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=head1 NAME |
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Proc::FastSpawn - fork+exec, or spawn, a subprocess as quickly as possible |
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=head1 SYNOPSIS |
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use Proc::FastSpawn; |
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=head1 DESCRIPTION |
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The purpose of this small (in scope and footprint) module is simple: |
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spawn a subprocess asynchronously as efficiently and/or fast as |
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possible. Basically the same as calling fork+exec (on POSIX), but |
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hopefully faster than those two syscalls. |
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Apart from fork overhead, this module also allows you to fork+exec |
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programs when otherwise you couldn't - for example, when you use POSIX |
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threads in your perl process then it generally isn't safe to call |
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fork from perl, but it is safe to use this module to execute external |
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processes. |
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If neither of these are problems for you, you can safely ignore this |
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module. |
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So when is fork+exec not fast enough, how can you do it faster, and why |
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would it matter? |
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Forking a process requires making a complete copy of a process. Even |
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thougth almost every implementation only copies page tables and not the |
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memory istelf, this is still not free. For example, on my 3.6GHz amd64 |
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box, I can fork a 5GB process only twenty times a second. For a realtime |
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process that must meet stricter deadlines, this is too slow. For a busy |
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and big webserver, starting CGI scripts might mean unacceptable overhead. |
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A workaround is to use C<vfork> - this function isn't very portable, but |
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it avoids the memory copy that C<fork> has to do. Some systems have an |
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optimised implementation of C<spawn>, and some systems have nothing. |
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This module tries to abstract these differences away. |
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As for what improvements to expect - on the 3.6GHz amd64 box that this |
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module was originally developed on, a 3MB perl process (basically just |
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perl + Proc::FastSpawn) takes 3.6s to run /bin/true 10000 times using |
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fork+exec, and only 2.6s when using vfork+exec. In a 22MB process, the |
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difference is already 5.0s vs 2.6s, and so on. |
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=head1 FUNCTIONS |
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All the following functions are currently exported by default. |
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=over 4 |
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=cut |
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package Proc::FastSpawn; |
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# only used on WIN32 - maddeningly complex and doesn't even work |
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sub _quote { |
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$_[0] = [@{ $_[0] }]; # make copy |
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for (@{ $_[0] }) { |
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if (/[\x01-\x20"]/) { # some sources say only space, "\t\n\v need to be escaped, microsoft says space and tab |
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s/(\\*)"/$1$1\\"/g; # double + extra escape before " |
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s/(\\+)$/$1$1/; # just double at end |
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$_ = '"' . $_ . '"'; |
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} |
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} |
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} |
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BEGIN { |
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$VERSION = '0.1'; |
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our @ISA = qw(Exporter); |
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our @EXPORT = qw(spawn fd_inherit); |
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require Exporter; |
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require XSLoader; |
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XSLoader::load (__PACKAGE__, $VERSION); |
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} |
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=item $pid = spawn $path, \@argv[, \@envp] |
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Creates a new process and tries to make it execute C<$path>, with the given |
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arguments and optionally the given environment variables, similar to |
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calling fork + execv, or execve. |
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Returns the PID of the new process if successful. On any error, C<undef> |
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is currently returned. Failure to execution might or might not be reported |
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as C<undef>, or via a subprocess exit status of C<127>. |
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=item fd_inherit $fileno[, $on] |
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File descriptors can be inherited by the spawned proceses or not. This is |
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decided on a per file descriptor basis. This module does nothing to any |
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preexisting handles, but with this call, you can change the state of a |
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single file descriptor to either be inherited (C<$on> is true or missing) |
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or not C<$on> is false). |
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=back |
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=head1 PORTABILITY NOTES |
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On POSIX systems, this module currently calls vfork+exec, spawn, or |
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fork+exec, depending on the platform. If your platform has a good vfork or |
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spawn but is misdetected and falls back on slow fork+exec, drop me a note. |
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On win32, the C<_spawn> family of functions is used, and the module tries |
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hard to patch the new process into perl's internal pid table, so the pid |
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returned should work with other perl functions such as waitpid. Also, |
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win32 doesn't have a meaningful way to quote arguments containing |
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"special" characters, so this module tries it's best to quote those |
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strings itself. Other typical platform limitations (such as being able to |
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only have 64 or so subprocesses) apply as well. |
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=head1 AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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=cut |
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1; |
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