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
#TODO#

=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

=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 ever<y previous
call to C<block> (i.e. calls can nest).

Since ensuring this in the presense 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

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