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1.1 |
=head1 NAME |
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1.4 |
AnyEvent::Fork - everything you wanted to use fork() for, but couldn't |
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1.1 |
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=head1 SYNOPSIS |
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1.4 |
use AnyEvent::Fork; |
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1.1 |
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1.9 |
################################################################## |
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# create a single new process, tell it to run your worker function |
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AnyEvent::Fork |
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->new |
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->require ("MyModule") |
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->run ("MyModule::worker, sub { |
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my ($master_filehandle) = @_; |
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# now $master_filehandle is connected to the |
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# $slave_filehandle in the new process. |
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}); |
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# MyModule::worker might look like this |
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sub MyModule::worker { |
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my ($slave_filehandle) = @_; |
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# now $slave_filehandle is connected to the $master_filehandle |
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# in the original prorcess. have fun! |
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} |
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################################################################## |
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# create a pool of server processes all accepting on the same socket |
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# create listener socket |
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my $listener = ...; |
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# create a pool template, initialise it and give it the socket |
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my $pool = AnyEvent::Fork |
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->new |
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->require ("Some::Stuff", "My::Server") |
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->send_fh ($listener); |
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# now create 10 identical workers |
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for my $id (1..10) { |
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$pool |
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->fork |
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->send_arg ($id) |
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->run ("My::Server::run"); |
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} |
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# now do other things - maybe use the filehandle provided by run |
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# to wait for the processes to die. or whatever. |
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# My::Server::run might look like this |
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sub My::Server::run { |
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my ($slave, $listener, $id) = @_; |
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close $slave; # we do not use the socket, so close it to save resources |
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# we could go ballistic and use e.g. AnyEvent here, or IO::AIO, |
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# or anything we usually couldn't do in a process forked normally. |
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while (my $socket = $listener->accept) { |
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# do sth. with new socket |
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} |
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} |
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1.1 |
=head1 DESCRIPTION |
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1.4 |
This module allows you to create new processes, without actually forking |
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them from your current process (avoiding the problems of forking), but |
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preserving most of the advantages of fork. |
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It can be used to create new worker processes or new independent |
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subprocesses for short- and long-running jobs, process pools (e.g. for use |
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in pre-forked servers) but also to spawn new external processes (such as |
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CGI scripts from a webserver), which can be faster (and more well behaved) |
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than using fork+exec in big processes. |
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1.1 |
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1.5 |
Special care has been taken to make this module useful from other modules, |
