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2 AnyEvent::Fork - everything you wanted to use fork() for, but couldn't 2 AnyEvent::Fork - everything you wanted to use fork() for, but couldn't
3 3
4SYNOPSIS 4SYNOPSIS
5 use AnyEvent::Fork; 5 use AnyEvent::Fork;
6 6
7 ################################################################## 7 AnyEvent::Fork
8 ->new
9 ->require ("MyModule")
10 ->run ("MyModule::server", my $cv = AE::cv);
11
12 my $fh = $cv->recv;
13
14DESCRIPTION
15 This module allows you to create new processes, without actually forking
16 them from your current process (avoiding the problems of forking), but
17 preserving most of the advantages of fork.
18
19 It can be used to create new worker processes or new independent
20 subprocesses for short- and long-running jobs, process pools (e.g. for
21 use in pre-forked servers) but also to spawn new external processes
22 (such as CGI scripts from a web server), which can be faster (and more
23 well behaved) than using fork+exec in big processes.
24
25 Special care has been taken to make this module useful from other
26 modules, while still supporting specialised environments such as
27 App::Staticperl or PAR::Packer.
28
29 WHAT THIS MODULE IS NOT
30 This module only creates processes and lets you pass file handles and
31 strings to it, and run perl code. It does not implement any kind of RPC
32 - there is no back channel from the process back to you, and there is no
33 RPC or message passing going on.
34
35 If you need some form of RPC, you can either implement it yourself in
36 whatever way you like, use some message-passing module such as
37 AnyEvent::MP, some pipe such as AnyEvent::ZeroMQ, use AnyEvent::Handle
38 on both sides to send e.g. JSON or Storable messages, and so on.
39
40 COMPARISON TO OTHER MODULES
41 There is an abundance of modules on CPAN that do "something fork", such
42 as Parallel::ForkManager, AnyEvent::ForkManager, AnyEvent::Worker or
43 AnyEvent::Subprocess. There are modules that implement their own process
44 management, such as AnyEvent::DBI.
45
46 The problems that all these modules try to solve are real, however, none
47 of them (from what I have seen) tackle the very real problems of
48 unwanted memory sharing, efficiency, not being able to use event
49 processing or similar modules in the processes they create.
50
51 This module doesn't try to replace any of them - instead it tries to
52 solve the problem of creating processes with a minimum of fuss and
53 overhead (and also luxury). Ideally, most of these would use
54 AnyEvent::Fork internally, except they were written before AnyEvent:Fork
55 was available, so obviously had to roll their own.
56
57 PROBLEM STATEMENT
58 There are two traditional ways to implement parallel processing on UNIX
59 like operating systems - fork and process, and fork+exec and process.
60 They have different advantages and disadvantages that I describe below,
61 together with how this module tries to mitigate the disadvantages.
62
63 Forking from a big process can be very slow.
64 A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box.
65 This overhead is often shared with exec (because you have to fork
66 first), but in some circumstances (e.g. when vfork is used),
67 fork+exec can be much faster.
68
69 This module can help here by telling a small(er) helper process to
70 fork, which is faster then forking the main process, and also uses
71 vfork where possible. This gives the speed of vfork, with the
72 flexibility of fork.
73
74 Forking usually creates a copy-on-write copy of the parent process.
75 For example, modules or data files that are loaded will not use
76 additional memory after a fork. When exec'ing a new process, modules
77 and data files might need to be loaded again, at extra CPU and
78 memory cost. But when forking, literally all data structures are
79 copied - if the program frees them and replaces them by new data,
80 the child processes will retain the old version even if it isn't
81 used, which can suddenly and unexpectedly increase memory usage when
82 freeing memory.
83
84 The trade-off is between more sharing with fork (which can be good
85 or bad), and no sharing with exec.
86
87 This module allows the main program to do a controlled fork, and
88 allows modules to exec processes safely at any time. When creating a
89 custom process pool you can take advantage of data sharing via fork
90 without risking to share large dynamic data structures that will
91 blow up child memory usage.
