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10 | |
10 | |
11 | This module implements a single feature only of interest to advanced perl |
11 | This module implements a single feature only of interest to advanced perl |
12 | modules, namely asynchronous interruptions (think "UNIX signals", which |
12 | modules, namely asynchronous interruptions (think "UNIX signals", which |
13 | are very similar). |
13 | are very similar). |
14 | |
14 | |
15 | Sometimes, modules wish to run code asynchronously (in another thread), |
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 |
16 | or from a signal handler), and then signal the perl interpreter on |
17 | to write some data to a pipe and use an event handling toolkit to watch |
17 | certain events. One common way is to write some data to a pipe and use an |
18 | for I/O events. Another way is to send a signal. Those methods are slow, |
18 | event handling toolkit to watch for I/O events. Another way is to send |
19 | and in the case of a pipe, also not asynchronous - it won't interrupt a |
19 | a signal. Those methods are slow, and in the case of a pipe, also not |
20 | running perl interpreter. |
20 | asynchronous - it won't interrupt a running perl interpreter. |
21 | |
21 | |
22 | This module implements asynchronous notifications that enable you to |
22 | This module implements asynchronous notifications that enable you to |
23 | signal running perl code form another thread, asynchronously, without |
23 | signal running perl code from another thread, asynchronously, and |
24 | issuing syscalls. |
24 | sometimes even without using a single syscall. |
25 | |
25 | |
26 | It works by creating an C<Async::Interrupt> object for each such use. This |
26 | =head2 USAGE SCENARIOS |
27 | object stores a perl and/or a C-level callback that is invoked when the |
27 | |
28 | C<Async::Interrupt> object gets signalled. It is executed at the next time |
28 | =over 4 |
29 | the perl interpreter is running (i.e. it will interrupt a computation, but |
29 | |
30 | not an XS function or a syscall). |
30 | =item Race-free signal handling |
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31 | |
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32 | There seems to be no way to do race-free signal handling in perl: to |
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33 | catch a signal, you have to execute Perl code, and between entering the |
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34 | interpreter C<select> function (or other blocking functions) and executing |
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35 | the select syscall is a small but relevant timespan during which signals |
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36 | will be queued, but perl signal handlers will not be executed and the |
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37 | blocking syscall will not be interrupted. |
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38 | |
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39 | You can use this module to bind a signal to a callback while at the same |
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40 | time activating an event pipe that you can C<select> on, fixing the race |
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41 | completely. |
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42 | |
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43 | This can be used to implement the signal hadling in event loops, |
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44 | e.g. L<AnyEvent>, L<POE>, L<IO::Async::Loop> and so on. |
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45 | |
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46 | =item Background threads want speedy reporting |
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47 | |
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48 | Assume you want very exact timing, and you can spare an extra cpu core |
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49 | for that. Then you can run an extra thread that signals your perl |
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50 | interpreter. This means you can get a very exact timing source while your |
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51 | perl code is number crunching, without even using a syscall to communicate |
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52 | between your threads. |
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53 | |
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54 | For example the deliantra game server uses a variant of this technique |
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55 | to interrupt background processes regularly to send map updates to game |
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56 | clients. |
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57 | |
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58 | L<IO::AIO> and L<BDB> could also use this to speed up result reporting. |
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59 | |
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60 | =item Speedy event loop invocation |
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61 | |
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62 | One could use this module e.g. in L<Coro> to interrupt a running coro-thread |
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63 | and cause it to enter the event loop. |
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64 | |
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65 | Or one could bind to C<SIGIO> and tell some important sockets to send this |
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66 | signal, causing the event loop to be entered to reduce network latency. |
