oracular (3) Proc::FastSpawn.3pm.gz

NAME

       Proc::FastSpawn - fork+exec, or spawn, a subprocess as quickly as possible

SYNOPSIS

          use Proc::FastSpawn;

          # simple use
          my $pid = spawn "/bin/echo", ["echo", "hello, world"];
          ...
          waitpid $pid, 0;

          # with environment
          my $pid = spawn "/bin/echo", ["echo", "hello, world"], ["PATH=/bin", "HOME=/tmp"];

          # inheriting file descriptors
          pipe R, W or die;
          fd_inherit fileno W;
          my $pid = spawn "/bin/sh", ["sh", "-c", "echo a pipe >&" . fileno W];
          close W;
          print <R>;

DESCRIPTION

       The purpose of this small (in scope and footprint) module is simple: spawn a subprocess asynchronously as
       efficiently and/or fast as possible. Basically the same as calling fork+exec (on POSIX), but hopefully
       faster than those two syscalls.

       Apart from fork overhead, this module also allows you to fork+exec programs when otherwise you couldn't -
       for example, when you use POSIX threads in your perl process then it generally isn't safe to call fork
       from perl, but it is safe to use this module to execute external processes.

       If neither of these are problems for you, you can safely ignore this module.

       So when is fork+exec not fast enough, how can you do it faster, and why would it matter?

       Forking a process requires making a complete copy of a process. Even thought almost every implementation
       only copies page tables and not the memory itself, this is still not free. For example, on my 3.6GHz
       amd64 box, I can fork a 5GB process only twenty times a second. For a real-time process that must meet
       stricter deadlines, this is too slow. For a busy and big web server, starting CGI scripts might mean
       unacceptable overhead.

       A workaround is to use "vfork" - this function isn't very portable, but it avoids the memory copy that
       "fork" has to do. Some systems have an optimised implementation of "spawn", and some systems have
       nothing.

       This module tries to abstract these differences away.

       As for what improvements to expect - on the 3.6GHz amd64 box that this module was originally developed
       on, a 3MB perl process (basically just perl + Proc::FastSpawn) takes 3.6s to run /bin/true 10000 times
       using fork+exec, and only 2.6s when using vfork+exec. In a 22MB process, the difference is already 5.0s
       vs 2.6s, and so on.

FUNCTIONS

       All the following functions are currently exported by default.

       $pid = spawn $path, \@argv[, \@envp]
           Creates a new process and tries to make it execute $path, with the given arguments and optionally the
           given environment variables, similar to calling fork + execv, or execve.

           Returns the PID of the new process if successful. On any error, "undef" is currently returned.
           Failure to execution might or might not be reported as "undef", or via a subprocess exit status of
           127.

       $pid = spawnp $file, \@argv[, \@envp]
           Like "spawn", but searches $file in $ENV{PATH} like the shell would do.

       fd_inherit $fileno[, $on]
           File descriptors can be inherited by the spawned processes or not. This is decided on a per file
           descriptor basis. This module does nothing to any preexisting handles, but with this call, you can
           change the state of a single file descriptor to either be inherited ($on is true or missing) or not
           $on is false).

           Free portability pro-tip: it seems native win32 perls ignore $^F and set all file handles to be
           inherited by default - but this function can switch it off.

PORTABILITY NOTES

       On POSIX systems, this module currently calls vfork+exec, spawn, or fork+exec, depending on the platform.
       If your platform has a good vfork or spawn but is misdetected and falls back to slow fork+exec, drop me a
       note.

       On win32, the "_spawn" family of functions is used, and the module tries hard to patch the new process
       into perl's internal pid table, so the pid returned should work with other Perl functions such as
       waitpid. Also, win32 doesn't have a meaningful way to quote arguments containing "special" characters, so
       this module tries it's best to quote those strings itself. Other typical platform limitations (such as
       being able to only have 64 or so subprocesses) are not worked around.

AUTHOR

        Marc Lehmann <schmorp@schmorp.de>
        http://home.schmorp.de/