92
93 In other words, this module puts you into control over what is being
94 shared and what isn't, at all times.
95
96 Exec'ing a new perl process might be difficult.
97 For example, it is not easy to find the correct path to the perl
98 interpreter - $^X might not be a perl interpreter at all.
99
100 This module tries hard to identify the correct path to the perl
101 interpreter. With a cooperative main program, exec'ing the
102 interpreter might not even be necessary, but even without help from
103 the main program, it will still work when used from a module.
104
105 Exec'ing a new perl process might be slow, as all necessary modules have
106 to be loaded from disk again, with no guarantees of success.
107 Long running processes might run into problems when perl is upgraded
108 and modules are no longer loadable because they refer to a different
109 perl version, or parts of a distribution are newer than the ones
110 already loaded.
111
112 This module supports creating pre-initialised perl processes to be
113 used as a template for new processes.
114
115 Forking might be impossible when a program is running.
116 For example, POSIX makes it almost impossible to fork from a
117 multi-threaded program while doing anything useful in the child - in
118 fact, if your perl program uses POSIX threads (even indirectly via
119 e.g. IO::AIO or threads), you cannot call fork on the perl level
120 anymore without risking corruption issues on a number of operating
121 systems.
122
123 This module can safely fork helper processes at any time, by calling
124 fork+exec in C, in a POSIX-compatible way (via Proc::FastSpawn).
125
126 Parallel processing with fork might be inconvenient or difficult to
127 implement. Modules might not work in both parent and child.
128 For example, when a program uses an event loop and creates watchers
129 it becomes very hard to use the event loop from a child program, as
130 the watchers already exist but are only meaningful in the parent.
131 Worse, a module might want to use such a module, not knowing whether
132 another module or the main program also does, leading to problems.
133
134 Apart from event loops, graphical toolkits also commonly fall into
135 the "unsafe module" category, or just about anything that
136 communicates with the external world, such as network libraries and
137 file I/O modules, which usually don't like being copied and then
138 allowed to continue in two processes.
139
140 With this module only the main program is allowed to create new
141 processes by forking (because only the main program can know when it
142 is still safe to do so) - all other processes are created via
143 fork+exec, which makes it possible to use modules such as event
144 loops or window interfaces safely.
145
146EXAMPLES
8 # create a single new process, tell it to run your worker function 147 Create a single new process, tell it to run your worker function.
9
10 AnyEvent::Fork 148 AnyEvent::Fork
11 ->new 149 ->new
12 ->require ("MyModule") 150 ->require ("MyModule")
13 ->run ("MyModule::worker, sub { 151 ->run ("MyModule::worker, sub {
14 my ($master_filehandle) = @_; 152 my ($master_filehandle) = @_;
15 153
16 # now $master_filehandle is connected to the 154 # now $master_filehandle is connected to the
17 # $slave_filehandle in the new process. 155 # $slave_filehandle in the new process.
18 }); 156 });
19 157
20 # MyModule::worker might look like this 158 "MyModule" might look like this:
159
160 package MyModule;
161
21 sub MyModule::worker { 162 sub worker {
22 my ($slave_filehandle) = @_; 163 my ($slave_filehandle) = @_;
23 164
24 # now $slave_filehandle is connected to the $master_filehandle 165 # now $slave_filehandle is connected to the $master_filehandle
25 # in the original prorcess. have fun! 166 # in the original prorcess. have fun!
26 } 167 }
27 168
28 ##################################################################
29 # create a pool of server processes all accepting on the same socket 169 Create a pool of server processes all accepting on the same socket.
30
31 # create listener socket 170 # create listener socket
32 my $listener = ...; 171 my $listener = ...;
33 172
34 # create a pool template, initialise it and give it the socket 173 # create a pool template, initialise it and give it the socket
35 my $pool = AnyEvent::Fork 174 my $pool = AnyEvent::Fork
… …
46 } 185 }
47 186
48 # now do other things - maybe use the filehandle provided by run 187 # now do other things - maybe use the filehandle provided by run
49 # to wait for the processes to die. or whatever. 188 # to wait for the processes to die. or whatever.
