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

Comparing cvsroot/Async-Interrupt/Interrupt.pm (file contents):
Revision 1.7 by root, Sat Jul 11 22:24:30 2009 UTC vs.
Revision 1.14 by root, Fri Jul 17 01:53:41 2009 UTC

…		…
10		10
11	This module implements a single feature only of interest to advanced perl	11	This module implements a single feature only of interest to advanced perl
12	modules, namely asynchronous interruptions (think "UNIX signals", which	12	modules, namely asynchronous interruptions (think "UNIX signals", which
13	are very similar).	13	are very similar).
14		14
15	Sometimes, modules wish to run code asynchronously (in another thread),	15	Sometimes, modules wish to run code asynchronously (in another thread,
16	and then signal the perl interpreter on certain events. One common way is	16	or from a signal handler), and then signal the perl interpreter on
17	to write some data to a pipe and use an event handling toolkit to watch	17	certain events. One common way is to write some data to a pipe and use an
18	for I/O events. Another way is to send a signal. Those methods are slow,	18	event handling toolkit to watch for I/O events. Another way is to send
19	and in the case of a pipe, also not asynchronous - it won't interrupt a	19	a signal. Those methods are slow, and in the case of a pipe, also not
20	running perl interpreter.	20	asynchronous - it won't interrupt a running perl interpreter.
21		21
22	This module implements asynchronous notifications that enable you to	22	This module implements asynchronous notifications that enable you to
23	signal running perl code form another thread, asynchronously, without	23	signal running perl code from another thread, asynchronously, and
24	issuing syscalls.	24	sometimes even without using a single syscall.
25		25
26	It works by creating an C<Async::Interrupt> object for each such use. This	26	=head2 USAGE SCENARIOS
27	object stores a perl and/or a C-level callback that is invoked when the	27
28	C<Async::Interrupt> object gets signalled. It is executed at the next time	28	=over 4
29	the perl interpreter is running (i.e. it will interrupt a computation, but	29
30	not an XS function or a syscall).	30	=item Race-free signal handling
		31
		32	There seems to be no way to do race-free signal handling in perl: to
		33	catch a signal, you have to execute Perl code, and between entering the
		34	interpreter C<select> function (or other blocking functions) and executing
		35	the select syscall is a small but relevant timespan during which signals
		36	will be queued, but perl signal handlers will not be executed and the
		37	blocking syscall will not be interrupted.
		38
		39	You can use this module to bind a signal to a callback while at the same
		40	time activating an event pipe that you can C<select> on, fixing the race
		41	completely.
		42
		43	This can be used to implement the signal hadling in event loops,
		44	e.g. L<AnyEvent>, L<POE>, L<IO::Async::Loop> and so on.
		45
		46	=item Background threads want speedy reporting
		47
		48	Assume you want very exact timing, and you can spare an extra cpu core
		49	for that. Then you can run an extra thread that signals your perl
		50	interpreter. This means you can get a very exact timing source while your
		51	perl code is number crunching, without even using a syscall to communicate
		52	between your threads.
		53
		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
		56	clients.
		57
		58	L<IO::AIO> and L<BDB> could also use this to speed up result reporting.
		59
		60	=item Speedy event loop invocation
		61
		62	One could use this module e.g. in L<Coro> to interrupt a running coro-thread
		63	and cause it to enter the event loop.
		64
		65	Or one could bind to C<SIGIO> and tell some important sockets to send this
		66	signal, causing the event loop to be entered to reduce network latency.
		67
		68	=back
		69
		70	=head2 HOW TO USE
		71
		72	You can use this module by creating an C<Async::Interrupt> object for each
		73	such event source. This object stores a perl and/or a C-level callback
		74	that is invoked when the C<Async::Interrupt> object gets signalled. It is
		75	executed at the next time the perl interpreter is running (i.e. it will
		76	interrupt a computation, but not an XS function or a syscall).
