1 | =head1 NAME |
1 | =head1 NAME |
2 | |
2 | |
3 | AnyEvent::Fork - everything you wanted to use fork() for, but couldn't |
3 | AnyEvent::Fork - everything you wanted to use fork() for, but couldn't |
4 | |
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5 | ATTENTION, this is a very early release, and very untested. Consider it a |
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6 | technology preview. |
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7 | |
4 | |
8 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
9 | |
6 | |
10 | use AnyEvent::Fork; |
7 | use AnyEvent::Fork; |
11 | |
8 | |
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64 | while (my $socket = $listener->accept) { |
61 | while (my $socket = $listener->accept) { |
65 | # do sth. with new socket |
62 | # do sth. with new socket |
66 | } |
63 | } |
67 | } |
64 | } |
68 | |
65 | |
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66 | ################################################################## |
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67 | # use AnyEvent::Fork as a faster fork+exec |
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68 | |
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69 | # this runs /bin/echo hi, with stdout redirected to /tmp/log |
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70 | # and stderr to the communications socket. it is usually faster |
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71 | # than fork+exec, but still let's you prepare the environment. |
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72 | |
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73 | open my $output, ">/tmp/log" or die "$!"; |
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74 | |
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75 | AnyEvent::Fork |
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76 | ->new |
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77 | ->eval (' |
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78 | sub run { |
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79 | my ($fh, $output, @cmd) = @_; |
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80 | |
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81 | # perl will clear close-on-exec on STDOUT/STDERR |
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82 | open STDOUT, ">&", $output or die; |
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83 | open STDERR, ">&", $fh or die; |
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84 | |
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85 | exec @cmd; |
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86 | } |
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87 | ') |
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88 | ->send_fh ($output) |
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89 | ->send_arg ("/bin/echo", "hi") |
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90 | ->run ("run", my $cv = AE::cv); |
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91 | |
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92 | my $stderr = $cv->recv; |
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93 | |
69 | =head1 DESCRIPTION |
94 | =head1 DESCRIPTION |
70 | |
95 | |
71 | This module allows you to create new processes, without actually forking |
96 | This module allows you to create new processes, without actually forking |
72 | them from your current process (avoiding the problems of forking), but |
97 | them from your current process (avoiding the problems of forking), but |
73 | preserving most of the advantages of fork. |
98 | preserving most of the advantages of fork. |
74 | |
99 | |
75 | It can be used to create new worker processes or new independent |
100 | It can be used to create new worker processes or new independent |
76 | subprocesses for short- and long-running jobs, process pools (e.g. for use |
101 | subprocesses for short- and long-running jobs, process pools (e.g. for use |
77 | in pre-forked servers) but also to spawn new external processes (such as |
102 | in pre-forked servers) but also to spawn new external processes (such as |
78 | CGI scripts from a webserver), which can be faster (and more well behaved) |
103 | CGI scripts from a web server), which can be faster (and more well behaved) |
79 | than using fork+exec in big processes. |
104 | than using fork+exec in big processes. |
80 | |
105 | |
81 | Special care has been taken to make this module useful from other modules, |
106 | Special care has been taken to make this module useful from other modules, |
82 | while still supporting specialised environments such as L<App::Staticperl> |
107 | while still supporting specialised environments such as L<App::Staticperl> |
83 | or L<PAR::Packer>. |
108 | or L<PAR::Packer>. |
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109 | |
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110 | =head1 WHAT THIS MODULE IS NOT |
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111 | |
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112 | This module only creates processes and lets you pass file handles and |