50 189
51 # My::Server::run might look like this 190 "My::Server" might look like this:
52 sub My::Server::run { 191
192 package My::Server;
193
194 sub run {
53 my ($slave, $listener, $id) = @_; 195 my ($slave, $listener, $id) = @_;
54 196
55 close $slave; # we do not use the socket, so close it to save resources 197 close $slave; # we do not use the socket, so close it to save resources
56 198
57 # we could go ballistic and use e.g. AnyEvent here, or IO::AIO, 199 # we could go ballistic and use e.g. AnyEvent here, or IO::AIO,
… …
59 while (my $socket = $listener->accept) { 201 while (my $socket = $listener->accept) {
60 # do sth. with new socket 202 # do sth. with new socket
61 } 203 }
62 } 204 }
63 205
64DESCRIPTION 206 use AnyEvent::Fork as a faster fork+exec
65 This module allows you to create new processes, without actually forking 207 This runs "/bin/echo hi", with stdandard output redirected to /tmp/log
66 them from your current process (avoiding the problems of forking), but 208 and standard error redirected to the communications socket. It is
67 preserving most of the advantages of fork. 209 usually faster than fork+exec, but still lets you prepare the
210 environment.
68 211
69 It can be used to create new worker processes or new independent 212 open my $output, ">/tmp/log" or die "$!";
70 subprocesses for short- and long-running jobs, process pools (e.g. for
71 use in pre-forked servers) but also to spawn new external processes
72 (such as CGI scripts from a web server), which can be faster (and more
73 well behaved) than using fork+exec in big processes.
74 213
75 Special care has been taken to make this module useful from other 214 AnyEvent::Fork
76 modules, while still supporting specialised environments such as 215 ->new
77 App::Staticperl or PAR::Packer. 216 ->eval ('
217 # compile a helper function for later use
218 sub run {
219 my ($fh, $output, @cmd) = @_;
78 220
79WHAT THIS MODULE IS NOT 221 # perl will clear close-on-exec on STDOUT/STDERR
80 This module only creates processes and lets you pass file handles and 222 open STDOUT, ">&", $output or die;
81 strings to it, and run perl code. It does not implement any kind of RPC 223 open STDERR, ">&", $fh or die;
82 - there is no back channel from the process back to you, and there is no
83 RPC or message passing going on.
84 224
85 If you need some form of RPC, you can either implement it yourself in 225 exec @cmd;
86 whatever way you like, use some message-passing module such as 226 }
87 AnyEvent::MP, some pipe such as AnyEvent::ZeroMQ, use AnyEvent::Handle 227 ')
88 on both sides to send e.g. JSON or Storable messages, and so on. 228 ->send_fh ($output)
229 ->send_arg ("/bin/echo", "hi")
230 ->run ("run", my $cv = AE::cv);
89 231
90PROBLEM STATEMENT 232 my $stderr = $cv->recv;
91 There are two ways to implement parallel processing on UNIX like
92 operating systems - fork and process, and fork+exec and process. They
93 have different advantages and disadvantages that I describe below,
94 together with how this module tries to mitigate the disadvantages.
95
96 Forking from a big process can be very slow (a 5GB process needs 0.05s
97 to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead is
98 often shared with exec (because you have to fork first), but in some
99 circumstances (e.g. when vfork is used), fork+exec can be much faster.
100 This module can help here by telling a small(er) helper process to
101 fork, or fork+exec instead.
102
103 Forking usually creates a copy-on-write copy of the parent process.
104 Memory (for example, modules or data files that have been will not take
105 additional memory). When exec'ing a new process, modules and data files
106 might need to be loaded again, at extra CPU and memory cost. Likewise
107 when forking, all data structures are copied as well - if the program
108 frees them and replaces them by new data, the child processes will
109 retain the memory even if it isn't used.
110 This module allows the main program to do a controlled fork, and
111 allows modules to exec processes safely at any time. When creating a
112 custom process pool you can take advantage of data sharing via fork
113 without risking to share large dynamic data structures that will
114 blow up child memory usage.
