[ViewVC] Diff of: cvs/Async-Interrupt/Interrupt.pm

Comparing Async-Interrupt/Interrupt.pm (file contents):
Revision 1.8 by root, Sun Jul 12 01:44:01 2009 UTC vs.
Revision 1.24 by root, Tue Sep 22 01:35:51 2009 UTC

…		…
53		53
54	For example the deliantra game server uses a variant of this technique	54	For example the deliantra game server uses a variant of this technique
55	to interrupt background processes regularly to send map updates to game	55	to interrupt background processes regularly to send map updates to game
56	clients.	56	clients.
57		57
		58	Or L<EV::Loop::Async> uses an interrupt object to wake up perl when new
		59	events have arrived.
		60
58	L<IO::AIO> and L<BDB> could also use this to speed up result reporting.	61	L<IO::AIO> and L<BDB> could also use this to speed up result reporting.
59		62
60	=item Speedy event loop invocation	63	=item Speedy event loop invocation
61		64
62	One could use this module e.g. in L<Coro> to interrupt a running coro-thread	65	One could use this module e.g. in L<Coro> to interrupt a running coro-thread
…		…
88	I<running> interpreter, there is optional support for signalling a pipe	91	I<running> interpreter, there is optional support for signalling a pipe
89	- that means you can also wait for the pipe to become readable (e.g. via	92	- that means you can also wait for the pipe to become readable (e.g. via
90	L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a C<read>	93	L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a C<read>
91	and C<write> syscall.	94	and C<write> syscall.
92		95
		96	=head1 USAGE EXAMPLES
		97
		98	=head2 Implementing race-free signal handling
		99
		100	This example uses a single event pipe for all signals, and one
		101	Async::Interrupt per signal. This code is actually what the L<AnyEvent>
		102	module uses itself when Async::Interrupt is available.
		103
		104	First, create the event pipe and hook it into the event loop
		105
		106	$SIGPIPE = new Async::Interrupt::EventPipe;
		107	$SIGPIPE_W = AnyEvent->io (
		108	fh => $SIGPIPE->fileno,
		109	poll => "r",
		110	cb => \&_signal_check, # defined later
		111	);
		112
		113	Then, for each signal to hook, create an Async::Interrupt object. The
		114	callback just sets a global variable, as we are only interested in
		115	synchronous signals (i.e. when the event loop polls), which is why the
		116	pipe draining is not done automatically.
		117
		118	my $interrupt = new Async::Interrupt
		119	cb => sub { undef $SIGNAL_RECEIVED{$signum} }
		120	signal => $signum,
		121	pipe => [$SIGPIPE->filenos],
		122	pipe_autodrain => 0,
		123	;
		124
		125	Finally, the I/O callback for the event pipe handles the signals:
		126
		127	sub _signal_check {
		128	# drain the pipe first
		129	$SIGPIPE->drain;
		130
		131	# two loops, just to be sure
		132	while (%SIGNAL_RECEIVED) {
		133	for (keys %SIGNAL_RECEIVED) {
		134	delete $SIGNAL_RECEIVED{$_};
		135	warn "signal $_ received\n";
		136	}
		137	}
		138	}
		139
		140	=head2 Interrupt perl from another thread
		141
		142	This example interrupts the Perl interpreter from another thread, via the
		143	XS API. This is used by e.g. the L<EV::Loop::Async> module.
		144
		145	On the Perl level, a new loop object (which contains the thread)
		146	is created, by first calling some XS constructor, querying the
		147	C-level callback function and feeding that as the C<c_cb> into the
		148	Async::Interrupt constructor:
		149
		150	my $self = XS_thread_constructor;
		151	my ($c_func, $c_arg) = _c_func $self; # return the c callback
		152	my $asy = new Async::Interrupt c_cb => [$c_func, $c_arg];
		153
		154	Then the newly created Interrupt object is queried for the signaling
		155	function that the newly created thread should call, and this is in turn
		156	told to the thread object:
		157
		158	_attach $self, $asy->signal_func;
		159
		160	So to repeat: first the XS object is created, then it is queried for the
		161	callback that should be called when the Interrupt object gets signalled.