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113 | strings to it, and run perl code. It does not implement any kind of RPC - |
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114 | there is no back channel from the process back to you, and there is no RPC |
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115 | or message passing going on. |
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116 | |
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117 | If you need some form of RPC, you can either implement it yourself |
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118 | in whatever way you like, use some message-passing module such |
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119 | as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use |
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120 | L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages, |
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121 | and so on. |
84 | |
122 | |
85 | =head1 PROBLEM STATEMENT |
123 | =head1 PROBLEM STATEMENT |
86 | |
124 | |
87 | There are two ways to implement parallel processing on UNIX like operating |
125 | There are two ways to implement parallel processing on UNIX like operating |
88 | systems - fork and process, and fork+exec and process. They have different |
126 | systems - fork and process, and fork+exec and process. They have different |
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100 | or fork+exec instead. |
138 | or fork+exec instead. |
101 | |
139 | |
102 | =item Forking usually creates a copy-on-write copy of the parent |
140 | =item Forking usually creates a copy-on-write copy of the parent |
103 | process. Memory (for example, modules or data files that have been |
141 | process. Memory (for example, modules or data files that have been |
104 | will not take additional memory). When exec'ing a new process, modules |
142 | will not take additional memory). When exec'ing a new process, modules |
105 | and data files might need to be loaded again, at extra cpu and memory |
143 | and data files might need to be loaded again, at extra CPU and memory |
106 | cost. Likewise when forking, all data structures are copied as well - if |
144 | cost. Likewise when forking, all data structures are copied as well - if |
107 | the program frees them and replaces them by new data, the child processes |
145 | the program frees them and replaces them by new data, the child processes |
108 | will retain the memory even if it isn't used. |
146 | will retain the memory even if it isn't used. |
109 | |
147 | |
110 | This module allows the main program to do a controlled fork, and allows |
148 | This module allows the main program to do a controlled fork, and allows |
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122 | as template, and also tries hard to identify the correct path to the perl |
160 | as template, and also tries hard to identify the correct path to the perl |
123 | interpreter. With a cooperative main program, exec'ing the interpreter |
161 | interpreter. With a cooperative main program, exec'ing the interpreter |
124 | might not even be necessary. |
162 | might not even be necessary. |
125 | |
163 | |
126 | =item Forking might be impossible when a program is running. For example, |
164 | =item Forking might be impossible when a program is running. For example, |
127 | POSIX makes it almost impossible to fork from a multithreaded program and |
165 | POSIX makes it almost impossible to fork from a multi-threaded program and |
128 | do anything useful in the child - strictly speaking, if your perl program |
166 | do anything useful in the child - strictly speaking, if your perl program |
129 | uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>), |
167 | uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>), |
130 | you cannot call fork on the perl level anymore, at all. |
168 | you cannot call fork on the perl level anymore, at all. |
131 | |
169 | |
132 | This module can safely fork helper processes at any time, by caling |
170 | This module can safely fork helper processes at any time, by calling |
133 | fork+exec in C, in a POSIX-compatible way. |
171 | fork+exec in C, in a POSIX-compatible way. |
134 | |
172 | |
135 | =item Parallel processing with fork might be inconvenient or difficult |
173 | =item Parallel processing with fork might be inconvenient or difficult |
136 | to implement. For example, when a program uses an event loop and creates |
174 | to implement. For example, when a program uses an event loop and creates |
137 | watchers it becomes very hard to use the event loop from a child |
175 | watchers it becomes very hard to use the event loop from a child |
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169 | needed the first time. Forking from this process shares the memory used |
207 | needed the first time. Forking from this process shares the memory used |
170 | for the perl interpreter with the new process, but loading modules takes |
208 | for the perl interpreter with the new process, but loading modules takes |
171 | time, and the memory is not shared with anything else. |
