|
1398 | more than 2000 watchers is a big setback, however, as correctness takes |
|
|
1399 | precedence over speed. Nevertheless, its performance is surprising, as |
|
|
1400 | the file descriptor is dup()ed for each watcher. This shows that the |
|
|
1401 | dup() employed by some adaptors is not a big performance issue (it does |
|
|
1402 | incur a hidden memory cost inside the kernel which is not reflected in |
|
|
1403 | the figures above). |
|
|
1404 | |
|
|
1405 | "POE", regardless of underlying event loop (whether using its pure perl |
|
|
1406 | select-based backend or the Event module, the POE-EV backend couldn't be |
|
|
1407 | tested because it wasn't working) shows abysmal performance and memory |
|
|
1408 | usage with AnyEvent: Watchers use almost 30 times as much memory as EV |
|
|
1409 | watchers, and 10 times as much memory as Event (the high memory |
|
|
1410 | requirements are caused by requiring a session for each watcher). |
|
|
1411 | Watcher invocation speed is almost 900 times slower than with AnyEvent's |
|
|
1412 | pure perl implementation. |
|
|
1413 | |
|
|
1414 | The design of the POE adaptor class in AnyEvent can not really account |
|
|
1415 | for the performance issues, though, as session creation overhead is |
|
|
1416 | small compared to execution of the state machine, which is coded pretty |
|
|
1417 | optimally within AnyEvent::Impl::POE (and while everybody agrees that |
|
|
1418 | using multiple sessions is not a good approach, especially regarding |
|
|
1419 | memory usage, even the author of POE could not come up with a faster |
|
|
1420 | design). |
|
|
1421 | |
|
|
1422 | Summary |
|
|
1423 | * Using EV through AnyEvent is faster than any other event loop (even |
|
|
1424 | when used without AnyEvent), but most event loops have acceptable |
|
|
1425 | performance with or without AnyEvent. |
|
|
1426 | |
|
|
1427 | * The overhead AnyEvent adds is usually much smaller than the overhead |
|
|
1428 | of the actual event loop, only with extremely fast event loops such |
|
|
1429 | as EV adds AnyEvent significant overhead. |
|
|
1430 | |
|
|
1431 | * You should avoid POE like the plague if you want performance or |
|
|
1432 | reasonable memory usage. |
|
|
1433 | |
|
|
1434 | BENCHMARKING THE LARGE SERVER CASE |
|
|
1435 | This benchmark actually benchmarks the event loop itself. It works by |
|
|
1436 | creating a number of "servers": each server consists of a socket pair, a |
|
|
1437 | timeout watcher that gets reset on activity (but never fires), and an |
|
|
1438 | I/O watcher waiting for input on one side of the socket. Each time the |
|
|
1439 | socket watcher reads a byte it will write that byte to a random other |
|
|
1440 | "server". |
|
|
1441 | |
|
|
1442 | The effect is that there will be a lot of I/O watchers, only part of |
|
|
1443 | which are active at any one point (so there is a constant number of |
|
|
1444 | active fds for each loop iteration, but which fds these are is random). |
|
|
1445 | The timeout is reset each time something is read because that reflects |
|
|
1446 | how most timeouts work (and puts extra pressure on the event loops). |
|
|
1447 | |
|
|
1448 | In this benchmark, we use 10000 socket pairs (20000 sockets), of which |
|
|
1449 | 100 (1%) are active. This mirrors the activity of large servers with |
|
|
1450 | many connections, most of which are idle at any one point in time. |
|
|
1451 | |
|
|
1452 | Source code for this benchmark is found as eg/bench2 in the AnyEvent |
|
|
1453 | distribution. |
|
|
1454 | |
|
|
1455 | Explanation of the columns |
|
|
1456 | *sockets* is the number of sockets, and twice the number of "servers" |
|
|
1457 | (as each server has a read and write socket end). |
|
|
1458 | |
|
|
1459 | *create* is the time it takes to create a socket pair (which is |
|
|
1460 | nontrivial) and two watchers: an I/O watcher and a timeout watcher. |
|
|
1461 | |
|
|
