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141 | =head2 I/O WATCHERS |
141 | =head2 I/O WATCHERS |
142 | |
142 | |
143 | You can create an I/O watcher by calling the C<< AnyEvent->io >> method |
143 | You can create an I/O watcher by calling the C<< AnyEvent->io >> method |
144 | with the following mandatory key-value pairs as arguments: |
144 | with the following mandatory key-value pairs as arguments: |
145 | |
145 | |
146 | C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for |
146 | C<fh> the Perl I<file handle> (I<not> file descriptor) to watch |
147 | events. C<poll> must be a string that is either C<r> or C<w>, which |
147 | for events. C<poll> must be a string that is either C<r> or C<w>, |
148 | creates a watcher waiting for "r"eadable or "w"ritable events, |
148 | which creates a watcher waiting for "r"eadable or "w"ritable events, |
149 | respectively. C<cb> is the callback to invoke each time the file handle |
149 | respectively. C<cb> is the callback to invoke each time the file handle |
150 | becomes ready. |
150 | becomes ready. |
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151 | |
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152 | Although the callback might get passed parameters, their value and |
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153 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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154 | callbacks cannot use arguments passed to I/O watcher callbacks. |
151 | |
155 | |
152 | The I/O watcher might use the underlying file descriptor or a copy of it. |
156 | The I/O watcher might use the underlying file descriptor or a copy of it. |
153 | You must not close a file handle as long as any watcher is active on the |
157 | You must not close a file handle as long as any watcher is active on the |
154 | underlying file descriptor. |
158 | underlying file descriptor. |
155 | |
159 | |
156 | Some event loops issue spurious readyness notifications, so you should |
160 | Some event loops issue spurious readyness notifications, so you should |
157 | always use non-blocking calls when reading/writing from/to your file |
161 | always use non-blocking calls when reading/writing from/to your file |
158 | handles. |
162 | handles. |
159 | |
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160 | Although the callback might get passed parameters, their value and |
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161 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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162 | callbacks cannot use arguments passed to I/O watcher callbacks. |
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163 | |
163 | |
164 | Example: |
164 | Example: |
165 | |
165 | |
166 | # wait for readability of STDIN, then read a line and disable the watcher |
166 | # wait for readability of STDIN, then read a line and disable the watcher |
167 | my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
167 | my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
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174 | |
174 | |
175 | You can create a time watcher by calling the C<< AnyEvent->timer >> |
175 | You can create a time watcher by calling the C<< AnyEvent->timer >> |
176 | method with the following mandatory arguments: |
176 | method with the following mandatory arguments: |
177 | |
177 | |
178 | C<after> specifies after how many seconds (fractional values are |
178 | C<after> specifies after how many seconds (fractional values are |
179 | supported) should the timer activate. C<cb> the callback to invoke in that |
179 | supported) the callback should be invoked. C<cb> is the callback to invoke |
180 | case. |
180 | in that case. |
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181 | |
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182 | Although the callback might get passed parameters, their value and |
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183 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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184 | callbacks cannot use arguments passed to time watcher callbacks. |
181 | |
185 | |
182 | The timer callback will be invoked at most once: if you want a repeating |
186 | The timer callback will be invoked at most once: if you want a repeating |
183 | timer you have to create a new watcher (this is a limitation by both Tk |
187 | timer you have to create a new watcher (this is a limitation by both Tk |
184 | and Glib). |
188 | and Glib). |
185 | |
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186 | Although the callback might get passed parameters, their value and |
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187 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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188 | callbacks cannot use arguments passed to time watcher callbacks. |
