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, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt - |
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5 | various supported event loops |
5 | |
6 | |
6 | SYNOPSIS |
7 | SYNOPSIS |
7 | use AnyEvent; |
8 | use AnyEvent; |
8 | |
9 | |
9 | my $w = AnyEvent->timer (fh => ..., poll => "[rw]+", cb => sub { |
10 | my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { |
10 | my ($poll_got) = @_; |
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11 | ... |
11 | ... |
12 | }); |
12 | }); |
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13 | |
13 | my $w = AnyEvent->io (after => $seconds, cb => sub { |
14 | my $w = AnyEvent->timer (after => $seconds, cb => sub { |
14 | ... |
15 | ... |
15 | }); |
16 | }); |
16 | |
17 | |
17 | # watchers get canceled whenever $w is destroyed |
18 | my $w = AnyEvent->condvar; # stores whether a condition was flagged |
18 | # only one watcher per $fh and $poll type is allowed |
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19 | # (i.e. on a socket you cna have one r + one w or one rw |
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20 | # watcher, not any more. |
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21 | # timers can only be used once |
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22 | |
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23 | my $w = AnyEvent->condvar; # kind of main loop replacement |
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24 | # can only be used once |
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25 | $w->wait; # enters main loop till $condvar gets ->send |
19 | $w->wait; # enters "main loop" till $condvar gets ->broadcast |
26 | $w->broadcast; # wake up waiting and future wait's |
20 | $w->broadcast; # wake up current and all future wait's |
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21 | |
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22 | WHY YOU SHOULD USE THIS MODULE (OR NOT) |
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23 | Glib, POE, IO::Async, Event... CPAN offers event models by the dozen |
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24 | nowadays. So what is different about AnyEvent? |
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25 | |
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26 | Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of |
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27 | policy* and AnyEvent is *small and efficient*. |
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28 | |
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29 | First and foremost, *AnyEvent is not an event model* itself, it only |
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30 | interfaces to whatever event model the main program happens to use in a |
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31 | pragmatic way. For event models and certain classes of immortals alike, |
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32 | the statement "there can only be one" is a bitter reality: In general, |
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33 | only one event loop can be active at the same time in a process. |
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34 | AnyEvent helps hiding the differences between those event loops. |
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35 | |
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36 | The goal of AnyEvent is to offer module authors the ability to do event |
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37 | programming (waiting for I/O or timer events) without subscribing to a |
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38 | religion, a way of living, and most importantly: without forcing your |
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39 | module users into the same thing by forcing them to use the same event |
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40 | model you use. |
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41 | |
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42 | For modules like POE or IO::Async (which is a total misnomer as it is |
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43 | actually doing all I/O *synchronously*...), using them in your module is |
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44 | like joining a cult: After you joined, you are dependent on them and you |
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45 | cannot use anything else, as it is simply incompatible to everything |
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46 | that isn't itself. What's worse, all the potential users of your module |
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47 | are *also* forced to use the same event loop you use. |
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48 | |
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49 | AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works |
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50 | fine. AnyEvent + Tk works fine etc. etc. but none of these work together |
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51 | with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your |
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52 | module uses one of those, every user of your module has to use it, too. |
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53 | But if your module uses AnyEvent, it works transparently with all event |
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54 | models it supports (including stuff like POE and IO::Async, as long as |
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55 | those use one of the supported event loops. It is trivial to add new |
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56 | event loops to AnyEvent, too, so it is future-proof). |
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57 | |
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58 | In addition to being free of having to use *the one and only true event |
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59 | model*, AnyEvent also is free of bloat and policy: with POE or similar |
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60 | modules, you get an enourmous amount of code and strict rules you have |
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61 | to follow. AnyEvent, on the other hand, is lean and up to the point, by |
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62 | only offering the functionality that is necessary, in as thin as a |
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63 | wrapper as technically possible. |
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64 | |
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65 | Of course, if you want lots of policy (this can arguably be somewhat |