1462 | *request*, the most important value, is the time it takes to handle a |
|
|
1463 | single "request", that is, reading the token from the pipe and |
|
|
1464 | forwarding it to another server. This includes deleting the old timeout |
|
|
1465 | and creating a new one that moves the timeout into the future. |
|
|
1466 | |
|
|
1467 | Results |
|
|
1468 | name sockets create request |
|
|
1469 | EV 20000 69.01 11.16 |
|
|
1470 | Perl 20000 73.32 35.87 |
|
|
1471 | IOAsync 20000 157.00 98.14 epoll |
|
|
1472 | IOAsync 20000 159.31 616.06 poll |
|
|
1473 | Event 20000 212.62 257.32 |
|
|
1474 | Glib 20000 651.16 1896.30 |
|
|
1475 | POE 20000 349.67 12317.24 uses POE::Loop::Event |
|
|
1476 | |
|
|
1477 | Discussion |
|
|
1478 | This benchmark *does* measure scalability and overall performance of the |
|
|
1479 | particular event loop. |
|
|
1480 | |
|
|
1481 | EV is again fastest. Since it is using epoll on my system, the setup |
|
|
1482 | time is relatively high, though. |
|
|
1483 | |
|
|
1484 | Perl surprisingly comes second. It is much faster than the C-based event |
|
|
1485 | loops Event and Glib. |
|
|
1486 | |
|
|
1487 | IO::Async performs very well when using its epoll backend, and still |
|
|
1488 | quite good compared to Glib when using its pure perl backend. |
|
|
1489 | |
|
|
1490 | Event suffers from high setup time as well (look at its code and you |
|
|
1491 | will understand why). Callback invocation also has a high overhead |
|
|
1492 | compared to the "$_->() for .."-style loop that the Perl event loop |
|
|
1493 | uses. Event uses select or poll in basically all documented |
|
|
1494 | configurations. |
|
|
1495 | |
|
|
1496 | Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It |
|
|
1497 | clearly fails to perform with many filehandles or in busy servers. |
|
|
1498 | |
|
|
1499 | POE is still completely out of the picture, taking over 1000 times as |
|
|
1500 | long as EV, and over 100 times as long as the Perl implementation, even |
|
|
1501 | though it uses a C-based event loop in this case. |
|
|
1502 | |
|
|
1503 | Summary |
|
|
1504 | * The pure perl implementation performs extremely well. |
|
|
1505 | |
|
|
1506 | * Avoid Glib or POE in large projects where performance matters. |
|
|
1507 | |
|
|
1508 | BENCHMARKING SMALL SERVERS |
|
|
1509 | While event loops should scale (and select-based ones do not...) even to |
|
|
1510 | large servers, most programs we (or I :) actually write have only a few |
|
|
1511 | I/O watchers. |
|
|
1512 | |
|
|
1513 | In this benchmark, I use the same benchmark program as in the large |
|
|
1514 | server case, but it uses only eight "servers", of which three are active |
|
|
1515 | at any one time. This should reflect performance for a small server |
|
|
1516 | relatively well. |
|
|
1517 | |
|
|
1518 | The columns are identical to the previous table. |
|
|
1519 | |
|
|
1520 | Results |
|
|
1521 | name sockets create request |
|
|
1522 | EV 16 20.00 6.54 |
|
|
1523 | Perl 16 25.75 12.62 |
|
|
1524 | Event 16 81.27 35.86 |
|
|
1525 | Glib 16 32.63 15.48 |
|
|
1526 | POE 16 261.87 276.28 uses POE::Loop::Event |
|
|
1527 | |
|
|
1528 | Discussion |
|
|
1529 | The benchmark tries to test the performance of a typical small server. |
|
|
1530 | While knowing how various event loops perform is interesting, keep in |
|
|
1531 | mind that their overhead in this case is usually not as important, due |
|
|
1532 | to the small absolute number of watchers (that is, you need efficiency |
|
|
1533 | and speed most when you have lots of watchers, not when you only have a |
|
|
1534 | few of them). |
|
|
1535 | |
|
|
1536 | EV is again fastest. |
|
|
1537 | |
|
|
1538 | Perl again comes second. It is noticeably faster than the C-based event |
|
|
1539 | loops Event and Glib, although the difference is too small to really |
|
|
1540 | matter. |
|
|
1541 | |
|
|
1542 | POE also performs much better in this case, but is is still far behind |
