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 (14 years, 11 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_02
Changes since 1.3:	+12 -11 lines
Log Message:	0.02
#	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 (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
46	=over 4
47
48	=cut
49
50	package Async::Interrupt;
51
52	no warnings;
53
54	BEGIN {
55	$VERSION = '0.02';
56
57	require XSLoader;
58	XSLoader::load Async::Interrupt::, $VERSION;
59	}
60
61	our $DIED = sub { warn "$@" };
62
63	=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	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<$@>, which are saved and restored by
84	Async::Interrupt.
85
86	If the callback should throw an exception, then it will be caught,
87	and C<$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, $c_arg]
92
93	Registers a C callback the be invoked whenever the async interrupt is
94	signalled.
95
96	The C callback must have the following prototype:
97
98	void c_func (pTHX_ void *c_arg, int value);
99
100	Both C<$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<$signal>
102	or the C<signal_func> function.
103
104	Note that, because the callback can be invoked at almost any time, you
105	have to be careful at saving and restoring global variables that Perl
106	might use (the exception is C<errno>, which is saved and restored by
107	Async::Interrupt). The callback itself runs as part of the perl context,
108	so you can call any perl functions and modify any perl data structures (in
109	which case the requirements set out for C<cb> apply as well).
110
111	=item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing]
112
113	Specifies two file descriptors (or file handles) that should be signalled
114	whenever the async interrupt is signalled. This means a single octet will
115	be written to it, and before the callback is being invoked, it will be
116	read again. Due to races, it is unlikely but possible that multiple octets
117	are written. It is required that the file handles are both in nonblocking
118	mode.
119
120	(You can get a portable pipe and set non-blocking mode portably by using
121	e.g. L<AnyEvent::Util> from the L<AnyEvent> distribution).
122
123	The object will keep a reference to the file handles.
124
125	This can be used to ensure that async notifications will interrupt event
126	frameworks as well.
127
128	=back
129
130	=cut
131
132	sub new {
133	my ($class, %arg) = @_;
134
135	bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1]), $class
136	}
137
138	=item ($signal_func, $signal_arg) = $async->signal_func
139
140	Returns the address of a function to call asynchronously. The function has
141	the following prototype and needs to be passed the specified C<$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	The function is safe to call from within signal and thread contexts, at
151	any time. The specified C<value> is passed to both C and Perl callback.
152
153	C<$value> must be in the valid range for a C<sig_atomic_t> (0..127 is
154	portable).
155
156	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	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
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	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	=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	Note that there must be exactly one call of C<unblock> for every previous
180	call to C<block> (i.e. calls can nest).
181
182	Since ensuring this in the presence of exceptions and threads is
183	usually more difficult than you imagine, I recommend using C<<
184	$async->scoped_block >> instead.
185
186	=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
194	=cut
195
196	1;
197
198	=back
199
200	=head1 EXAMPLE
201
202	There really should be a complete C/XS example. Bug me about it.
203
204	=head1 IMPLEMENTATION DETAILS AND LIMITATIONS
205
206	This module works by "hijacking" SIGKILL, which is guaranteed to be always
207	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	C<int>, so we can assume that this is quite portable, at least w.r.t.
217	signals).
218
219	=head1 AUTHOR
220
221	Marc Lehmann <schmorp@schmorp.de>
222	http://home.schmorp.de/
223
224	=cut
225