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66 | useful) and you want to force your users to use the one and only event |
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67 | model, you should *not* use this module. |
27 | |
68 | |
28 | DESCRIPTION |
69 | DESCRIPTION |
29 | AnyEvent provides an identical interface to multiple event loops. This |
70 | AnyEvent provides an identical interface to multiple event loops. This |
30 | allows module authors to utilizy an event loop without forcing module |
71 | allows module authors to utilise an event loop without forcing module |
31 | users to use the same event loop (as only a single event loop can |
72 | users to use the same event loop (as only a single event loop can |
32 | coexist peacefully at any one time). |
73 | coexist peacefully at any one time). |
33 | |
74 | |
34 | The interface itself is vaguely similar but not identical to the Event |
75 | The interface itself is vaguely similar, but not identical to the Event |
35 | module. |
76 | module. |
36 | |
77 | |
37 | On the first call of any method, the module tries to detect the |
78 | During the first call of any watcher-creation method, the module tries |
38 | currently loaded event loop by probing wether any of the following |
79 | to detect the currently loaded event loop by probing whether one of the |
39 | modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is |
80 | following modules is already loaded: Coro::EV, Coro::Event, EV, Event, |
40 | used. If none is found, the module tries to load these modules in the |
81 | Glib, Tk, Event::Lib, Qt. The first one found is used. If none are |
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82 | found, the module tries to load these modules (excluding Event::Lib and |
41 | order given. The first one that could be successfully loaded will be |
83 | Qt) in the order given. The first one that can be successfully loaded |
42 | used. If still none could be found, it will issue an error. |
84 | will be used. If, after this, still none could be found, AnyEvent will |
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85 | fall back to a pure-perl event loop, which is not very efficient, but |
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86 | should work everywhere. |
43 | |
87 | |
44 | EXAMPLE |
88 | Because AnyEvent first checks for modules that are already loaded, |
45 | The following program uses an io watcher to read data from stdin, a |
89 | loading an event model explicitly before first using AnyEvent will |
46 | timer to display a message once per second, and a condvar to exit the |
90 | likely make that model the default. For example: |
47 | program when the user enters quit: |
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48 | |
91 | |
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92 | use Tk; |
49 | use AnyEvent; |
93 | use AnyEvent; |
50 | |
94 | |
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95 | # .. AnyEvent will likely default to Tk |
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96 | |
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97 | The *likely* means that, if any module loads another event model and |
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98 | starts using it, all bets are off. Maybe you should tell their authors |
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99 | to use AnyEvent so their modules work together with others seamlessly... |
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100 | |
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101 | The pure-perl implementation of AnyEvent is called |
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102 | "AnyEvent::Impl::Perl". Like other event modules you can load it |
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103 | explicitly. |
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104 | |
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105 | WATCHERS |
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106 | AnyEvent has the central concept of a *watcher*, which is an object that |
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107 | stores relevant data for each kind of event you are waiting for, such as |
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108 | the callback to call, the filehandle to watch, etc. |
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109 | |
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110 | These watchers are normal Perl objects with normal Perl lifetime. After |
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111 | creating a watcher it will immediately "watch" for events and invoke the |
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112 | callback when the event occurs (of course, only when the event model is |
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113 | in control). |
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114 | |
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115 | To disable the watcher you have to destroy it (e.g. by setting the |
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116 | variable you store it in to "undef" or otherwise deleting all references |
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117 | to it). |
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118 | |
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119 | All watchers are created by calling a method on the "AnyEvent" class. |
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120 | |
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121 | Many watchers either are used with "recursion" (repeating timers for |
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122 | example), or need to refer to their watcher object in other ways. |
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123 | |
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124 | An any way to achieve that is this pattern: |
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125 | |
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126 | my $w; $w = AnyEvent->type (arg => value ..., cb => sub { |
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127 | # you can use $w here, for example to undef it |
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128 | undef $w; |
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129 | }); |
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130 | |
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131 | Note that "my $w; $w =" combination. This is necessary because in Perl, |
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132 | my variables are only visible after the statement in which they are |
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133 | declared. |
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134 | |
