… | |
… | |
91 | I<running> interpreter, there is optional support for signalling a pipe |
91 | I<running> interpreter, there is optional support for signalling a pipe |
92 | - that means you can also wait for the pipe to become readable (e.g. via |
92 | - that means you can also wait for the pipe to become readable (e.g. via |
93 | L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a C<read> |
93 | L<EV> or L<AnyEvent>). This, of course, incurs the overhead of a C<read> |
94 | and C<write> syscall. |
94 | and C<write> syscall. |
95 | |
95 | |
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96 | =head1 USAGE EXAMPLES |
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97 | |
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98 | =head2 Implementing race-free signal handling |
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99 | |
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100 | This example uses a single event pipe for all signals, and one |
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101 | Async::Interrupt per signal. This code is actually what the L<AnyEvent> |
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102 | module uses itself when Async::Interrupt is available. |
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103 | |
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104 | First, create the event pipe and hook it into the event loop |
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105 | |
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106 | $SIGPIPE = new Async::Interrupt::EventPipe; |
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107 | $SIGPIPE_W = AnyEvent->io ( |
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108 | fh => $SIGPIPE->fileno, |
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109 | poll => "r", |
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110 | cb => \&_signal_check, # defined later |
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111 | ); |
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112 | |
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113 | Then, for each signal to hook, create an Async::Interrupt object. The |
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114 | callback just sets a global variable, as we are only interested in |
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115 | synchronous signals (i.e. when the event loop polls), which is why the |
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116 | pipe draining is not done automatically. |
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117 | |
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118 | my $interrupt = new Async::Interrupt |
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119 | cb => sub { undef $SIGNAL_RECEIVED{$signum} }, |
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120 | signal => $signum, |
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121 | pipe => [$SIGPIPE->filenos], |
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122 | pipe_autodrain => 0, |
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123 | ; |
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124 | |
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125 | Finally, the I/O callback for the event pipe handles the signals: |
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126 | |
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127 | sub _signal_check { |
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128 | # drain the pipe first |
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129 | $SIGPIPE->drain; |
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130 | |
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131 | # two loops, just to be sure |
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132 | while (%SIGNAL_RECEIVED) { |
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133 | for (keys %SIGNAL_RECEIVED) { |
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134 | delete $SIGNAL_RECEIVED{$_}; |
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135 | warn "signal $_ received\n"; |
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136 | } |
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137 | } |
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138 | } |
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139 | |
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140 | =head2 Interrupt perl from another thread |
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141 | |
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142 | This example interrupts the Perl interpreter from another thread, via the |
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143 | XS API. This is used by e.g. the L<EV::Loop::Async> module. |
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144 | |
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145 | On the Perl level, a new loop object (which contains the thread) |
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146 | is created, by first calling some XS constructor, querying the |
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147 | C-level callback function and feeding that as the C<c_cb> into the |
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148 | Async::Interrupt constructor: |
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149 | |
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150 | my $self = XS_thread_constructor; |