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while still supporting specialised environments such as L<App::Staticperl> |
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or L<PAR::Packer>. |
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1.16 |
=head1 WHAT THIS MODULE IS NOT |
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This module only creates processes and lets you pass file handles and |
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strings to it, and run perl code. It does not implement any kind of RPC - |
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there is no back channel from the process back to you, and there is no RPC |
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or message passing going on. |
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If you need some form of RPC, you can either implement it yourself |
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in whatever way you like, use some message-passing module such |
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as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use |
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L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages, |
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and so on. |
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1.1 |
=head1 PROBLEM STATEMENT |
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There are two ways to implement parallel processing on UNIX like operating |
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systems - fork and process, and fork+exec and process. They have different |
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advantages and disadvantages that I describe below, together with how this |
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module tries to mitigate the disadvantages. |
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=over 4 |
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=item Forking from a big process can be very slow (a 5GB process needs |
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0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead |
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is often shared with exec (because you have to fork first), but in some |
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circumstances (e.g. when vfork is used), fork+exec can be much faster. |
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This module can help here by telling a small(er) helper process to fork, |
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or fork+exec instead. |
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=item Forking usually creates a copy-on-write copy of the parent |
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process. Memory (for example, modules or data files that have been |
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will not take additional memory). When exec'ing a new process, modules |
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and data files might need to be loaded again, at extra cpu and memory |
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cost. Likewise when forking, all data structures are copied as well - if |
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the program frees them and replaces them by new data, the child processes |
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will retain the memory even if it isn't used. |
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This module allows the main program to do a controlled fork, and allows |
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modules to exec processes safely at any time. When creating a custom |
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process pool you can take advantage of data sharing via fork without |
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risking to share large dynamic data structures that will blow up child |
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memory usage. |
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=item Exec'ing a new perl process might be difficult and slow. For |
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example, it is not easy to find the correct path to the perl interpreter, |
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and all modules have to be loaded from disk again. Long running processes |
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might run into problems when perl is upgraded for example. |
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This module supports creating pre-initialised perl processes to be used |
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as template, and also tries hard to identify the correct path to the perl |
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interpreter. With a cooperative main program, exec'ing the interpreter |
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might not even be necessary. |
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=item Forking might be impossible when a program is running. For example, |
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POSIX makes it almost impossible to fork from a multithreaded program and |
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do anything useful in the child - strictly speaking, if your perl program |
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uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>), |