209 | time, and the memory is not shared with anything else. |
172 | |
210 | |
173 | This is ideal for when you only need one extra process of a kind, with the |
211 | This is ideal for when you only need one extra process of a kind, with the |
174 | option of starting and stipping it on demand. |
212 | option of starting and stopping it on demand. |
175 | |
213 | |
176 | Example: |
214 | Example: |
177 | |
215 | |
178 | AnyEvent::Fork |
216 | AnyEvent::Fork |
179 | ->new |
217 | ->new |
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194 | modules you loaded) is shared between the processes, and each new process |
232 | modules you loaded) is shared between the processes, and each new process |
195 | consumes relatively little memory of its own. |
233 | consumes relatively little memory of its own. |
196 | |
234 | |
197 | The disadvantage of this approach is that you need to create a template |
235 | The disadvantage of this approach is that you need to create a template |
198 | process for the sole purpose of forking new processes from it, but if you |
236 | process for the sole purpose of forking new processes from it, but if you |
199 | only need a fixed number of proceses you can create them, and then destroy |
237 | only need a fixed number of processes you can create them, and then destroy |
200 | the template process. |
238 | the template process. |
201 | |
239 | |
202 | Example: |
240 | Example: |
203 | |
241 | |
204 | my $template = AnyEvent::Fork->new->require ("Some::Module"); |
242 | my $template = AnyEvent::Fork->new->require ("Some::Module"); |
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241 | |
279 | |
242 | package AnyEvent::Fork; |
280 | package AnyEvent::Fork; |
243 | |
281 | |
244 | use common::sense; |
282 | use common::sense; |
245 | |
283 | |
246 | use Socket (); |
284 | use Errno (); |
247 | |
285 | |
248 | use AnyEvent; |
286 | use AnyEvent; |
249 | use AnyEvent::Fork::Util; |
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250 | use AnyEvent::Util (); |
287 | use AnyEvent::Util (); |
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288 | |
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289 | use IO::FDPass; |
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290 | |
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291 | our $VERSION = 0.5; |
251 | |
292 | |
252 | our $PERL; # the path to the perl interpreter, deduces with various forms of magic |
293 | our $PERL; # the path to the perl interpreter, deduces with various forms of magic |
253 | |
294 | |
254 | =item my $pool = new AnyEvent::Fork key => value... |
295 | =item my $pool = new AnyEvent::Fork key => value... |
255 | |
296 | |
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268 | our $TEMPLATE; |
309 | our $TEMPLATE; |
269 | |
310 | |
270 | sub _cmd { |
311 | sub _cmd { |
271 | my $self = shift; |
312 | my $self = shift; |
272 | |
313 | |
273 | #TODO: maybe append the packet to any existing string command already in the queue |
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274 | |
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275 | # ideally, we would want to use "a (w/a)*" as format string, but perl versions |
314 | # ideally, we would want to use "a (w/a)*" as format string, but perl |
276 | # from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it. |
315 | # versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack |
277 | push @{ $self->[2] }, pack "N/a*", pack "(w/a*)*", @_; |
316 | # it. |
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317 | push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1]; |
278 | |
318 | |
279 | $self->[3] ||= AE::io $self->[1], 1, sub { |
319 | $self->[3] ||= AE::io $self->[1], 1, sub { |
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320 | do { |
280 | # send the next "thing" in the queue - either a reference to an fh, |
321 | # send the next "thing" in the queue - either a reference to an fh, |
281 | # or a plain string. |
322 | # or a plain string. |
282 | |
323 | |
283 | if (ref $self->[2][0]) { |
324 | if (ref $self->[2][0]) { |
284 | # send fh |
325 | # send fh |
285 | AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] } |
326 | unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) { |
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327 | return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK; |
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328 | undef $self->[3]; |
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329 | die "AnyEvent::Fork: file descriptor send failure: $!"; |
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330 | } |
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331 | |
286 | and shift @{ $self->[2] }; |
332 | shift @{ $self->[2] }; |
287 | |
333 | |
288 | } else { |
334 | } else { |
289 | # send string |
335 | # send string |
290 | my $len = syswrite $self->[1], $self->[2][0] |
336 | my $len = syswrite $self->[1], $self->[2][0]; |
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337 | |
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338 | unless ($len) { |
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339 | return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK; |