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189 | |
189 | |
190 | Example: |
190 | Example: |
191 | |
191 | |
192 | # fire an event after 7.7 seconds |
192 | # fire an event after 7.7 seconds |
193 | my $w = AnyEvent->timer (after => 7.7, cb => sub { |
193 | my $w = AnyEvent->timer (after => 7.7, cb => sub { |
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234 | |
234 | |
235 | You can watch for signals using a signal watcher, C<signal> is the signal |
235 | You can watch for signals using a signal watcher, C<signal> is the signal |
236 | I<name> without any C<SIG> prefix, C<cb> is the Perl callback to |
236 | I<name> without any C<SIG> prefix, C<cb> is the Perl callback to |
237 | be invoked whenever a signal occurs. |
237 | be invoked whenever a signal occurs. |
238 | |
238 | |
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239 | Although the callback might get passed parameters, their value and |
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240 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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241 | callbacks cannot use arguments passed to signal watcher callbacks. |
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242 | |
239 | Multiple signal occurances can be clumped together into one callback |
243 | Multiple signal occurances can be clumped together into one callback |
240 | invocation, and callback invocation will be synchronous. synchronous means |
244 | invocation, and callback invocation will be synchronous. synchronous means |
241 | that it might take a while until the signal gets handled by the process, |
245 | that it might take a while until the signal gets handled by the process, |
242 | but it is guarenteed not to interrupt any other callbacks. |
246 | but it is guarenteed not to interrupt any other callbacks. |
243 | |
247 | |
… | |
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257 | |
261 | |
258 | The child process is specified by the C<pid> argument (if set to C<0>, it |
262 | The child process is specified by the C<pid> argument (if set to C<0>, it |
259 | watches for any child process exit). The watcher will trigger as often |
263 | watches for any child process exit). The watcher will trigger as often |
260 | as status change for the child are received. This works by installing a |
264 | as status change for the child are received. This works by installing a |
261 | signal handler for C<SIGCHLD>. The callback will be called with the pid |
265 | signal handler for C<SIGCHLD>. The callback will be called with the pid |
262 | and exit status (as returned by waitpid). |
266 | and exit status (as returned by waitpid), so unlike other watcher types, |
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267 | you I<can> rely on child watcher callback arguments. |
263 | |
268 | |
264 | There is a slight catch to child watchers, however: you usually start them |
269 | There is a slight catch to child watchers, however: you usually start them |
265 | I<after> the child process was created, and this means the process could |
270 | I<after> the child process was created, and this means the process could |
266 | have exited already (and no SIGCHLD will be sent anymore). |
271 | have exited already (and no SIGCHLD will be sent anymore). |
267 | |
272 | |
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959 | maximal/minimal, respectively. Even when going through AnyEvent, it uses |
964 | maximal/minimal, respectively. Even when going through AnyEvent, it uses |
960 | far less memory than any other event loop and is still faster than Event |
965 | far less memory than any other event loop and is still faster than Event |
961 | natively. |
966 | natively. |
962 | |
967 | |
963 | The pure perl implementation is hit in a few sweet spots (both the |
968 | The pure perl implementation is hit in a few sweet spots (both the |
964 | zero timeout and the use of a single fd hit optimisations in the perl |
969 | constant timeout and the use of a single fd hit optimisations in the perl |
965 | interpreter and the backend itself, and all watchers become ready at the |
970 | interpreter and the backend itself). Nevertheless this shows that it |
966 | same time). Nevertheless this shows that it adds very little overhead in |
971 | adds very little overhead in itself. Like any select-based backend its |
967 | itself. Like any select-based backend its performance becomes really bad |
972 | performance becomes really bad with lots of file descriptors (and few of |
968 | with lots of file descriptors (and few of them active), of course, but |
973 | them active), of course, but this was not subject of this benchmark. |
969 | this was not subject of this benchmark. |
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970 | |
974 | |
