cvsroot/Async-Interrupt/Interrupt.pm

=head1 NAME

Async::Interrupt - allow C/XS libraries to interrupt perl asynchronously

=head1 SYNOPSIS

 use Async::Interrupt;

=head1 DESCRIPTION

This module implements a single feature only of interest to advanced perl
modules, namely asynchronous interruptions (think "UNIX signals", which
are very similar).

Sometimes, modules wish to run code asynchronously (in another thread),
and then signal the perl interpreter on certain events. One common way is
to write some data to a pipe and use an event handling toolkit to watch
for I/O events. Another way is to send a signal. Those methods are slow,
and in the case of a pipe, also not asynchronous - it won't interrupt a
running perl interpreter.

This module implements asynchronous notifications that enable you to
signal running perl code form another thread, asynchronously, without
issuing syscalls.

It works by creating an C<Async::Interrupt> object for each such use. This
object stores a perl and/or a C-level callback that is invoked when the
C<Async::Interrupt> object gets signalled. It is executed at the next time
the perl interpreter is running (i.e. it will interrupt a computation, but
not an XS function or a syscall).

You can signal the C<Async::Interrupt> object either by calling it's C<<
->signal >> method, or, more commonly, by calling a C function.

The C<< ->signal_func >> returns the address of the C function that is to
be called (plus an argument to be used during the call). The signalling
function also takes an integer argument in the range SIG_ATOMIC_MIN to
SIG_ATOMIC_MAX (guaranteed to allow at least 0..127).

Since this kind of interruption is fast, but can only interrupt a
I<running> interpreter, there is optional support for also signalling a
pipe - that means you can also wait for the pipe to become readable (e.g.
via L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a
C<read> and C<write> syscall.

=over 4

=cut

package Async::Interrupt;

no warnings;

BEGIN {
   $VERSION = '0.02';

   require XSLoader;
   XSLoader::load Async::Interrupt::, $VERSION;
}

our $DIED = sub { warn "$@" };

=item $async = new Async::Interrupt key => value...

Creates a new Async::Interrupt object. You may only use async
notifications on this object while it exists, so you need to keep a
reference to it at all times while it is used.

Optional constructor arguments include (normally you would specify at
least one of C<cb> or C<c_cb>).

=over 4

=item cb => $coderef->($value)

Registers a perl callback to be invoked whenever the async interrupt is
signalled.

Note that, since this callback can be invoked at basically any time, it
must not modify any well-known global variables such as C<$/> without
restoring them again before returning.

The exceptions are C<$!> and C<$@>, which are saved and restored by
Async::Interrupt.

If the callback should throw an exception, then it will be caught,
and C<$Async::Interrupt::DIED> will be called with C<$@> containing
the exception.  The default will simply C<warn> about the message and
continue.

=item c_cb => [$c_func, $c_arg]

Registers a C callback the be invoked whenever the async interrupt is
signalled.

The C callback must have the following prototype:

   void c_func (pTHX_ void *c_arg, int value);

Both C<$c_func> and C<$c_arg> must be specified as integers/IVs, and
C<$value> is the C<value> passed to some earlier call to either C<$signal>
or the C<signal_func> function.

Note that, because the callback can be invoked at almost any time, you
have to be careful at saving and restoring global variables that Perl
might use (the exception is C<errno>, which is saved and restored by
Async::Interrupt). The callback itself runs as part of the perl context,
so you can call any perl functions and modify any perl data structures (in
which case the requirements set out for C<cb> apply as well).

=item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing]

Specifies two file descriptors (or file handles) that should be signalled
whenever the async interrupt is signalled. This means a single octet will
be written to it, and before the callback is being invoked, it will be
read again. Due to races, it is unlikely but possible that multiple octets
are written. It is required that the file handles are both in nonblocking
mode.

(You can get a portable pipe and set non-blocking mode portably by using
e.g. L<AnyEvent::Util> from the L<AnyEvent> distribution).

The object will keep a reference to the file handles.

This can be used to ensure that async notifications will interrupt event
frameworks as well.

=back

=cut

sub new {
   my ($class, %arg) = @_;

   bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1]), $class
}

=item ($signal_func, $signal_arg) = $async->signal_func

Returns the address of a function to call asynchronously. The function has
the following prototype and needs to be passed the specified C<$c_arg>,
which is a C<void *> cast to C<IV>:

   void (*signal_func) (void *signal_arg, int value)

An example call would look like:

   signal_func (signal_arg, 0);

The function is safe to call from within signal and thread contexts, at
any time. The specified C<value> is passed to both C and Perl callback.

C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
portable).

If the function is called while the Async::Interrupt object is already
signaled but before the callbacks are being executed, then the stored
C<value> is either the old or the new one. Due to the asynchronous
nature of the code, the C<value> can even be passed to two consecutive
invocations of the callback.

=item $async->signal ($value=0)

This signals the given async object from Perl code. Semi-obviously, this
will instantly trigger the callback invocation.

