[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.185 by root, Tue Sep 23 09:13:59 2008 UTC vs.
Revision 1.191 by root, Tue Sep 30 19:45:23 2008 UTC

…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	215	recommended ones.
216		216
217	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
218		218
219	=item ev_set_allocator (void (cb)(void *ptr, long size))	219	=item ev_set_allocator (void (cb)(void *ptr, long size)) [NOT REENTRANT]
220		220
221	Sets the allocation function to use (the prototype is similar - the	221	Sets the allocation function to use (the prototype is similar - the
222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
223	used to allocate and free memory (no surprises here). If it returns zero	223	used to allocate and free memory (no surprises here). If it returns zero
224	when memory needs to be allocated (C<size != 0>), the library might abort	224	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	250	}
251		251
252	...	252	...
253	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
254		254
255	=item ev_set_syserr_cb (void (cb)(const char msg));	255	=item ev_set_syserr_cb (void (cb)(const char msg)); [NOT REENTRANT]
256		256
257	Set the callback function to call on a retryable system call error (such	257	Set the callback function to call on a retryable system call error (such
258	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
260	callback is set, then libev will expect it to remedy the situation, no	260	callback is set, then libev will expect it to remedy the situation, no
…		…
1625		1625
1626	=back	1626	=back
1627		1627
1628	=head3 Examples	1628	=head3 Examples
1629		1629
1630	Example: Try to exit cleanly on SIGINT and SIGTERM.	1630	Example: Try to exit cleanly on SIGINT.
1631		1631
1632	static void	1632	static void
1633	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1633	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
1634	{	1634	{
1635	ev_unloop (loop, EVUNLOOP_ALL);	1635	ev_unloop (loop, EVUNLOOP_ALL);
1636	}	1636	}
1637		1637
1638	struct ev_signal signal_watcher;	1638	struct ev_signal signal_watcher;
1639	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1639	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1640	ev_signal_start (loop, &sigint_cb);	1640	ev_signal_start (loop, &signal_watcher);
1641		1641
1642		1642
1643	=head2 C<ev_child> - watch out for process status changes	1643	=head2 C<ev_child> - watch out for process status changes
1644		1644
1645	Child watchers trigger when your process receives a SIGCHLD in response to	1645	Child watchers trigger when your process receives a SIGCHLD in response to
…		…
2242	So when you want to use this feature you will always have to be prepared	2242	So when you want to use this feature you will always have to be prepared
2243	that you cannot get an embeddable loop. The recommended way to get around	2243	that you cannot get an embeddable loop. The recommended way to get around
2244	this is to have a separate variables for your embeddable loop, try to	2244	this is to have a separate variables for your embeddable loop, try to
2245	create it, and if that fails, use the normal loop for everything.	2245	create it, and if that fails, use the normal loop for everything.
2246		2246
		2247	=head3 C<ev_embed> and fork
		2248
		2249	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2250	automatically be applied to the embedded loop as well, so no special
		2251	fork handling is required in that case. When the watcher is not running,
		2252	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2253	as applicable.
		2254
2247	=head3 Watcher-Specific Functions and Data Members	2255	=head3 Watcher-Specific Functions and Data Members
2248		2256
2249	=over 4	2257	=over 4
2250		2258
2251	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)	2259	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)
…		…
2376	=over 4	2384	=over 4
2377		2385
2378	=item queueing from a signal handler context	2386	=item queueing from a signal handler context
2379		2387
2380	To implement race-free queueing, you simply add to the queue in the signal	2388	To implement race-free queueing, you simply add to the queue in the signal
2381	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2389	handler but you block the signal handler in the watcher callback. Here is
2382	some fictitious SIGUSR1 handler:	2390	an example that does that for some fictitious SIGUSR1 handler:
2383		2391
2384	static ev_async mysig;	2392	static ev_async mysig;
2385		2393
2386	static void	2394	static void
2387	sigusr1_handler (void)	2395	sigusr1_handler (void)
…		…
3298	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3306	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3299		3307
3300	#include "ev_cpp.h"	3308	#include "ev_cpp.h"
3301	#include "ev.c"	3309	#include "ev.c"
3302		3310
		3311	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3303		3312
3304	=head1 THREADS AND COROUTINES	3313	=head2 THREADS AND COROUTINES
3305		3314
3306	=head2 THREADS	3315	=head3 THREADS
3307		3316
3308	Libev itself is thread-safe (unless the opposite is specifically	3317	All libev functions are reentrant and thread-safe unless explicitly
3309	documented for a function), but it uses no locking itself. This means that	3318	documented otherwise, but libev implements no locking itself. This means
3310	you can use as many loops as you want in parallel, as long as only one	3319	that you can use as many loops as you want in parallel, as long as there
3311	thread ever calls into one libev function with the same loop parameter:	3320	are no concurrent calls into any libev function with the same loop
		3321	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3312	libev guarantees that different event loops share no data structures that	3322	of course): libev guarantees that different event loops share no data
3313	need locking.	3323	structures that need any locking.