971 | The C<Event> module has a relatively high setup and callback invocation cost, |
975 | The C<Event> module has a relatively high setup and callback invocation cost, |
972 | but overall scores on the third place. |
976 | but overall scores on the third place. |
973 | |
977 | |
974 | C<Glib>'s memory usage is quite a bit bit higher, but it features a |
978 | C<Glib>'s memory usage is quite a bit bit higher, but it features a |
… | |
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982 | The C<Tk> adaptor works relatively well. The fact that it crashes with |
986 | The C<Tk> adaptor works relatively well. The fact that it crashes with |
983 | more than 2000 watchers is a big setback, however, as correctness takes |
987 | more than 2000 watchers is a big setback, however, as correctness takes |
984 | precedence over speed. Nevertheless, its performance is surprising, as the |
988 | precedence over speed. Nevertheless, its performance is surprising, as the |
985 | file descriptor is dup()ed for each watcher. This shows that the dup() |
989 | file descriptor is dup()ed for each watcher. This shows that the dup() |
986 | employed by some adaptors is not a big performance issue (it does incur a |
990 | employed by some adaptors is not a big performance issue (it does incur a |
987 | hidden memory cost inside the kernel, though, that is not reflected in the |
991 | hidden memory cost inside the kernel which is not reflected in the figures |
988 | figures above). |
992 | above). |
989 | |
993 | |
990 | C<POE>, regardless of underlying event loop (wether using its pure perl |
994 | C<POE>, regardless of underlying event loop (whether using its pure |
991 | select-based backend or the Event module) shows abysmal performance and |
995 | perl select-based backend or the Event module, the POE-EV backend |
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996 | couldn't be tested because it wasn't working) shows abysmal performance |
992 | memory usage: Watchers use almost 30 times as much memory as EV watchers, |
997 | and memory usage: Watchers use almost 30 times as much memory as |
993 | and 10 times as much memory as both Event or EV via AnyEvent. Watcher |
998 | EV watchers, and 10 times as much memory as Event (the high memory |
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999 | requirements are caused by requiring a session for each watcher). Watcher |
994 | invocation is almost 900 times slower than with AnyEvent's pure perl |
1000 | invocation speed is almost 900 times slower than with AnyEvent's pure perl |
995 | implementation. The design of the POE adaptor class in AnyEvent can not |
1001 | implementation. The design of the POE adaptor class in AnyEvent can not |
996 | really account for this, as session creation overhead is small compared |
1002 | really account for this, as session creation overhead is small compared |
997 | to execution of the state machine, which is coded pretty optimally within |
1003 | to execution of the state machine, which is coded pretty optimally within |
998 | L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow. |
1004 | L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow. |
999 | |
1005 | |
1000 | =head2 Summary |
1006 | =head2 Summary |
1001 | |
1007 | |
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1008 | =over 4 |
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1009 | |
1002 | Using EV through AnyEvent is faster than any other event loop, but most |
1010 | =item * Using EV through AnyEvent is faster than any other event loop |
1003 | event loops have acceptable performance with or without AnyEvent. |
1011 | (even when used without AnyEvent), but most event loops have acceptable |
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1012 | performance with or without AnyEvent. |
1004 | |
1013 | |
1005 | The overhead AnyEvent adds is usually much smaller than the overhead of |
1014 | =item * The overhead AnyEvent adds is usually much smaller than the overhead of |
1006 | the actual event loop, only with extremely fast event loops such as the EV |
1015 | the actual event loop, only with extremely fast event loops such as EV |
1007 | adds AnyEvent significant overhead. |
1016 | adds AnyEvent significant overhead. |
1008 | |
1017 | |
1009 | And you should simply avoid POE like the plague if you want performance or |
1018 | =item * You should simply avoid POE like the plague if you want performance or |
1010 | reasonable memory usage. |
1019 | reasonable memory usage. |
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1020 | |
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1021 | =back |
1011 | |
1022 | |
1012 | |
1023 | |
1013 | =head1 FORK |
1024 | =head1 FORK |
1014 | |
1025 | |
1015 | Most event libraries are not fork-safe. The ones who are usually are |
1026 | Most event libraries are not fork-safe. The ones who are usually are |