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you cannot call fork on the perl level anymore, at all. |
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This module can safely fork helper processes at any time, by caling |
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fork+exec in C, in a POSIX-compatible way. |
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=item Parallel processing with fork might be inconvenient or difficult |
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to implement. For example, when a program uses an event loop and creates |
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watchers it becomes very hard to use the event loop from a child |
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program, as the watchers already exist but are only meaningful in the |
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parent. Worse, a module might want to use such a system, not knowing |
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whether another module or the main program also does, leading to problems. |
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This module only lets the main program create pools by forking (because |
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only the main program can know when it is still safe to do so) - all other |
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pools are created by fork+exec, after which such modules can again be |
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loaded. |
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=back |
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root |
1.3 |
=head1 CONCEPTS |
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This module can create new processes either by executing a new perl |
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process, or by forking from an existing "template" process. |
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Each such process comes with its own file handle that can be used to |
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communicate with it (it's actually a socket - one end in the new process, |
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one end in the main process), and among the things you can do in it are |
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load modules, fork new processes, send file handles to it, and execute |
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functions. |
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There are multiple ways to create additional processes to execute some |
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jobs: |
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=over 4 |
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=item fork a new process from the "default" template process, load code, |
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run it |
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This module has a "default" template process which it executes when it is |
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needed the first time. Forking from this process shares the memory used |
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for the perl interpreter with the new process, but loading modules takes |
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time, and the memory is not shared with anything else. |
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This is ideal for when you only need one extra process of a kind, with the |
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option of starting and stipping it on demand. |
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root |
1.9 |
Example: |
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AnyEvent::Fork |
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->new |
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->require ("Some::Module") |
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->run ("Some::Module::run", sub { |
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my ($fork_fh) = @_; |
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}); |
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1.3 |
=item fork a new template process, load code, then fork processes off of |
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it and run the code |
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When you need to have a bunch of processes that all execute the same (or |
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very similar) tasks, then a good way is to create a new template process |
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for them, loading all the modules you need, and then create your worker |
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processes from this new template process. |
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This way, all code (and data structures) that can be shared (e.g. the |
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modules you loaded) is shared between the processes, and each new process |
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consumes relatively little memory of its own. |
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The disadvantage of this approach is that you need to create a template |
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process for the sole purpose of forking new processes from it, but if you |
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only need a fixed number of proceses you can create them, and then destroy |