		162
		163	Then the interrupt object is queried for the callback fucntion that the
		164	thread should call to signal the Interrupt object, and this callback is
		165	then attached to the thread.
		166
		167	You have to be careful that your new thread is not signalling before the
		168	signal function was configured, for example by starting the background
		169	thread only within C<_attach>.
		170
		171	That concludes the Perl part.
		172
		173	The XS part consists of the actual constructor which creates a thread,
		174	which is not relevant for this example, and two functions, C<_c_func>,
		175	which returns the Perl-side callback, and C<_attach>, which configures
		176	the signalling functioon that is safe toc all from another thread. For
		177	simplicity, we will use global variables to store the functions, normally
		178	you would somehow attach them to C<$self>.
		179
		180	The C<c_func> simply returns the address of a static function and arranges
		181	for the object pointed to by C<$self> to be passed to it, as an integer:
		182
		183	void
		184	_c_func (SV *loop)
		185	PPCODE:
		186	EXTEND (SP, 2);
		187	PUSHs (sv_2mortal (newSViv (PTR2IV (c_func))));
		188	PUSHs (sv_2mortal (newSViv (SvRV (loop))));
		189
		190	This would be the callback (since it runs in a normal Perl context, it is
		191	permissible to manipulate Perl values):
		192
		193	static void
		194	c_func (pTHX_ void *loop_, int value)
		195	{
		196	SV loop_object = (SV )loop_;
		197	...
		198	}
		199
		200	And this attaches the signalling callback:
		201
		202	static void (my_sig_func) (void signal_arg, int value);
		203	static void *my_sig_arg;
		204
		205	void
		206	_attach (SV loop_, IV sig_func, void sig_arg)
		207	CODE:
		208	{
		209	my_sig_func = sig_func;
		210	my_sig_arg = sig_arg;
		211
		212	/* now run the thread */
		213	thread_create (&u->tid, l_run, 0);
		214	}
		215
		216	And C<l_run> (the background thread) would eventually call the signaling
		217	function:
		218
		219	my_sig_func (my_sig_arg, 0);
		220
		221	You can have a look at L<EV::Loop::Async> for an actual example using
		222	intra-thread communication, locking and so on.
		223
		224
		225	=head1 THE Async::Interrupt CLASS
		226
93	=over 4	227	=over 4
94		228
95	=cut	229	=cut
96		230
97	package Async::Interrupt;	231	package Async::Interrupt;
98		232
99	no warnings;	233	use common::sense;
100		234
101	BEGIN {	235	BEGIN {
		236	# the next line forces initialisation of internal
		237	# signal handling variables, otherwise, PL_sig_pending
		238	# etc. will be null pointers.
		239	$SIG{KILL} = sub { };
		240
102	$VERSION = '0.04';	241	our $VERSION = '1.02';
103		242
104	require XSLoader;	243	require XSLoader;
105	XSLoader::load Async::Interrupt::, $VERSION;	244	XSLoader::load ("Async::Interrupt", $VERSION);
106	}	245	}
107		246
108	our $DIED = sub { warn "$@" };	247	our $DIED = sub { warn "$@" };
109		248
110	=item $async = new Async::Interrupt key => value...	249	=item $async = new Async::Interrupt key => value...
…		…
130	The exceptions are C<$!> and C<$@>, which are saved and restored by	269	The exceptions are C<$!> and C<$@>, which are saved and restored by
131	Async::Interrupt.	270	Async::Interrupt.
132		271
133	If the callback should throw an exception, then it will be caught,	272	If the callback should throw an exception, then it will be caught,
134	and C<$Async::Interrupt::DIED> will be called with C<$@> containing	273	and C<$Async::Interrupt::DIED> will be called with C<$@> containing
135	the exception. The default will simply C<warn> about the message and	274	the exception. The default will simply C<warn> about the message and
136	continue.	275	continue.