3314		3324
3315	Or to put it differently: calls with different loop parameters can be done	3325	Or to put it differently: calls with different loop parameters can be done
3316	concurrently from multiple threads, calls with the same loop parameter	3326	concurrently from multiple threads, calls with the same loop parameter
3317	must be done serially (but can be done from different threads, as long as	3327	must be done serially (but can be done from different threads, as long as
3318	only one thread ever is inside a call at any point in time, e.g. by using	3328	only one thread ever is inside a call at any point in time, e.g. by using
3319	a mutex per loop).	3329	a mutex per loop).
3320		3330
3321	Specifically to support threads (and signal handlers), libev implements	3331	Specifically to support threads (and signal handlers), libev implements
3322	so-called C<ev_async> watchers, which allow some limited form of	3332	so-called C<ev_async> watchers, which allow some limited form of
3323	concurrency on the same event loop.	3333	concurrency on the same event loop, namely waking it up "from the
		3334	outside".
3324		3335
3325	If you want to know which design (one loop, locking, or multiple loops	3336	If you want to know which design (one loop, locking, or multiple loops
3326	without or something else still) is best for your problem, then I cannot	3337	without or something else still) is best for your problem, then I cannot
3327	help you. I can give some generic advice however:	3338	help you, but here is some generic advice:
3328		3339
3329	=over 4	3340	=over 4
3330		3341
3331	=item * most applications have a main thread: use the default libev loop	3342	=item * most applications have a main thread: use the default libev loop
3332	in that thread, or create a separate thread running only the default loop.	3343	in that thread, or create a separate thread running only the default loop.
…		…
3356	default loop and triggering an C<ev_async> watcher from the default loop	3367	default loop and triggering an C<ev_async> watcher from the default loop
3357	watcher callback into the event loop interested in the signal.	3368	watcher callback into the event loop interested in the signal.
3358		3369
3359	=back	3370	=back
3360		3371
3361	=head2 COROUTINES	3372	=head3 COROUTINES
3362		3373
3363	Libev is much more accommodating to coroutines ("cooperative threads"):	3374	Libev is very accommodating to coroutines ("cooperative threads"):
3364	libev fully supports nesting calls to it's functions from different	3375	libev fully supports nesting calls to its functions from different
3365	coroutines (e.g. you can call C<ev_loop> on the same loop from two	3376	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3366	different coroutines and switch freely between both coroutines running the	3377	different coroutines, and switch freely between both coroutines running the
3367	loop, as long as you don't confuse yourself). The only exception is that	3378	loop, as long as you don't confuse yourself). The only exception is that
3368	you must not do this from C<ev_periodic> reschedule callbacks.	3379	you must not do this from C<ev_periodic> reschedule callbacks.
3369		3380
3370	Care has been taken to ensure that libev does not keep local state inside	3381	Care has been taken to ensure that libev does not keep local state inside
3371	C<ev_loop>, and other calls do not usually allow coroutine switches.	3382	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3383	they do not clal any callbacks.
3372		3384
		3385	=head2 COMPILER WARNINGS
3373		3386
3374	=head1 COMPLEXITIES	3387	Depending on your compiler and compiler settings, you might get no or a
		3388	lot of warnings when compiling libev code. Some people are apparently
		3389	scared by this.
