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

Comparing libev/ev.pod (file contents):
Revision 1.187 by root, Mon Sep 29 03:31:14 2008 UTC vs.
Revision 1.192 by root, Tue Sep 30 19:51:44 2008 UTC

…		…
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
…		…
2384	=over 4	2384	=over 4
2385		2385
2386	=item queueing from a signal handler context	2386	=item queueing from a signal handler context
2387		2387
2388	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
2389	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
2390	some fictitious SIGUSR1 handler:	2390	an example that does that for some fictitious SIGUSR1 handler:
2391		2391
2392	static ev_async mysig;	2392	static ev_async mysig;
2393		2393
2394	static void	2394	static void
2395	sigusr1_handler (void)	2395	sigusr1_handler (void)
…		…
2502	=over 4	2502	=over 4
2503		2503
2504	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2504	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2505		2505
2506	This function combines a simple timer and an I/O watcher, calls your	2506	This function combines a simple timer and an I/O watcher, calls your
2507	callback on whichever event happens first and automatically stop both	2507	callback on whichever event happens first and automatically stops both
2508	watchers. This is useful if you want to wait for a single event on an fd	2508	watchers. This is useful if you want to wait for a single event on an fd
2509	or timeout without having to allocate/configure/start/stop/free one or	2509	or timeout without having to allocate/configure/start/stop/free one or
2510	more watchers yourself.	2510	more watchers yourself.
2511		2511
2512	If C<fd> is less than 0, then no I/O watcher will be started and events	2512	If C<fd> is less than 0, then no I/O watcher will be started and the
2513	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2513	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2514	C<events> set will be created and started.	2514	the given C<fd> and C<events> set will be created and started.
2515		2515
2516	If C<timeout> is less than 0, then no timeout watcher will be	2516	If C<timeout> is less than 0, then no timeout watcher will be
2517	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2517	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2518	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2518	repeat = 0) will be started. While C<0> is a valid timeout, it is of
2519	dubious value.	2519	dubious value.
…		…
3306	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:
3307		3307
3308	#include "ev_cpp.h"	3308	#include "ev_cpp.h"
3309	#include "ev.c"	3309	#include "ev.c"
3310		3310
		3311	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3311		3312
3312	=head1 THREADS AND COROUTINES	3313	=head2 THREADS AND COROUTINES
3313		3314
3314	=head2 THREADS	3315	=head3 THREADS
3315		3316
3316	All libev functions are reentrant and thread-safe unless explicitly	3317	All libev functions are reentrant and thread-safe unless explicitly
3317	documented otherwise, but it uses no locking itself. This means that you	3318	documented otherwise, but libev implements no locking itself. This means
3318	can use as many loops as you want in parallel, as long as there are no	3319	that you can use as many loops as you want in parallel, as long as there
3319	concurrent calls into any libev function with the same loop parameter	3320	are no concurrent calls into any libev function with the same loop
3320	(C<ev_default_*> calls have an implicit default loop parameter, of	3321	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3321	course): libev guarantees that different event loops share no data	3322	of course): libev guarantees that different event loops share no data
3322	structures that need any locking.	3323	structures that need any locking.
3323		3324
3324	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
3325	concurrently from multiple threads, calls with the same loop parameter	3326	concurrently from multiple threads, calls with the same loop parameter
3326	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
…		…
3366	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
3367	watcher callback into the event loop interested in the signal.	3368	watcher callback into the event loop interested in the signal.
3368		3369
3369	=back	3370	=back
3370		3371
3371	=head2 COROUTINES	3372	=head3 COROUTINES
3372		3373
3373	Libev is much more accommodating to coroutines ("cooperative threads"):	3374	Libev is very accommodating to coroutines ("cooperative threads"):
3374	libev fully supports nesting calls to it's functions from different	3375	libev fully supports nesting calls to its functions from different
3375	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
3376	different coroutines and switch freely between both coroutines running the	3377	different coroutines, and switch freely between both coroutines running the
3377	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
3378	you must not do this from C<ev_periodic> reschedule callbacks.	3379	you must not do this from C<ev_periodic> reschedule callbacks.
3379		3380
3380	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
3381	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.
3382		3384
		3385	=head2 COMPILER WARNINGS
3383		3386
3384	=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.
3385		3390
3386	In this section the complexities of (many of) the algorithms used inside	3391	However, these are unavoidable for many reasons. For one, each compiler
3387	libev will be explained. For complexity discussions about backends see the	3392	has different warnings, and each user has different tastes regarding
3388	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.
3389		3395
3390	All of the following are about amortised time: If an array needs to be	3396	Another reason is that some compiler warnings require elaborate
3391	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
3392	happens asymptotically never with higher number of elements, so O(1) might	3398	maintainable.
3393	mean it might do a lengthy realloc operation in rare cases, but on average
3394	it is much faster and asymptotically approaches constant time.
3395		3399
3396	=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.
3397		3406
3398	=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.
3399		3412
3400	This means that, when you have a watcher that triggers in one hour and
3401	there are 100 watchers that would trigger before that then inserting will
3402	have to skip roughly seven (C<ld 100>) of these watchers.
3403		3413
3404	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3414	=head2 VALGRIND
3405		3415
3406	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
3407	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.
3408		3418
3409	=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:
3410		3421
3411	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.
3412		3425
3413	=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.
3414		3428
3415	=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.
3416		3433
