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51 | AnyEvent::Subprocess. There are modules that implement their own process |
51 | AnyEvent::Subprocess. There are modules that implement their own process |
52 | management, such as AnyEvent::DBI. |
52 | management, such as AnyEvent::DBI. |
53 | |
53 | |
54 | The problems that all these modules try to solve are real, however, none |
54 | The problems that all these modules try to solve are real, however, none |
55 | of them (from what I have seen) tackle the very real problems of |
55 | of them (from what I have seen) tackle the very real problems of |
56 | unwanted memory sharing, efficiency, not being able to use event |
56 | unwanted memory sharing, efficiency or not being able to use event |
57 | processing or similar modules in the processes they create. |
57 | processing, GUI toolkits or similar modules in the processes they |
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58 | create. |
58 | |
59 | |
59 | This module doesn't try to replace any of them - instead it tries to |
60 | This module doesn't try to replace any of them - instead it tries to |
60 | solve the problem of creating processes with a minimum of fuss and |
61 | solve the problem of creating processes with a minimum of fuss and |
61 | overhead (and also luxury). Ideally, most of these would use |
62 | overhead (and also luxury). Ideally, most of these would use |
62 | AnyEvent::Fork internally, except they were written before AnyEvent:Fork |
63 | AnyEvent::Fork internally, except they were written before AnyEvent:Fork |
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79 | vfork where possible. This gives the speed of vfork, with the |
80 | vfork where possible. This gives the speed of vfork, with the |
80 | flexibility of fork. |
81 | flexibility of fork. |
81 | |
82 | |
82 | Forking usually creates a copy-on-write copy of the parent process. |
83 | Forking usually creates a copy-on-write copy of the parent process. |
83 | For example, modules or data files that are loaded will not use |
84 | For example, modules or data files that are loaded will not use |
84 | additional memory after a fork. When exec'ing a new process, modules |
85 | additional memory after a fork. Exec'ing a new process, in contrast, |
85 | and data files might need to be loaded again, at extra CPU and |
86 | means modules and data files might need to be loaded again, at extra |
86 | memory cost. But when forking, literally all data structures are |
87 | CPU and memory cost. |
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88 | |
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89 | But when forking, you still create a copy of your data structures - |
87 | copied - if the program frees them and replaces them by new data, |
90 | if the program frees them and replaces them by new data, the child |
88 | the child processes will retain the old version even if it isn't |
91 | processes will retain the old version even if it isn't used, which |
89 | used, which can suddenly and unexpectedly increase memory usage when |
92 | can suddenly and unexpectedly increase memory usage when freeing |
90 | freeing memory. |
93 | memory. |
91 | |
94 | |
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95 | For example, Gtk2::CV is an image viewer optimised for large |
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96 | directories (millions of pictures). It also forks subprocesses for |
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97 | thumbnail generation, which inherit the data structure that stores |
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98 | all file information. If the user changes the directory, it gets |
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99 | freed in the main process, leaving a copy in the thumbnailer |
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100 | processes. This can lead to many times the memory usage that would |
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101 | actually be required. The solution is to fork early (and being |
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102 | unable to dynamically generate more subprocesses or do this from a |
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103 | module)... or to use <AnyEvent:Fork>. |
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104 | |
92 | The trade-off is between more sharing with fork (which can be good |
105 | There is a trade-off between more sharing with fork (which can be |
93 | or bad), and no sharing with exec. |
106 | good or bad), and no sharing with exec. |
94 | |
107 | |
95 | This module allows the main program to do a controlled fork, and |
108 | This module allows the main program to do a controlled fork, and |
96 | allows modules to exec processes safely at any time. When creating a |
109 | allows modules to exec processes safely at any time. When creating a |
97 | custom process pool you can take advantage of data sharing via fork |
110 | custom process pool you can take advantage of data sharing via fork |
98 | without risking to share large dynamic data structures that will |
111 | without risking to share large dynamic data structures that will |
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101 | In other words, this module puts you into control over what is being |
114 | In other words, this module puts you into control over what is being |
102 | shared and what isn't, at all times. |
115 | shared and what isn't, at all times. |
103 | |
116 | |
104 | Exec'ing a new perl process might be difficult. |
117 | Exec'ing a new perl process might be difficult. |
105 | For example, it is not easy to find the correct path to the perl |
118 | For example, it is not easy to find the correct path to the perl |