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the template process. |
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1.9 |
Example: |
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my $template = AnyEvent::Fork->new->require ("Some::Module"); |
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for (1..10) { |
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$template->fork->run ("Some::Module::run", sub { |
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my ($fork_fh) = @_; |
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}); |
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} |
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# at this point, you can keep $template around to fork new processes |
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# later, or you can destroy it, which causes it to vanish. |
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1.3 |
=item execute a new perl interpreter, load some code, run it |
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This is relatively slow, and doesn't allow you to share memory between |
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multiple processes. |
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The only advantage is that you don't have to have a template process |
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hanging around all the time to fork off some new processes, which might be |
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an advantage when there are long time spans where no extra processes are |
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needed. |
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root |
1.9 |
Example: |
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AnyEvent::Fork |
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->new_exec |
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->require ("Some::Module") |
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->run ("Some::Module::run", sub { |
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my ($fork_fh) = @_; |
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}); |
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root |
1.3 |
=back |
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=head1 FUNCTIONS |
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248 |
root |
1.1 |
=over 4 |
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=cut |
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252 |
root |
1.4 |
package AnyEvent::Fork; |
253 |
root |
1.1 |
|
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use common::sense; |
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use Socket (); |
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use AnyEvent; |
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use AnyEvent::Util (); |
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root |
1.15 |
use IO::FDPass; |
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our $VERSION = 0.2; |
264 |
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1.12 |
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1.4 |
our $PERL; # the path to the perl interpreter, deduces with various forms of magic |
266 |
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1.1 |
|
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1.4 |
=item my $pool = new AnyEvent::Fork key => value... |
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1.1 |
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Create a new process pool. The following named parameters are supported: |
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=over 4 |
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=back |
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=cut |
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277 |
root |
1.5 |
# the early fork template process |
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our $EARLY; |
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280 |
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1.4 |
# the empty template process |
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our $TEMPLATE; |
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sub _cmd { |
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my $self = shift; |
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286 |
root |
1.9 |
#TODO: maybe append the packet to any existing string command already in the queue |
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288 |
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1.4 |
# ideally, we would want to use "a (w/a)*" as format string, but perl versions |
289 |
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1.5 |
# from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it. |
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1.16 |
push @{ $self->[2] }, pack "L/a*", pack "(w/a*)*", @_; |
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1.4 |
|
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$self->[3] ||= AE::io $self->[1], 1, sub { |
293 |
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1.9 |
# send the next "thing" in the queue - either a reference to an fh, |
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# or a plain string. |
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296 |
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1.4 |
if (ref $self->[2][0]) { |
297 |
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1.9 |
# send fh |
298 |
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1.15 |
IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] } |
299 |
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1.4 |
and shift @{ $self->[2] }; |
300 |
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1.5 |
|
301 |
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1.4 |
} else { |
302 |
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1.9 |
# send string |
303 |
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1.4 |
my $len = syswrite $self->[1], $self->[2][0] |
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or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" }; |
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1.5 |
|
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1.4 |
substr $self->[2][0], 0, $len, ""; |
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shift @{ $self->[2] } unless length $self->[2][0]; |
308 |
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} |
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unless (@{ $self->[2] }) { |
311 |
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undef $self->[3]; |
312 |
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1.9 |
# invoke run callback |
313 |
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1.4 |
$self->[0]->($self->[1]) if $self->[0]; |
314 |
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} |
315 |
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}; |
316 |
root |
1.14 |
|
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() # make sure we don't leak the watcher |
318 |
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1.4 |
} |
319 |
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1.1 |
|
320 |
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1.4 |
sub _new { |
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my ($self, $fh) = @_; |
322 |
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1.1 |
|
323 |
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1.6 |
AnyEvent::Util::fh_nonblocking $fh, 1; |
324 |
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325 |
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1.4 |
$self = bless [ |
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undef, # run callback |
327 |
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1.1 |
$fh, |
328 |
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1.4 |
[], # write queue - strings or fd's |
329 |
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undef, # AE watcher |
330 |
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], $self; |
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$self |
333 |
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1.1 |
} |
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335 |
root |
1.6 |
# fork template from current process, used by AnyEvent::Fork::Early/Template |
336 |
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sub _new_fork { |
337 |
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my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
338 |
root |
1.7 |
my $parent = $$; |
339 |
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340 |
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1.6 |
my $pid = fork; |
341 |
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342 |
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if ($pid eq 0) { |
343 |
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require AnyEvent::Fork::Serve; |
344 |
root |
1.7 |
$AnyEvent::Fork::Serve::OWNER = $parent; |
345 |
root |
1.6 |
close $fh; |
346 |
root |
1.7 |
$0 = "$_[1] of $parent"; |
347 |
root |
1.16 |
$SIG{CHLD} = 'IGNORE'; |
348 |
root |
1.6 |
AnyEvent::Fork::Serve::serve ($slave); |
349 |
root |
1.15 |
exit 0; |
350 |
root |
1.6 |
} elsif (!$pid) { |
351 |
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die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; |
352 |
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} |
353 |
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AnyEvent::Fork->_new ($fh) |
355 |
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} |
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357 |
root |
1.4 |
=item my $proc = new AnyEvent::Fork |
358 |
root |
1.1 |
|
359 |
root |
1.4 |
Create a new "empty" perl interpreter process and returns its process |
360 |
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object for further manipulation. |
361 |
root |
1.1 |
|
362 |
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1.4 |
The new process is forked from a template process that is kept around |
363 |
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for this purpose. When it doesn't exist yet, it is created by a call to |
364 |
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C<new_exec> and kept around for future calls. |
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|
366 |
root |
1.9 |
When the process object is destroyed, it will release the file handle |
367 |
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that connects it with the new process. When the new process has not yet |
368 |
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called C<run>, then the process will exit. Otherwise, what happens depends |
369 |
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entirely on the code that is executed. |
370 |
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371 |
root |
1.4 |
=cut |
372 |
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373 |
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sub new { |
374 |