137		276
138	=item c_cb => [$c_func, $c_arg]	277	=item c_cb => [$c_func, $c_arg]
139		278
140	Registers a C callback the be invoked whenever the async interrupt is	279	Registers a C callback the be invoked whenever the async interrupt is
…		…
153	might use (the exception is C<errno>, which is saved and restored by	292	might use (the exception is C<errno>, which is saved and restored by
154	Async::Interrupt). The callback itself runs as part of the perl context,	293	Async::Interrupt). The callback itself runs as part of the perl context,
155	so you can call any perl functions and modify any perl data structures (in	294	so you can call any perl functions and modify any perl data structures (in
156	which case the requirements set out for C<cb> apply as well).	295	which case the requirements set out for C<cb> apply as well).
157		296
		297	=item var => $scalar_ref
		298
		299	When specified, then the given argument must be a reference to a
		300	scalar. The scalar will be set to C<0> initially. Signalling the interrupt
		301	object will set it to the passed value, handling the interrupt will reset
		302	it to C<0> again.
		303
		304	Note that the only thing you are legally allowed to do is to is to check
		305	the variable in a boolean or integer context (e.g. comparing it with a
		306	string, or printing it, will I<destroy> it and might cause your program to
		307	crash or worse).
		308
158	=item signal => $signame_or_value	309	=item signal => $signame_or_value
159		310
160	When this parameter is specified, then the Async::Interrupt will hook the	311	When this parameter is specified, then the Async::Interrupt will hook the
161	given signal, that is, it will effectively call C<< ->signal (0) >> each time	312	given signal, that is, it will effectively call C<< ->signal (0) >> each time
162	the given signal is caught by the process.	313	the given signal is caught by the process.
163		314
164	Only one async can hook a given signal, and the signal will be restored to	315	Only one async can hook a given signal, and the signal will be restored to
165	defaults when the Async::Interrupt object gets destroyed.	316	defaults when the Async::Interrupt object gets destroyed.
		317
		318	=item signal_hysteresis => $boolean
		319
		320	Sets the initial signal hysteresis state, see the C<signal_hysteresis>
		321	method, below.
166		322
167	=item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing]	323	=item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing]
168		324
169	Specifies two file descriptors (or file handles) that should be signalled	325	Specifies two file descriptors (or file handles) that should be signalled
170	whenever the async interrupt is signalled. This means a single octet will	326	whenever the async interrupt is signalled. This means a single octet will
171	be written to it, and before the callback is being invoked, it will be	327	be written to it, and before the callback is being invoked, it will be
172	read again. Due to races, it is unlikely but possible that multiple octets	328	read again. Due to races, it is unlikely but possible that multiple octets
173	are written. It is required that the file handles are both in nonblocking	329	are written. It is required that the file handles are both in nonblocking
174	mode.	330	mode.
175		331
176	You can get a portable pipe and set non-blocking mode portably by using
177	e.g. L<AnyEvent::Util> from the L<AnyEvent> distribution.
178
179	It is also possible to pass in a linux eventfd as both read and write
180	handle (which is faster than a pipe).
181
182	The object will keep a reference to the file handles.	332	The object will keep a reference to the file handles.
183		333
184	This can be used to ensure that async notifications will interrupt event	334	This can be used to ensure that async notifications will interrupt event
185	frameworks as well.	335	frameworks as well.
186		336
		337	Note that C<Async::Interrupt> will create a suitable signal fd
		338	automatically when your program requests one, so you don't have to specify
		339	this argument when all you want is an extra file descriptor to watch.
		340
		341	If you want to share a single event pipe between multiple Async::Interrupt
		342	objects, you can use the C<Async::Interrupt::EventPipe> class to manage
		343	those.