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340 | undef $self->[3]; |
291 | or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" }; |
341 | die "AnyEvent::Fork: command write failure: $!"; |
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342 | } |
292 | |
343 | |
293 | substr $self->[2][0], 0, $len, ""; |
344 | substr $self->[2][0], 0, $len, ""; |
294 | shift @{ $self->[2] } unless length $self->[2][0]; |
345 | shift @{ $self->[2] } unless length $self->[2][0]; |
295 | } |
346 | } |
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347 | } while @{ $self->[2] }; |
296 | |
348 | |
297 | unless (@{ $self->[2] }) { |
349 | # everything written |
298 | undef $self->[3]; |
350 | undef $self->[3]; |
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351 | |
299 | # invoke run callback |
352 | # invoke run callback, if any |
300 | $self->[0]->($self->[1]) if $self->[0]; |
353 | $self->[4]->($self->[1]) if $self->[4]; |
301 | } |
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302 | }; |
354 | }; |
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355 | |
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356 | () # make sure we don't leak the watcher |
303 | } |
357 | } |
304 | |
358 | |
305 | sub _new { |
359 | sub _new { |
306 | my ($self, $fh) = @_; |
360 | my ($self, $fh, $pid) = @_; |
307 | |
361 | |
308 | AnyEvent::Util::fh_nonblocking $fh, 1; |
362 | AnyEvent::Util::fh_nonblocking $fh, 1; |
309 | |
363 | |
310 | $self = bless [ |
364 | $self = bless [ |
311 | undef, # run callback |
365 | $pid, |
312 | $fh, |
366 | $fh, |
313 | [], # write queue - strings or fd's |
367 | [], # write queue - strings or fd's |
314 | undef, # AE watcher |
368 | undef, # AE watcher |
315 | ], $self; |
369 | ], $self; |
316 | |
370 | |
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327 | if ($pid eq 0) { |
381 | if ($pid eq 0) { |
328 | require AnyEvent::Fork::Serve; |
382 | require AnyEvent::Fork::Serve; |
329 | $AnyEvent::Fork::Serve::OWNER = $parent; |
383 | $AnyEvent::Fork::Serve::OWNER = $parent; |
330 | close $fh; |
384 | close $fh; |
331 | $0 = "$_[1] of $parent"; |
385 | $0 = "$_[1] of $parent"; |
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386 | $SIG{CHLD} = 'IGNORE'; |
332 | AnyEvent::Fork::Serve::serve ($slave); |
387 | AnyEvent::Fork::Serve::serve ($slave); |
333 | AnyEvent::Fork::Util::_exit 0; |
388 | exit 0; |
334 | } elsif (!$pid) { |
389 | } elsif (!$pid) { |
335 | die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; |
390 | die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; |
336 | } |
391 | } |
337 | |
392 | |
338 | AnyEvent::Fork->_new ($fh) |
393 | AnyEvent::Fork->_new ($fh, $pid) |
339 | } |
394 | } |
340 | |
395 | |
341 | =item my $proc = new AnyEvent::Fork |
396 | =item my $proc = new AnyEvent::Fork |
342 | |
397 | |
343 | Create a new "empty" perl interpreter process and returns its process |
398 | Create a new "empty" perl interpreter process and returns its process |
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394 | reduces the amount of memory sharing that is possible, and is also slower. |
449 | reduces the amount of memory sharing that is possible, and is also slower. |
395 | |
450 | |
396 | You should use C<new> whenever possible, except when having a template |
451 | You should use C<new> whenever possible, except when having a template |
397 | process around is unacceptable. |
452 | process around is unacceptable. |
398 | |
453 | |
399 | The path to the perl interpreter is divined usign various methods - first |
454 | The path to the perl interpreter is divined using various methods - first |
400 | C<$^X> is investigated to see if the path ends with something that sounds |
455 | C<$^X> is investigated to see if the path ends with something that sounds |
401 | as if it were the perl interpreter. Failing this, the module falls back to |
456 | as if it were the perl interpreter. Failing this, the module falls back to |
402 | using C<$Config::Config{perlpath}>. |
457 | using C<$Config::Config{perlpath}>. |
403 | |
458 | |
404 | =cut |
459 | =cut |
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413 | my $perl = $; |
468 | my $perl = $; |
414 | |
469 | |
415 | # first we try $^X, but the path must be absolute (always on win32), and end in sth. |
470 | # first we try $^X, but the path must be absolute (always on win32), and end in sth. |
416 | # that looks like perl. this obviously only works for posix and win32 |
471 | # that looks like perl. this obviously only works for posix and win32 |
417 | unless ( |
472 | unless ( |
418 | (AnyEvent::Fork::Util::WIN32 || $perl =~ m%^/%) |
473 | ($^O eq "MSWin32" || $perl =~ m%^/%) |
419 | && $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
474 | && $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
420 | ) { |
475 | ) { |
421 | # if it doesn't look perlish enough, try Config |
476 | # if it doesn't look perlish enough, try Config |
422 | require Config; |
477 | require Config; |
423 | $perl = $Config::Config{perlpath}; |
478 | $perl = $Config::Config{perlpath}; |