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my $class = shift; |
375 |
root |
1.1 |
|
376 |
root |
1.4 |
$TEMPLATE ||= $class->new_exec; |
377 |
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$TEMPLATE->fork |
378 |
root |
1.1 |
} |
379 |
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380 |
root |
1.4 |
=item $new_proc = $proc->fork |
381 |
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382 |
|
|
Forks C<$proc>, creating a new process, and returns the process object |
383 |
|
|
of the new process. |
384 |
|
|
|
385 |
|
|
If any of the C<send_> functions have been called before fork, then they |
386 |
|
|
will be cloned in the child. For example, in a pre-forked server, you |
387 |
|
|
might C<send_fh> the listening socket into the template process, and then |
388 |
|
|
keep calling C<fork> and C<run>. |
389 |
|
|
|
390 |
|
|
=cut |
391 |
|
|
|
392 |
|
|
sub fork { |
393 |
|
|
my ($self) = @_; |
394 |
root |
1.1 |
|
395 |
|
|
my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
396 |
root |
1.4 |
|
397 |
|
|
$self->send_fh ($slave); |
398 |
|
|
$self->_cmd ("f"); |
399 |
|
|
|
400 |
|
|
AnyEvent::Fork->_new ($fh) |
401 |
|
|
} |
402 |
|
|
|
403 |
|
|
=item my $proc = new_exec AnyEvent::Fork |
404 |
|
|
|
405 |
|
|
Create a new "empty" perl interpreter process and returns its process |
406 |
|
|
object for further manipulation. |
407 |
|
|
|
408 |
|
|
Unlike the C<new> method, this method I<always> spawns a new perl process |
409 |
|
|
(except in some cases, see L<AnyEvent::Fork::Early> for details). This |
410 |
|
|
reduces the amount of memory sharing that is possible, and is also slower. |
411 |
|
|
|
412 |
|
|
You should use C<new> whenever possible, except when having a template |
413 |
|
|
process around is unacceptable. |
414 |
|
|
|
415 |
|
|
The path to the perl interpreter is divined usign various methods - first |
416 |
|
|
C<$^X> is investigated to see if the path ends with something that sounds |
417 |
|
|
as if it were the perl interpreter. Failing this, the module falls back to |
418 |
|
|
using C<$Config::Config{perlpath}>. |
419 |
|
|
|
420 |
|
|
=cut |
421 |
|
|
|
422 |
|
|
sub new_exec { |
423 |
|
|
my ($self) = @_; |
424 |
|
|
|
425 |
root |
1.5 |
return $EARLY->fork |
426 |
|
|
if $EARLY; |
427 |
|
|
|
428 |
root |
1.4 |
# first find path of perl |
429 |
|
|
my $perl = $; |
430 |
|
|
|
431 |
|
|
# first we try $^X, but the path must be absolute (always on win32), and end in sth. |
432 |
|
|
# that looks like perl. this obviously only works for posix and win32 |
433 |
|
|
unless ( |
434 |
root |
1.15 |
($^O eq "MSWin32" || $perl =~ m%^/%) |
435 |
root |
1.4 |
&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
436 |
|
|
) { |
437 |
|
|
# if it doesn't look perlish enough, try Config |
438 |
|
|
require Config; |
439 |
|
|
$perl = $Config::Config{perlpath}; |
440 |
|
|
$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/; |
441 |
|
|
} |
442 |
|
|
|
443 |
|
|
require Proc::FastSpawn; |
444 |
|
|
|
445 |
|
|
my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
446 |
|
|
Proc::FastSpawn::fd_inherit (fileno $slave); |
447 |
|
|
|
448 |
root |
1.10 |
# new fh's should always be set cloexec (due to $^F), |
449 |
|
|
# but hey, not on win32, so we always clear the inherit flag. |
450 |
|
|
Proc::FastSpawn::fd_inherit (fileno $fh, 0); |
451 |
|
|
|
452 |
root |
1.4 |
# quick. also doesn't work in win32. of course. what did you expect |
453 |
|
|
#local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
454 |
root |
1.1 |
my %env = %ENV; |
455 |
root |
1.15 |
$env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC; |
456 |
root |
1.1 |
|
457 |
root |
1.4 |
Proc::FastSpawn::spawn ( |
458 |
|
|
$perl, |
459 |
root |
1.7 |
["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$], |
460 |
root |
1.4 |
[map "$_=$env{$_}", keys %env], |
461 |
|
|
) or die "unable to spawn AnyEvent::Fork server: $!"; |
462 |
|
|
|
463 |
|
|
$self->_new ($fh) |
464 |
|
|
} |
465 |
|
|
|
466 |
root |
1.9 |
=item $proc = $proc->eval ($perlcode, @args) |
467 |
|
|
|
468 |
|
|
Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to |
469 |
|
|
the strings specified by C<@args>. |
470 |
|
|
|
471 |
|
|
This call is meant to do any custom initialisation that might be required |
472 |
|
|
(for example, the C<require> method uses it). It's not supposed to be used |
473 |
|
|
to completely take over the process, use C<run> for that. |
474 |
|
|
|
475 |
|
|
The code will usually be executed after this call returns, and there is no |
476 |
|
|
way to pass anything back to the calling process. Any evaluation errors |
477 |
|
|
will be reported to stderr and cause the process to exit. |
478 |
|
|
|
479 |
|
|
Returns the process object for easy chaining of method calls. |
480 |
|
|
|
481 |
|
|
=cut |
482 |
|
|
|
483 |
|
|
sub eval { |
484 |
|
|
my ($self, $code, @args) = @_; |
485 |
|
|
|
486 |
|
|
$self->_cmd (e => $code, @args); |
487 |
|
|
|
488 |
|
|
$self |
489 |
|
|
} |
490 |
|
|
|
491 |
root |
1.4 |
=item $proc = $proc->require ($module, ...) |
492 |
root |
1.1 |
|
493 |
root |
1.9 |
Tries to load the given module(s) into the process |
494 |
root |
1.1 |
|
495 |
root |
1.4 |
Returns the process object for easy chaining of method calls. |
496 |
root |
1.1 |
|
497 |
root |
1.9 |
=cut |
498 |
|
|
|
499 |
|
|
sub require { |
500 |
|
|
my ($self, @modules) = @_; |
501 |
|
|
|
502 |
|
|
s%::%/%g for @modules; |
503 |
|
|
$self->eval ('require "$_.pm" for @_', @modules); |
504 |
|
|
|
505 |
|
|
$self |
506 |
|
|
} |
507 |
|
|
|
508 |
root |
1.4 |
=item $proc = $proc->send_fh ($handle, ...) |
