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1 | NAME |
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2 | AnyEvent - provide framework for multiple event loops |
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3 | |
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4 | Event, Coro, Glib, Tk, Perl - various supported event loops |
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5 | |
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6 | SYNOPSIS |
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7 | use AnyEvent; |
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8 | |
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9 | my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { |
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10 | ... |
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11 | }); |
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12 | |
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13 | my $w = AnyEvent->timer (after => $seconds, cb => sub { |
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14 | ... |
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15 | }); |
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16 | |
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17 | my $w = AnyEvent->condvar; # stores wether a condition was flagged |
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18 | $w->wait; # enters "main loop" till $condvar gets ->broadcast |
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19 | $w->broadcast; # wake up current and all future wait's |
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20 | |
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21 | DESCRIPTION |
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22 | AnyEvent provides an identical interface to multiple event loops. This |
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23 | allows module authors to utilise an event loop without forcing module |
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24 | users to use the same event loop (as only a single event loop can |
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25 | coexist peacefully at any one time). |
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26 | |
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27 | The interface itself is vaguely similar but not identical to the Event |
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28 | module. |
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29 | |
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30 | On the first call of any method, the module tries to detect the |
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31 | currently loaded event loop by probing wether any of the following |
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32 | modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is |
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33 | used. If none is found, the module tries to load these modules in the |
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34 | order given. The first one that could be successfully loaded will be |
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35 | used. If still none could be found, AnyEvent will fall back to a |
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36 | pure-perl event loop, which is also not very efficient. |
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37 | |
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38 | Because AnyEvent first checks for modules that are already loaded, |
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39 | loading an Event model explicitly before first using AnyEvent will |
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40 | likely make that model the default. For example: |
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41 | |
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42 | use Tk; |
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43 | use AnyEvent; |
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44 | |
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45 | # .. AnyEvent will likely default to Tk |
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46 | |
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47 | The pure-perl implementation of AnyEvent is called |
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48 | "AnyEvent::Impl::Perl". Like other event modules you can load it |
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49 | explicitly. |
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50 | |
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51 | WATCHERS |
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52 | AnyEvent has the central concept of a *watcher*, which is an object that |
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53 | stores relevant data for each kind of event you are waiting for, such as |
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54 | the callback to call, the filehandle to watch, etc. |
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55 | |
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56 | These watchers are normal Perl objects with normal Perl lifetime. After |
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57 | creating a watcher it will immediately "watch" for events and invoke the |
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58 | callback. To disable the watcher you have to destroy it (e.g. by setting |
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59 | the variable that stores it to "undef" or otherwise deleting all |
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60 | references to it). |
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61 | |
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62 | All watchers are created by calling a method on the "AnyEvent" class. |
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63 | |
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64 | IO WATCHERS |
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65 | You can create I/O watcher by calling the "AnyEvent->io" method with the |
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66 | following mandatory arguments: |
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67 | |
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68 | "fh" the Perl *filehandle* (not filedescriptor) to watch for events. |
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69 | "poll" must be a string that is either "r" or "w", that creates a |
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70 | watcher waiting for "r"eadable or "w"ritable events. "cb" the callback |
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71 | to invoke everytime the filehandle becomes ready. |
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72 | |
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73 | Only one io watcher per "fh" and "poll" combination is allowed (i.e. on |
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74 | a socket you can have one r + one w, not any more (limitation comes from |
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75 | Tk - if you are sure you are not using Tk this limitation is gone). |
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76 | |
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77 | Filehandles will be kept alive, so as long as the watcher exists, the |
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78 | filehandle exists, too. |
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79 | |
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80 | Example: |
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81 | |
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82 | # wait for readability of STDIN, then read a line and disable the watcher |
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83 | my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
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84 | chomp (my $input = <STDIN>); |
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85 | warn "read: $input\n"; |
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86 | undef $w; |
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87 | }); |
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88 | |
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89 | TIME WATCHERS |
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90 | You can create a time watcher by calling the "AnyEvent->timer" method |
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91 | with the following mandatory arguments: |
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92 | |
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93 | "after" after how many seconds (fractions are supported) should the |
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94 | timer activate. "cb" the callback to invoke. |
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95 | |
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96 | The timer callback will be invoked at most once: if you want a repeating |
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97 | timer you have to create a new watcher (this is a limitation by both Tk |
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98 | and Glib). |
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99 | |
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100 | Example: |
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101 | |
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102 | # fire an event after 7.7 seconds |
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103 | my $w = AnyEvent->timer (after => 7.7, cb => sub { |
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104 | warn "timeout\n"; |
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105 | }); |
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106 | |
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107 | # to cancel the timer: |