31		77
32	You can signal the C<Async::Interrupt> object either by calling it's C<<	78	You can signal the C<Async::Interrupt> object either by calling it's C<<
33	->signal >> method, or, more commonly, by calling a C function.	79	->signal >> method, or, more commonly, by calling a C function. There is
		80	also the built-in (POSIX) signal source.
34		81
35	The C<< ->signal_func >> returns the address of the C function that is to	82	The C<< ->signal_func >> returns the address of the C function that is to
36	be called (plus an argument to be used during the call). The signalling	83	be called (plus an argument to be used during the call). The signalling
37	function also takes an integer argument in the range SIG_ATOMIC_MIN to	84	function also takes an integer argument in the range SIG_ATOMIC_MIN to
38	SIG_ATOMIC_MAX (guaranteed to allow at least 0..127).	85	SIG_ATOMIC_MAX (guaranteed to allow at least 0..127).
39		86
40	Since this kind of interruption is fast, but can only interrupt a	87	Since this kind of interruption is fast, but can only interrupt a
41	I<running> interpreter, there is optional support for also signalling a	88	I<running> interpreter, there is optional support for signalling a pipe
42	pipe - that means you can also wait for the pipe to become readable (e.g.	89	- that means you can also wait for the pipe to become readable (e.g. via
43	via L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a	90	L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a C<read>
44	C<read> and C<write> syscall.	91	and C<write> syscall.
45		92
46	=over 4	93	=over 4
47		94
48	=cut	95	=cut
49		96
50	package Async::Interrupt;	97	package Async::Interrupt;
51		98
52	no warnings;	99	use common::sense;
53		100
54	BEGIN {	101	BEGIN {
		102	# the next line forces initialisation of internal
		103	# signal handling # variables
		104	$SIG{KILL} = sub { };
		105
55	$VERSION = '0.04';	106	our $VERSION = '0.5';
56		107
57	require XSLoader;	108	require XSLoader;
58	XSLoader::load Async::Interrupt::, $VERSION;	109	XSLoader::load ("Async::Interrupt", $VERSION);
59	}	110	}
60		111
61	our $DIED = sub { warn "$@" };	112	our $DIED = sub { warn "$@" };
62		113
63	=item $async = new Async::Interrupt key => value...	114	=item $async = new Async::Interrupt key => value...
…		…
106	might use (the exception is C<errno>, which is saved and restored by	157	might use (the exception is C<errno>, which is saved and restored by
107	Async::Interrupt). The callback itself runs as part of the perl context,	158	Async::Interrupt). The callback itself runs as part of the perl context,
108	so you can call any perl functions and modify any perl data structures (in	159	so you can call any perl functions and modify any perl data structures (in
109	which case the requirements set out for C<cb> apply as well).	160	which case the requirements set out for C<cb> apply as well).
110		161
		162	=item var => $scalar_ref
		163
		164	When specified, then the given argument must be a reference to a
		165	scalar. The scalar will be set to C<0> intiially. Signalling the interrupt
		166	object will set it to the passed value, handling the interrupt will reset
		167	it to C<0> again.
		168
		169	Note that the only thing you are legally allowed to do is to is to check
		170	the variable in a boolean or integer context (e.g. comparing it with a
		171	string, or printing it, will I<destroy> it and might cause your program to
		172	crash or worse).
		173
111	=item signal => $signame_or_value	174	=item signal => $signame_or_value
112		175
113	When this parameter is specified, then the Async::Interrupt will hook the	176	When this parameter is specified, then the Async::Interrupt will hook the
114	given signal, that is, it will effectively call C<< ->signal (0) >> each time	177	given signal, that is, it will effectively call C<< ->signal (0) >> each time
115	the given signal is caught by the process.	178	the given signal is caught by the process.
…		…
124	be written to it, and before the callback is being invoked, it will be	187	be written to it, and before the callback is being invoked, it will be
125	read again. Due to races, it is unlikely but possible that multiple octets	188	read again. Due to races, it is unlikely but possible that multiple octets
126	are written. It is required that the file handles are both in nonblocking	189	are written. It is required that the file handles are both in nonblocking
127	mode.	190	mode.