3417	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
3418	correct watcher to remove. The lists are usually short (you don't usually	3435	make it into some kind of religion.
3419	have many watchers waiting for the same fd or signal).
3420		3436
3421	=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.
3422		3442
3423	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
3424	fixed position in the storage array.	3444	I suggest using suppression lists.
3425		3445
3426	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3427		3446
3428	A change means an I/O watcher gets started or stopped, which requires	3447	=head1 PORTABILITY NOTES
3429	libev to recalculate its status (and possibly tell the kernel, depending
3430	on backend and whether C<ev_io_set> was used).
3431		3448
3432	=item Activating one watcher (putting it into the pending state): O(1)
3433
3434	=item Priority handling: O(number_of_priorities)
3435
3436	Priorities are implemented by allocating some space for each
3437	priority. When doing priority-based operations, libev usually has to
3438	linearly search all the priorities, but starting/stopping and activating
3439	watchers becomes O(1) with respect to priority handling.
3440
3441	=item Sending an ev_async: O(1)
3442
3443	=item Processing ev_async_send: O(number_of_async_watchers)
3444
3445	=item Processing signals: O(max_signal_number)
3446
3447	Sending involves a system call I<iff> there were no other C<ev_async_send>
3448	calls in the current loop iteration. Checking for async and signal events
3449	involves iterating over all running async watchers or all signal numbers.
3450
3451	=back
3452
3453
3454	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	3449	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3455		3450
3456	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
3457	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
3458	model. Libev still offers limited functionality on this platform in	3453	model. Libev still offers limited functionality on this platform in
3459	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
…		…
3546	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
3547	calling select (O(n²)) will likely make this unworkable.	3542	calling select (O(n²)) will likely make this unworkable.
3548		3543
3549	=back	3544	=back
3550		3545
3551
3552	=head1 PORTABILITY REQUIREMENTS	3546	=head2 PORTABILITY REQUIREMENTS
3553		3547
3554	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
3555	additional extensions:	3549	backend-specific APIs, libev relies on a few additional extensions:
3556		3550
3557	=over 4	3551	=over 4
3558		3552
3559	=item C<void ()(ev_watcher_type , int revents)> must have compatible	3553	=item C<void ()(ev_watcher_type , int revents)> must have compatible
3560	calling conventions regardless of C<ev_watcher_type *>.	3554	calling conventions regardless of C<ev_watcher_type *>.
…		…
3585	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
3586	well.	3580	well.
3587		3581
3588	=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
3589		3583
3590	To improve portability and simplify using libev, libev uses C<long>	3584	To improve portability and simplify its API, libev uses C<long> internally
3591	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
3592	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	3586	systems (Microsoft...) this might be unexpectedly low, but is still at
3593	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
3594	millions of watchers.	3588	watchers.
3595		3589
3596	=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
3597		3591
3598	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
3599	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
…		…
3603	=back	3597	=back
3604		3598
3605	If you know of other additional requirements drop me a note.	3599	If you know of other additional requirements drop me a note.
3606		3600
3607		3601
3608	=head1 COMPILER WARNINGS	3602	=head1 ALGORITHMIC COMPLEXITIES
3609		3603
3610	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
3611	lot of warnings when compiling libev code. Some people are apparently	3605	libev will be documented. For complexity discussions about backends see
3612	scared by this.	3606	the documentation for C<ev_default_init>.
3613		3607
3614	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
3615	has different warnings, and each user has different tastes regarding	3609	extended, libev needs to realloc and move the whole array, but this
3616	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
3617	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.
3618		3613
3619	Another reason is that some compiler warnings require elaborate	3614	=over 4
3620	workarounds, or other changes to the code that make it less clear and less
3621	maintainable.
3622		3615
3623	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)
3624	wrong (because they don't actually warn about the condition their message
3625	seems to warn about).
3626		3617
3627	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
3628	"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
3629	with any compiler warnings enabled unless you are prepared to cope with	3620	have to skip roughly seven (C<ld 100>) of these watchers.
3630	them (e.g. by ignoring them). Remember that warnings are just that:
3631	warnings, not errors, or proof of bugs.
3632		3621
		3622	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3633		3623
3634	=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.
3635		3626
3636	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)
3637	highly useful, but valgrind reports are very hard to interpret.
3638		3628
3639	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.
3640	in libev, then check twice: If valgrind reports something like:
3641		3630
3642	==2274== definitely lost: 0 bytes in 0 blocks.	3631	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3643	==2274== possibly lost: 0 bytes in 0 blocks.
3644	==2274== still reachable: 256 bytes in 1 blocks.
3645		3632
3646	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))
3647	valgrind might report kernel bugs as if it were a bug in libev, or it
3648	might be confused (it is a very good tool, but only a tool).
3649		3634
3650	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
3651	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
3652	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
3653	no bug" answer and take the chance of learning how to interpret valgrind	3638	is rare).
3654	properly.
3655		3639
3656	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)
3657	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
3658		3671
3659		3672
3660	=head1 AUTHOR	3673	=head1 AUTHOR
3661		3674
3662	Marc Lehmann <libev@schmorp.de>.	3675	Marc Lehmann <libev@schmorp.de>.

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Comparing libev/ev.pod (file contents): Revision 1.187 by root, Mon Sep 29 03:31:14 2008 UTC vs. Revision 1.192 by root, Tue Sep 30 19:51:44 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.187 by root, Mon Sep 29 03:31:14 2008 UTC vs.
Revision 1.192 by root, Tue Sep 30 19:51:44 2008 UTC