|
|
1543 | the others. |
|
|
1544 | |
|
|
1545 | Summary |
|
|
1546 | * C-based event loops perform very well with small number of watchers, |
|
|
1547 | as the management overhead dominates. |
|
|
1548 | |
|
|
1549 | THE IO::Lambda BENCHMARK |
|
|
1550 | Recently I was told about the benchmark in the IO::Lambda manpage, which |
|
|
1551 | could be misinterpreted to make AnyEvent look bad. In fact, the |
|
|
1552 | benchmark simply compares IO::Lambda with POE, and IO::Lambda looks |
|
|
1553 | better (which shouldn't come as a surprise to anybody). As such, the |
|
|
1554 | benchmark is fine, and mostly shows that the AnyEvent backend from |
|
|
1555 | IO::Lambda isn't very optimal. But how would AnyEvent compare when used |
|
|
1556 | without the extra baggage? To explore this, I wrote the equivalent |
|
|
1557 | benchmark for AnyEvent. |
|
|
1558 | |
|
|
1559 | The benchmark itself creates an echo-server, and then, for 500 times, |
|
|
1560 | connects to the echo server, sends a line, waits for the reply, and then |
|
|
1561 | creates the next connection. This is a rather bad benchmark, as it |
|
|
1562 | doesn't test the efficiency of the framework or much non-blocking I/O, |
|
|
1563 | but it is a benchmark nevertheless. |
|
|
1564 | |
|
|
1565 | name runtime |
|
|
1566 | Lambda/select 0.330 sec |
|
|
1567 | + optimized 0.122 sec |
|
|
1568 | Lambda/AnyEvent 0.327 sec |
|
|
1569 | + optimized 0.138 sec |
|
|
1570 | Raw sockets/select 0.077 sec |
|
|
1571 | POE/select, components 0.662 sec |
|
|
1572 | POE/select, raw sockets 0.226 sec |
|
|
1573 | POE/select, optimized 0.404 sec |
|
|
1574 | |
|
|
1575 | AnyEvent/select/nb 0.085 sec |
|
|
1576 | AnyEvent/EV/nb 0.068 sec |
|
|
1577 | +state machine 0.134 sec |
|
|
1578 | |
|
|
1579 | The benchmark is also a bit unfair (my fault): the IO::Lambda/POE |
|
|
1580 | benchmarks actually make blocking connects and use 100% blocking I/O, |
|
|
1581 | defeating the purpose of an event-based solution. All of the newly |
|
|
1582 | written AnyEvent benchmarks use 100% non-blocking connects (using |
|
|
1583 | AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS |
|
|
1584 | resolver), so AnyEvent is at a disadvantage here, as non-blocking |
|
|
1585 | connects generally require a lot more bookkeeping and event handling |
|
|
1586 | than blocking connects (which involve a single syscall only). |
|
|
1587 | |
|
|
1588 | The last AnyEvent benchmark additionally uses AnyEvent::Handle, which |
|
|
1589 | offers similar expressive power as POE and IO::Lambda, using |
|
|
1590 | conventional Perl syntax. This means that both the echo server and the |
|
|
1591 | client are 100% non-blocking, further placing it at a disadvantage. |
|
|
1592 | |
|
|
1593 | As you can see, the AnyEvent + EV combination even beats the |
|
|
1594 | hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl |
|
|
1595 | backend easily beats IO::Lambda and POE. |
|
|
1596 | |
|
|
1597 | And even the 100% non-blocking version written using the high-level (and |
|
|
1598 | slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a |
|
|
1599 | large margin, even though it does all of DNS, tcp-connect and socket I/O |
|
|
1600 | in a non-blocking way. |
|
|
1601 | |
|
|
1602 | The two AnyEvent benchmarks programs can be found as eg/ae0.pl and |
|
|
1603 | eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are |
|
|
1604 | part of the IO::lambda distribution and were used without any changes. |
|
|
1605 | |
|
|
1606 | SIGNALS |
|
|
1607 | AnyEvent currently installs handlers for these signals: |
|
|
1608 | |
|
|
1609 | SIGCHLD |
|
|
1610 | A handler for "SIGCHLD" is installed by AnyEvent's child watcher |
|
|
1611 | emulation for event loops that do not support them natively. Also, |
|
|
1612 | some event loops install a similar handler. |
|
|
1613 | |
|
|
1614 | Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, |