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108 | undef $w; |
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109 | |
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110 | CONDITION WATCHERS |
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111 | Condition watchers can be created by calling the "AnyEvent->condvar" |
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112 | method without any arguments. |
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113 | |
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114 | A condition watcher watches for a condition - precisely that the |
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115 | "->broadcast" method has been called. |
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116 | |
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117 | The watcher has only two methods: |
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118 | |
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119 | $cv->wait |
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120 | Wait (blocking if necessary) until the "->broadcast" method has been |
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121 | called on c<$cv>, while servicing other watchers normally. |
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122 | |
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123 | Not all event models support a blocking wait - some die in that |
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124 | case, so if you are using this from a module, never require a |
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125 | blocking wait, but let the caller decide wether the call will block |
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126 | or not (for example, by coupling condition variables with some kind |
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127 | of request results and supporting callbacks so the caller knows that |
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128 | getting the result will not block, while still suppporting blockign |
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129 | waits if the caller so desires). |
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130 | |
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131 | You can only wait once on a condition - additional calls will return |
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132 | immediately. |
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133 | |
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134 | $cv->broadcast |
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135 | Flag the condition as ready - a running "->wait" and all further |
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136 | calls to "wait" will return after this method has been called. If |
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137 | nobody is waiting the broadcast will be remembered.. |
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138 | |
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139 | Example: |
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140 | |
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141 | # wait till the result is ready |
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142 | my $result_ready = AnyEvent->condvar; |
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143 | |
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144 | # do something such as adding a timer |
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145 | # or socket watcher the calls $result_ready->broadcast |
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146 | # when the "result" is ready. |
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147 | |
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148 | $result_ready->wait; |
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149 | |
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150 | SIGNAL WATCHERS |
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151 | You can listen for signals using a signal watcher, "signal" is the |
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152 | signal *name* without any "SIG" prefix. Multiple signals events can be |
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153 | clumped together into one callback invocation, and callback invocation |
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154 | might or might not be asynchronous. |
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155 | |
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156 | These watchers might use %SIG, so programs overwriting those signals |
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157 | directly will likely not work correctly. |
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158 | |
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159 | Example: exit on SIGINT |
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160 | |
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161 | my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); |
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162 | |
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163 | CHILD PROCESS WATCHERS |
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164 | You can also listen for the status of a child process specified by the |
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165 | "pid" argument (or any child if the pid argument is 0). The watcher will |
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166 | trigger as often as status change for the child are received. This works |
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167 | by installing a signal handler for "SIGCHLD". The callback will be |
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168 | called with the pid and exit status (as returned by waitpid). |
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169 | |
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170 | Example: wait for pid 1333 |
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171 | |
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172 | my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" }); |
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173 | |
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174 | GLOBALS |
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175 | $AnyEvent::MODEL |
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176 | Contains "undef" until the first watcher is being created. Then it |
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177 | contains the event model that is being used, which is the name of |
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178 | the Perl class implementing the model. This class is usually one of |
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179 | the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
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180 | case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
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181 | |
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182 | The known classes so far are: |
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183 | |
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184 | AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
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185 | AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). |
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186 | AnyEvent::Impl::Coro based on Coro::Event, second best choice. |
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187 | AnyEvent::Impl::Event based on Event, also second best choice :) |
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188 | AnyEvent::Impl::Glib based on Glib, second-best choice. |
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189 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
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190 | AnyEvent::Impl::Perl pure-perl implementation, inefficient. |
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191 | |
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192 | AnyEvent::detect |
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193 | Returns $AnyEvent::MODEL, forcing autodetection of the event model |
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194 | if necessary. You should only call this function right before you |
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195 | would have created an AnyEvent watcher anyway, that is, very late at |
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196 | runtime. |
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197 | |
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198 | WHAT TO DO IN A MODULE |
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199 | As a module author, you should "use AnyEvent" and call AnyEvent methods |
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200 | freely, but you should not load a specific event module or rely on it. |
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201 | |
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202 | Be careful when you create watchers in the module body - Anyevent will |
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203 | decide which event module to use as soon as the first method is called, |
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204 | so by calling AnyEvent in your module body you force the user of your |
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205 | module to load the event module first. |
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206 | |
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207 | WHAT TO DO IN THE MAIN PROGRAM |
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208 | There will always be a single main program - the only place that should |