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135 | IO WATCHERS |
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136 | You can create an I/O watcher by calling the "AnyEvent->io" method with |
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137 | the following mandatory key-value pairs as arguments: |
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138 | |
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139 | "fh" the Perl *file handle* (*not* file descriptor) to watch for events. |
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140 | "poll" must be a string that is either "r" or "w", which creates a |
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141 | watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" |
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142 | is the callback to invoke each time the file handle becomes ready. |
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143 | |
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144 | As long as the I/O watcher exists it will keep the file descriptor or a |
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145 | copy of it alive/open. |
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146 | |
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147 | It is not allowed to close a file handle as long as any watcher is |
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148 | active on the underlying file descriptor. |
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149 | |
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150 | Some event loops issue spurious readyness notifications, so you should |
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151 | always use non-blocking calls when reading/writing from/to your file |
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152 | handles. |
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153 | |
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154 | Example: |
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155 | |
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156 | # wait for readability of STDIN, then read a line and disable the watcher |
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157 | my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
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158 | chomp (my $input = <STDIN>); |
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159 | warn "read: $input\n"; |
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160 | undef $w; |
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161 | }); |
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162 | |
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163 | TIME WATCHERS |
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164 | You can create a time watcher by calling the "AnyEvent->timer" method |
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165 | with the following mandatory arguments: |
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166 | |
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167 | "after" specifies after how many seconds (fractional values are |
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168 | supported) should the timer activate. "cb" the callback to invoke in |
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169 | that case. |
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170 | |
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171 | The timer callback will be invoked at most once: if you want a repeating |
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172 | timer you have to create a new watcher (this is a limitation by both Tk |
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173 | and Glib). |
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174 | |
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175 | Example: |
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176 | |
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177 | # fire an event after 7.7 seconds |
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178 | my $w = AnyEvent->timer (after => 7.7, cb => sub { |
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179 | warn "timeout\n"; |
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180 | }); |
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181 | |
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182 | # to cancel the timer: |
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183 | undef $w; |
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184 | |
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185 | Example 2: |
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186 | |
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187 | # fire an event after 0.5 seconds, then roughly every second |
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188 | my $w; |
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189 | |
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190 | my $cb = sub { |
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191 | # cancel the old timer while creating a new one |
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192 | $w = AnyEvent->timer (after => 1, cb => $cb); |
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193 | }; |
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194 | |
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195 | # start the "loop" by creating the first watcher |
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196 | $w = AnyEvent->timer (after => 0.5, cb => $cb); |
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197 | |
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198 | TIMING ISSUES |
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199 | There are two ways to handle timers: based on real time (relative, "fire |
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200 | in 10 seconds") and based on wallclock time (absolute, "fire at 12 |
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201 | o'clock"). |
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202 | |
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203 | While most event loops expect timers to specified in a relative way, |
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204 | they use absolute time internally. This makes a difference when your |
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205 | clock "jumps", for example, when ntp decides to set your clock backwards |
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206 | from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is |
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207 | supposed to fire "after" a second might actually take six years to |
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208 | finally fire. |
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209 | |