115
116 Exec'ing a new perl process might be difficult and slow. For example, it
117 is not easy to find the correct path to the perl interpreter, and all
118 modules have to be loaded from disk again. Long running processes might
119 run into problems when perl is upgraded for example.
120 This module supports creating pre-initialised perl processes to be
121 used as template, and also tries hard to identify the correct path
122 to the perl interpreter. With a cooperative main program, exec'ing
123 the interpreter might not even be necessary.
124
125 Forking might be impossible when a program is running. For example,
126 POSIX makes it almost impossible to fork from a multi-threaded program
127 and do anything useful in the child - strictly speaking, if your perl
128 program uses posix threads (even indirectly via e.g. IO::AIO or
129 threads), you cannot call fork on the perl level anymore, at all.
130 This module can safely fork helper processes at any time, by calling
131 fork+exec in C, in a POSIX-compatible way.
132
133 Parallel processing with fork might be inconvenient or difficult to
134 implement. For example, when a program uses an event loop and creates
135 watchers it becomes very hard to use the event loop from a child
136 program, as the watchers already exist but are only meaningful in the
137 parent. Worse, a module might want to use such a system, not knowing
138 whether another module or the main program also does, leading to
139 problems.
140 This module only lets the main program create pools by forking
141 (because only the main program can know when it is still safe to do
142 so) - all other pools are created by fork+exec, after which such
143 modules can again be loaded.
144 233
145CONCEPTS 234CONCEPTS
146 This module can create new processes either by executing a new perl 235 This module can create new processes either by executing a new perl
147 process, or by forking from an existing "template" process. 236 process, or by forking from an existing "template" process.
148 237
… …
220 ->require ("Some::Module") 309 ->require ("Some::Module")
221 ->run ("Some::Module::run", sub { 310 ->run ("Some::Module::run", sub {
222 my ($fork_fh) = @_; 311 my ($fork_fh) = @_;
223 }); 312 });
224 313
225FUNCTIONS 314THE "AnyEvent::Fork" CLASS
226 my $pool = new AnyEvent::Fork key => value... 315 This module exports nothing, and only implements a single class -
227 Create a new process pool. The following named parameters are 316 "AnyEvent::Fork".
228 supported:
229 317
318 There are two class constructors that both create new processes - "new"
319 and "new_exec". The "fork" method creates a new process by forking an
320 existing one and could be considered a third constructor.
321
322 Most of the remaining methods deal with preparing the new process, by
323 loading code, evaluating code and sending data to the new process. They
324 usually return the process object, so you can chain method calls.
325
326 If a process object is destroyed before calling its "run" method, then
327 the process simply exits. After "run" is called, all responsibility is
328 passed to the specified function.
329
330 As long as there is any outstanding work to be done, process objects
331 resist being destroyed, so there is no reason to store them unless you
332 need them later - configure and forget works just fine.
333
230 my $proc = new AnyEvent::Fork 334 my $proc = new AnyEvent::Fork
335
231 Create a new "empty" perl interpreter process and returns its 336 Create a new "empty" perl interpreter process and returns its
232 process object for further manipulation. 337 process object for further manipulation.
233 338
234 The new process is forked from a template process that is kept 339 The new process is forked from a template process that is kept
235 around for this purpose. When it doesn't exist yet, it is created by 340 around for this purpose. When it doesn't exist yet, it is created by
236 a call to "new_exec" and kept around for future calls. 341 a call to "new_exec" first and then stays around for future calls.
237 342
238 When the process object is destroyed, it will release the file
239 handle that connects it with the new process. When the new process
240 has not yet called "run", then the process will exit. Otherwise,
241 what happens depends entirely on the code that is executed.
242
243 $new_proc = $proc->fork 343 $new_proc = $proc->fork
344
244 Forks $proc, creating a new process, and returns the process object 345 Forks $proc, creating a new process, and returns the process object
245 of the new process. 346 of the new process.
