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=head1 NAME |
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|
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AnyEvent::Fork - everything you wanted to use fork() for, but couldn't |
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|
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=head1 SYNOPSIS |
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|
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use AnyEvent::Fork; |
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|
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=head1 DESCRIPTION |
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|
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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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|
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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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|
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=head1 PROBLEM STATEMENT |
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|
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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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|
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=over 4 |
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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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=back |
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|
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=head1 CONCEPTS |
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|
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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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|
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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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|
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There are multiple ways to create additional processes to execute some |
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jobs: |
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|
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=over 4 |
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|
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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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|
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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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|
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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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|
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=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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|
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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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|
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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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|
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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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|
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=item execute a new perl interpreter, load some code, run it |
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|
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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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|
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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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|
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=back |
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|
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=head1 FUNCTIONS |
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|
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=over 4 |
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|
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=cut |
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|
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package AnyEvent::Fork; |
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|
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use common::sense; |
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|
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use Socket (); |
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|
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use AnyEvent; |
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use AnyEvent::Fork::Util; |
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use AnyEvent::Util (); |
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|
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our $PERL; # the path to the perl interpreter, deduces with various forms of magic |
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|
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=item my $pool = new AnyEvent::Fork key => value... |
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|
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Create a new process pool. The following named parameters are supported: |
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|
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=over 4 |
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|
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=back |
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|
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=cut |
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|
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# the empty template process |
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our $TEMPLATE; |
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|
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sub _cmd { |
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my $self = shift; |
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|
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# ideally, we would want to use "a (w/a)*" as format string, but perl versions |
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# form at least 5.8.9 to 5.16.3 are all buggy and can't unpack it. |
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push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_; |
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|
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$self->[3] ||= AE::io $self->[1], 1, sub { |
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if (ref $self->[2][0]) { |
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AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] } |
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and shift @{ $self->[2] }; |
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} else { |
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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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substr $self->[2][0], 0, $len, ""; |
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shift @{ $self->[2] } unless length $self->[2][0]; |
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} |
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|
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unless (@{ $self->[2] }) { |
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undef $self->[3]; |
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$self->[0]->($self->[1]) if $self->[0]; |
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} |
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}; |
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} |
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|
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sub _new { |
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my ($self, $fh) = @_; |
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|
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$self = bless [ |
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undef, # run callback |
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$fh, |
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[], # write queue - strings or fd's |
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undef, # AE watcher |
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], $self; |
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|
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# my ($a, $b) = AnyEvent::Util::portable_socketpair; |
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|
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# queue_cmd $template, "Iabc"; |
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# push @{ $template->[2] }, \$b; |
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|
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# use Coro::AnyEvent; Coro::AnyEvent::sleep 1; |
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# undef $b; |
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# die "x" . <$a>; |
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|
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$self |
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} |
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|
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=item my $proc = new AnyEvent::Fork |
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|
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Create a new "empty" perl interpreter process and returns its process |
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object for further manipulation. |
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|
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The new process is forked from a template process that is kept around |
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for this purpose. When it doesn't exist yet, it is created by a call to |
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C<new_exec> and kept around for future calls. |
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|
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=cut |
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|
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sub new { |
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my $class = shift; |
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|
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$TEMPLATE ||= $class->new_exec; |
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$TEMPLATE->fork |
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} |
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|
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=item $new_proc = $proc->fork |
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|
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Forks C<$proc>, creating a new process, and returns the process object |
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of the new process. |
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|
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If any of the C<send_> functions have been called before fork, then they |
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will be cloned in the child. For example, in a pre-forked server, you |
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might C<send_fh> the listening socket into the template process, and then |
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keep calling C<fork> and C<run>. |
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|
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=cut |
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|
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sub fork { |
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my ($self) = @_; |
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|
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my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
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|
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$self->send_fh ($slave); |