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67 | |
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68 | =back |
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69 | |
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70 | =head2 HOW TO USE |
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71 | |
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72 | You can use this module by creating an C<Async::Interrupt> object for each |
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73 | such event source. This object stores a perl and/or a C-level callback |
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74 | that is invoked when the C<Async::Interrupt> object gets signalled. It is |
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75 | executed at the next time the perl interpreter is running (i.e. it will |
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76 | interrupt a computation, but not an XS function or a syscall). |
31 | |
77 | |
32 | You can signal the C<Async::Interrupt> object either by calling it's C<< |
78 | 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. |
79 | ->signal >> method, or, more commonly, by calling a C function. There is |
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80 | also the built-in (POSIX) signal source. |
34 | |
81 | |
35 | The C<< ->signal_func >> returns the address of the C function that is to |
82 | 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 |
83 | 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 |
84 | function also takes an integer argument in the range SIG_ATOMIC_MIN to |
38 | SIG_ATOMIC_MAX (guaranteed to allow at least 0..127). |
85 | SIG_ATOMIC_MAX (guaranteed to allow at least 0..127). |
39 | |
86 | |
40 | Since this kind of interruption is fast, but can only interrupt a |
87 | Since this kind of interruption is fast, but can only interrupt a |
41 | I<running> interpreter, there is optional support for also signalling a |
88 | I<running> interpreter, there is optional support for signalling a pipe |
42 | pipe - that means you can also wait for the pipe to become readable (e.g. |
89 | - that means you can also wait for the pipe to become readable (e.g. via |
43 | via L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a |
90 | L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a C<read> |
44 | C<read> and C<write> syscall. |
91 | and C<write> syscall. |
45 | |
92 | |
46 | =over 4 |
93 | =over 4 |
47 | |
94 | |
48 | =cut |
95 | =cut |
49 | |
96 | |
50 | package Async::Interrupt; |
97 | package Async::Interrupt; |
51 | |
98 | |
52 | no warnings; |
99 | use common::sense; |
53 | |
100 | |
54 | BEGIN { |
101 | BEGIN { |
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102 | # the next line forces initialisation of internal |
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103 | # signal handling # variables |
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104 | $SIG{KILL} = sub { }; |
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105 | |
55 | $VERSION = '0.03'; |
106 | our $VERSION = '0.041'; |
56 | |
107 | |
57 | require XSLoader; |
108 | require XSLoader; |
58 | XSLoader::load Async::Interrupt::, $VERSION; |
109 | XSLoader::load ("Async::Interrupt", $VERSION); |
59 | } |
110 | } |
60 | |
111 | |
61 | our $DIED = sub { warn "$@" }; |
112 | our $DIED = sub { warn "$@" }; |
62 | |
113 | |
63 | =item $async = new Async::Interrupt key => value... |
114 | =item $async = new Async::Interrupt key => value... |
… | |
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106 | might use (the exception is C<errno>, which is saved and restored by |
157 | 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, |
158 | 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 |
159 | 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). |
160 | which case the requirements set out for C<cb> apply as well). |
110 | |
161 | |
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162 | =item signal => $signame_or_value |
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163 | |
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164 | When this parameter is specified, then the Async::Interrupt will hook the |
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165 | given signal, that is, it will effectively call C<< ->signal (0) >> each time |
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166 | the given signal is caught by the process. |
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167 | |
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168 | Only one async can hook a given signal, and the signal will be restored to |
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169 | defaults when the Async::Interrupt object gets destroyed. |
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170 | |
111 | =item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing] |
171 | =item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing] |
112 | |
172 | |
113 | Specifies two file descriptors (or file handles) that should be signalled |
173 | Specifies two file descriptors (or file handles) that should be signalled |
114 | whenever the async interrupt is signalled. This means a single octet will |
174 | whenever the async interrupt is signalled. This means a single octet will |
115 | be written to it, and before the callback is being invoked, it will be |
175 | be written to it, and before the callback is being invoked, it will be |
116 | read again. Due to races, it is unlikely but possible that multiple octets |
176 | read again. Due to races, it is unlikely but possible that multiple octets |
117 | are written. It is required that the file handles are both in nonblocking |