|
|
1615 | then AnyEvent will reset it to default, to avoid losing child exit |
|
|
1616 | statuses. |
|
|
1617 | |
|
|
1618 | SIGPIPE |
|
|
1619 | A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is |
|
|
1620 | "undef" when AnyEvent gets loaded. |
|
|
1621 | |
|
|
1622 | The rationale for this is that AnyEvent users usually do not really |
|
|
1623 | depend on SIGPIPE delivery (which is purely an optimisation for |
|
|
1624 | shell use, or badly-written programs), but "SIGPIPE" can cause |
|
|
1625 | spurious and rare program exits as a lot of people do not expect |
|
|
1626 | "SIGPIPE" when writing to some random socket. |
|
|
1627 | |
|
|
1628 | The rationale for installing a no-op handler as opposed to ignoring |
|
|
1629 | it is that this way, the handler will be restored to defaults on |
|
|
1630 | exec. |
|
|
1631 | |
|
|
1632 | Feel free to install your own handler, or reset it to defaults. |
|
|
1633 | |
|
|
1634 | RECOMMENDED/OPTIONAL MODULES |
|
|
1635 | One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and |
|
|
1636 | it's built-in modules) are required to use it. |
|
|
1637 | |
|
|
1638 | That does not mean that AnyEvent won't take advantage of some additional |
|
|
1639 | modules if they are installed. |
|
|
1640 | |
|
|
1641 | This section epxlains which additional modules will be used, and how |
|
|
1642 | they affect AnyEvent's operetion. |
|
|
1643 | |
|
|
1644 | Async::Interrupt |
|
|
1645 | This slightly arcane module is used to implement fast signal |
|
|
1646 | handling: To my knowledge, there is no way to do completely |
|
|
1647 | race-free and quick signal handling in pure perl. To ensure that |
|
|
1648 | signals still get delivered, AnyEvent will start an interval timer |
|
|
1649 | to wake up perl (and catch the signals) with soemd elay (default is |
|
|
1650 | 10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY). |
|
|
1651 | |
|
|
1652 | If this module is available, then it will be used to implement |
|
|
1653 | signal catching, which means that signals will not be delayed, and |
|
|
1654 | the event loop will not be interrupted regularly, which is more |
|
|
1655 | efficient (And good for battery life on laptops). |
|
|
1656 | |
|
|
1657 | This affects not just the pure-perl event loop, but also other event |
|
|
1658 | loops that have no signal handling on their own (e.g. Glib, Tk, Qt). |
|
|
1659 | |
|
|
1660 | EV This module isn't really "optional", as it is simply one of the |
|
|
1661 | backend event loops that AnyEvent can use. However, it is simply the |
|
|
1662 | best event loop available in terms of features, speed and stability: |
|
|
1663 | It supports the AnyEvent API optimally, implements all the watcher |
|
|
1664 | types in XS, does automatic timer adjustments even when no monotonic |
|
|
1665 | clock is available, can take avdantage of advanced kernel interfaces |
|
|
1666 | such as "epoll" and "kqueue", and is the fastest backend *by far*. |
|
|
1667 | You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and |
|
|
1668 | Glib::EV). |
|
|
1669 | |
|
|
1670 | Guard |
|
|
1671 | The guard module, when used, will be used to implement |
|
|
1672 | "AnyEvent::Util::guard". This speeds up guards considerably (and |
|
|
1673 | uses a lot less memory), but otherwise doesn't affect guard |
|
|
1674 | operation much. It is purely used for performance. |
|
|
1675 | |
|
|
1676 | JSON and JSON::XS |
|
|
1677 | This module is required when you want to read or write JSON data via |
|
|
1678 | AnyEvent::Handle. It is also written in pure-perl, but can take |
|
|
1679 | advantage of the ulta-high-speed JSON::XS module when it is |
|
|
1680 | installed. |
|
|
1681 | |
|
|
1682 | In fact, AnyEvent::Handle will use JSON::XS by default if it is |
|
|
1683 | installed. |
|
|
1684 | |
|
|
1685 | Net::SSLeay |
|
|
1686 | Implementing TLS/SSL in Perl is certainly interesting, but not very |
|
|