106 | interpreter - $^X might not be a perl interpreter at all. |
119 | interpreter - $^X might not be a perl interpreter at all. Worse, |
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120 | there might not even be a perl binary installed on the system. |
107 | |
121 | |
108 | This module tries hard to identify the correct path to the perl |
122 | This module tries hard to identify the correct path to the perl |
109 | interpreter. With a cooperative main program, exec'ing the |
123 | interpreter. With a cooperative main program, exec'ing the |
110 | interpreter might not even be necessary, but even without help from |
124 | interpreter might not even be necessary, but even without help from |
111 | the main program, it will still work when used from a module. |
125 | the main program, it will still work when used from a module. |
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116 | and modules are no longer loadable because they refer to a different |
130 | and modules are no longer loadable because they refer to a different |
117 | perl version, or parts of a distribution are newer than the ones |
131 | perl version, or parts of a distribution are newer than the ones |
118 | already loaded. |
132 | already loaded. |
119 | |
133 | |
120 | This module supports creating pre-initialised perl processes to be |
134 | This module supports creating pre-initialised perl processes to be |
121 | used as a template for new processes. |
135 | used as a template for new processes at a later time, e.g. for use |
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136 | in a process pool. |
122 | |
137 | |
123 | Forking might be impossible when a program is running. |
138 | Forking might be impossible when a program is running. |
124 | For example, POSIX makes it almost impossible to fork from a |
139 | For example, POSIX makes it almost impossible to fork from a |
125 | multi-threaded program while doing anything useful in the child - in |
140 | multi-threaded program while doing anything useful in the child - in |
126 | fact, if your perl program uses POSIX threads (even indirectly via |
141 | fact, if your perl program uses POSIX threads (even indirectly via |
127 | e.g. IO::AIO or threads), you cannot call fork on the perl level |
142 | e.g. IO::AIO or threads), you cannot call fork on the perl level |
128 | anymore without risking corruption issues on a number of operating |
143 | anymore without risking memory corruption or worse on a number of |
129 | systems. |
144 | operating systems. |
130 | |
145 | |
131 | This module can safely fork helper processes at any time, by calling |
146 | This module can safely fork helper processes at any time, by calling |
132 | fork+exec in C, in a POSIX-compatible way (via Proc::FastSpawn). |
147 | fork+exec in C, in a POSIX-compatible way (via Proc::FastSpawn). |
133 | |
148 | |
134 | Parallel processing with fork might be inconvenient or difficult to |
149 | Parallel processing with fork might be inconvenient or difficult to |
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150 | is still safe to do so) - all other processes are created via |
165 | is still safe to do so) - all other processes are created via |
151 | fork+exec, which makes it possible to use modules such as event |
166 | fork+exec, which makes it possible to use modules such as event |
152 | loops or window interfaces safely. |
167 | loops or window interfaces safely. |
153 | |
168 | |
154 | EXAMPLES |
169 | EXAMPLES |
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170 | This is where the wall of text ends and code speaks. |
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171 | |
155 | Create a single new process, tell it to run your worker function. |
172 | Create a single new process, tell it to run your worker function. |
156 | AnyEvent::Fork |
173 | AnyEvent::Fork |
157 | ->new |
174 | ->new |
158 | ->require ("MyModule") |
175 | ->require ("MyModule") |
159 | ->run ("MyModule::worker, sub { |
176 | ->run ("MyModule::worker, sub { |
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169 | |
186 | |
170 | sub worker { |
187 | sub worker { |
171 | my ($slave_filehandle) = @_; |
188 | my ($slave_filehandle) = @_; |
172 | |
189 | |
173 | # now $slave_filehandle is connected to the $master_filehandle |
190 | # now $slave_filehandle is connected to the $master_filehandle |
174 | # in the original prorcess. have fun! |
191 | # in the original process. have fun! |
175 | } |
192 | } |
176 | |
193 | |
177 | Create a pool of server processes all accepting on the same socket. |
194 | Create a pool of server processes all accepting on the same socket. |
178 | # create listener socket |
195 | # create listener socket |
179 | my $listener = ...; |
196 | my $listener = ...; |
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238 | ->run ("run", my $cv = AE::cv); |
255 | ->run ("run", my $cv = AE::cv); |
239 | |
256 | |
240 | my $stderr = $cv->recv; |
257 | my $stderr = $cv->recv; |
241 | |
258 | |
242 | For stingy users: put the worker code into a "DATA" section. |
259 | For stingy users: put the worker code into a "DATA" section. |
243 | When you want to be stingy with files, you cna put your code into the |
260 | When you want to be stingy with files, you can put your code into the |
244 | "DATA" section of your module (or program): |
261 | "DATA" section of your module (or program): |
245 | |
262 | |
246 | use AnyEvent::Fork; |
263 | use AnyEvent::Fork; |
247 | |
264 | |
248 | AnyEvent::Fork |
265 | AnyEvent::Fork |
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257 | } |
274 | } |
258 | |
275 | |
259 | For stingy standalone programs: do not rely on external files at |