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210 | AnyEvent cannot compensate for this. The only event loop that is |
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211 | conscious about these issues is EV, which offers both relative |
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212 | (ev_timer, based on true relative time) and absolute (ev_periodic, based |
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213 | on wallclock time) timers. |
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214 | |
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215 | AnyEvent always prefers relative timers, if available, matching the |
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216 | AnyEvent API. |
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217 | |
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218 | SIGNAL WATCHERS |
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219 | You can watch for signals using a signal watcher, "signal" is the signal |
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220 | *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked |
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221 | whenever a signal occurs. |
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222 | |
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223 | Multiple signal occurances can be clumped together into one callback |
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224 | invocation, and callback invocation will be synchronous. synchronous |
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225 | means that it might take a while until the signal gets handled by the |
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226 | process, but it is guarenteed not to interrupt any other callbacks. |
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227 | |
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228 | The main advantage of using these watchers is that you can share a |
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229 | signal between multiple watchers. |
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230 | |
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231 | This watcher might use %SIG, so programs overwriting those signals |
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232 | directly will likely not work correctly. |
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233 | |
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234 | Example: exit on SIGINT |
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235 | |
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236 | my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); |
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237 | |
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238 | CHILD PROCESS WATCHERS |
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239 | You can also watch on a child process exit and catch its exit status. |
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240 | |
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241 | The child process is specified by the "pid" argument (if set to 0, it |
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242 | watches for any child process exit). The watcher will trigger as often |
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243 | as status change for the child are received. This works by installing a |
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244 | signal handler for "SIGCHLD". The callback will be called with the pid |
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245 | and exit status (as returned by waitpid). |
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246 | |
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247 | Example: wait for pid 1333 |
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248 | |
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249 | my $w = AnyEvent->child ( |
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250 | pid => 1333, |
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251 | cb => sub { |
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252 | my ($pid, $status) = @_; |
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253 | warn "pid $pid exited with status $status"; |
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254 | }, |
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255 | ); |
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256 | |
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257 | CONDITION VARIABLES |
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258 | Condition variables can be created by calling the "AnyEvent->condvar" |
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259 | method without any arguments. |
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260 | |
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261 | A condition variable waits for a condition - precisely that the |
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262 | "->broadcast" method has been called. |
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263 | |
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264 | They are very useful to signal that a condition has been fulfilled, for |
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265 | example, if you write a module that does asynchronous http requests, |
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266 | then a condition variable would be the ideal candidate to signal the |
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267 | availability of results. |
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268 | |
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269 | You can also use condition variables to block your main program until an |
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270 | event occurs - for example, you could "->wait" in your main program |
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271 | until the user clicks the Quit button in your app, which would |
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272 | "->broadcast" the "quit" event. |
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273 | |
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274 | Note that condition variables recurse into the event loop - if you have |
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275 | two pirces of code that call "->wait" in a round-robbin fashion, you |
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276 | lose. Therefore, condition variables are good to export to your caller, |
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277 | but you should avoid making a blocking wait yourself, at least in |
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278 | callbacks, as this asks for trouble. |