C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
portable).

=item $async->block

=item $async->unblock

Sometimes you need a "critical section" of code that will not be
interrupted by an Async::Interrupt. This can be implemented by calling C<<
$async->block >> before the critical section, and C<< $async->unblock >>
afterwards.

Note that there must be exactly one call of C<unblock> for every previous
call to C<block> (i.e. calls can nest).

Since ensuring this in the presence of exceptions and threads is
usually more difficult than you imagine, I recommend using C<<
$async->scoped_block >> instead.

=item $async->scope_block

This call C<< $async->block >> and installs a handler that is called when
the current scope is exited (via an exception, by canceling the Coro
thread, by calling last/goto etc.).

This is the recommended (and fastest) way to implement critical sections.

=cut

1;

=back

=head1 EXAMPLE

There really should be a complete C/XS example. Bug me about it.

=head1 IMPLEMENTATION DETAILS AND LIMITATIONS

This module works by "hijacking" SIGKILL, which is guaranteed to be always
available in perl, but also cannot be caught, so is always available.

Basically, this module fakes the receive of a SIGKILL signal and
then catches it. This makes normal signal handling slower (probably
unmeasurably), but has the advantage of not requiring a special runops nor
slowing down normal perl execution a bit.

It assumes that C<sig_atomic_t> and C<int> are both exception-safe to
modify (C<sig_atomic_> is used by this module, and perl itself uses
C<int>, so we can assume that this is quite portable, at least w.r.t.
signals).

