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 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 (15 years ago) by root
Branch:	MAIN
Changes since 1.1:	+83 -20 lines
Log Message:	* empty log message *
#	Content
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	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	=over 4
45
46	=cut
47
48	package Async::Interrupt;
49
50	no warnings;
51
52	BEGIN {
53	$VERSION = '0.02';
54
55	require XSLoader;
56	XSLoader::load Async::Interrupt::, $VERSION;
57	}
58
59	our $DIED = sub { warn "$@" };
60
61	=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	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<$@>, which are saved and restored by
82	Async::Interrupt.
83
84	If the callback should throw an exception, then it will be caught,
85	and C<$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, $c_arg]
90
91	Registers a C callback the be invoked whenever the async interrupt is
92	signalled.
93
94	The C callback must have the following prototype:
95
96	void c_func (pTHX_ void *c_arg, int value);
97
98	Both C<$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<$signal>
100	or the C<signal_func> function.
101
102	Note that, because the callback can be invoked at almost any time, you
103	have to be careful at saving and restoring global variables that Perl
104	might use (the excetpion is C<errno>, which is aved and restored by
105	Async::Interrupt). The callback itself runs as part of the perl context,
106	so you can call any perl functions and modify any perl data structures (in
107	which case the requireemnts set out for C<cb> apply as well).
108
109	=item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing]
110
111	Specifies two file descriptors (or file handles) that should be signalled
112	whenever the async interrupt is signalled. This means a single octet will
113	be written to it, and before the callback is being invoked, it will be
114	read again. Due to races, it is unlikely but possible that multiple octets
115	are written. It is required that the file handles are both in nonblocking
116	mode.
117
118	(You can get a portable pipe and set non-blocking mode portably by using
119	e.g. L<AnyEvent::Util> from the L<AnyEvent> distro).
120
121	The object will keep a reference to the file handles.
122
123	This can be used to ensure that async notifications will interrupt event
124	frameworks as well.
125
126	=back
127
128	=cut
129
130	sub new {
131	my ($class, %arg) = @_;
132
133	bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1]), $class
134	}
135
136	=item ($signal_func, $signal_arg) = $async->signal_func
137
138	Returns the address of a function to call asynchronously. The function has
139	the following prototype and needs to be passed the specified C<$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	The function is safe to call from within signal and thread contexts, at
149	any time. The specified C<value> is passed to both C and Perl callback.
150
151	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
152	portable).
153
154	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	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
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	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	=cut
175
176	1;
177
178	=back
179
180	=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	=head1 AUTHOR
200
201	Marc Lehmann <schmorp@schmorp.de>
202	http://home.schmorp.de/
203
204	=cut
205