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151 | my ($c_func, $c_arg) = _c_func $self; # return the c callback |
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152 | my $asy = new Async::Interrupt c_cb => [$c_func, $c_arg]; |
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153 | |
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154 | Then the newly created Interrupt object is queried for the signaling |
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155 | function that the newly created thread should call, and this is in turn |
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156 | told to the thread object: |
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157 | |
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158 | _attach $self, $asy->signal_func; |
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159 | |
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160 | So to repeat: first the XS object is created, then it is queried for the |
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161 | callback that should be called when the Interrupt object gets signalled. |
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162 | |
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163 | Then the interrupt object is queried for the callback fucntion that the |
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164 | thread should call to signal the Interrupt object, and this callback is |
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165 | then attached to the thread. |
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166 | |
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167 | You have to be careful that your new thread is not signalling before the |
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168 | signal function was configured, for example by starting the background |
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169 | thread only within C<_attach>. |
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170 | |
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171 | That concludes the Perl part. |
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172 | |
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173 | The XS part consists of the actual constructor which creates a thread, |
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174 | which is not relevant for this example, and two functions, C<_c_func>, |
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175 | which returns the Perl-side callback, and C<_attach>, which configures |
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176 | the signalling functioon that is safe toc all from another thread. For |
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177 | simplicity, we will use global variables to store the functions, normally |
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178 | you would somehow attach them to C<$self>. |
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179 | |
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180 | The C<c_func> simply returns the address of a static function and arranges |
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181 | for the object pointed to by C<$self> to be passed to it, as an integer: |
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182 | |
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183 | void |
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184 | _c_func (SV *loop) |
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185 | PPCODE: |
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186 | EXTEND (SP, 2); |
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187 | PUSHs (sv_2mortal (newSViv (PTR2IV (c_func)))); |
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188 | PUSHs (sv_2mortal (newSViv (SvRV (loop)))); |
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189 | |
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190 | This would be the callback (since it runs in a normal Perl context, it is |
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191 | permissible to manipulate Perl values): |
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192 | |
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193 | static void |
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194 | c_func (pTHX_ void *loop_, int value) |
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195 | { |
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196 | SV *loop_object = (SV *)loop_; |
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197 | ... |
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198 | } |
|
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199 | |
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200 | And this attaches the signalling callback: |
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201 | |
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202 | static void (*my_sig_func) (void *signal_arg, int value); |
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203 | static void *my_sig_arg; |
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204 | |
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205 | void |
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206 | _attach (SV *loop_, IV sig_func, void *sig_arg) |
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207 | CODE: |