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$self->_cmd ("f"); |
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|
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AnyEvent::Util::fh_nonblocking $fh, 1; |
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|
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AnyEvent::Fork->_new ($fh) |
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} |
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|
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=item my $proc = new_exec AnyEvent::Fork |
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|
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Create a new "empty" perl interpreter process and returns its process |
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object for further manipulation. |
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|
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Unlike the C<new> method, this method I<always> spawns a new perl process |
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(except in some cases, see L<AnyEvent::Fork::Early> for details). This |
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reduces the amount of memory sharing that is possible, and is also slower. |
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|
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You should use C<new> whenever possible, except when having a template |
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process around is unacceptable. |
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|
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The path to the perl interpreter is divined usign various methods - first |
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C<$^X> is investigated to see if the path ends with something that sounds |
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as if it were the perl interpreter. Failing this, the module falls back to |
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using C<$Config::Config{perlpath}>. |
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|
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=cut |
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|
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sub new_exec { |
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my ($self) = @_; |
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|
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# first find path of perl |
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my $perl = $; |
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|
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# first we try $^X, but the path must be absolute (always on win32), and end in sth. |
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# that looks like perl. this obviously only works for posix and win32 |
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unless ( |
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(AnyEvent::Fork::Util::WIN32 || $perl =~ m%^/%) |
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&& $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
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) { |
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# if it doesn't look perlish enough, try Config |
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require Config; |
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$perl = $Config::Config{perlpath}; |
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$perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/; |
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} |
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|
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require Proc::FastSpawn; |
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|
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my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
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AnyEvent::Util::fh_nonblocking $fh, 1; |
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Proc::FastSpawn::fd_inherit (fileno $slave); |
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|
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# quick. also doesn't work in win32. of course. what did you expect |
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#local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
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my %env = %ENV; |
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$env{PERL5LIB} = join ":", grep !ref, @INC; |
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|
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Proc::FastSpawn::spawn ( |
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$perl, |
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["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave], |
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[map "$_=$env{$_}", keys %env], |
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) or die "unable to spawn AnyEvent::Fork server: $!"; |
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|
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$self->_new ($fh) |
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} |
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|
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=item $proc = $proc->require ($module, ...) |
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|
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Tries to load the given modules into the process |
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|
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Returns the process object for easy chaining of method calls. |
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|
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=item $proc = $proc->send_fh ($handle, ...) |
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|
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Send one or more file handles (I<not> file descriptors) to the process, |
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to prepare a call to C<run>. |
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|
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The process object keeps a reference to the handles until this is done, |
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so you must not explicitly close the handles. This is most easily |
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accomplished by simply not storing the file handles anywhere after passing |
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them to this method. |
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|
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Returns the process object for easy chaining of method calls. |
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|
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=cut |
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|
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sub send_fh { |
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my ($self, @fh) = @_; |
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|
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for my $fh (@fh) { |
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$self->_cmd ("h"); |
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push @{ $self->[2] }, \$fh; |
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} |
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|
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$self |
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} |
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|
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=item $proc = $proc->send_arg ($string, ...) |
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|
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Send one or more argument strings to the process, to prepare a call to |
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C<run>. The strings can be any octet string. |
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|
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Returns the process object for easy chaining of emthod calls. |
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|
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=cut |
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|
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sub send_arg { |
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my ($self, @arg) = @_; |
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|
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$self->_cmd (a => @arg); |
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|
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$self |
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} |
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|
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=item $proc->run ($func, $cb->($fh)) |
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|
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Enter the function specified by the fully qualified name in C<$func> in |
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the process. The function is called with the communication socket as first |
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argument, followed by all file handles and string arguments sent earlier |
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via C<send_fh> and C<send_arg> methods, in the order they were called. |
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|
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If the called function returns, the process exits. |
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|
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Preparing the process can take time - when the process is ready, the |
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callback is invoked with the local communications socket as argument. |
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|
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The process object becomes unusable on return from this function. |
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|
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If the communication socket isn't used, it should be closed on both sides, |
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to save on kernel memory. |
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|
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The socket is non-blocking in the parent, and blocking in the newly |
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created process. The close-on-exec flag is set on both. Even if not used |
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otherwise, the socket can be a good indicator for the existance of the |
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process - if the othe rprocess exits, you get a readable event on it, |
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because exiting the process closes the socket (if it didn't create any |
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children using fork). |
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|
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=cut |
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|
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sub run { |
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my ($self, $func, $cb) = @_; |
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|
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$self->[0] = $cb; |
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$self->_cmd ("r", $func); |
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} |
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|
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=back |
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|
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=head1 AUTHOR |
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|
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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|
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=cut |
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|
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1 |
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|