177 | are written. It is required that the file handles are both in nonblocking |
118 | mode. |
178 | mode. |
119 | |
179 | |
120 | (You can get a portable pipe and set non-blocking mode portably by using |
180 | You can get a portable pipe and set non-blocking mode portably by using |
121 | e.g. L<AnyEvent::Util> from the L<AnyEvent> distribution). |
181 | e.g. L<AnyEvent::Util> from the L<AnyEvent> distribution. |
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182 | |
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183 | It is also possible to pass in a linux eventfd as both read and write |
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184 | handle (which is faster than a pipe). |
122 | |
185 | |
123 | The object will keep a reference to the file handles. |
186 | The object will keep a reference to the file handles. |
124 | |
187 | |
125 | This can be used to ensure that async notifications will interrupt event |
188 | This can be used to ensure that async notifications will interrupt event |
126 | frameworks as well. |
189 | frameworks as well. |
… | |
… | |
130 | =cut |
193 | =cut |
131 | |
194 | |
132 | sub new { |
195 | sub new { |
133 | my ($class, %arg) = @_; |
196 | my ($class, %arg) = @_; |
134 | |
197 | |
135 | bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1]), $class |
198 | bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1], $arg{signal}), $class |
136 | } |
199 | } |
137 | |
200 | |
138 | =item ($signal_func, $signal_arg) = $async->signal_func |
201 | =item ($signal_func, $signal_arg) = $async->signal_func |
139 | |
202 | |
140 | Returns the address of a function to call asynchronously. The function has |
203 | Returns the address of a function to call asynchronously. The function has |
… | |
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189 | the current scope is exited (via an exception, by canceling the Coro |
252 | the current scope is exited (via an exception, by canceling the Coro |
190 | thread, by calling last/goto etc.). |
253 | thread, by calling last/goto etc.). |
191 | |
254 | |
192 | This is the recommended (and fastest) way to implement critical sections. |
255 | This is the recommended (and fastest) way to implement critical sections. |
193 | |
256 | |
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257 | =item $async->pipe_enable |
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258 | |
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259 | =item $async->pipe_disable |
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260 | |
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261 | Enable/disable signalling the pipe when the interrupt occurs (default is |
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262 | enabled). Writing to a pipe is relatively expensive, so it can be disabled |
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263 | when you know you are not waiting for it (for example, with L<EV> you |
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264 | could disable the pipe in a check watcher, and enable it in a prepare |
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265 | watcher). |
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266 | |
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267 | Note that when C<fd_disable> is in effect, no attempt to read from the |
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268 | pipe will be done. |
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269 | |
194 | =cut |
270 | =cut |
195 | |
271 | |
196 | 1; |
272 | 1; |
197 | |
273 | |
198 | =back |
274 | =back |
199 | |
275 | |
200 | =head1 EXAMPLE |
276 | =head1 EXAMPLE |
201 | |
277 | |
202 | There really should be a complete C/XS example. Bug me about it. |
278 | There really should be a complete C/XS example. Bug me about it. Better |
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279 | yet, create one. |
203 | |
280 | |
204 | =head1 IMPLEMENTATION DETAILS AND LIMITATIONS |
281 | =head1 IMPLEMENTATION DETAILS AND LIMITATIONS |
205 | |
282 | |
206 | This module works by "hijacking" SIGKILL, which is guaranteed to be always |
283 | This module works by "hijacking" SIGKILL, which is guaranteed to always |
207 | available in perl, but also cannot be caught, so is always available. |
284 | exist, but also cannot be caught, so is always available. |
208 | |
285 | |
209 | Basically, this module fakes the receive of a SIGKILL signal and |
286 | Basically, this module fakes the occurance of a SIGKILL signal and |
210 | then catches it. This makes normal signal handling slower (probably |
287 | then intercepts the interpreter handling it. This makes normal signal |
211 | unmeasurably), but has the advantage of not requiring a special runops nor |
288 | handling slower (probably unmeasurably, though), but has the advantage |
212 | slowing down normal perl execution a bit. |
289 | of not requiring a special runops function, nor slowing down normal perl |
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290 | execution a bit. |
213 | |
291 | |
214 | It assumes that C<sig_atomic_t> and C<int> are both exception-safe to |
292 | It assumes that C<sig_atomic_t> and C<int> are both async-safe to modify |
215 | modify (C<sig_atomic_> is used by this module, and perl itself uses |
293 | (C<sig_atomic_> is used by this module, and perl itself uses C<int>, so we |
216 | C<int>, so we can assume that this is quite portable, at least w.r.t. |
294 | can assume that this is quite portable, at least w.r.t. signals). |
217 | signals). |
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218 | |
295 | |
219 | =head1 AUTHOR |
296 | =head1 AUTHOR |
220 | |
297 | |
221 | Marc Lehmann <schmorp@schmorp.de> |
298 | Marc Lehmann <schmorp@schmorp.de> |
222 | http://home.schmorp.de/ |
299 | http://home.schmorp.de/ |