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208 | { |
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209 | my_sig_func = sig_func; |
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210 | my_sig_arg = sig_arg; |
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211 | |
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212 | /* now run the thread */ |
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213 | thread_create (&u->tid, l_run, 0); |
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214 | } |
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215 | |
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216 | And C<l_run> (the background thread) would eventually call the signaling |
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217 | function: |
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218 | |
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219 | my_sig_func (my_sig_arg, 0); |
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220 | |
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221 | You can have a look at L<EV::Loop::Async> for an actual example using |
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222 | intra-thread communication, locking and so on. |
|
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223 | |
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224 | |
96 | =head1 THE Async::Interrupt CLASS |
225 | =head1 THE Async::Interrupt CLASS |
97 | |
226 | |
98 | =over 4 |
227 | =over 4 |
99 | |
228 | |
100 | =cut |
229 | =cut |
… | |
… | |
103 | |
232 | |
104 | use common::sense; |
233 | use common::sense; |
105 | |
234 | |
106 | BEGIN { |
235 | BEGIN { |
107 | # the next line forces initialisation of internal |
236 | # the next line forces initialisation of internal |
108 | # signal handling # variables |
237 | # signal handling variables, otherwise, PL_sig_pending |
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238 | # etc. might be null pointers. |
109 | $SIG{KILL} = sub { }; |
239 | $SIG{KILL} = sub { }; |
110 | |
240 | |
111 | our $VERSION = '0.6'; |
241 | our $VERSION = '1.1'; |
112 | |
242 | |
113 | require XSLoader; |
243 | require XSLoader; |
114 | XSLoader::load ("Async::Interrupt", $VERSION); |
244 | XSLoader::load ("Async::Interrupt", $VERSION); |
115 | } |
245 | } |
116 | |
246 | |
… | |
… | |
139 | The exceptions are C<$!> and C<$@>, which are saved and restored by |
269 | The exceptions are C<$!> and C<$@>, which are saved and restored by |
140 | Async::Interrupt. |
270 | Async::Interrupt. |
141 | |
271 | |
142 | If the callback should throw an exception, then it will be caught, |
272 | If the callback should throw an exception, then it will be caught, |
143 | and C<$Async::Interrupt::DIED> will be called with C<$@> containing |
273 | and C<$Async::Interrupt::DIED> will be called with C<$@> containing |
144 | the exception. The default will simply C<warn> about the message and |
274 | the exception. The default will simply C<warn> about the message and |
145 | continue. |
275 | continue. |
146 | |
276 | |
147 | =item c_cb => [$c_func, $c_arg] |
277 | =item c_cb => [$c_func, $c_arg] |
148 | |
278 | |
149 | Registers a C callback the be invoked whenever the async interrupt is |
279 | Registers a C callback the be invoked whenever the async interrupt is |
… | |
… | |
183 | the given signal is caught by the process. |
313 | the given signal is caught by the process. |
184 | |
314 | |
185 | Only one async can hook a given signal, and the signal will be restored to |
315 | Only one async can hook a given signal, and the signal will be restored to |
186 | defaults when the Async::Interrupt object gets destroyed. |
316 | defaults when the Async::Interrupt object gets destroyed. |
187 | |
317 | |
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318 | =item signal_hysteresis => $boolean |
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319 | |
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320 | Sets the initial signal hysteresis state, see the C<signal_hysteresis> |
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321 | method, below. |
|
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322 | |
188 | =item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing] |
323 | =item pipe => [$fileno_or_fh_for_reading, $fileno_or_fh_for_writing] |
189 | |
324 | |
190 | Specifies two file descriptors (or file handles) that should be signalled |
325 | Specifies two file descriptors (or file handles) that should be signalled |
191 | whenever the async interrupt is signalled. This means a single octet will |
326 | whenever the async interrupt is signalled. This means a single octet will |
192 | be written to it, and before the callback is being invoked, it will be |
327 | be written to it, and before the callback is being invoked, it will be |
… | |
… | |
205 | |
340 | |
206 | If you want to share a single event pipe between multiple Async::Interrupt |
341 | If you want to share a single event pipe between multiple Async::Interrupt |
207 | objects, you can use the C<Async::Interrupt::EventPipe> class to manage |
342 | objects, you can use the C<Async::Interrupt::EventPipe> class to manage |
208 | those. |
343 | those. |
209 | |
344 | |
|
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345 | =item pipe_autodrain => $boolean |
|
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346 | |
|
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347 | Sets the initial autodrain state, see the C<pipe_autodrain> method, below. |