		344
		345	=item pipe_autodrain => $boolean
		346
		347	Sets the initial autodrain state, see the C<pipe_autodrain> method, below.
		348
187	=back	349	=back
188		350
189	=cut	351	=cut
190		352
191	sub new {	353	sub new {
192	my ($class, %arg) = @_;	354	my ($class, %arg) = @_;
193		355
194	bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1], $arg{signal}), $class	356	my $self = bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1], $arg{signal}, $arg{var}), $class;
		357
		358	# urgs, reminds me of Event
		359	for my $attr (qw(pipe_autodrain signal_hysteresis)) {
		360	$self->$attr ($arg{$attr}) if exists $arg{$attr};
		361	}
		362
		363	$self
195	}	364	}
196		365
197	=item ($signal_func, $signal_arg) = $async->signal_func	366	=item ($signal_func, $signal_arg) = $async->signal_func
198		367
199	Returns the address of a function to call asynchronously. The function has	368	Returns the address of a function to call asynchronously. The function
200	the following prototype and needs to be passed the specified C<$c_arg>,	369	has the following prototype and needs to be passed the specified
201	which is a C<void *> cast to C<IV>:	370	C<$signal_arg>, which is a C<void *> cast to C<IV>:
202		371
203	void (signal_func) (void signal_arg, int value)	372	void (signal_func) (void signal_arg, int value)
204		373
205	An example call would look like:	374	An example call would look like:
206		375
207	signal_func (signal_arg, 0);	376	signal_func (signal_arg, 0);
208		377
209	The function is safe to call from within signal and thread contexts, at	378	The function is safe to call from within signal and thread contexts, at
210	any time. The specified C<value> is passed to both C and Perl callback.	379	any time. The specified C<value> is passed to both C and Perl callback.
211		380
212	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is	381	C<$value> must be in the valid range for a C<sig_atomic_t>, except C<0>
213	portable).	382	(1..127 is portable).
214		383
215	If the function is called while the Async::Interrupt object is already	384	If the function is called while the Async::Interrupt object is already
216	signaled but before the callbacks are being executed, then the stored	385	signaled but before the callbacks are being executed, then the stored
217	C<value> is either the old or the new one. Due to the asynchronous	386	C<value> is either the old or the new one. Due to the asynchronous
218	nature of the code, the C<value> can even be passed to two consecutive	387	nature of the code, the C<value> can even be passed to two consecutive
219	invocations of the callback.	388	invocations of the callback.
220		389
		390	=item $address = $async->c_var
		391
		392	Returns the address (cast to IV) of an C<IV> variable. The variable is set
		393	to C<0> initially and gets set to the passed value whenever the object
		394	gets signalled, and reset to C<0> once the interrupt has been handled.
		395
		396	Note that it is often beneficial to just call C<PERL_ASYNC_CHECK ()> to
		397	handle any interrupts.
		398
		399	Example: call some XS function to store the address, then show C code
		400	waiting for it.
		401
		402	my_xs_func $async->c_var;
		403
		404	static IV *valuep;
		405
		406	void
		407	my_xs_func (void *addr)
		408	CODE:
		409	valuep = (IV *)addr;
		410
		411	// code in a loop, waiting
		412	while (!*valuep)
		413	; // do something
		414
221	=item $async->signal ($value=0)	415	=item $async->signal ($value=1)
222		416
223	This signals the given async object from Perl code. Semi-obviously, this	417	This signals the given async object from Perl code. Semi-obviously, this
224	will instantly trigger the callback invocation.	418	will instantly trigger the callback invocation (it does not, as the name
		419	might imply, do anything with POSIX signals).
225		420
226	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is	421	C<$value> must be in the valid range for a C<sig_atomic_t>, except C<0>
227	portable).	422	(1..127 is portable).
		423
		424	=item $async->signal_hysteresis ($enable)
		425
		426	Enables or disables signal hysteresis (default: disabled). If a POSIX
		427	signal is used as a signal source for the interrupt object, then enabling
		428	signal hysteresis causes Async::Interrupt to reset the signal action to
		429	C<SIG_IGN> in the signal handler and restore it just before handling the
		430	interruption.
		431
		432	When you expect a lot of signals (e.g. when using SIGIO), then enabling
		433	signal hysteresis can reduce the number of handler invocations
		434	considerably, at the cost of two extra syscalls.
		435
		436	Note that setting the signal to C<SIG_IGN> can have unintended side
		437	effects when you fork and exec other programs, as often they do nto expect
		438	signals to be ignored by default.