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434 | Proc::FastSpawn::fd_inherit (fileno $fh, 0); |
489 | Proc::FastSpawn::fd_inherit (fileno $fh, 0); |
435 | |
490 | |
436 | # quick. also doesn't work in win32. of course. what did you expect |
491 | # quick. also doesn't work in win32. of course. what did you expect |
437 | #local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
492 | #local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
438 | my %env = %ENV; |
493 | my %env = %ENV; |
439 | $env{PERL5LIB} = join +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), grep !ref, @INC; |
494 | $env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC; |
440 | |
495 | |
441 | Proc::FastSpawn::spawn ( |
496 | my $pid = Proc::FastSpawn::spawn ( |
442 | $perl, |
497 | $perl, |
443 | ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$], |
498 | ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$], |
444 | [map "$_=$env{$_}", keys %env], |
499 | [map "$_=$env{$_}", keys %env], |
445 | ) or die "unable to spawn AnyEvent::Fork server: $!"; |
500 | ) or die "unable to spawn AnyEvent::Fork server: $!"; |
446 | |
501 | |
447 | $self->_new ($fh) |
502 | $self->_new ($fh, $pid) |
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503 | } |
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504 | |
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505 | =item $pid = $proc->pid |
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506 | |
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507 | Returns the process id of the process I<iff it is a direct child of the |
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508 | process> running AnyEvent::Fork, and C<undef> otherwise. |
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509 | |
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510 | Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and |
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511 | L<AnyEvent::Fork::Template> are direct children, and you are responsible |
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512 | to clean up their zombies when they die. |
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513 | |
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514 | All other processes are not direct children, and will be cleaned up by |
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515 | AnyEvent::Fork. |
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516 | |
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517 | =cut |
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518 | |
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519 | sub pid { |
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520 | $_[0][0] |
448 | } |
521 | } |
449 | |
522 | |
450 | =item $proc = $proc->eval ($perlcode, @args) |
523 | =item $proc = $proc->eval ($perlcode, @args) |
451 | |
524 | |
452 | Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to |
525 | Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to |
453 | the strings specified by C<@args>. |
526 | the strings specified by C<@args>, in the "main" package. |
454 | |
527 | |
455 | This call is meant to do any custom initialisation that might be required |
528 | This call is meant to do any custom initialisation that might be required |
456 | (for example, the C<require> method uses it). It's not supposed to be used |
529 | (for example, the C<require> method uses it). It's not supposed to be used |
457 | to completely take over the process, use C<run> for that. |
530 | to completely take over the process, use C<run> for that. |
458 | |
531 | |
459 | The code will usually be executed after this call returns, and there is no |
532 | The code will usually be executed after this call returns, and there is no |
460 | way to pass anything back to the calling process. Any evaluation errors |
533 | way to pass anything back to the calling process. Any evaluation errors |
461 | will be reported to stderr and cause the process to exit. |
534 | will be reported to stderr and cause the process to exit. |
462 | |
535 | |
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536 | If you want to execute some code to take over the process (see the |
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537 | "fork+exec" example in the SYNOPSIS), you should compile a function via |
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538 | C<eval> first, and then call it via C<run>. This also gives you access to |
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539 | any arguments passed via the C<send_xxx> methods, such as file handles. |
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540 | |
463 | Returns the process object for easy chaining of method calls. |
541 | Returns the process object for easy chaining of method calls. |
464 | |
542 | |
465 | =cut |
543 | =cut |
466 | |
544 | |
467 | sub eval { |
545 | sub eval { |
468 | my ($self, $code, @args) = @_; |
546 | my ($self, $code, @args) = @_; |
469 | |
547 | |
470 | $self->_cmd (e => $code, @args); |
548 | $self->_cmd (e => pack "(w/a*)*", $code, @args); |
471 | |
549 | |
472 | $self |
550 | $self |
473 | } |
551 | } |
474 | |
552 | |
475 | =item $proc = $proc->require ($module, ...) |