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.4
Committed:	Thu Jul 2 16:15:52 2009 UTC (15 years ago) by root
Branch:	MAIN
CVS Tags:	rel-0_02
Changes since 1.3:	+12 -11 lines
Log Message:	0.02
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			Async::Interrupt - allow C/XS libraries to interrupt perl asynchronously
4
5			=head1 SYNOPSIS
6
7			use Async::Interrupt;
8
9			=head1 DESCRIPTION
10
11			This module implements a single feature only of interest to advanced perl
12	root	1.4	modules, namely asynchronous interruptions (think "UNIX signals", which
13	root	1.1	are very similar).
14
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
17			to write some data to a pipe and use an event handling toolkit to watch
18			for I/O events. Another way is to send a signal. Those methods are slow,
19			and in the case of a pipe, also not asynchronous - it won't interrupt a
20			running perl interpreter.
21
22			This module implements asynchronous notifications that enable you to
23			signal running perl code form another thread, asynchronously, without
24			issuing syscalls.
25
26	root	1.2	It works by creating an C<Async::Interrupt> object for each such use. This
27			object stores a perl and/or a C-level callback that is invoked when the
28			C<Async::Interrupt> object gets signalled. It is executed at the next time
29			the perl interpreter is running (i.e. it will interrupt a computation, but
30			not an XS function or a syscall).
31
32			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.
34
35			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
37			function also takes an integer argument in the range SIG_ATOMIC_MIN to
38			SIG_ATOMIC_MAX (guaranteed to allow at least 0..127).
39
40			Since this kind of interruption is fast, but can only interrupt a
41			I<running> interpreter, there is optional support for also signalling a
42	root	1.4	pipe - that means you can also wait for the pipe to become readable (e.g.
43			via L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a
44			C<read> and C<write> syscall.
45	root	1.2
46	root	1.1	=over 4
47
48			=cut
49
50			package Async::Interrupt;
51
52	root	1.2	no warnings;
53
54	root	1.1	BEGIN {
55			$VERSION = '0.02';
56
57			require XSLoader;
58			XSLoader::load Async::Interrupt::, $VERSION;
59			}
60
61	root	1.2	our $DIED = sub { warn "$@" };
62
63	root	1.1	=item $async = new Async::Interrupt key => value...
64
65			Creates a new Async::Interrupt object. You may only use async
66			notifications on this object while it exists, so you need to keep a
67			reference to it at all times while it is used.
68
69			Optional constructor arguments include (normally you would specify at
70			least one of C<cb> or C<c_cb>).
71
72			=over 4
73
74			=item cb => $coderef->($value)
75
76			Registers a perl callback to be invoked whenever the async interrupt is
77			signalled.
78
79			Note that, since this callback can be invoked at basically any time, it
80	root	1.2	must not modify any well-known global variables such as C<$/> without
81			restoring them again before returning.
82
83			The exceptions are C<$!> and C<$@>, which are saved and restored by
84			Async::Interrupt.
85	root	1.1
86	root	1.2	If the callback should throw an exception, then it will be caught,
87			and C<$Async::Interrupt::DIED> will be called with C<$@> containing
88			the exception. The default will simply C<warn> about the message and
89			continue.
90
91			=item c_cb => [$c_func, $c_arg]
92	root	1.1
93			Registers a C callback the be invoked whenever the async interrupt is
94			signalled.
95
96			The C callback must have the following prototype:
97
98	root	1.2	void c_func (pTHX_ void *c_arg, int value);
99	root	1.1
100	root	1.2	Both C<$c_func> and C<$c_arg> must be specified as integers/IVs, and
101			C<$value> is the C<value> passed to some earlier call to either C<$signal>
102			or the C<signal_func> function.
103	root	1.1
104			Note that, because the callback can be invoked at almost any time, you
105			have to be careful at saving and restoring global variables that Perl
106	root	1.4	might use (the exception is C<errno>, which is saved and restored by
107	root	1.2	Async::Interrupt). The callback itself runs as part of the perl context,
108			so you can call any perl functions and modify any perl data structures (in
109	root	1.4	which case the requirements set out for C<cb> apply as well).
110	root	1.1
111	root	1.2	=item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing]
112	root	1.1
113	root	1.2	Specifies two file descriptors (or file handles) that should be signalled
114	root	1.1	whenever the async interrupt is signalled. This means a single octet will
115			be written to it, and before the callback is being invoked, it will be
116			read again. Due to races, it is unlikely but possible that multiple octets
117	root	1.2	are written. It is required that the file handles are both in nonblocking
118			mode.
119	root	1.1
120			(You can get a portable pipe and set non-blocking mode portably by using
121	root	1.4	e.g. L<AnyEvent::Util> from the L<AnyEvent> distribution).
122	root	1.1
123	root	1.2	The object will keep a reference to the file handles.
124	root	1.1
125			This can be used to ensure that async notifications will interrupt event
126			frameworks as well.
127
128			=back
129
130			=cut
131
132			sub new {
133			my ($class, %arg) = @_;
134
135	root	1.2	bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1]), $class
136	root	1.1	}
137
138	root	1.2	=item ($signal_func, $signal_arg) = $async->signal_func
139	root	1.1
140			Returns the address of a function to call asynchronously. The function has
141			the following prototype and needs to be passed the specified C<$c_arg>,
142			which is a C<void *> cast to C<IV>:
143
144			void (signal_func) (void signal_arg, int value)
145
146			An example call would look like:
147
148			signal_func (signal_arg, 0);
149
150	root	1.2	The function is safe to call from within signal and thread contexts, at
151	root	1.1	any time. The specified C<value> is passed to both C and Perl callback.
152
153	root	1.2	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
154			portable).
155
156	root	1.1	If the function is called while the Async::Interrupt object is already
157			signaled but before the callbacks are being executed, then the stored
158	root	1.2	C<value> is either the old or the new one. Due to the asynchronous
159			nature of the code, the C<value> can even be passed to two consecutive
160			invocations of the callback.
161	root	1.1
162			=item $async->signal ($value=0)
163
164			This signals the given async object from Perl code. Semi-obviously, this
165			will instantly trigger the callback invocation.
166
167	root	1.2	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
168			portable).
169
170			=item $async->block
171
172	root	1.3	=item $async->unblock
173
174			Sometimes you need a "critical section" of code that will not be
175			interrupted by an Async::Interrupt. This can be implemented by calling C<<
176			$async->block >> before the critical section, and C<< $async->unblock >>
177			afterwards.
178
179	root	1.4	Note that there must be exactly one call of C<unblock> for every previous
180	root	1.3	call to C<block> (i.e. calls can nest).
181
182	root	1.4	Since ensuring this in the presence of exceptions and threads is
183	root	1.3	usually more difficult than you imagine, I recommend using C<<
184			$async->scoped_block >> instead.
185	root	1.2
186	root	1.3	=item $async->scope_block
187
188			This call C<< $async->block >> and installs a handler that is called when
189			the current scope is exited (via an exception, by canceling the Coro
190			thread, by calling last/goto etc.).
191
192			This is the recommended (and fastest) way to implement critical sections.
193	root	1.2
194	root	1.1	=cut
195
196			1;
197
198			=back
199
200	root	1.2	=head1 EXAMPLE
201
202	root	1.4	There really should be a complete C/XS example. Bug me about it.
203	root	1.2
204			=head1 IMPLEMENTATION DETAILS AND LIMITATIONS
205
206	root	1.4	This module works by "hijacking" SIGKILL, which is guaranteed to be always
207	root	1.2	available in perl, but also cannot be caught, so is always available.
208
209			Basically, this module fakes the receive of a SIGKILL signal and
210			then catches it. This makes normal signal handling slower (probably
211			unmeasurably), but has the advantage of not requiring a special runops nor
212			slowing down normal perl execution a bit.
213
214			It assumes that C<sig_atomic_t> and C<int> are both exception-safe to
215			modify (C<sig_atomic_> is used by this module, and perl itself uses
216	root	1.4	C<int>, so we can assume that this is quite portable, at least w.r.t.
217	root	1.2	signals).
218
219	root	1.1	=head1 AUTHOR
220
221			Marc Lehmann <schmorp@schmorp.de>
222			http://home.schmorp.de/
223
224			=cut
225