228		439
229	=item $async->block	440	=item $async->block
230		441
231	=item $async->unblock	442	=item $async->unblock
232		443
…		…
247	This call C<< $async->block >> and installs a handler that is called when	458	This call C<< $async->block >> and installs a handler that is called when
248	the current scope is exited (via an exception, by canceling the Coro	459	the current scope is exited (via an exception, by canceling the Coro
249	thread, by calling last/goto etc.).	460	thread, by calling last/goto etc.).
250		461
251	This is the recommended (and fastest) way to implement critical sections.	462	This is the recommended (and fastest) way to implement critical sections.
		463
		464	=item ($block_func, $block_arg) = $async->scope_block_func
		465
		466	Returns the address of a function that implements the C<scope_block>
		467	functionality.
		468
		469	It has the following prototype and needs to be passed the specified
		470	C<$block_arg>, which is a C<void *> cast to C<IV>:
		471
		472	void (block_func) (void block_arg)
		473
		474	An example call would look like:
		475
		476	block_func (block_arg);
		477
		478	The function is safe to call only from within the toplevel of a perl XS
		479	function and will call C<LEAVE> and C<ENTER> (in this order!).
252		480
253	=item $async->pipe_enable	481	=item $async->pipe_enable
254		482
255	=item $async->pipe_disable	483	=item $async->pipe_disable
256		484
…		…
258	enabled). Writing to a pipe is relatively expensive, so it can be disabled	486	enabled). Writing to a pipe is relatively expensive, so it can be disabled
259	when you know you are not waiting for it (for example, with L<EV> you	487	when you know you are not waiting for it (for example, with L<EV> you
260	could disable the pipe in a check watcher, and enable it in a prepare	488	could disable the pipe in a check watcher, and enable it in a prepare
261	watcher).	489	watcher).
262		490
263	Note that when C<fd_disable> is in effect, no attempt to read from the	491	Note that currently, while C<pipe_disable> is in effect, no attempt to
264	pipe will be done.	492	read from the pipe will be done when handling events. This might change as
		493	soon as I realize why this is a mistake.
		494
		495	=item $fileno = $async->pipe_fileno
		496
		497	Returns the reading side of the signalling pipe. If no signalling pipe is
		498	currently attached to the object, it will dynamically create one.
		499
		500	Note that the only valid oepration on this file descriptor is to wait
		501	until it is readable. The fd might belong currently to a pipe, a tcp
		502	socket, or an eventfd, depending on the platform, and is guaranteed to be
		503	C<select>able.
		504
		505	=item $async->pipe_autodrain ($enable)
		506
		507	Enables (C<1>) or disables (C<0>) automatic draining of the pipe (default:
		508	enabled). When automatic draining is enabled, then Async::Interrupt will
		509	automatically clear the pipe. Otherwise the user is responsible for this
		510	draining.
		511
		512	This is useful when you want to share one pipe among many Async::Interrupt
		513	objects.
		514
		515	=item $async->post_fork
		516
		517	The object will not normally be usable after a fork (as the pipe fd is
		518	shared between processes). Calling this method after a fork in the child
		519	ensures that the object will work as expected again. It only needs to be
		520	called when the async object is used in the child.
		521
		522	This only works when the pipe was created by Async::Interrupt.
		523
		524	Async::Interrupt ensures that the reading file descriptor does not change
		525	it's value.
		526
		527	=item $signum = Async::Interrupt::sig2num $signame_or_number
		528
		529	=item $signame = Async::Interrupt::sig2name $signame_or_number
		530
		531	These two convenience functions simply convert a signal name or number to
		532	the corresponding name or number. They are not used by this module and
		533	exist just because perl doesn't have a nice way to do this on its own.
		534
		535	They will return C<undef> on illegal names or numbers.
		536
		537	=back
		538
		539	=head1 THE Async::Interrupt::EventPipe CLASS
		540
		541	Pipes are the predominant utility to make asynchronous signals
		542	synchronous. However, pipes are hard to come by: they don't exist on the
		543	broken windows platform, and on GNU/Linux systems, you might want to use
		544	an C<eventfd> instead.
		545
		546	This class creates selectable event pipes in a portable fashion: on
		547	windows, it will try to create a tcp socket pair, on GNU/Linux, it will
		548	try to create an eventfd and everywhere else it will try to use a normal
		549	pipe.