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279 | |
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280 | This object has two methods: |
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281 | |
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282 | $cv->wait |
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283 | Wait (blocking if necessary) until the "->broadcast" method has been |
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284 | called on c<$cv>, while servicing other watchers normally. |
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285 | |
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286 | You can only wait once on a condition - additional calls will return |
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287 | immediately. |
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288 | |
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289 | Not all event models support a blocking wait - some die in that case |
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290 | (programs might want to do that to stay interactive), so *if you are |
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291 | using this from a module, never require a blocking wait*, but let |
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292 | the caller decide whether the call will block or not (for example, |
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293 | by coupling condition variables with some kind of request results |
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294 | and supporting callbacks so the caller knows that getting the result |
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295 | will not block, while still suppporting blocking waits if the caller |
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296 | so desires). |
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297 | |
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298 | Another reason *never* to "->wait" in a module is that you cannot |
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299 | sensibly have two "->wait"'s in parallel, as that would require |
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300 | multiple interpreters or coroutines/threads, none of which |
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301 | "AnyEvent" can supply (the coroutine-aware backends |
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302 | AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly |
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303 | support concurrent "->wait"'s from different coroutines, however). |
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304 | |
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305 | $cv->broadcast |
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306 | Flag the condition as ready - a running "->wait" and all further |
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307 | calls to "wait" will (eventually) return after this method has been |
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308 | called. If nobody is waiting the broadcast will be remembered.. |
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309 | |
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310 | Example: |
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311 | |
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312 | # wait till the result is ready |
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313 | my $result_ready = AnyEvent->condvar; |
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314 | |
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315 | # do something such as adding a timer |
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316 | # or socket watcher the calls $result_ready->broadcast |
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317 | # when the "result" is ready. |
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318 | # in this case, we simply use a timer: |
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319 | my $w = AnyEvent->timer ( |
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320 | after => 1, |
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321 | cb => sub { $result_ready->broadcast }, |
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322 | ); |
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323 | |
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324 | # this "blocks" (while handling events) till the watcher |
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325 | # calls broadcast |
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326 | $result_ready->wait; |
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327 | |
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328 | GLOBAL VARIABLES AND FUNCTIONS |
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329 | $AnyEvent::MODEL |
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330 | Contains "undef" until the first watcher is being created. Then it |
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331 | contains the event model that is being used, which is the name of |
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332 | the Perl class implementing the model. This class is usually one of |
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333 | the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
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334 | case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
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335 | |
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336 | The known classes so far are: |
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337 | |
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338 | AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
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339 | AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
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340 | AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
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341 | AnyEvent::Impl::Event based on Event, second best choice. |
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342 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
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343 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
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344 | AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. |
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345 | AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). |
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346 | AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
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347 | |
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348 | AnyEvent::detect |