246 347
247 If any of the "send_" functions have been called before fork, then 348 If any of the "send_" functions have been called before fork, then
248 they will be cloned in the child. For example, in a pre-forked 349 they will be cloned in the child. For example, in a pre-forked
249 server, you might "send_fh" the listening socket into the template 350 server, you might "send_fh" the listening socket into the template
250 process, and then keep calling "fork" and "run". 351 process, and then keep calling "fork" and "run".
251 352
252 my $proc = new_exec AnyEvent::Fork 353 my $proc = new_exec AnyEvent::Fork
354
253 Create a new "empty" perl interpreter process and returns its 355 Create a new "empty" perl interpreter process and returns its
254 process object for further manipulation. 356 process object for further manipulation.
255 357
256 Unlike the "new" method, this method *always* spawns a new perl 358 Unlike the "new" method, this method *always* spawns a new perl
257 process (except in some cases, see AnyEvent::Fork::Early for 359 process (except in some cases, see AnyEvent::Fork::Early for
… …
264 The path to the perl interpreter is divined using various methods - 366 The path to the perl interpreter is divined using various methods -
265 first $^X is investigated to see if the path ends with something 367 first $^X is investigated to see if the path ends with something
266 that sounds as if it were the perl interpreter. Failing this, the 368 that sounds as if it were the perl interpreter. Failing this, the
267 module falls back to using $Config::Config{perlpath}. 369 module falls back to using $Config::Config{perlpath}.
268 370
269 $pid = $proc->pid 371 $pid = $proc->pid
372
270 Returns the process id of the process *iff it is a direct child of 373 Returns the process id of the process *iff it is a direct child of
271 the process* running AnyEvent::Fork, and "undef" otherwise. 374 the process running AnyEvent::Fork*, and "undef" otherwise.
272 375
273 Normally, only processes created via "AnyEvent::Fork->new_exec" and 376 Normally, only processes created via "AnyEvent::Fork->new_exec" and
274 AnyEvent::Fork::Template are direct children, and you are 377 AnyEvent::Fork::Template are direct children, and you are
275 responsible to clean up their zombies when they die. 378 responsible to clean up their zombies when they die.
276 379
277 All other processes are not direct children, and will be cleaned up 380 All other processes are not direct children, and will be cleaned up
278 by AnyEvent::Fork. 381 by AnyEvent::Fork itself.
279 382
280 $proc = $proc->eval ($perlcode, @args) 383 $proc = $proc->eval ($perlcode, @args)
384
281 Evaluates the given $perlcode as ... perl code, while setting @_ to 385 Evaluates the given $perlcode as ... perl code, while setting @_ to
282 the strings specified by @args. 386 the strings specified by @args, in the "main" package.
283 387
284 This call is meant to do any custom initialisation that might be 388 This call is meant to do any custom initialisation that might be
285 required (for example, the "require" method uses it). It's not 389 required (for example, the "require" method uses it). It's not
286 supposed to be used to completely take over the process, use "run" 390 supposed to be used to completely take over the process, use "run"
287 for that. 391 for that.
… …
289 The code will usually be executed after this call returns, and there 393 The code will usually be executed after this call returns, and there
290 is no way to pass anything back to the calling process. Any 394 is no way to pass anything back to the calling process. Any
291 evaluation errors will be reported to stderr and cause the process 395 evaluation errors will be reported to stderr and cause the process
292 to exit. 396 to exit.
293 397
398 If you want to execute some code (that isn't in a module) to take
399 over the process, you should compile a function via "eval" first,
400 and then call it via "run". This also gives you access to any
401 arguments passed via the "send_xxx" methods, such as file handles.
402 See the "use AnyEvent::Fork as a faster fork+exec" example to see it
403 in action.
404
294 Returns the process object for easy chaining of method calls. 405 Returns the process object for easy chaining of method calls.
295 406
296 $proc = $proc->require ($module, ...) 407 $proc = $proc->require ($module, ...)