		550
		551	=over 4
		552
		553	=item $epipe = new Async::Interrupt::EventPipe
		554
		555	This creates and returns an eventpipe object. This object is simply a
		556	blessed array reference:
		557
		558	=item ($r_fd, $w_fd) = $epipe->filenos
		559
		560	Returns the read-side file descriptor and the write-side file descriptor.
		561
		562	Example: pass an eventpipe object as pipe to the Async::Interrupt
		563	constructor, and create an AnyEvent watcher for the read side.
		564
		565	my $epipe = new Async::Interrupt::EventPipe;
		566	my $asy = new Async::Interrupt pipe => [$epipe->filenos];
		567	my $iow = AnyEvent->io (fh => $epipe->fileno, poll => 'r', cb => sub { });
		568
		569	=item $r_fd = $epipe->fileno
		570
		571	Return only the reading/listening side.
		572
		573	=item $epipe->signal
		574
		575	Write something to the pipe, in a portable fashion.
		576
		577	=item $epipe->drain
		578
		579	Drain (empty) the pipe.
		580
		581	=item ($c_func, $c_arg) = $epipe->drain_func
		582
		583	Returns a function pointer and C<void *> argument that can be called to
		584	have the effect of C<< $epipe->drain >> on the XS level.
		585
		586	It has the following prototype and needs to be passed the specified
		587	C<$c_arg>, which is a C<void *> cast to C<IV>:
		588
		589	void (c_func) (void c_arg)
		590
		591	An example call would look like:
		592
		593	c_func (c_arg);
		594
		595	=item $epipe->renew
		596
		597	Recreates the pipe (useful after a fork). The reading side will not change
		598	it's file descriptor number, but the writing side might.
		599
		600	=item $epipe->wait
		601
		602	This method blocks the process until there are events on the pipe. This is
		603	not a very event-based or ncie way of usign an event pipe, but it can be
		604	occasionally useful.
		605
		606	=back
265		607
266	=cut	608	=cut
267		609
268	1;	610	1;
269
270	=back
271
272	=head1 EXAMPLE
273
274	There really should be a complete C/XS example. Bug me about it. Better
275	yet, create one.
276		611
277	=head1 IMPLEMENTATION DETAILS AND LIMITATIONS	612	=head1 IMPLEMENTATION DETAILS AND LIMITATIONS
278		613
279	This module works by "hijacking" SIGKILL, which is guaranteed to always	614	This module works by "hijacking" SIGKILL, which is guaranteed to always
280	exist, but also cannot be caught, so is always available.	615	exist, but also cannot be caught, so is always available.
…		…
283	then intercepts the interpreter handling it. This makes normal signal	618	then intercepts the interpreter handling it. This makes normal signal
284	handling slower (probably unmeasurably, though), but has the advantage	619	handling slower (probably unmeasurably, though), but has the advantage
285	of not requiring a special runops function, nor slowing down normal perl	620	of not requiring a special runops function, nor slowing down normal perl
286	execution a bit.	621	execution a bit.
287		622
288	It assumes that C<sig_atomic_t> and C<int> are both async-safe to modify	623	It assumes that C<sig_atomic_t>, C<int> and C<IV> are all async-safe to
289	(C<sig_atomic_> is used by this module, and perl itself uses C<int>, so we	624	modify.
290	can assume that this is quite portable, at least w.r.t. signals).
291		625
292	=head1 AUTHOR	626	=head1 AUTHOR
293		627
294	Marc Lehmann <schmorp@schmorp.de>	628	Marc Lehmann <schmorp@schmorp.de>
295	http://home.schmorp.de/	629	http://home.schmorp.de/

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Comparing Async-Interrupt/Interrupt.pm (file contents): Revision 1.8 by root, Sun Jul 12 01:44:01 2009 UTC vs. Revision 1.24 by root, Tue Sep 22 01:35:51 2009 UTC

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Comparing Async-Interrupt/Interrupt.pm (file contents):
Revision 1.8 by root, Sun Jul 12 01:44:01 2009 UTC vs.
Revision 1.24 by root, Tue Sep 22 01:35:51 2009 UTC