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349 | Returns $AnyEvent::MODEL, forcing autodetection of the event model |
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350 | if necessary. You should only call this function right before you |
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351 | would have created an AnyEvent watcher anyway, that is, as late as |
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352 | possible at runtime. |
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353 | |
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354 | WHAT TO DO IN A MODULE |
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355 | As a module author, you should "use AnyEvent" and call AnyEvent methods |
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356 | freely, but you should not load a specific event module or rely on it. |
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357 | |
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358 | Be careful when you create watchers in the module body - AnyEvent will |
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359 | decide which event module to use as soon as the first method is called, |
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360 | so by calling AnyEvent in your module body you force the user of your |
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361 | module to load the event module first. |
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362 | |
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363 | Never call "->wait" on a condition variable unless you *know* that the |
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364 | "->broadcast" method has been called on it already. This is because it |
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365 | will stall the whole program, and the whole point of using events is to |
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366 | stay interactive. |
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367 | |
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368 | It is fine, however, to call "->wait" when the user of your module |
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369 | requests it (i.e. if you create a http request object ad have a method |
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370 | called "results" that returns the results, it should call "->wait" |
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371 | freely, as the user of your module knows what she is doing. always). |
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372 | |
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373 | WHAT TO DO IN THE MAIN PROGRAM |
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374 | There will always be a single main program - the only place that should |
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375 | dictate which event model to use. |
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376 | |
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377 | If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
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378 | do anything special (it does not need to be event-based) and let |
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379 | AnyEvent decide which implementation to chose if some module relies on |
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380 | it. |
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381 | |
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382 | If the main program relies on a specific event model. For example, in |
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383 | Gtk2 programs you have to rely on the Glib module. You should load the |
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384 | event module before loading AnyEvent or any module that uses it: |
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385 | generally speaking, you should load it as early as possible. The reason |
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386 | is that modules might create watchers when they are loaded, and AnyEvent |
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387 | will decide on the event model to use as soon as it creates watchers, |
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388 | and it might chose the wrong one unless you load the correct one |
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389 | yourself. |
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390 | |
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391 | You can chose to use a rather inefficient pure-perl implementation by |
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392 | loading the "AnyEvent::Impl::Perl" module, which gives you similar |
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393 | behaviour everywhere, but letting AnyEvent chose is generally better. |
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394 | |
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395 | SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
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396 | This is an advanced topic that you do not normally need to use AnyEvent |
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397 | in a module. This section is only of use to event loop authors who want |
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398 | to provide AnyEvent compatibility. |
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399 | |
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400 | If you need to support another event library which isn't directly |
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401 | supported by AnyEvent, you can supply your own interface to it by |
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402 | pushing, before the first watcher gets created, the package name of the |
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403 | event module and the package name of the interface to use onto |
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404 | @AnyEvent::REGISTRY. You can do that before and even without loading |
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405 | AnyEvent, so it is reasonably cheap. |
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406 | |
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407 | Example: |
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408 | |
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409 | push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
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410 | |
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411 | This tells AnyEvent to (literally) use the "urxvt::anyevent::" |
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412 | package/class when it finds the "urxvt" package/module is already |