408
297 Tries to load the given module(s) into the process 409 Tries to load the given module(s) into the process
298 410
299 Returns the process object for easy chaining of method calls. 411 Returns the process object for easy chaining of method calls.
300 412
301 $proc = $proc->send_fh ($handle, ...) 413 $proc = $proc->send_fh ($handle, ...)
414
302 Send one or more file handles (*not* file descriptors) to the 415 Send one or more file handles (*not* file descriptors) to the
303 process, to prepare a call to "run". 416 process, to prepare a call to "run".
304 417
305 The process object keeps a reference to the handles until this is 418 The process object keeps a reference to the handles until they have
306 done, so you must not explicitly close the handles. This is most 419 been passed over to the process, so you must not explicitly close
307 easily accomplished by simply not storing the file handles anywhere 420 the handles. This is most easily accomplished by simply not storing
308 after passing them to this method. 421 the file handles anywhere after passing them to this method - when
422 AnyEvent::Fork is finished using them, perl will automatically close
423 them.
309 424
310 Returns the process object for easy chaining of method calls. 425 Returns the process object for easy chaining of method calls.
311 426
312 Example: pass a file handle to a process, and release it without 427 Example: pass a file handle to a process, and release it without
313 closing. It will be closed automatically when it is no longer used. 428 closing. It will be closed automatically when it is no longer used.
314 429
315 $proc->send_fh ($my_fh); 430 $proc->send_fh ($my_fh);
316 undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT 431 undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
317 432
318 $proc = $proc->send_arg ($string, ...) 433 $proc = $proc->send_arg ($string, ...)
434
319 Send one or more argument strings to the process, to prepare a call 435 Send one or more argument strings to the process, to prepare a call
320 to "run". The strings can be any octet string. 436 to "run". The strings can be any octet strings.
321 437
322 The protocol is optimised to pass a moderate number of relatively 438 The protocol is optimised to pass a moderate number of relatively
323 short strings - while you can pass up to 4GB of data in one go, this 439 short strings - while you can pass up to 4GB of data in one go, this
324 is more meant to pass some ID information or other startup info, not 440 is more meant to pass some ID information or other startup info, not
325 big chunks of data. 441 big chunks of data.
326 442
327 Returns the process object for easy chaining of method calls. 443 Returns the process object for easy chaining of method calls.
328 444
329 $proc->run ($func, $cb->($fh)) 445 $proc->run ($func, $cb->($fh))
446
330 Enter the function specified by the fully qualified name in $func in 447 Enter the function specified by the function name in $func in the
331 the process. The function is called with the communication socket as 448 process. The function is called with the communication socket as
332 first argument, followed by all file handles and string arguments 449 first argument, followed by all file handles and string arguments
333 sent earlier via "send_fh" and "send_arg" methods, in the order they 450 sent earlier via "send_fh" and "send_arg" methods, in the order they
334 were called. 451 were called.
335 452
336 If the called function returns, the process exits.
337
338 Preparing the process can take time - when the process is ready, the
339 callback is invoked with the local communications socket as
340 argument.
341
342 The process object becomes unusable on return from this function. 453 The process object becomes unusable on return from this function -
454 any further method calls result in undefined behaviour.
455
456 The function name should be fully qualified, but if it isn't, it
457 will be looked up in the "main" package.
458
459 If the called function returns, doesn't exist, or any error occurs,
460 the process exits.
461
462 Preparing the process is done in the background - when all commands
463 have been sent, the callback is invoked with the local
464 communications socket as argument. At this point you can start using
465 the socket in any way you like.
343 466
344 If the communication socket isn't used, it should be closed on both 467 If the communication socket isn't used, it should be closed on both
345 sides, to save on kernel memory. 468 sides, to save on kernel memory.
346 469
347 The socket is non-blocking in the parent, and blocking in the newly 470 The socket is non-blocking in the parent, and blocking in the newly
348 created process. The close-on-exec flag is set on both. Even if not 471 created process. The close-on-exec flag is set in both.
