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 while

=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 excetpion is C<errno>, which is aved 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 requireemnts 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> distro).

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

Sometimes you need a "critical section" of code where

=item $async->unblock

=cut

1;

=back

=head1 EXAMPLE

#TODO

=head1 IMPLEMENTATION DETAILS AND LIMITATIONS

This module works by "hijacking" SIGKILL, which is guarenteed 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 portbale, at least w.r.t.
signals).

=head1 AUTHOR

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

=cut

Revision:	1.2
Committed:	Thu Jul 2 15:13:03 2009 UTC (14 years, 11 months ago) by root
Branch:	MAIN
Changes since 1.1:	+83 -20 lines
Log Message:	* empty log message *
#	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			modules, namely asynchronous interruptions (think "unix signals", which
13			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			pipe - that means you can also wait for the pipe to become readable while
43
44	root	1.1	=over 4
45
46			=cut
47
48			package Async::Interrupt;
49
50	root	1.2	no warnings;
51
52	root	1.1	BEGIN {
53			$VERSION = '0.02';
54
55			require XSLoader;
56			XSLoader::load Async::Interrupt::, $VERSION;
57			}
58
59	root	1.2	our $DIED = sub { warn "$@" };
60
61	root	1.1	=item $async = new Async::Interrupt key => value...
62
63			Creates a new Async::Interrupt object. You may only use async
64			notifications on this object while it exists, so you need to keep a
65			reference to it at all times while it is used.
66
67			Optional constructor arguments include (normally you would specify at
68			least one of C<cb> or C<c_cb>).
69
70			=over 4
71
72			=item cb => $coderef->($value)
73
74			Registers a perl callback to be invoked whenever the async interrupt is
75			signalled.
76
77			Note that, since this callback can be invoked at basically any time, it
78	root	1.2	must not modify any well-known global variables such as C<$/> without
79			restoring them again before returning.
80
81			The exceptions are C<$!> and C<$@>, which are saved and restored by
82			Async::Interrupt.
83	root	1.1
84	root	1.2	If the callback should throw an exception, then it will be caught,
85			and C<$Async::Interrupt::DIED> will be called with C<$@> containing
86			the exception. The default will simply C<warn> about the message and
87			continue.
88
89			=item c_cb => [$c_func, $c_arg]
90	root	1.1
91			Registers a C callback the be invoked whenever the async interrupt is
92			signalled.
93
94			The C callback must have the following prototype:
95
96	root	1.2	void c_func (pTHX_ void *c_arg, int value);
97	root	1.1
98	root	1.2	Both C<$c_func> and C<$c_arg> must be specified as integers/IVs, and
99			C<$value> is the C<value> passed to some earlier call to either C<$signal>
100			or the C<signal_func> function.
101	root	1.1
102			Note that, because the callback can be invoked at almost any time, you
103			have to be careful at saving and restoring global variables that Perl
104	root	1.2	might use (the excetpion is C<errno>, which is aved and restored by
105			Async::Interrupt). The callback itself runs as part of the perl context,
106			so you can call any perl functions and modify any perl data structures (in
107			which case the requireemnts set out for C<cb> apply as well).
108	root	1.1
109	root	1.2	=item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing]
110	root	1.1
111	root	1.2	Specifies two file descriptors (or file handles) that should be signalled
112	root	1.1	whenever the async interrupt is signalled. This means a single octet will
113			be written to it, and before the callback is being invoked, it will be
114			read again. Due to races, it is unlikely but possible that multiple octets
115	root	1.2	are written. It is required that the file handles are both in nonblocking
116			mode.
117	root	1.1
118			(You can get a portable pipe and set non-blocking mode portably by using
119			e.g. L<AnyEvent::Util> from the L<AnyEvent> distro).
120
121	root	1.2	The object will keep a reference to the file handles.
122	root	1.1
123			This can be used to ensure that async notifications will interrupt event
124			frameworks as well.
125
126			=back
127
128			=cut
129
130			sub new {
131			my ($class, %arg) = @_;
132
133	root	1.2	bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1]), $class
134	root	1.1	}
135
136	root	1.2	=item ($signal_func, $signal_arg) = $async->signal_func
137	root	1.1
138			Returns the address of a function to call asynchronously. The function has
139			the following prototype and needs to be passed the specified C<$c_arg>,
140			which is a C<void *> cast to C<IV>:
141
142			void (signal_func) (void signal_arg, int value)
143
144			An example call would look like:
145
146			signal_func (signal_arg, 0);
147
148	root	1.2	The function is safe to call from within signal and thread contexts, at
149	root	1.1	any time. The specified C<value> is passed to both C and Perl callback.
150
151	root	1.2	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
152			portable).
153
154	root	1.1	If the function is called while the Async::Interrupt object is already
155			signaled but before the callbacks are being executed, then the stored
156	root	1.2	C<value> is either the old or the new one. Due to the asynchronous
157			nature of the code, the C<value> can even be passed to two consecutive
158			invocations of the callback.
159	root	1.1
160			=item $async->signal ($value=0)
161
162			This signals the given async object from Perl code. Semi-obviously, this
163			will instantly trigger the callback invocation.
164
165	root	1.2	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
166			portable).
167
168			=item $async->block
169
170			Sometimes you need a "critical section" of code where
171
172			=item $async->unblock
173
174	root	1.1	=cut
175
176			1;
177
178			=back
179
180	root	1.2	=head1 EXAMPLE
181
182			#TODO
183
184			=head1 IMPLEMENTATION DETAILS AND LIMITATIONS
185
186			This module works by "hijacking" SIGKILL, which is guarenteed to be always
187			available in perl, but also cannot be caught, so is always available.
188
189			Basically, this module fakes the receive of a SIGKILL signal and
190			then catches it. This makes normal signal handling slower (probably
191			unmeasurably), but has the advantage of not requiring a special runops nor
192			slowing down normal perl execution a bit.
193
194			It assumes that C<sig_atomic_t> and C<int> are both exception-safe to
195			modify (C<sig_atomic_> is used by this module, and perl itself uses
196			C<int>, so we can assume that this is quite portbale, at least w.r.t.
197			signals).
198
199	root	1.1	=head1 AUTHOR
200
201			Marc Lehmann <schmorp@schmorp.de>
202			http://home.schmorp.de/
203
204			=cut
205