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209 | dictate which event model to use. |
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210 | |
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211 | If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
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212 | do anything special and let AnyEvent decide which implementation to |
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213 | chose. |
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214 | |
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215 | If the main program relies on a specific event model (for example, in |
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216 | Gtk2 programs you have to rely on either Glib or Glib::Event), you |
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217 | should load it before loading AnyEvent or any module that uses it, |
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218 | generally, as early as possible. The reason is that modules might create |
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219 | watchers when they are loaded, and AnyEvent will decide on the event |
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220 | model to use as soon as it creates watchers, and it might chose the |
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221 | wrong one unless you load the correct one yourself. |
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222 | |
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223 | You can chose to use a rather inefficient pure-perl implementation by |
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224 | loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is |
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225 | generally better. |
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226 | |
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227 | SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
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228 | If you need to support another event library which isn't directly |
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229 | supported by AnyEvent, you can supply your own interface to it by |
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230 | pushing, before the first watcher gets created, the package name of the |
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231 | event module and the package name of the interface to use onto |
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232 | @AnyEvent::REGISTRY. You can do that before and even without loading |
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233 | AnyEvent. |
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234 | |
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235 | Example: |
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236 | |
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237 | push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
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238 | |
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239 | This tells AnyEvent to (literally) use the "urxvt::anyevent::" |
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240 | package/class when it finds the "urxvt" package/module is loaded. When |
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241 | AnyEvent is loaded and asked to find a suitable event model, it will |
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242 | first check for the presence of urxvt. |
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243 | |
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244 | The class should provide implementations for all watcher types (see |
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245 | AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code) |
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246 | and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to |
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247 | see the sources). |
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248 | |
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249 | The above isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) uses the |
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250 | above line as-is. An interface isn't included in AnyEvent because it |
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251 | doesn't make sense outside the embedded interpreter inside |
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252 | *rxvt-unicode*, and it is updated and maintained as part of the |
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253 | *rxvt-unicode* distribution. |
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254 | |
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255 | *rxvt-unicode* also cheats a bit by not providing blocking access to |
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256 | condition variables: code blocking while waiting for a condition will |
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257 | "die". This still works with most modules/usages, and blocking calls |
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258 | must not be in an interactive application, so it makes sense. |
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259 | |
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260 | ENVIRONMENT VARIABLES |
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261 | The following environment variables are used by this module: |
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262 | |
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263 | "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event |
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264 | model gets used. |
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265 | |
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266 | EXAMPLE |
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267 | The following program uses an io watcher to read data from stdin, a |
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268 | timer to display a message once per second, and a condvar to exit the |
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269 | program when the user enters quit: |
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270 | |
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271 | use AnyEvent; |
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272 | |
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273 | my $cv = AnyEvent->condvar; |
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274 | |
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275 | my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
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276 | warn "io event <$_[0]>\n"; # will always output <r> |
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277 | chomp (my $input = <STDIN>); # read a line |
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278 | warn "read: $input\n"; # output what has been read |
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279 | $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
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280 | }); |
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281 | |
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282 | my $time_watcher; # can only be used once |
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283 | |
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284 | sub new_timer { |
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285 | $timer = AnyEvent->timer (after => 1, cb => sub { |
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286 | warn "timeout\n"; # print 'timeout' about every second |
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287 | &new_timer; # and restart the time |
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288 | }); |
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289 | } |
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290 | |
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291 | new_timer; # create first timer |
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292 | |
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293 | $cv->wait; # wait until user enters /^q/i |
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294 | |
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295 | REAL-WORLD EXAMPLE |
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296 | Consider the Net::FCP module. It features (among others) the following |
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297 | API calls, which are to freenet what HTTP GET requests are to http: |
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298 | |
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299 | my $data = $fcp->client_get ($url); # blocks |
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300 | |
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301 | my $transaction = $fcp->txn_client_get ($url); # does not block |
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302 | $transaction->cb ( sub { ... } ); # set optional result callback |
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303 | my $data = $transaction->result; # possibly blocks |
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304 | |
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305 | The "client_get" method works like "LWP::Simple::get": it requests the |
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306 | given URL and waits till the data has arrived. It is defined to be: |
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307 | |
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308 | sub client_get { $_[0]->txn_client_get ($_[1])->result } |
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309 | |
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310 | And in fact is automatically generated. This is the blocking API of |