1687 | worthwhile: If this module is installed, then AnyEvent::Handle (with |
|
|
1688 | the help of AnyEvent::TLS), gains the ability to do TLS/SSL. |
|
|
1689 | |
|
|
1690 | Time::HiRes |
|
|
1691 | This module is part of perl since release 5.008. It will be used |
|
|
1692 | when the chosen event library does not come with a timing source on |
|
|
1693 | it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will |
|
|
1694 | additionally use it to try to use a monotonic clock for timing |
|
|
1695 | stability. |
|
|
1696 | |
|
|
1697 | FORK |
|
|
1698 | Most event libraries are not fork-safe. The ones who are usually are |
|
|
1699 | because they rely on inefficient but fork-safe "select" or "poll" calls. |
|
|
1700 | Only EV is fully fork-aware. |
|
|
1701 | |
|
|
1702 | If you have to fork, you must either do so *before* creating your first |
|
|
1703 | watcher OR you must not use AnyEvent at all in the child OR you must do |
|
|
1704 | something completely out of the scope of AnyEvent. |
|
|
1705 | |
|
|
1706 | SECURITY CONSIDERATIONS |
|
|
1707 | AnyEvent can be forced to load any event model via |
|
|
1708 | $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used |
|
|
1709 | to execute arbitrary code or directly gain access, it can easily be used |
|
|
1710 | to make the program hang or malfunction in subtle ways, as AnyEvent |
|
|
1711 | watchers will not be active when the program uses a different event |
|
|
1712 | model than specified in the variable. |
|
|
1713 | |
|
|
1714 | You can make AnyEvent completely ignore this variable by deleting it |
|
|
1715 | before the first watcher gets created, e.g. with a "BEGIN" block: |
|
|
1716 | |
|
|
1717 | BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
|
|
1718 | |
|
|
1719 | use AnyEvent; |
|
|
1720 | |
|
|
1721 | Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can |
|
|
1722 | be used to probe what backend is used and gain other information (which |
|
|
1723 | is probably even less useful to an attacker than PERL_ANYEVENT_MODEL), |
|
|
1724 | and $ENV{PERL_ANYEVENT_STRICT}. |
|
|
1725 | |
|
|
1726 | Note that AnyEvent will remove *all* environment variables starting with |
|
|
1727 | "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is |
|
|
1728 | enabled. |
|
|
1729 | |
|
|
1730 | BUGS |
|
|
1731 | Perl 5.8 has numerous memleaks that sometimes hit this module and are |
|
|
1732 | hard to work around. If you suffer from memleaks, first upgrade to Perl |
|
|
1733 | 5.10 and check wether the leaks still show up. (Perl 5.10.0 has other |
|
|
1734 | annoying memleaks, such as leaking on "map" and "grep" but it is usually |
|
|
1735 | not as pronounced). |
216 | |
1736 | |
217 | SEE ALSO |
1737 | SEE ALSO |
218 | Event modules: Coro::Event, Coro, Event, Glib::Event, Glib. |
1738 | Utility functions: AnyEvent::Util. |
219 | |
1739 | |
|
|
1740 | Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, |
|
|
1741 | Event::Lib, Qt, POE. |
|
|
1742 | |
220 | Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event, |
1743 | Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, |
221 | AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. |
1744 | AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, |
|
|
1745 | AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE, |
|
|
1746 | AnyEvent::Impl::IOAsync. |
222 | |
1747 | |
223 | Nontrivial usage example: Net::FCP. |
1748 | Non-blocking file handles, sockets, TCP clients and servers: |
|
|
1749 | AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS. |
224 | |
1750 | |
|
|
1751 | Asynchronous DNS: AnyEvent::DNS. |
225 | |
1752 | |
|
|
1753 | Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, |
|
|
1754 | |
|
|
1755 | Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP, |
|
|
1756 | AnyEvent::HTTP. |
|
|
1757 | |
|
|
1758 | AUTHOR |
|
|
1759 | Marc Lehmann <schmorp@schmorp.de> |
|
|
1760 | http://home.schmorp.de/ |
|
|
1761 | |