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 *
#	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	#TODO#
44
45	=over 4
46
47	=cut
48
49	package Async::Interrupt;
50
51	no warnings;
52
53	BEGIN {
54	$VERSION = '0.02';
55
56	require XSLoader;
57	XSLoader::load Async::Interrupt::, $VERSION;
58	}
59
60	our $DIED = sub { warn "$@" };
61
62	=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	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<$@>, which are saved and restored by
83	Async::Interrupt.
84
85	If the callback should throw an exception, then it will be caught,
86	and C<$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, $c_arg]
91
92	Registers a C callback the be invoked whenever the async interrupt is
93	signalled.
94
95	The C callback must have the following prototype:
96
97	void c_func (pTHX_ void *c_arg, int value);
98
99	Both C<$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<$signal>
101	or the C<signal_func> function.
102
103	Note that, because the callback can be invoked at almost any time, you
104	have to be careful at saving and restoring global variables that Perl
105	might use (the excetpion is C<errno>, which is aved and restored by
106	Async::Interrupt). The callback itself runs as part of the perl context,
107	so you can call any perl functions and modify any perl data structures (in
108	which case the requireemnts set out for C<cb> apply as well).
109
110	=item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing]
111
112	Specifies two file descriptors (or file handles) that should be signalled
113	whenever the async interrupt is signalled. This means a single octet will
114	be written to it, and before the callback is being invoked, it will be
115	read again. Due to races, it is unlikely but possible that multiple octets
116	are written. It is required that the file handles are both in nonblocking
117	mode.
118
119	(You can get a portable pipe and set non-blocking mode portably by using
120	e.g. L<AnyEvent::Util> from the L<AnyEvent> distro).
121
122	The object will keep a reference to the file handles.
123
124	This can be used to ensure that async notifications will interrupt event
125	frameworks as well.
126
127	=back
128
129	=cut
130
131	sub new {
132	my ($class, %arg) = @_;
133
134	bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1]), $class
135	}
136
137	=item ($signal_func, $signal_arg) = $async->signal_func
138
139	Returns the address of a function to call asynchronously. The function has
140	the following prototype and needs to be passed the specified C<$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	The function is safe to call from within signal and thread contexts, at
150	any time. The specified C<value> is passed to both C and Perl callback.
151
152	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
153	portable).
154
155	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	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
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	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	=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
185	=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
193	=cut
194
195	1;
196
197	=back
198
199	=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	=head1 AUTHOR
219
220	Marc Lehmann <schmorp@schmorp.de>
221	http://home.schmorp.de/
222
223	=cut
224