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311 | Net::FCP, and it works as simple as in any other, similar, module. |
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312 | |
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313 | More complicated is "txn_client_get": It only creates a transaction |
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314 | (completion, result, ...) object and initiates the transaction. |
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315 | |
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316 | my $txn = bless { }, Net::FCP::Txn::; |
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317 | |
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318 | It also creates a condition variable that is used to signal the |
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319 | completion of the request: |
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320 | |
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321 | $txn->{finished} = AnyAvent->condvar; |
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322 | |
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323 | It then creates a socket in non-blocking mode. |
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324 | |
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325 | socket $txn->{fh}, ...; |
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326 | fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
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327 | connect $txn->{fh}, ... |
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328 | and !$!{EWOULDBLOCK} |
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329 | and !$!{EINPROGRESS} |
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330 | and Carp::croak "unable to connect: $!\n"; |
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331 | |
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332 | Then it creates a write-watcher which gets called whenever an error |
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333 | occurs or the connection succeeds: |
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334 | |
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335 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
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336 | |
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337 | And returns this transaction object. The "fh_ready_w" callback gets |
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338 | called as soon as the event loop detects that the socket is ready for |
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339 | writing. |
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340 | |
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341 | The "fh_ready_w" method makes the socket blocking again, writes the |
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342 | request data and replaces the watcher by a read watcher (waiting for |
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343 | reply data). The actual code is more complicated, but that doesn't |
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344 | matter for this example: |
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345 | |
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346 | fcntl $txn->{fh}, F_SETFL, 0; |
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347 | syswrite $txn->{fh}, $txn->{request} |
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348 | or die "connection or write error"; |
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349 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
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350 | |
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351 | Again, "fh_ready_r" waits till all data has arrived, and then stores the |
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352 | result and signals any possible waiters that the request ahs finished: |
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353 | |
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354 | sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
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355 | |
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356 | if (end-of-file or data complete) { |
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357 | $txn->{result} = $txn->{buf}; |
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358 | $txn->{finished}->broadcast; |
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359 | $txb->{cb}->($txn) of $txn->{cb}; # also call callback |
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360 | } |
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361 | |
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362 | The "result" method, finally, just waits for the finished signal (if the |
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363 | request was already finished, it doesn't wait, of course, and returns |
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364 | the data: |
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365 | |
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366 | $txn->{finished}->wait; |
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367 | return $txn->{result}; |
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368 | |
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369 | The actual code goes further and collects all errors ("die"s, |
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370 | exceptions) that occured during request processing. The "result" method |
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371 | detects wether an exception as thrown (it is stored inside the $txn |
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372 | object) and just throws the exception, which means connection errors and |
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373 | other problems get reported tot he code that tries to use the result, |
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374 | not in a random callback. |
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375 | |
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376 | All of this enables the following usage styles: |
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377 | |
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378 | 1. Blocking: |
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379 | |
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380 | my $data = $fcp->client_get ($url); |
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381 | |
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382 | 2. Blocking, but parallelizing: |
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383 | |
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384 | my @datas = map $_->result, |
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385 | map $fcp->txn_client_get ($_), |
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386 | @urls; |
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387 | |
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388 | Both blocking examples work without the module user having to know |
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389 | anything about events. |
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390 | |
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391 | 3a. Event-based in a main program, using any support Event module: |
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392 | |
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393 | use Event; |
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394 | |
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395 | $fcp->txn_client_get ($url)->cb (sub { |
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396 | my $txn = shift; |
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397 | my $data = $txn->result; |
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398 | ... |
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399 | }); |
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400 | |
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401 | Event::loop; |
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402 | |
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403 | 3b. The module user could use AnyEvent, too: |
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404 | |
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405 | use AnyEvent; |
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406 | |
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407 | my $quit = AnyEvent->condvar; |
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408 | |
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409 | $fcp->txn_client_get ($url)->cb (sub { |
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410 | ... |
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411 | $quit->broadcast; |
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412 | }); |
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413 | |
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414 | $quit->wait; |
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415 | |
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416 | SEE ALSO |
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417 | Event modules: Coro::Event, Coro, Event, Glib::Event, Glib. |
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418 | |
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419 | Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event, |
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420 | AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. |
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421 | |
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422 | Nontrivial usage example: Net::FCP. |
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423 | |
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424 | |