128		191
129	You can get a portable pipe and set non-blocking mode portably by using
130	e.g. L<AnyEvent::Util> from the L<AnyEvent> distribution.
131
132	It is also possible to pass in a linux eventfd as both read and write
133	handle (which is faster than a pipe).
134
135	The object will keep a reference to the file handles.	192	The object will keep a reference to the file handles.
136		193
137	This can be used to ensure that async notifications will interrupt event	194	This can be used to ensure that async notifications will interrupt event
138	frameworks as well.	195	frameworks as well.
139		196
		197	Note that C<Async::Interrupt> will create a suitable signal fd
		198	automatically when your program requests one, so you don't have to specify
		199	this agrument when all you want is an extra file descriptor to watch.
		200
140	=back	201	=back
141		202
142	=cut	203	=cut
143		204
144	sub new {	205	sub new {
145	my ($class, %arg) = @_;	206	my ($class, %arg) = @_;
146		207
147	bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1], $arg{signal}), $class	208	bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1], $arg{signal}, $arg{var}), $class
148	}	209	}
149		210
150	=item ($signal_func, $signal_arg) = $async->signal_func	211	=item ($signal_func, $signal_arg) = $async->signal_func
151		212
152	Returns the address of a function to call asynchronously. The function has	213	Returns the address of a function to call asynchronously. The function has
…		…
160	signal_func (signal_arg, 0);	221	signal_func (signal_arg, 0);
161		222
162	The function is safe to call from within signal and thread contexts, at	223	The function is safe to call from within signal and thread contexts, at
163	any time. The specified C<value> is passed to both C and Perl callback.	224	any time. The specified C<value> is passed to both C and Perl callback.
164		225
165	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is	226	C<$value> must be in the valid range for a C<sig_atomic_t>, except C<0>
166	portable).	227	(1..127 is portable).
167		228
168	If the function is called while the Async::Interrupt object is already	229	If the function is called while the Async::Interrupt object is already
169	signaled but before the callbacks are being executed, then the stored	230	signaled but before the callbacks are being executed, then the stored
170	C<value> is either the old or the new one. Due to the asynchronous	231	C<value> is either the old or the new one. Due to the asynchronous
171	nature of the code, the C<value> can even be passed to two consecutive	232	nature of the code, the C<value> can even be passed to two consecutive
172	invocations of the callback.	233	invocations of the callback.
173		234
		235	=item $address = $async->c_var
		236
		237	Returns the address (cast to IV) of an C<IV> variable. The variable is set
		238	to C<0> initially and gets set to the passed value whenever the object
		239	gets signalled, and reset to C<0> once the interrupt has been handled.
		240
		241	Note that it is often beneficial to just call C<PERL_ASYNC_CHECK ()> to
		242	handle any interrupts.
		243
		244	Example: call some XS function to store the address, then show C code
		245	waiting for it.
		246
		247	my_xs_func $async->c_var;
		248
		249	static IV *valuep;
		250
		251	void
		252	my_xs_func (void *addr)
		253	CODE:
		254	valuep = (IV *)addr;
		255
		256	// code in a loop, waiting
		257	while (!*valuep)
		258	; // do soemthing
		259
174	=item $async->signal ($value=0)	260	=item $async->signal ($value=1)
175		261
176	This signals the given async object from Perl code. Semi-obviously, this	262	This signals the given async object from Perl code. Semi-obviously, this
177	will instantly trigger the callback invocation.	263	will instantly trigger the callback invocation.
178		264
179	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is	265	C<$value> must be in the valid range for a C<sig_atomic_t>, except C<0>
180	portable).	266	(1..127 is portable).
