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NAME |
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Proc::FastSpawn - fork+exec, or spawn, a subprocess as quickly as |
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possible |
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|
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SYNOPSIS |
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use Proc::FastSpawn; |
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|
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# simple use |
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my $pid = spawn "/bin/echo", ["echo", "hello, world"]; |
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... |
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waitpid $pid, 0; |
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|
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# with environment |
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my $pid = spawn "/bin/echo", ["echo", "hello, world"], ["PATH=/bin", "HOME=/tmp"]; |
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|
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# inheriting file descriptors |
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pipe R, W or die; |
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fd_inherit fileno W; |
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my $pid = spawn "/bin/sh", ["sh", "-c", "echo a pipe >&" . fileno W]; |
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close W; |
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print <R>; |
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|
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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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|
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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 fork |
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from perl, but it is safe to use this module to execute external |
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processes. |
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|
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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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|
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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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|
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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 |
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overhead. |
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|
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A workaround is to use "vfork" - this function isn't very portable, but |
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it avoids the memory copy that "fork" has to do. Some systems have an |
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optimised implementation of "spawn", and some systems have nothing. |
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|
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This module tries to abstract these differences away. |
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|
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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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|
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FUNCTIONS |
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All the following functions are currently exported by default. |
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|
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$pid = spawn $path, \@argv[, \@envp] |
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Creates a new process and tries to make it execute $path, with the |
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given arguments and optionally the given environment variables, |
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similar to calling fork + execv, or execve. |
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|
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Returns the PID of the new process if successful. On any error, |
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"undef" is currently returned. Failure to execution might or might |
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not be reported as "undef", or via a subprocess exit status of 127. |
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|
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fd_inherit $fileno[, $on] |
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File descriptors can be inherited by the spawned proceses or not. |
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This is decided on a per file descriptor basis. This module does |
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nothing to any preexisting handles, but with this call, you can |
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change the state of a single file descriptor to either be inherited |
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($on is true or missing) or not $on is false). |
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|
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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 |
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or spawn but is misdetected and falls back to slow fork+exec, drop me a |
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note. |
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|
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On win32, the "_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 |
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to only have 64 or so subprocesses) are not worked around. |
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|
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AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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