509 |
root |
1.1 |
|
510 |
root |
1.4 |
Send one or more file handles (I<not> file descriptors) to the process, |
511 |
|
|
to prepare a call to C<run>. |
512 |
root |
1.1 |
|
513 |
root |
1.4 |
The process object keeps a reference to the handles until this is done, |
514 |
|
|
so you must not explicitly close the handles. This is most easily |
515 |
|
|
accomplished by simply not storing the file handles anywhere after passing |
516 |
|
|
them to this method. |
517 |
|
|
|
518 |
|
|
Returns the process object for easy chaining of method calls. |
519 |
|
|
|
520 |
root |
1.9 |
Example: pass an fh to a process, and release it without closing. it will |
521 |
|
|
be closed automatically when it is no longer used. |
522 |
|
|
|
523 |
|
|
$proc->send_fh ($my_fh); |
524 |
|
|
undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT |
525 |
|
|
|
526 |
root |
1.4 |
=cut |
527 |
|
|
|
528 |
|
|
sub send_fh { |
529 |
|
|
my ($self, @fh) = @_; |
530 |
|
|
|
531 |
|
|
for my $fh (@fh) { |
532 |
|
|
$self->_cmd ("h"); |
533 |
|
|
push @{ $self->[2] }, \$fh; |
534 |
|
|
} |
535 |
|
|
|
536 |
|
|
$self |
537 |
root |
1.1 |
} |
538 |
|
|
|
539 |
root |
1.4 |
=item $proc = $proc->send_arg ($string, ...) |
540 |
|
|
|
541 |
|
|
Send one or more argument strings to the process, to prepare a call to |
542 |
|
|
C<run>. The strings can be any octet string. |
543 |
|
|
|
544 |
|
|
Returns the process object for easy chaining of emthod calls. |
545 |
|
|
|
546 |
|
|
=cut |
547 |
root |
1.1 |
|
548 |
root |
1.4 |
sub send_arg { |
549 |
|
|
my ($self, @arg) = @_; |
550 |
root |
1.1 |
|
551 |
root |
1.4 |
$self->_cmd (a => @arg); |
552 |
root |
1.1 |
|
553 |
|
|
$self |
554 |
|
|
} |
555 |
|
|
|
556 |
root |
1.4 |
=item $proc->run ($func, $cb->($fh)) |
557 |
|
|
|
558 |
|
|
Enter the function specified by the fully qualified name in C<$func> in |
559 |
|
|
the process. The function is called with the communication socket as first |
560 |
|
|
argument, followed by all file handles and string arguments sent earlier |
561 |
|
|
via C<send_fh> and C<send_arg> methods, in the order they were called. |
562 |
|
|
|
563 |
|
|
If the called function returns, the process exits. |
564 |
|
|
|
565 |
|
|
Preparing the process can take time - when the process is ready, the |
566 |
|
|
callback is invoked with the local communications socket as argument. |
567 |
|
|
|
568 |
|
|
The process object becomes unusable on return from this function. |
569 |
|
|
|
570 |
|
|
If the communication socket isn't used, it should be closed on both sides, |
571 |
|
|
to save on kernel memory. |
572 |
|
|
|
573 |
|
|
The socket is non-blocking in the parent, and blocking in the newly |
574 |
|
|
created process. The close-on-exec flag is set on both. Even if not used |
575 |
|
|
otherwise, the socket can be a good indicator for the existance of the |
576 |
root |
1.8 |
process - if the other process exits, you get a readable event on it, |
577 |
root |
1.4 |
because exiting the process closes the socket (if it didn't create any |
578 |
|
|
children using fork). |
579 |
|
|
|
580 |
root |
1.9 |
Example: create a template for a process pool, pass a few strings, some |
581 |
|
|
file handles, then fork, pass one more string, and run some code. |
582 |
|
|
|
583 |
|
|
my $pool = AnyEvent::Fork |
584 |
|
|
->new |
585 |
|
|
->send_arg ("str1", "str2") |
586 |
|
|
->send_fh ($fh1, $fh2); |
587 |
|
|
|
588 |
|
|
for (1..2) { |
589 |
|
|
$pool |
590 |
|
|
->fork |
591 |
|
|
->send_arg ("str3") |
592 |
|
|
->run ("Some::function", sub { |
593 |
|
|
my ($fh) = @_; |
594 |
|
|
|
595 |
|
|
# fh is nonblocking, but we trust that the OS can accept these |
596 |
|
|
# extra 3 octets anyway. |
597 |
|
|
syswrite $fh, "hi #$_\n"; |
598 |
|
|
|
599 |
|
|
# $fh is being closed here, as we don't store it anywhere |
600 |
|
|
}); |
601 |
|
|
} |
602 |
|
|
|
603 |
|
|
# Some::function might look like this - all parameters passed before fork |
604 |
|
|
# and after will be passed, in order, after the communications socket. |
605 |
|
|
sub Some::function { |
606 |
|
|
my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
607 |
|
|
|
608 |
|
|
print scalar <$fh>; # prints "hi 1\n" and "hi 2\n" |
609 |
|
|
} |
610 |
|
|
|
611 |
root |
1.4 |
=cut |
612 |
|
|
|
613 |
|
|
sub run { |
614 |
|
|
my ($self, $func, $cb) = @_; |
615 |
|
|
|
616 |
|
|
$self->[0] = $cb; |
617 |
root |
1.9 |
$self->_cmd (r => $func); |
618 |
root |
1.4 |
} |
619 |
|
|
|
620 |
root |
1.1 |
=back |
621 |
|
|
|
622 |
root |
1.16 |
=head1 PERFORMANCE |
623 |
|
|
|
624 |
|
|
Now for some unscientific benchmark numbers (all done on an amd64 |
625 |
|
|
GNU/Linux box). These are intended to give you an idea of the relative |
626 |
|
|
performance you can expect. |
627 |
|
|
|
628 |
|
|
Ok, so, I ran a simple benchmark that creates a socketpair, forks, calls |
629 |
|
|
exit in the child and waits for the socket to close in the parent. I did |
630 |
|
|
load AnyEvent, EV and AnyEvent::Fork, for a total process size of 6312kB. |
631 |
|
|
|
632 |
|
|
2079 new processes per second, using socketpair + fork manually |
633 |
|
|
|
634 |
|
|
Then I did the same thing, but instead of calling fork, I called |
635 |
|
|
AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the |
636 |
|
|
socket form the child to close on exit. This does the same thing as manual |
637 |
|
|
socketpair + fork, except that what is forked is the template process |
638 |
|
|
(2440kB), and the socket needs to be passed to the server at the other end |
639 |
|
|
of the socket first. |
640 |
