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Revision 1.337 by root, Sun Oct 31 20:20:20 2010 UTC vs.
Revision 1.339 by root, Sun Oct 31 22:19:38 2010 UTC

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241the current system, you would need to look at C<ev_embeddable_backends () 241the current system, you would need to look at C<ev_embeddable_backends ()
242& ev_supported_backends ()>, likewise for recommended ones. 242& ev_supported_backends ()>, likewise for recommended ones.
243 243
244See the description of C<ev_embed> watchers for more info. 244See the description of C<ev_embed> watchers for more info.
245 245
246=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT] 246=item ev_set_allocator (void *(*cb)(void *ptr, long size))
247 247
248Sets the allocation function to use (the prototype is similar - the 248Sets the allocation function to use (the prototype is similar - the
249semantics are identical to the C<realloc> C89/SuS/POSIX function). It is 249semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
250used to allocate and free memory (no surprises here). If it returns zero 250used to allocate and free memory (no surprises here). If it returns zero
251when memory needs to be allocated (C<size != 0>), the library might abort 251when memory needs to be allocated (C<size != 0>), the library might abort
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277 } 277 }
278 278
279 ... 279 ...
280 ev_set_allocator (persistent_realloc); 280 ev_set_allocator (persistent_realloc);
281 281
282=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT] 282=item ev_set_syserr_cb (void (*cb)(const char *msg))
283 283
284Set the callback function to call on a retryable system call error (such 284Set the callback function to call on a retryable system call error (such
285as failed select, poll, epoll_wait). The message is a printable string 285as failed select, poll, epoll_wait). The message is a printable string
286indicating the system call or subsystem causing the problem. If this 286indicating the system call or subsystem causing the problem. If this
287callback is set, then libev will expect it to remedy the situation, no 287callback is set, then libev will expect it to remedy the situation, no
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464 464
465The epoll mechanism deserves honorable mention as the most misdesigned 465The epoll mechanism deserves honorable mention as the most misdesigned
466of the more advanced event mechanisms: mere annoyances include silently 466of the more advanced event mechanisms: mere annoyances include silently
467dropping file descriptors, requiring a system call per change per file 467dropping file descriptors, requiring a system call per change per file
468descriptor (and unnecessary guessing of parameters), problems with dup, 468descriptor (and unnecessary guessing of parameters), problems with dup,
469returning before the timeout value requiring additional iterations and so 469returning before the timeout value, resulting in additional iterations
470(and only giving 5ms accuracy while select on the same platform gives
470on. The biggest issue is fork races, however - if a program forks then 4710.1ms) and so on. The biggest issue is fork races, however - if a program
471I<both> parent and child process have to recreate the epoll set, which can 472forks then I<both> parent and child process have to recreate the epoll
472take considerable time (one syscall per file descriptor) and is of course 473set, which can take considerable time (one syscall per file descriptor)
473hard to detect. 474and is of course hard to detect.
474 475
475Epoll is also notoriously buggy - embedding epoll fds I<should> work, but 476Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
476of course I<doesn't>, and epoll just loves to report events for totally 477of course I<doesn't>, and epoll just loves to report events for totally
477I<different> file descriptors (even already closed ones, so one cannot 478I<different> file descriptors (even already closed ones, so one cannot
478even remove them from the set) than registered in the set (especially 479even remove them from the set) than registered in the set (especially
479on SMP systems). Libev tries to counter these spurious notifications by 480on SMP systems). Libev tries to counter these spurious notifications by
480employing an additional generation counter and comparing that against the 481employing an additional generation counter and comparing that against the
481events to filter out spurious ones, recreating the set when required. Last 482events to filter out spurious ones, recreating the set when required. Last
482not least, it also refuses to work with some file descriptors which work 483not least, it also refuses to work with some file descriptors which work
483perfectly fine with C<select> (files, many character devices...). 484perfectly fine with C<select> (files, many character devices...).
485
486Epoll is truly the train wreck analog among event poll mechanisms.
484 487
485While stopping, setting and starting an I/O watcher in the same iteration 488While stopping, setting and starting an I/O watcher in the same iteration
486will result in some caching, there is still a system call per such 489will result in some caching, there is still a system call per such
487incident (because the same I<file descriptor> could point to a different 490incident (because the same I<file descriptor> could point to a different
488I<file description> now), so its best to avoid that. Also, C<dup ()>'ed 491I<file description> now), so its best to avoid that. Also, C<dup ()>'ed

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