553 | =item $proc = $proc->require ($module, ...) |
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499 | accomplished by simply not storing the file handles anywhere after passing |
577 | accomplished by simply not storing the file handles anywhere after passing |
500 | them to this method. |
578 | them to this method. |
501 | |
579 | |
502 | Returns the process object for easy chaining of method calls. |
580 | Returns the process object for easy chaining of method calls. |
503 | |
581 | |
504 | Example: pass an fh to a process, and release it without closing. it will |
582 | Example: pass a file handle to a process, and release it without |
505 | be closed automatically when it is no longer used. |
583 | closing. It will be closed automatically when it is no longer used. |
506 | |
584 | |
507 | $proc->send_fh ($my_fh); |
585 | $proc->send_fh ($my_fh); |
508 | undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT |
586 | undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT |
509 | |
587 | |
510 | =cut |
588 | =cut |
… | |
… | |
523 | =item $proc = $proc->send_arg ($string, ...) |
601 | =item $proc = $proc->send_arg ($string, ...) |
524 | |
602 | |
525 | Send one or more argument strings to the process, to prepare a call to |
603 | Send one or more argument strings to the process, to prepare a call to |
526 | C<run>. The strings can be any octet string. |
604 | C<run>. The strings can be any octet string. |
527 | |
605 | |
|
|
606 | The protocol is optimised to pass a moderate number of relatively short |
|
|
607 | strings - while you can pass up to 4GB of data in one go, this is more |
|
|
608 | meant to pass some ID information or other startup info, not big chunks of |
|
|
609 | data. |
|
|
610 | |
528 | Returns the process object for easy chaining of emthod calls. |
611 | Returns the process object for easy chaining of method calls. |
529 | |
612 | |
530 | =cut |
613 | =cut |
531 | |
614 | |
532 | sub send_arg { |
615 | sub send_arg { |
533 | my ($self, @arg) = @_; |
616 | my ($self, @arg) = @_; |
534 | |
617 | |
535 | $self->_cmd (a => @arg); |
618 | $self->_cmd (a => pack "(w/a*)*", @arg); |
536 | |
619 | |
537 | $self |
620 | $self |
538 | } |
621 | } |
539 | |
622 | |
540 | =item $proc->run ($func, $cb->($fh)) |
623 | =item $proc->run ($func, $cb->($fh)) |
541 | |
624 | |
542 | Enter the function specified by the fully qualified name in C<$func> in |
625 | Enter the function specified by the function name in C<$func> in the |
543 | the process. The function is called with the communication socket as first |
626 | process. The function is called with the communication socket as first |
544 | argument, followed by all file handles and string arguments sent earlier |
627 | argument, followed by all file handles and string arguments sent earlier |
545 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
628 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
546 | |
629 | |
547 | If the called function returns, the process exits. |
630 | The function name should be fully qualified, but if it isn't, it will be |
|
|
631 | looked up in the main package. |
548 | |
632 | |
549 | Preparing the process can take time - when the process is ready, the |
633 | If the called function returns, doesn't exist, or any error occurs, the |
|
|
634 | process exits. |
|
|
635 | |
|
|
636 | Preparing the process is done in the background - when all commands have |
550 | callback is invoked with the local communications socket as argument. |
637 | been sent, the callback is invoked with the local communications socket |
|
|
638 | as argument. At this point you can start using the socket in any way you |
|
|
639 | like. |
551 | |
640 | |
552 | The process object becomes unusable on return from this function. |
641 | The process object becomes unusable on return from this function - any |
|
|
642 | further method calls result in undefined behaviour. |
553 | |
643 | |
554 | If the communication socket isn't used, it should be closed on both sides, |
644 | If the communication socket isn't used, it should be closed on both sides, |
555 | to save on kernel memory. |
645 | to save on kernel memory. |
556 | |
646 | |
557 | The socket is non-blocking in the parent, and blocking in the newly |
647 | The socket is non-blocking in the parent, and blocking in the newly |
558 | created process. The close-on-exec flag is set on both. Even if not used |
648 | created process. The close-on-exec flag is set in both. |
|
|
649 | |
559 | otherwise, the socket can be a good indicator for the existance of the |
650 | Even if not used otherwise, the socket can be a good indicator for the |
560 | process - if the other process exits, you get a readable event on it, |
651 | existence of the process - if the other process exits, you get a readable |
561 | because exiting the process closes the socket (if it didn't create any |
652 | event on it, because exiting the process closes the socket (if it didn't |
562 | children using fork). |
653 | create any children using fork). |
563 | |
654 | |
564 | Example: create a template for a process pool, pass a few strings, some |