472
349 used otherwise, the socket can be a good indicator for the existence 473 Even if not used otherwise, the socket can be a good indicator for
350 of the process - if the other process exits, you get a readable 474 the existence of the process - if the other process exits, you get a
351 event on it, because exiting the process closes the socket (if it 475 readable event on it, because exiting the process closes the socket
352 didn't create any children using fork). 476 (if it didn't create any children using fork).
353 477
354 Example: create a template for a process pool, pass a few strings, 478 Example: create a template for a process pool, pass a few strings,
355 some file handles, then fork, pass one more string, and run some 479 some file handles, then fork, pass one more string, and run some
356 code. 480 code.
357 481
… …
366 ->send_arg ("str3") 490 ->send_arg ("str3")
367 ->run ("Some::function", sub { 491 ->run ("Some::function", sub {
368 my ($fh) = @_; 492 my ($fh) = @_;
369 493
370 # fh is nonblocking, but we trust that the OS can accept these 494 # fh is nonblocking, but we trust that the OS can accept these
371 # extra 3 octets anyway. 495 # few octets anyway.
372 syswrite $fh, "hi #$_\n"; 496 syswrite $fh, "hi #$_\n";
373 497
374 # $fh is being closed here, as we don't store it anywhere 498 # $fh is being closed here, as we don't store it anywhere
375 }); 499 });
376 } 500 }
… …
378 # Some::function might look like this - all parameters passed before fork 502 # Some::function might look like this - all parameters passed before fork
379 # and after will be passed, in order, after the communications socket. 503 # and after will be passed, in order, after the communications socket.
380 sub Some::function { 504 sub Some::function {
381 my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; 505 my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
382 506
383 print scalar <$fh>; # prints "hi 1\n" and "hi 2\n" 507 print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
384 } 508 }
385 509
386PERFORMANCE 510PERFORMANCE
387 Now for some unscientific benchmark numbers (all done on an amd64 511 Now for some unscientific benchmark numbers (all done on an amd64
388 GNU/Linux box). These are intended to give you an idea of the relative 512 GNU/Linux box). These are intended to give you an idea of the relative
… …
411 479 vfork+execs per second, using AnyEvent::Fork->new_exec 535 479 vfork+execs per second, using AnyEvent::Fork->new_exec
412 536
413 So how can "AnyEvent->new" be faster than a standard fork, even though 537 So how can "AnyEvent->new" be faster than a standard fork, even though
414 it uses the same operations, but adds a lot of overhead? 538 it uses the same operations, but adds a lot of overhead?
415 539
416 The difference is simply the process size: forking the 6MB process takes 540 The difference is simply the process size: forking the 5MB process takes
417 so much longer than forking the 2.5MB template process that the overhead 541 so much longer than forking the 2.5MB template process that the extra
418 introduced is canceled out. 542 overhead introduced is canceled out.
419 543
420 If the benchmark process grows, the normal fork becomes even slower: 544 If the benchmark process grows, the normal fork becomes even slower:
421 545
422 1340 new processes, manual fork in a 20MB process 546 1340 new processes, manual fork of a 20MB process
423 731 new processes, manual fork in a 200MB process 547 731 new processes, manual fork of a 200MB process
424 235 new processes, manual fork in a 2000MB process 548 235 new processes, manual fork of a 2000MB process
425 549
426 What that means (to me) is that I can use this module without having a 550 What that means (to me) is that I can use this module without having a
427 very bad conscience because of the extra overhead required to start new 551 bad conscience because of the extra overhead required to start new
428 processes. 552 processes.
429 553
430TYPICAL PROBLEMS 554TYPICAL PROBLEMS
431 This section lists typical problems that remain. I hope by recognising 555 This section lists typical problems that remain. I hope by recognising
432 them, most can be avoided. 556 them, most can be avoided.
433 557
434 "leaked" file descriptors for exec'ed processes 558 leaked file descriptors for exec'ed processes
435 POSIX systems inherit file descriptors by default when exec'ing a 559 POSIX systems inherit file descriptors by default when exec'ing a
436 new process. While perl itself laudably sets the close-on-exec flags 560 new process. While perl itself laudably sets the close-on-exec flags
437 on new file handles, most C libraries don't care, and even if all 561 on new file handles, most C libraries don't care, and even if all
438 cared, it's often not possible to set the flag in a race-free 562 cared, it's often not possible to set the flag in a race-free
439 manner. 563 manner.