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413 | loaded. |
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414 | |
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415 | When AnyEvent is loaded and asked to find a suitable event model, it |
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416 | will first check for the presence of urxvt by trying to "use" the |
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417 | "urxvt::anyevent" module. |
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418 | |
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419 | The class should provide implementations for all watcher types. See |
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420 | AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and |
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421 | so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see |
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422 | the sources. |
|
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423 | |
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424 | If you don't provide "signal" and "child" watchers than AnyEvent will |
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425 | provide suitable (hopefully) replacements. |
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426 | |
|
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427 | The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) |
|
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428 | terminal emulator uses the above line as-is. An interface isn't included |
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429 | in AnyEvent because it doesn't make sense outside the embedded |
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430 | interpreter inside *rxvt-unicode*, and it is updated and maintained as |
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431 | part of the *rxvt-unicode* distribution. |
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432 | |
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433 | *rxvt-unicode* also cheats a bit by not providing blocking access to |
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434 | condition variables: code blocking while waiting for a condition will |
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435 | "die". This still works with most modules/usages, and blocking calls |
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436 | must not be done in an interactive application, so it makes sense. |
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437 | |
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438 | ENVIRONMENT VARIABLES |
|
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439 | The following environment variables are used by this module: |
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440 | |
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441 | "PERL_ANYEVENT_VERBOSE" |
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442 | When set to 2 or higher, cause AnyEvent to report to STDERR which |
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443 | event model it chooses. |
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444 | |
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445 | "PERL_ANYEVENT_MODEL" |
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446 | This can be used to specify the event model to be used by AnyEvent, |
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447 | before autodetection and -probing kicks in. It must be a string |
|
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448 | consisting entirely of ASCII letters. The string "AnyEvent::Impl::" |
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449 | gets prepended and the resulting module name is loaded and if the |
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450 | load was successful, used as event model. If it fails to load |
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451 | AnyEvent will proceed with autodetection and -probing. |
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452 | |
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453 | This functionality might change in future versions. |
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454 | |
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455 | For example, to force the pure perl model (AnyEvent::Impl::Perl) you |
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456 | could start your program like this: |
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457 | |
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458 | PERL_ANYEVENT_MODEL=Perl perl ... |
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459 | |
|
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460 | EXAMPLE PROGRAM |
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461 | The following program uses an IO watcher to read data from STDIN, a |
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462 | timer to display a message once per second, and a condition variable to |
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463 | quit the program when the user enters quit: |
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464 | |
|
|
465 | use AnyEvent; |
|
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466 | |
51 | my $cv = AnyEvent->condvar; |
467 | my $cv = AnyEvent->condvar; |
52 | |
468 | |
53 | my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
469 | my $io_watcher = AnyEvent->io ( |
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470 | fh => \*STDIN, |
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471 | poll => 'r', |
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472 | cb => sub { |
54 | warn "io event <$_[0]>\n"; # will always output <r> |
473 | warn "io event <$_[0]>\n"; # will always output <r> |
55 | chomp (my $input = <STDIN>); # read a line |
474 | chomp (my $input = <STDIN>); # read a line |
56 | warn "read: $input\n"; # output what has been read |
475 | warn "read: $input\n"; # output what has been read |
57 | $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
476 | $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
|
|
477 | }, |
58 | }); |
478 | ); |
59 | |
479 | |
60 | my $time_watcher; # can only be used once |
480 | my $time_watcher; # can only be used once |
61 | |
481 | |
62 | sub new_timer { |
482 | sub new_timer { |
63 | $timer = AnyEvent->timer (after => 1, cb => sub { |
483 | $timer = AnyEvent->timer (after => 1, cb => sub { |
… | |
… | |
68 | |
488 | |
69 | new_timer; # create first timer |
489 | new_timer; # create first timer |
70 | |
490 | |
71 | $cv->wait; # wait until user enters /^q/i |
491 | $cv->wait; # wait until user enters /^q/i |
72 | |
492 | |
|
|
493 | REAL-WORLD EXAMPLE |
|
|
494 | Consider the Net::FCP module. It features (among others) the following |