|
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348 | |
210 | =back |
349 | =back |
211 | |
350 | |
212 | =cut |
351 | =cut |
213 | |
352 | |
214 | sub new { |
353 | sub new { |
215 | my ($class, %arg) = @_; |
354 | my ($class, %arg) = @_; |
216 | |
355 | |
217 | bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1], $arg{signal}, $arg{var}), $class |
356 | my $self = bless \(_alloc $arg{cb}, @{$arg{c_cb}}[0,1], @{$arg{pipe}}[0,1], $arg{signal}, $arg{var}), $class; |
|
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357 | |
|
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358 | # urgs, reminds me of Event |
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359 | for my $attr (qw(pipe_autodrain signal_hysteresis)) { |
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360 | $self->$attr ($arg{$attr}) if exists $arg{$attr}; |
|
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361 | } |
|
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362 | |
|
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363 | $self |
218 | } |
364 | } |
219 | |
365 | |
220 | =item ($signal_func, $signal_arg) = $async->signal_func |
366 | =item ($signal_func, $signal_arg) = $async->signal_func |
221 | |
367 | |
222 | Returns the address of a function to call asynchronously. The function |
368 | Returns the address of a function to call asynchronously. The function |
… | |
… | |
273 | might imply, do anything with POSIX signals). |
419 | might imply, do anything with POSIX signals). |
274 | |
420 | |
275 | C<$value> must be in the valid range for a C<sig_atomic_t>, except C<0> |
421 | C<$value> must be in the valid range for a C<sig_atomic_t>, except C<0> |
276 | (1..127 is portable). |
422 | (1..127 is portable). |
277 | |
423 | |
|
|
424 | =item $async->handle |
|
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425 | |
|
|
426 | Calls the callback if the object is pending. |
|
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427 | |
|
|
428 | This method does not need to be called normally, as it will be invoked |
|
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429 | automatically. However, it can be used to force handling of outstanding |
|
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430 | interrupts while the object is blocked. |
|
|
431 | |
|
|
432 | One reason why one might want to do that is when you want to switch |
|
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433 | from asynchronous interruptions to synchronous one, using e.g. an event |
|
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434 | loop. To do that, one would first C<< $async->block >> the interrupt |
|
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435 | object, then register a read watcher on the C<pipe_fileno> that calls C<< |
|
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436 | $async->handle >>. |
|
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437 | |
|
|
438 | This disables asynchronous interruptions, but ensures that interrupts are |
|
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439 | handled by the event loop. |
|
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440 | |
278 | =item $async->signal_hysteresis ($enable) |
441 | =item $async->signal_hysteresis ($enable) |
279 | |
442 | |
280 | Enables or disables signal hysteresis (default: disabled). If a POSIX |
443 | Enables or disables signal hysteresis (default: disabled). If a POSIX |
281 | signal is used as a signal source for the interrupt object, then enabling |
444 | signal is used as a signal source for the interrupt object, then enabling |
282 | signal hysteresis causes Async::Interrupt to reset the signal action to |
445 | signal hysteresis causes Async::Interrupt to reset the signal action to |
… | |
… | |
286 | When you expect a lot of signals (e.g. when using SIGIO), then enabling |
449 | When you expect a lot of signals (e.g. when using SIGIO), then enabling |
287 | signal hysteresis can reduce the number of handler invocations |
450 | signal hysteresis can reduce the number of handler invocations |
288 | considerably, at the cost of two extra syscalls. |
451 | considerably, at the cost of two extra syscalls. |
289 | |
452 | |
290 | Note that setting the signal to C<SIG_IGN> can have unintended side |
453 | Note that setting the signal to C<SIG_IGN> can have unintended side |
291 | effects when you fork and exec other programs, as often they do nto expect |
454 | effects when you fork and exec other programs, as often they do not expect |
292 | signals to be ignored by default. |
455 | signals to be ignored by default. |
293 | |
456 | |
294 | =item $async->block |
457 | =item $async->block |
295 | |
458 | |
296 | =item $async->unblock |
459 | =item $async->unblock |
… | |
… | |
349 | =item $fileno = $async->pipe_fileno |
512 | =item $fileno = $async->pipe_fileno |
350 | |
513 | |
351 | Returns the reading side of the signalling pipe. If no signalling pipe is |
514 | Returns the reading side of the signalling pipe. If no signalling pipe is |
352 | currently attached to the object, it will dynamically create one. |
515 | currently attached to the object, it will dynamically create one. |
353 | |
516 | |
354 | Note that the only valid oepration on this file descriptor is to wait |
517 | Note that the only valid operation on this file descriptor is to wait |