… …
459 libraries or the code that leaks those file descriptors. 583 libraries or the code that leaks those file descriptors.
460 584
461 Fortunately, most of these leaked descriptors do no harm, other than 585 Fortunately, most of these leaked descriptors do no harm, other than
462 sitting on some resources. 586 sitting on some resources.
463 587
464 "leaked" file descriptors for fork'ed processes 588 leaked file descriptors for fork'ed processes
465 Normally, AnyEvent::Fork does start new processes by exec'ing them, 589 Normally, AnyEvent::Fork does start new processes by exec'ing them,
466 which closes file descriptors not marked for being inherited. 590 which closes file descriptors not marked for being inherited.
467 591
468 However, AnyEvent::Fork::Early and AnyEvent::Fork::Template offer a 592 However, AnyEvent::Fork::Early and AnyEvent::Fork::Template offer a
469 way to create these processes by forking, and this leaks more file 593 way to create these processes by forking, and this leaks more file
… …
477 601
478 The solution is to either not load these modules before use'ing 602 The solution is to either not load these modules before use'ing
479 AnyEvent::Fork::Early or AnyEvent::Fork::Template, or to delay 603 AnyEvent::Fork::Early or AnyEvent::Fork::Template, or to delay
480 initialising them, for example, by calling "init Gtk2" manually. 604 initialising them, for example, by calling "init Gtk2" manually.
481 605
482 exit runs destructors 606 exiting calls object destructors
483 This only applies to users of Lc<AnyEvent::Fork:Early> and 607 This only applies to users of AnyEvent::Fork:Early and
484 AnyEvent::Fork::Template. 608 AnyEvent::Fork::Template, or when initialiasing code creates objects
609 that reference external resources.
485 610
486 When a process created by AnyEvent::Fork exits, it might do so by 611 When a process created by AnyEvent::Fork exits, it might do so by
487 calling exit, or simply letting perl reach the end of the program. 612 calling exit, or simply letting perl reach the end of the program.
488 At which point Perl runs all destructors. 613 At which point Perl runs all destructors.
489 614
… …
505 and sweat to make it so, mostly due to the bloody broken perl that 630 and sweat to make it so, mostly due to the bloody broken perl that
506 nobody seems to care about. The fork emulation is a bad joke - I have 631 nobody seems to care about. The fork emulation is a bad joke - I have
507 yet to see something useful that you can do with it without running into 632 yet to see something useful that you can do with it without running into
508 memory corruption issues or other braindamage. Hrrrr. 633 memory corruption issues or other braindamage. Hrrrr.
509 634
510 Cygwin perl is not supported at the moment, as it should implement fd 635 Cygwin perl is not supported at the moment due to some hilarious
511 passing, but doesn't, and rolling my own is hard, as cygwin doesn't 636 shortcomings of its API - see IO::FDPoll for more details.
512 support enough functionality to do it.
513 637
514SEE ALSO 638SEE ALSO
515 AnyEvent::Fork::Early (to avoid executing a perl interpreter), 639 AnyEvent::Fork::Early (to avoid executing a perl interpreter),
516 AnyEvent::Fork::Template (to create a process by forking the main 640 AnyEvent::Fork::Template (to create a process by forking the main
517 program at a convenient time). 641 program at a convenient time).
518 642
519AUTHOR 643AUTHOR
520 Marc Lehmann <schmorp@schmorp.de> 644 Marc Lehmann <schmorp@schmorp.de>
521 http://home.schmorp.de/ 645 http://home.schmorp.de/
522 646
647POD ERRORS
648 Hey! The above document had some coding errors, which are explained
649 below:
650
651 Around line 360:
652 You can't have =items (as at line 476) unless the first thing after
653 the =over is an =item
654

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