655 | Example: create a template for a process pool, pass a few strings, some |
565 | file handles, then fork, pass one more string, and run some code. |
656 | file handles, then fork, pass one more string, and run some code. |
566 | |
657 | |
567 | my $pool = AnyEvent::Fork |
658 | my $pool = AnyEvent::Fork |
… | |
… | |
575 | ->send_arg ("str3") |
666 | ->send_arg ("str3") |
576 | ->run ("Some::function", sub { |
667 | ->run ("Some::function", sub { |
577 | my ($fh) = @_; |
668 | my ($fh) = @_; |
578 | |
669 | |
579 | # fh is nonblocking, but we trust that the OS can accept these |
670 | # fh is nonblocking, but we trust that the OS can accept these |
580 | # extra 3 octets anyway. |
671 | # few octets anyway. |
581 | syswrite $fh, "hi #$_\n"; |
672 | syswrite $fh, "hi #$_\n"; |
582 | |
673 | |
583 | # $fh is being closed here, as we don't store it anywhere |
674 | # $fh is being closed here, as we don't store it anywhere |
584 | }); |
675 | }); |
585 | } |
676 | } |
… | |
… | |
587 | # Some::function might look like this - all parameters passed before fork |
678 | # Some::function might look like this - all parameters passed before fork |
588 | # and after will be passed, in order, after the communications socket. |
679 | # and after will be passed, in order, after the communications socket. |
589 | sub Some::function { |
680 | sub Some::function { |
590 | my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
681 | my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
591 | |
682 | |
592 | print scalar <$fh>; # prints "hi 1\n" and "hi 2\n" |
683 | print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order |
593 | } |
684 | } |
594 | |
685 | |
595 | =cut |
686 | =cut |
596 | |
687 | |
597 | sub run { |
688 | sub run { |
598 | my ($self, $func, $cb) = @_; |
689 | my ($self, $func, $cb) = @_; |
599 | |
690 | |
600 | $self->[0] = $cb; |
691 | $self->[4] = $cb; |
601 | $self->_cmd (r => $func); |
692 | $self->_cmd (r => $func); |
602 | } |
693 | } |
|
|
694 | |
|
|
695 | =back |
|
|
696 | |
|
|
697 | =head1 PERFORMANCE |
|
|
698 | |
|
|
699 | Now for some unscientific benchmark numbers (all done on an amd64 |
|
|
700 | GNU/Linux box). These are intended to give you an idea of the relative |
|
|
701 | performance you can expect, they are not meant to be absolute performance |
|
|
702 | numbers. |
|
|
703 | |
|
|
704 | OK, so, I ran a simple benchmark that creates a socket pair, forks, calls |
|
|
705 | exit in the child and waits for the socket to close in the parent. I did |
|
|
706 | load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB. |
|
|
707 | |
|
|
708 | 2079 new processes per second, using manual socketpair + fork |
|
|
709 | |
|
|
710 | Then I did the same thing, but instead of calling fork, I called |
|
|
711 | AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the |
|
|
712 | socket form the child to close on exit. This does the same thing as manual |
|
|
713 | socket pair + fork, except that what is forked is the template process |
|
|
714 | (2440kB), and the socket needs to be passed to the server at the other end |
|
|
715 | of the socket first. |
|
|
716 | |
|
|
717 | 2307 new processes per second, using AnyEvent::Fork->new |
|
|
718 | |
|
|
719 | And finally, using C<new_exec> instead C<new>, using vforks+execs to exec |
|
|
720 | a new perl interpreter and compile the small server each time, I get: |
|
|
721 | |
|
|
722 | 479 vfork+execs per second, using AnyEvent::Fork->new_exec |
|
|
723 | |
|
|
724 | So how can C<< AnyEvent->new >> be faster than a standard fork, even |
|
|
725 | though it uses the same operations, but adds a lot of overhead? |
|
|
726 | |
|
|
727 | The difference is simply the process size: forking the 6MB process takes |
|
|
728 | so much longer than forking the 2.5MB template process that the overhead |
|
|
729 | introduced is canceled out. |
|
|
730 | |
|
|
731 | If the benchmark process grows, the normal fork becomes even slower: |
|
|
732 | |
|
|
733 | 1340 new processes, manual fork in a 20MB process |
|
|
734 | 731 new processes, manual fork in a 200MB process |
|
|
735 | 235 new processes, manual fork in a 2000MB process |
|
|
736 | |
|
|
737 | What that means (to me) is that I can use this module without having a |
|
|
738 | very bad conscience because of the extra overhead required to start new |
|
|
739 | processes. |
|
|
740 | |
|
|
741 | =head1 TYPICAL PROBLEMS |
|
|
742 | |
|
|
743 | This section lists typical problems that remain. I hope by recognising |
|
|
744 | them, most can be avoided. |
|
|
745 | |
|
|
746 | =over 4 |
|
|
747 | |
|
|
748 | =item "leaked" file descriptors for exec'ed processes |
|
|
749 | |
|
|
750 | POSIX systems inherit file descriptors by default when exec'ing a new |
|
|
751 | process. While perl itself laudably sets the close-on-exec flags on new |
|
|
752 | file handles, most C libraries don't care, and even if all cared, it's |
|
|
753 | often not possible to set the flag in a race-free manner. |
|
|
754 | |
|
|
755 | That means some file descriptors can leak through. And since it isn't |
|
|
756 | possible to know which file descriptors are "good" and "necessary" (or |
|
|