|
|
495 | API calls, which are to freenet what HTTP GET requests are to http: |
|
|
496 | |
|
|
497 | my $data = $fcp->client_get ($url); # blocks |
|
|
498 | |
|
|
499 | my $transaction = $fcp->txn_client_get ($url); # does not block |
|
|
500 | $transaction->cb ( sub { ... } ); # set optional result callback |
|
|
501 | my $data = $transaction->result; # possibly blocks |
|
|
502 | |
|
|
503 | The "client_get" method works like "LWP::Simple::get": it requests the |
|
|
504 | given URL and waits till the data has arrived. It is defined to be: |
|
|
505 | |
|
|
506 | sub client_get { $_[0]->txn_client_get ($_[1])->result } |
|
|
507 | |
|
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508 | And in fact is automatically generated. This is the blocking API of |
|
|
509 | Net::FCP, and it works as simple as in any other, similar, module. |
|
|
510 | |
|
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511 | More complicated is "txn_client_get": It only creates a transaction |
|
|
512 | (completion, result, ...) object and initiates the transaction. |
|
|
513 | |
|
|
514 | my $txn = bless { }, Net::FCP::Txn::; |
|
|
515 | |
|
|
516 | It also creates a condition variable that is used to signal the |
|
|
517 | completion of the request: |
|
|
518 | |
|
|
519 | $txn->{finished} = AnyAvent->condvar; |
|
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520 | |
|
|
521 | It then creates a socket in non-blocking mode. |
|
|
522 | |
|
|
523 | socket $txn->{fh}, ...; |
|
|
524 | fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
|
|
525 | connect $txn->{fh}, ... |
|
|
526 | and !$!{EWOULDBLOCK} |
|
|
527 | and !$!{EINPROGRESS} |
|
|
528 | and Carp::croak "unable to connect: $!\n"; |
|
|
529 | |
|
|
530 | Then it creates a write-watcher which gets called whenever an error |
|
|
531 | occurs or the connection succeeds: |
|
|
532 | |
|
|
533 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
|
|
534 | |
|
|
535 | And returns this transaction object. The "fh_ready_w" callback gets |
|
|
536 | called as soon as the event loop detects that the socket is ready for |
|
|
537 | writing. |
|
|
538 | |
|
|
539 | The "fh_ready_w" method makes the socket blocking again, writes the |
|
|
540 | request data and replaces the watcher by a read watcher (waiting for |
|
|
541 | reply data). The actual code is more complicated, but that doesn't |
|
|
542 | matter for this example: |
|
|
543 | |
|
|
544 | fcntl $txn->{fh}, F_SETFL, 0; |
|
|
545 | syswrite $txn->{fh}, $txn->{request} |
|
|
546 | or die "connection or write error"; |
|
|
547 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
|
|
548 | |
|
|
549 | Again, "fh_ready_r" waits till all data has arrived, and then stores the |
|
|
550 | result and signals any possible waiters that the request ahs finished: |
|
|
551 | |
|
|
552 | sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
|
|
553 | |
|
|
554 | if (end-of-file or data complete) { |
|
|
555 | $txn->{result} = $txn->{buf}; |
|
|
556 | $txn->{finished}->broadcast; |
|
|
557 | $txb->{cb}->($txn) of $txn->{cb}; # also call callback |
|
|
558 | } |
|
|
559 | |
|
|
560 | The "result" method, finally, just waits for the finished signal (if the |
|
|
561 | request was already finished, it doesn't wait, of course, and returns |
|
|
562 | the data: |
|
|
563 | |
|
|
564 | $txn->{finished}->wait; |
|
|
565 | return $txn->{result}; |
|
|
566 | |
|
|
567 | The actual code goes further and collects all errors ("die"s, |
|
|
568 | exceptions) that occured during request processing. The "result" method |
|
|
569 | detects whether an exception as thrown (it is stored inside the $txn |
|
|
570 | object) and just throws the exception, which means connection errors and |
|
|
571 | other problems get reported tot he code that tries to use the result, |
|
|
572 | not in a random callback. |
|
|
573 | |
|
|
574 | All of this enables the following usage styles: |
|
|
575 | |
|
|
576 | 1. Blocking: |
|
|
577 | |
|
|
578 | my $data = $fcp->client_get ($url); |
|
|
579 | |
|
|
580 | 2. Blocking, but running in parallel: |
|
|
581 | |
|
|
582 | my @datas = map $_->result, |
|
|
583 | map $fcp->txn_client_get ($_), |
|
|
584 | @urls; |
|
|
585 | |
|
|
586 | Both blocking examples work without the module user having to know |
|
|
587 | anything about events. |
|
|
588 | |
|
|
589 | 3a. Event-based in a main program, using any supported event module: |
|
|
590 | |
|
|
591 | use EV; |
|
|
592 | |
|
|
593 | $fcp->txn_client_get ($url)->cb (sub { |
|
|
594 | my $txn = shift; |
|
|
595 | my $data = $txn->result; |
|
|
596 | ... |
|
|
597 | }); |
|
|
598 | |
|
|
599 | EV::loop; |
|
|
600 | |
|
|
601 | 3b. The module user could use AnyEvent, too: |
|
|
602 | |
|
|
603 | use AnyEvent; |
|
|
604 | |
|
|
605 | my $quit = AnyEvent->condvar; |
|
|
606 | |
|
|
607 | $fcp->txn_client_get ($url)->cb (sub { |
|
|
608 | ... |
|
|
609 | $quit->broadcast; |
|
|
610 | }); |
|
|
611 | |
|
|
612 | $quit->wait; |
|
|
613 | |
|
|
614 | FORK |
|
|
615 | Most event libraries are not fork-safe. The ones who are usually are |
|
|
616 | because they are so inefficient. Only EV is fully fork-aware. |
|
|
617 | |
|
|
618 | If you have to fork, you must either do so *before* creating your first |
|
|
619 | watcher OR you must not use AnyEvent at all in the child. |
|
|
620 | |
|
|
621 | SECURITY CONSIDERATIONS |
|
|
622 | AnyEvent can be forced to load any event model via |
|
|
623 | $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used |
|
|
624 | to execute arbitrary code or directly gain access, it can easily be used |
|
|
625 | to make the program hang or malfunction in subtle ways, as AnyEvent |
|
|
626 | watchers will not be active when the program uses a different event |
|
|
627 | model than specified in the variable. |
|
|
628 | |
|
|
629 | You can make AnyEvent completely ignore this variable by deleting it |
|
|
630 | before the first watcher gets created, e.g. with a "BEGIN" block: |
|
|
631 | |
|
|
632 | BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
|
|
633 | |
|
|
634 | use AnyEvent; |
|
|
635 | |
73 | SEE ALSO |
636 | SEE ALSO |
74 | Coro::Event, Coro, Event, Glib::Event, Glib, AnyEvent::Impl::Coro, |
637 | Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event, |
75 | AnyEvent::Impl::Event, AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. |
638 | Glib::Event, Glib, Coro, Tk, Event::Lib, Qt. |
76 | |
639 | |
|
|
640 | Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV, |
|
|
641 | AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib, |
|
|
642 | AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib, |
|
|
643 | AnyEvent::Impl::Qt. |
77 | |
644 | |
|
|
645 | Nontrivial usage examples: Net::FCP, Net::XMPP2. |
|
|
646 | |
|
|
647 | AUTHOR |
|
|
648 | Marc Lehmann <schmorp@schmorp.de> |
|
|
649 | http://home.schmorp.de/ |
|
|
650 | |