276 | For stingy standalone programs: do not rely on external files at |
260 | all. |
277 | all. |
261 | For single-file scripts it can be inconvenient to rely on external files |
278 | For single-file scripts it can be inconvenient to rely on external files |
262 | - even when using < "DATA" section, you still need to "exec" an external |
279 | - even when using a "DATA" section, you still need to "exec" an external |
263 | perl interpreter, which might not be available when using |
280 | perl interpreter, which might not be available when using |
264 | App::Staticperl, Urlader or PAR::Packer for example. |
281 | App::Staticperl, Urlader or PAR::Packer for example. |
265 | |
282 | |
266 | Two modules help here - AnyEvent::Fork::Early forks a template process |
283 | Two modules help here - AnyEvent::Fork::Early forks a template process |
267 | for all further calls to "new_exec", and AnyEvent::Fork::Template forks |
284 | for all further calls to "new_exec", and AnyEvent::Fork::Template forks |
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285 | my ($fh, @args) = @_; |
302 | my ($fh, @args) = @_; |
286 | ... |
303 | ... |
287 | } |
304 | } |
288 | |
305 | |
289 | # now preserve everything so far as AnyEvent::Fork object |
306 | # now preserve everything so far as AnyEvent::Fork object |
290 | # in ยงTEMPLATE. |
307 | # in $TEMPLATE. |
291 | use AnyEvent::Fork::Template; |
308 | use AnyEvent::Fork::Template; |
292 | |
309 | |
293 | # do not put code outside of BEGIN blocks until here |
310 | # do not put code outside of BEGIN blocks until here |
294 | |
311 | |
295 | # now use the $TEMPLATE process in any way you like |
312 | # now use the $TEMPLATE process in any way you like |
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482 | See the "use AnyEvent::Fork as a faster fork+exec" example to see it |
499 | See the "use AnyEvent::Fork as a faster fork+exec" example to see it |
483 | in action. |
500 | in action. |
484 | |
501 | |
485 | Returns the process object for easy chaining of method calls. |
502 | Returns the process object for easy chaining of method calls. |
486 | |
503 | |
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504 | It's common to want to call an iniitalisation function with some |
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505 | arguments. Make sure you actually pass @_ to that function (for |
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506 | example by using &name syntax), and do not just specify a function |
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507 | name: |
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508 | |
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509 | $proc->eval ('&MyModule::init', $string1, $string2); |
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510 | |
487 | $proc = $proc->require ($module, ...) |
511 | $proc = $proc->require ($module, ...) |
488 | Tries to load the given module(s) into the process |
512 | Tries to load the given module(s) into the process |
489 | |
513 | |
490 | Returns the process object for easy chaining of method calls. |
514 | Returns the process object for easy chaining of method calls. |
491 | |
515 | |
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765 | Cygwin perl is not supported at the moment due to some hilarious |
789 | Cygwin perl is not supported at the moment due to some hilarious |
766 | shortcomings of its API - see IO::FDPoll for more details. If you never |
790 | shortcomings of its API - see IO::FDPoll for more details. If you never |
767 | use "send_fh" and always use "new_exec" to create processes, it should |
791 | use "send_fh" and always use "new_exec" to create processes, it should |
768 | work though. |
792 | work though. |
769 | |
793 | |
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794 | USING AnyEvent::Fork IN SUBPROCESSES |
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795 | AnyEvent::Fork itself cannot generally be used in subprocesses. As long |
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796 | as only one process ever forks new processes, sharing the template |
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797 | processes is possible (you could use a pipe as a lock by writing a byte |
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798 | into it to unlock, and reading the byte to lock for example) |
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799 | |
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800 | To make concurrent calls possible after fork, you should get rid of the |
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801 | template and early fork processes. AnyEvent::Fork will create a new |
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802 | template process as needed. |
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803 | |
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804 | undef $AnyEvent::Fork::EARLY; |
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805 | undef $AnyEvent::Fork::TEMPLATE; |
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806 | |
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807 | It doesn't matter whether you get rid of them in the parent or child |
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808 | after a fork. |
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809 | |
770 | SEE ALSO |
810 | SEE ALSO |
771 | AnyEvent::Fork::Early, to avoid executing a perl interpreter at all |
811 | AnyEvent::Fork::Early, to avoid executing a perl interpreter at all |
772 | (part of this distribution). |
812 | (part of this distribution). |
773 | |
813 | |
774 | AnyEvent::Fork::Template, to create a process by forking the main |
814 | AnyEvent::Fork::Template, to create a process by forking the main |