|
|
|
641 |
|
|
2307 new processes per second, using AnyEvent::Fork->new |
642 |
|
|
|
643 |
|
|
And finally, using C<new_exec> instead C<new>, using vforks+execs to exec |
644 |
|
|
a new perl interpreter and compile the small server each time, I get: |
645 |
|
|
|
646 |
|
|
479 vfork+execs per second, using AnyEvent::Fork->new_exec |
647 |
|
|
|
648 |
|
|
So how can C<< AnyEvent->new >> be faster than a standard fork, een though |
649 |
|
|
it uses the same operations, but adds a lot of overhead? |
650 |
|
|
|
651 |
|
|
The difference is simply the process size: forking the 6MB process takes |
652 |
|
|
so much longer than forking the 2.5MB template process that the overhead |
653 |
|
|
introduced is canceled out. |
654 |
|
|
|
655 |
|
|
If the benchmark process grows, the normal fork becomes even slower: |
656 |
|
|
|
657 |
|
|
1340 new processes, manual fork in a 20MB process |
658 |
|
|
731 new processes, manual fork in a 200MB process |
659 |
|
|
235 new processes, manual fork in a 2000MB process |
660 |
|
|
|
661 |
|
|
What that means (to me) is that I can use this module without havign a |
662 |
|
|
very bad conscience because of the extra overhead requried to strat new |
663 |
|
|
processes. |
664 |
|
|
|
665 |
root |
1.15 |
=head1 TYPICAL PROBLEMS |
666 |
|
|
|
667 |
|
|
This section lists typical problems that remain. I hope by recognising |
668 |
|
|
them, most can be avoided. |
669 |
|
|
|
670 |
|
|
=over 4 |
671 |
|
|
|
672 |
|
|
=item "leaked" file descriptors for exec'ed processes |
673 |
|
|
|
674 |
|
|
POSIX systems inherit file descriptors by default when exec'ing a new |
675 |
|
|
process. While perl itself laudably sets the close-on-exec flags on new |
676 |
|
|
file handles, most C libraries don't care, and even if all cared, it's |
677 |
|
|
often not possible to set the flag in a race-free manner. |
678 |
|
|
|
679 |
|
|
That means some file descriptors can leak through. And since it isn't |
680 |
|
|
possible to know which file descriptors are "good" and "neccessary" (or |
681 |
|
|
even to know which file descreiptors are open), there is no good way to |
682 |
|
|
close the ones that might harm. |
683 |
|
|
|
684 |
|
|
As an example of what "harm" can be done consider a web server that |
685 |
|
|
accepts connections and afterwards some module uses AnyEvent::Fork for the |
686 |
|
|
first time, causing it to fork and exec a new process, which might inherit |
687 |
|
|
the network socket. When the server closes the socket, it is still open |
688 |
|
|
in the child (which doesn't even know that) and the client might conclude |
689 |
|
|
that the connection is still fine. |
690 |
|
|
|
691 |
|
|
For the main program, there are multiple remedies available - |
692 |
|
|
L<AnyEvent::Fork::Early> is one, creating a process early and not using |
693 |
|
|
C<new_exec> is another, as in both cases, the first process can be exec'ed |
694 |
|
|
well before many random file descriptors are open. |
695 |
|
|
|
696 |
|
|
In general, the solution for these kind of problems is to fix the |
697 |
|
|
libraries or the code that leaks those file descriptors. |
698 |
|
|
|
699 |
|
|
Fortunately, most of these lekaed descriptors do no harm, other than |
700 |
|
|
sitting on some resources. |
701 |
|
|
|
702 |
|
|
=item "leaked" file descriptors for fork'ed processes |
703 |
|
|
|
704 |
|
|
Normally, L<AnyEvent::Fork> does start new processes by exec'ing them, |
705 |
|
|
which closes file descriptors not marked for being inherited. |
706 |
|
|
|
707 |
|
|
However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer |
708 |
|
|
a way to create these processes by forking, and this leaks more file |
709 |
|
|
descriptors than exec'ing them, as there is no way to mark descriptors as |
710 |
|
|
"close on fork". |
711 |
|
|
|
712 |
|
|
An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create |
713 |
|
|
pipes for internal uses, and L<Gtk2> might open a connection to the X |
714 |
|
|
server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have |
715 |
|
|
trouble with a fork. |
716 |
|
|
|
717 |
|
|
The solution is to either not load these modules before use'ing |
718 |
|
|
L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay |
719 |
|
|
initialising them, for example, by calling C<init Gtk2> manually. |
720 |
|
|
|
721 |
|
|
=back |
722 |
|
|
|
723 |
root |
1.8 |
=head1 PORTABILITY NOTES |
724 |
|
|
|
725 |
root |
1.10 |
Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop, |
726 |
|
|
and ::Template is not going to work), and it cost a lot of blood and sweat |
727 |
|
|
to make it so, mostly due to the bloody broken perl that nobody seems to |
728 |
|
|
care about. The fork emulation is a bad joke - I have yet to see something |
729 |
|
|
useful that you cna do with it without running into memory corruption |
730 |
|
|
issues or other braindamage. Hrrrr. |
731 |
|
|
|
732 |
|
|
Cygwin perl is not supported at the moment, as it should implement fd |
733 |
|
|
passing, but doesn't, and rolling my own is hard, as cygwin doesn't |
734 |
|
|
support enough functionality to do it. |
735 |
root |
1.8 |
|
736 |
root |
1.13 |
=head1 SEE ALSO |
737 |
|
|
|
738 |
|
|
L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter), |
739 |
|
|
L<AnyEvent::Fork::Template> (to create a process by forking the main |
740 |
|
|
program at a convenient time). |
741 |
|
|
|
742 |
root |
1.1 |
=head1 AUTHOR |
743 |
|
|
|
744 |
|
|
Marc Lehmann <schmorp@schmorp.de> |
745 |
|
|
http://home.schmorp.de/ |
746 |
|
|
|
747 |
|
|
=cut |
748 |
|
|
|
749 |
|
|
1 |
750 |
|
|
|