181		267
182	=item $async->block	268	=item $async->block
183		269
184	=item $async->unblock	270	=item $async->unblock
185		271
…		…
211	enabled). Writing to a pipe is relatively expensive, so it can be disabled	297	enabled). Writing to a pipe is relatively expensive, so it can be disabled
212	when you know you are not waiting for it (for example, with L<EV> you	298	when you know you are not waiting for it (for example, with L<EV> you
213	could disable the pipe in a check watcher, and enable it in a prepare	299	could disable the pipe in a check watcher, and enable it in a prepare
214	watcher).	300	watcher).
215		301
216	Note that when C<fd_disable> is in effect, no attempt to read from the	302	Note that currently, while C<pipe_disable> is in effect, no attempt to
217	pipe will be done.	303	read from the pipe will be done when handling events. This might change as
		304	soon as I realize why this is a mistake.
		305
		306	=item $fileno = $async->pipe_fileno
		307
		308	Returns the reading side of the signalling pipe. If no signalling pipe is
		309	currently attached to the object, it will dynamically create one.
		310
		311	Note that the only valid oepration on this file descriptor is to wait
		312	until it is readable. The fd might belong currently to a pipe, a tcp
		313	socket, or an eventfd, depending on the platform, and is guaranteed to be
		314	C<select>able.
		315
		316	=item $async->post_fork
		317
		318	The object will not normally be usable after a fork (as the pipe fd is
		319	shared between processes). Calling this method after a fork in the child
		320	ensures that the object will work as expected again. It only needs to be
		321	called when the async object is used in the child.
		322
		323	This only works when the pipe was created by Async::Interrupt.
		324
		325	Async::Interrupt ensures that the reading file descriptor does not change
		326	it's value.
218		327
219	=cut	328	=cut
220		329
221	1;	330	1;
222		331
223	=back	332	=back
224		333
225	=head1 EXAMPLE	334	=head1 EXAMPLE
226		335
227	There really should be a complete C/XS example. Bug me about it.	336	There really should be a complete C/XS example. Bug me about it. Better
		337	yet, create one.
228		338
229	=head1 IMPLEMENTATION DETAILS AND LIMITATIONS	339	=head1 IMPLEMENTATION DETAILS AND LIMITATIONS
230		340
231	This module works by "hijacking" SIGKILL, which is guaranteed to be always	341	This module works by "hijacking" SIGKILL, which is guaranteed to always
232	available in perl, but also cannot be caught, so is always available.	342	exist, but also cannot be caught, so is always available.
233		343
234	Basically, this module fakes the receive of a SIGKILL signal and	344	Basically, this module fakes the occurance of a SIGKILL signal and
235	then catches it. This makes normal signal handling slower (probably	345	then intercepts the interpreter handling it. This makes normal signal
236	unmeasurably), but has the advantage of not requiring a special runops nor	346	handling slower (probably unmeasurably, though), but has the advantage
237	slowing down normal perl execution a bit.	347	of not requiring a special runops function, nor slowing down normal perl
		348	execution a bit.
238		349
239	It assumes that C<sig_atomic_t> and C<int> are both exception-safe to	350	It assumes that C<sig_atomic_t>, C<int> and C<IV> are all async-safe to
240	modify (C<sig_atomic_> is used by this module, and perl itself uses	351	modify.
241	C<int>, so we can assume that this is quite portable, at least w.r.t.
242	signals).
243		352
244	=head1 AUTHOR	353	=head1 AUTHOR
245		354
246	Marc Lehmann <schmorp@schmorp.de>	355	Marc Lehmann <schmorp@schmorp.de>
247	http://home.schmorp.de/	356	http://home.schmorp.de/

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Comparing cvsroot/Async-Interrupt/Interrupt.pm (file contents): Revision 1.7 by root, Sat Jul 11 22:24:30 2009 UTC vs. Revision 1.14 by root, Fri Jul 17 01:53:41 2009 UTC

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Comparing cvsroot/Async-Interrupt/Interrupt.pm (file contents):
Revision 1.7 by root, Sat Jul 11 22:24:30 2009 UTC vs.
Revision 1.14 by root, Fri Jul 17 01:53:41 2009 UTC