757 | even to know which file descriptors are open), there is no good way to |
|
|
758 | close the ones that might harm. |
|
|
759 | |
|
|
760 | As an example of what "harm" can be done consider a web server that |
|
|
761 | accepts connections and afterwards some module uses AnyEvent::Fork for the |
|
|
762 | first time, causing it to fork and exec a new process, which might inherit |
|
|
763 | the network socket. When the server closes the socket, it is still open |
|
|
764 | in the child (which doesn't even know that) and the client might conclude |
|
|
765 | that the connection is still fine. |
|
|
766 | |
|
|
767 | For the main program, there are multiple remedies available - |
|
|
768 | L<AnyEvent::Fork::Early> is one, creating a process early and not using |
|
|
769 | C<new_exec> is another, as in both cases, the first process can be exec'ed |
|
|
770 | well before many random file descriptors are open. |
|
|
771 | |
|
|
772 | In general, the solution for these kind of problems is to fix the |
|
|
773 | libraries or the code that leaks those file descriptors. |
|
|
774 | |
|
|
775 | Fortunately, most of these leaked descriptors do no harm, other than |
|
|
776 | sitting on some resources. |
|
|
777 | |
|
|
778 | =item "leaked" file descriptors for fork'ed processes |
|
|
779 | |
|
|
780 | Normally, L<AnyEvent::Fork> does start new processes by exec'ing them, |
|
|
781 | which closes file descriptors not marked for being inherited. |
|
|
782 | |
|
|
783 | However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer |
|
|
784 | a way to create these processes by forking, and this leaks more file |
|
|
785 | descriptors than exec'ing them, as there is no way to mark descriptors as |
|
|
786 | "close on fork". |
|
|
787 | |
|
|
788 | An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create |
|
|
789 | pipes for internal uses, and L<Gtk2> might open a connection to the X |
|
|
790 | server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have |
|
|
791 | trouble with a fork. |
|
|
792 | |
|
|
793 | The solution is to either not load these modules before use'ing |
|
|
794 | L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay |
|
|
795 | initialising them, for example, by calling C<init Gtk2> manually. |
|
|
796 | |
|
|
797 | =item exit runs destructors |
|
|
798 | |
|
|
799 | This only applies to users of Lc<AnyEvent::Fork:Early> and |
|
|
800 | L<AnyEvent::Fork::Template>. |
|
|
801 | |
|
|
802 | When a process created by AnyEvent::Fork exits, it might do so by calling |
|
|
803 | exit, or simply letting perl reach the end of the program. At which point |
|
|
804 | Perl runs all destructors. |
|
|
805 | |
|
|
806 | Not all destructors are fork-safe - for example, an object that represents |
|
|
807 | the connection to an X display might tell the X server to free resources, |
|
|
808 | which is inconvenient when the "real" object in the parent still needs to |
|
|
809 | use them. |
|
|
810 | |
|
|
811 | This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used |
|
|
812 | it as the very first thing, right? |
|
|
813 | |
|
|
814 | It is a problem for L<AnyEvent::Fork::Template> though - and the solution |
|
|
815 | is to not create objects with nontrivial destructors that might have an |
|
|
816 | effect outside of Perl. |
603 | |
817 | |
604 | =back |
818 | =back |
605 | |
819 | |
606 | =head1 PORTABILITY NOTES |
820 | =head1 PORTABILITY NOTES |
607 | |
821 | |
608 | Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop, |
822 | Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop, |
609 | and ::Template is not going to work), and it cost a lot of blood and sweat |
823 | and ::Template is not going to work), and it cost a lot of blood and sweat |
610 | to make it so, mostly due to the bloody broken perl that nobody seems to |
824 | to make it so, mostly due to the bloody broken perl that nobody seems to |
611 | care about. The fork emulation is a bad joke - I have yet to see something |
825 | care about. The fork emulation is a bad joke - I have yet to see something |
612 | useful that you cna do with it without running into memory corruption |
826 | useful that you can do with it without running into memory corruption |
613 | issues or other braindamage. Hrrrr. |
827 | issues or other braindamage. Hrrrr. |
614 | |
828 | |
615 | Cygwin perl is not supported at the moment, as it should implement fd |
829 | Cygwin perl is not supported at the moment, as it should implement fd |
616 | passing, but doesn't, and rolling my own is hard, as cygwin doesn't |
830 | passing, but doesn't, and rolling my own is hard, as cygwin doesn't |
617 | support enough functionality to do it. |
831 | support enough functionality to do it. |
618 | |
832 | |
|
|
833 | =head1 SEE ALSO |
|
|
834 | |
|
|
835 | L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter), |
|
|
836 | L<AnyEvent::Fork::Template> (to create a process by forking the main |
|
|
837 | program at a convenient time). |
|
|
838 | |
619 | =head1 AUTHOR |
839 | =head1 AUTHOR |
620 | |
840 | |
621 | Marc Lehmann <schmorp@schmorp.de> |
841 | Marc Lehmann <schmorp@schmorp.de> |
622 | http://home.schmorp.de/ |
842 | http://home.schmorp.de/ |
623 | |
843 | |