3375		3390
3376	In this section the complexities of (many of) the algorithms used inside	3391	However, these are unavoidable for many reasons. For one, each compiler
3377	libev will be explained. For complexity discussions about backends see the	3392	has different warnings, and each user has different tastes regarding
3378	documentation for C<ev_default_init>.	3393	warning options. "Warn-free" code therefore cannot be a goal except when
		3394	targeting a specific compiler and compiler-version.
3379		3395
3380	All of the following are about amortised time: If an array needs to be	3396	Another reason is that some compiler warnings require elaborate
3381	extended, libev needs to realloc and move the whole array, but this	3397	workarounds, or other changes to the code that make it less clear and less
3382	happens asymptotically never with higher number of elements, so O(1) might	3398	maintainable.
3383	mean it might do a lengthy realloc operation in rare cases, but on average
3384	it is much faster and asymptotically approaches constant time.
3385		3399
3386	=over 4	3400	And of course, some compiler warnings are just plain stupid, or simply
		3401	wrong (because they don't actually warn about the condition their message
		3402	seems to warn about). For example, certain older gcc versions had some
		3403	warnings that resulted an extreme number of false positives. These have
		3404	been fixed, but some people still insist on making code warn-free with
		3405	such buggy versions.
3387		3406
3388	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3407	While libev is written to generate as few warnings as possible,
		3408	"warn-free" code is not a goal, and it is recommended not to build libev
		3409	with any compiler warnings enabled unless you are prepared to cope with
		3410	them (e.g. by ignoring them). Remember that warnings are just that:
		3411	warnings, not errors, or proof of bugs.
3389		3412
3390	This means that, when you have a watcher that triggers in one hour and
3391	there are 100 watchers that would trigger before that then inserting will
3392	have to skip roughly seven (C<ld 100>) of these watchers.
3393		3413
3394	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3414	=head2 VALGRIND
3395		3415
3396	That means that changing a timer costs less than removing/adding them	3416	Valgrind has a special section here because it is a popular tool that is
3397	as only the relative motion in the event queue has to be paid for.	3417	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3398		3418
3399	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	3419	If you think you found a bug (memory leak, uninitialised data access etc.)
		3420	in libev, then check twice: If valgrind reports something like:
3400		3421
3401	These just add the watcher into an array or at the head of a list.	3422	==2274== definitely lost: 0 bytes in 0 blocks.
		3423	==2274== possibly lost: 0 bytes in 0 blocks.
		3424	==2274== still reachable: 256 bytes in 1 blocks.
3402		3425
3403	=item Stopping check/prepare/idle/fork/async watchers: O(1)	3426	Then there is no memory leak, just as memory accounted to global variables
		3427	is not a memleak - the memory is still being refernced, and didn't leak.
3404		3428
3405	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3429	Similarly, under some circumstances, valgrind might report kernel bugs
		3430	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3431	although an acceptable workaround has been found here), or it might be
		3432	confused.
3406		3433
3407	These watchers are stored in lists then need to be walked to find the	3434	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3408	correct watcher to remove. The lists are usually short (you don't usually	3435	make it into some kind of religion.
3409	have many watchers waiting for the same fd or signal).
3410		3436
3411	=item Finding the next timer in each loop iteration: O(1)	3437	If you are unsure about something, feel free to contact the mailing list
		3438	with the full valgrind report and an explanation on why you think this
		3439	is a bug in libev (best check the archives, too :). However, don't be
		3440	annoyed when you get a brisk "this is no bug" answer and take the chance
		3441	of learning how to interpret valgrind properly.
3412		3442
3413	By virtue of using a binary or 4-heap, the next timer is always found at a	3443	If you need, for some reason, empty reports from valgrind for your project
3414	fixed position in the storage array.	3444	I suggest using suppression lists.
3415		3445
3416	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3417		3446
3418	A change means an I/O watcher gets started or stopped, which requires	3447	=head1 PORTABILITY NOTES
3419	libev to recalculate its status (and possibly tell the kernel, depending
3420	on backend and whether C<ev_io_set> was used).
3421		3448
3422	=item Activating one watcher (putting it into the pending state): O(1)
3423
3424	=item Priority handling: O(number_of_priorities)
3425
3426	Priorities are implemented by allocating some space for each
3427	priority. When doing priority-based operations, libev usually has to
3428	linearly search all the priorities, but starting/stopping and activating
3429	watchers becomes O(1) with respect to priority handling.
