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 |
|