355 | until it is readable. The fd might belong currently to a pipe, a tcp |
518 | until it is readable. The fd might belong currently to a pipe, a tcp |
356 | socket, or an eventfd, depending on the platform, and is guaranteed to be |
519 | socket, or an eventfd, depending on the platform, and is guaranteed to be |
357 | C<select>able. |
520 | C<select>able. |
358 | |
521 | |
359 | =item $async->pipe_autodrain ($enable) |
522 | =item $async->pipe_autodrain ($enable) |
… | |
… | |
364 | draining. |
527 | draining. |
365 | |
528 | |
366 | This is useful when you want to share one pipe among many Async::Interrupt |
529 | This is useful when you want to share one pipe among many Async::Interrupt |
367 | objects. |
530 | objects. |
368 | |
531 | |
|
|
532 | =item $async->pipe_drain |
|
|
533 | |
|
|
534 | Drains the pipe manually, for example, when autodrain is disabled. Does |
|
|
535 | nothing when no pipe is enabled. |
|
|
536 | |
369 | =item $async->post_fork |
537 | =item $async->post_fork |
370 | |
538 | |
371 | The object will not normally be usable after a fork (as the pipe fd is |
539 | The object will not normally be usable after a fork (as the pipe fd is |
372 | shared between processes). Calling this method after a fork in the child |
540 | shared between processes). Calling this method after a fork in the child |
373 | ensures that the object will work as expected again. It only needs to be |
541 | ensures that the object will work as expected again. It only needs to be |
… | |
… | |
376 | This only works when the pipe was created by Async::Interrupt. |
544 | This only works when the pipe was created by Async::Interrupt. |
377 | |
545 | |
378 | Async::Interrupt ensures that the reading file descriptor does not change |
546 | Async::Interrupt ensures that the reading file descriptor does not change |
379 | it's value. |
547 | it's value. |
380 | |
548 | |
|
|
549 | =item $signum = Async::Interrupt::sig2num $signame_or_number |
|
|
550 | |
|
|
551 | =item $signame = Async::Interrupt::sig2name $signame_or_number |
|
|
552 | |
|
|
553 | These two convenience functions simply convert a signal name or number to |
|
|
554 | the corresponding name or number. They are not used by this module and |
|
|
555 | exist just because perl doesn't have a nice way to do this on its own. |
|
|
556 | |
|
|
557 | They will return C<undef> on illegal names or numbers. |
|
|
558 | |
381 | =back |
559 | =back |
382 | |
560 | |
383 | =head1 THE Async::Interrupt::EventPipe CLASS |
561 | =head1 THE Async::Interrupt::EventPipe CLASS |
384 | |
562 | |
385 | Pipes are the predominent utility to make asynchronous signals |
563 | Pipes are the predominant utility to make asynchronous signals |
386 | synchronous. However, pipes are hard to come by: they don't exist on the |
564 | synchronous. However, pipes are hard to come by: they don't exist on the |
387 | broken windows platform, and on GNU/Linux systems, you might want to use |
565 | broken windows platform, and on GNU/Linux systems, you might want to use |
388 | an C<eventfd> instead. |
566 | an C<eventfd> instead. |
389 | |
567 | |
390 | This class creates selectable event pipes in a portable fashion: on |
568 | This class creates selectable event pipes in a portable fashion: on |
… | |
… | |
420 | |
598 | |
421 | =item $epipe->drain |
599 | =item $epipe->drain |
422 | |
600 | |
423 | Drain (empty) the pipe. |
601 | Drain (empty) the pipe. |
424 | |
602 | |
|
|
603 | =item ($c_func, $c_arg) = $epipe->signal_func |
|
|
604 | |
|
|
605 | =item ($c_func, $c_arg) = $epipe->drain_func |
|
|
606 | |
|
|
607 | These two methods returns a function pointer and C<void *> argument |
|
|
608 | that can be called to have the effect of C<< $epipe->signal >> or C<< |
|
|
609 | $epipe->drain >>, respectively, on the XS level. |
|
|
610 | |
|
|
611 | They both have the following prototype and need to be passed their |
|
|
612 | C<$c_arg>, which is a C<void *> cast to an C<IV>: |
|
|
613 | |
|
|
614 | void (*c_func) (void *c_arg) |
|
|
615 | |
|
|
616 | An example call would look like: |
|
|
617 | |
|
|
618 | c_func (c_arg); |
|
|
619 | |
425 | =item $epipe->renew |
620 | =item $epipe->renew |
426 | |
621 | |
427 | Recreates the pipe (useful after a fork). The reading side will not change |
622 | Recreates the pipe (useful after a fork). The reading side will not change |
428 | it's file descriptor number, but the writing side might. |
623 | it's file descriptor number, but the writing side might. |
429 | |
624 | |
|
|
625 | =item $epipe->wait |
|
|
626 | |
|
|
627 | This method blocks the process until there are events on the pipe. This is |
|
|
628 | not a very event-based or ncie way of usign an event pipe, but it can be |
|
|
629 | occasionally useful. |
|
|
630 | |
430 | =back |
631 | =back |
431 | |
632 | |
432 | =cut |
633 | =cut |
433 | |
634 | |
434 | 1; |
635 | 1; |
435 | |
|
|
436 | =head1 EXAMPLE |
|
|
437 | |
|
|
438 | There really should be a complete C/XS example. Bug me about it. Better |
|
|
439 | yet, create one. |
|
|
440 | |
636 | |
441 | =head1 IMPLEMENTATION DETAILS AND LIMITATIONS |
637 | =head1 IMPLEMENTATION DETAILS AND LIMITATIONS |
442 | |
638 | |
443 | This module works by "hijacking" SIGKILL, which is guaranteed to always |
639 | This module works by "hijacking" SIGKILL, which is guaranteed to always |
444 | exist, but also cannot be caught, so is always available. |
640 | exist, but also cannot be caught, so is always available. |