3430
3431	=item Sending an ev_async: O(1)
3432
3433	=item Processing ev_async_send: O(number_of_async_watchers)
3434
3435	=item Processing signals: O(max_signal_number)
3436
3437	Sending involves a system call I<iff> there were no other C<ev_async_send>
3438	calls in the current loop iteration. Checking for async and signal events
3439	involves iterating over all running async watchers or all signal numbers.
3440
3441	=back
3442
3443
3444	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	3449	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3445		3450
3446	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3451	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3447	requires, and its I/O model is fundamentally incompatible with the POSIX	3452	requires, and its I/O model is fundamentally incompatible with the POSIX
3448	model. Libev still offers limited functionality on this platform in	3453	model. Libev still offers limited functionality on this platform in
3449	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3454	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3536	wrap all I/O functions and provide your own fd management, but the cost of	3541	wrap all I/O functions and provide your own fd management, but the cost of
3537	calling select (O(n²)) will likely make this unworkable.	3542	calling select (O(n²)) will likely make this unworkable.
3538		3543
3539	=back	3544	=back
3540		3545
3541
3542	=head1 PORTABILITY REQUIREMENTS	3546	=head2 PORTABILITY REQUIREMENTS
3543		3547
3544	In addition to a working ISO-C implementation, libev relies on a few	3548	In addition to a working ISO-C implementation and of course the
3545	additional extensions:	3549	backend-specific APIs, libev relies on a few additional extensions:
3546		3550
3547	=over 4	3551	=over 4
3548		3552
3549	=item C<void ()(ev_watcher_type , int revents)> must have compatible	3553	=item C<void ()(ev_watcher_type , int revents)> must have compatible
3550	calling conventions regardless of C<ev_watcher_type *>.	3554	calling conventions regardless of C<ev_watcher_type *>.
…		…
3575	except the initial one, and run the default loop in the initial thread as	3579	except the initial one, and run the default loop in the initial thread as
3576	well.	3580	well.
3577		3581
3578	=item C<long> must be large enough for common memory allocation sizes	3582	=item C<long> must be large enough for common memory allocation sizes
3579		3583
3580	To improve portability and simplify using libev, libev uses C<long>	3584	To improve portability and simplify its API, libev uses C<long> internally
3581	internally instead of C<size_t> when allocating its data structures. On	3585	instead of C<size_t> when allocating its data structures. On non-POSIX
3582	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	3586	systems (Microsoft...) this might be unexpectedly low, but is still at
3583	is still at least 31 bits everywhere, which is enough for hundreds of	3587	least 31 bits everywhere, which is enough for hundreds of millions of
3584	millions of watchers.	3588	watchers.
3585		3589
3586	=item C<double> must hold a time value in seconds with enough accuracy	3590	=item C<double> must hold a time value in seconds with enough accuracy
3587		3591
3588	The type C<double> is used to represent timestamps. It is required to	3592	The type C<double> is used to represent timestamps. It is required to
3589	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	3593	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
…		…
3593	=back	3597	=back
3594		3598
3595	If you know of other additional requirements drop me a note.	3599	If you know of other additional requirements drop me a note.
3596		3600
3597		3601
3598	=head1 COMPILER WARNINGS	3602	=head1 ALGORITHMIC COMPLEXITIES
3599		3603
3600	Depending on your compiler and compiler settings, you might get no or a	3604	In this section the complexities of (many of) the algorithms used inside
3601	lot of warnings when compiling libev code. Some people are apparently	3605	libev will be documented. For complexity discussions about backends see
3602	scared by this.	3606	the documentation for C<ev_default_init>.
3603		3607
3604	However, these are unavoidable for many reasons. For one, each compiler	3608	All of the following are about amortised time: If an array needs to be
3605	has different warnings, and each user has different tastes regarding	3609	extended, libev needs to realloc and move the whole array, but this
3606	warning options. "Warn-free" code therefore cannot be a goal except when	3610	happens asymptotically rarer with higher number of elements, so O(1) might
3607	targeting a specific compiler and compiler-version.	3611	mean that libev does a lengthy realloc operation in rare cases, but on
		3612	average it is much faster and asymptotically approaches constant time.
3608		3613
3609	Another reason is that some compiler warnings require elaborate	3614	=over 4
3610	workarounds, or other changes to the code that make it less clear and less
3611	maintainable.
3612		3615
3613	And of course, some compiler warnings are just plain stupid, or simply	3616	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3614	wrong (because they don't actually warn about the condition their message
3615	seems to warn about).
3616		3617
3617	While libev is written to generate as few warnings as possible,	3618	This means that, when you have a watcher that triggers in one hour and
3618	"warn-free" code is not a goal, and it is recommended not to build libev	3619	there are 100 watchers that would trigger before that, then inserting will
3619	with any compiler warnings enabled unless you are prepared to cope with	3620	have to skip roughly seven (C<ld 100>) of these watchers.
3620	them (e.g. by ignoring them). Remember that warnings are just that:
3621	warnings, not errors, or proof of bugs.
3622		3621
		3622	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3623		3623
3624	=head1 VALGRIND	3624	That means that changing a timer costs less than removing/adding them,
		3625	as only the relative motion in the event queue has to be paid for.
3625		3626
3626	Valgrind has a special section here because it is a popular tool that is	3627	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3627	highly useful, but valgrind reports are very hard to interpret.
3628		3628
3629	If you think you found a bug (memory leak, uninitialised data access etc.)	3629	These just add the watcher into an array or at the head of a list.
3630	in libev, then check twice: If valgrind reports something like:
3631		3630
3632	==2274== definitely lost: 0 bytes in 0 blocks.	3631	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3633	==2274== possibly lost: 0 bytes in 0 blocks.
3634	==2274== still reachable: 256 bytes in 1 blocks.
3635		3632
3636	Then there is no memory leak. Similarly, under some circumstances,	3633	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3637	valgrind might report kernel bugs as if it were a bug in libev, or it
3638	might be confused (it is a very good tool, but only a tool).
3639		3634
3640	If you are unsure about something, feel free to contact the mailing list	3635	These watchers are stored in lists, so they need to be walked to find the
3641	with the full valgrind report and an explanation on why you think this is	3636	correct watcher to remove. The lists are usually short (you don't usually
3642	a bug in libev. However, don't be annoyed when you get a brisk "this is	3637	have many watchers waiting for the same fd or signal: one is typical, two
3643	no bug" answer and take the chance of learning how to interpret valgrind	3638	is rare).
3644	properly.
3645		3639
3646	If you need, for some reason, empty reports from valgrind for your project	3640	=item Finding the next timer in each loop iteration: O(1)
3647	I suggest using suppression lists.	3641
		3642	By virtue of using a binary or 4-heap, the next timer is always found at a
		3643	fixed position in the storage array.
		3644
		3645	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3646
		3647	A change means an I/O watcher gets started or stopped, which requires
		3648	libev to recalculate its status (and possibly tell the kernel, depending
		3649	on backend and whether C<ev_io_set> was used).
		3650
		3651	=item Activating one watcher (putting it into the pending state): O(1)
		3652
		3653	=item Priority handling: O(number_of_priorities)
		3654
		3655	Priorities are implemented by allocating some space for each
		3656	priority. When doing priority-based operations, libev usually has to
		3657	linearly search all the priorities, but starting/stopping and activating
		3658	watchers becomes O(1) with respect to priority handling.
		3659
		3660	=item Sending an ev_async: O(1)
		3661
		3662	=item Processing ev_async_send: O(number_of_async_watchers)
		3663
		3664	=item Processing signals: O(max_signal_number)
		3665
		3666	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3667	calls in the current loop iteration. Checking for async and signal events
		3668	involves iterating over all running async watchers or all signal numbers.
		3669
		3670	=back
3648		3671
3649		3672
3650	=head1 AUTHOR	3673	=head1 AUTHOR
3651		3674
3652	Marc Lehmann <libev@schmorp.de>.	3675	Marc Lehmann <libev@schmorp.de>.

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Comparing libev/ev.pod (file contents): Revision 1.185 by root, Tue Sep 23 09:13:59 2008 UTC vs. Revision 1.191 by root, Tue Sep 30 19:45:23 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.185 by root, Tue Sep 23 09:13:59 2008 UTC vs.
Revision 1.191 by root, Tue Sep 30 19:45:23 2008 UTC