| 1 |
NAME |
| 2 |
Proc::FastSpawn - fork+exec, or spawn, a subprocess as quickly as |
| 3 |
possible |
| 4 |
|
| 5 |
SYNOPSIS |
| 6 |
use Proc::FastSpawn; |
| 7 |
|
| 8 |
# simple use |
| 9 |
my $pid = spawn "/bin/echo", ["echo", "hello, world"]; |
| 10 |
... |
| 11 |
waitpid $pid, 0; |
| 12 |
|
| 13 |
# with environment |
| 14 |
my $pid = spawn "/bin/echo", ["echo", "hello, world"], ["PATH=/bin", "HOME=/tmp"]; |
| 15 |
|
| 16 |
# inheriting file descriptors |
| 17 |
pipe R, W or die; |
| 18 |
fd_inherit fileno W; |
| 19 |
my $pid = spawn "/bin/sh", ["sh", "-c", "echo a pipe >&" . fileno W]; |
| 20 |
close W; |
| 21 |
print <R>; |
| 22 |
|
| 23 |
DESCRIPTION |
| 24 |
The purpose of this small (in scope and footprint) module is simple: |
| 25 |
spawn a subprocess asynchronously as efficiently and/or fast as |
| 26 |
possible. Basically the same as calling fork+exec (on POSIX), but |
| 27 |
hopefully faster than those two syscalls. |
| 28 |
|
| 29 |
Apart from fork overhead, this module also allows you to fork+exec |
| 30 |
programs when otherwise you couldn't - for example, when you use POSIX |
| 31 |
threads in your perl process then it generally isn't safe to call fork |
| 32 |
from perl, but it is safe to use this module to execute external |
| 33 |
processes. |
| 34 |
|
| 35 |
If neither of these are problems for you, you can safely ignore this |
| 36 |
module. |
| 37 |
|
| 38 |
So when is fork+exec not fast enough, how can you do it faster, and why |
| 39 |
would it matter? |
| 40 |
|
| 41 |
Forking a process requires making a complete copy of a process. Even |
| 42 |
thought almost every implementation only copies page tables and not the |
| 43 |
memory itself, this is still not free. For example, on my 3.6GHz amd64 |
| 44 |
box, I can fork a 5GB process only twenty times a second. For a |
| 45 |
real-time process that must meet stricter deadlines, this is too slow. |
| 46 |
For a busy and big web server, starting CGI scripts might mean |
| 47 |
unacceptable overhead. |
| 48 |
|
| 49 |
A workaround is to use "vfork" - this function isn't very portable, but |
| 50 |
it avoids the memory copy that "fork" has to do. Some systems have an |
| 51 |
optimised implementation of "spawn", and some systems have nothing. |
| 52 |
|
| 53 |
This module tries to abstract these differences away. |
| 54 |
|
| 55 |
As for what improvements to expect - on the 3.6GHz amd64 box that this |
| 56 |
module was originally developed on, a 3MB perl process (basically just |
| 57 |
perl + Proc::FastSpawn) takes 3.6s to run /bin/true 10000 times using |
| 58 |
fork+exec, and only 2.6s when using vfork+exec. In a 22MB process, the |
| 59 |
difference is already 5.0s vs 2.6s, and so on. |
| 60 |
|
| 61 |
FUNCTIONS |
| 62 |
All the following functions are currently exported by default. |
| 63 |
|
| 64 |
$pid = spawn $path, \@argv[, \@envp] |
| 65 |
Creates a new process and tries to make it execute $path, with the |
| 66 |
given arguments and optionally the given environment variables, |
| 67 |
similar to calling fork + execv, or execve. |
| 68 |
|
| 69 |
Returns the PID of the new process if successful. On any error, |
| 70 |
"undef" is currently returned. Failure to execution might or might |
| 71 |
not be reported as "undef", or via a subprocess exit status of 127. |
| 72 |
|
| 73 |
$pid = spawnp $file, \@argv[, \@envp] |
| 74 |
Like "spawn", but searches $file in $ENV{PATH} like the shell would |
| 75 |
do. |
| 76 |
|
| 77 |
fd_inherit $fileno[, $on] |
| 78 |
File descriptors can be inherited by the spawned processes or not. |
| 79 |
This is decided on a per file descriptor basis. This module does |
| 80 |
nothing to any preexisting handles, but with this call, you can |
| 81 |
change the state of a single file descriptor to either be inherited |
| 82 |
($on is true or missing) or not $on is false). |
| 83 |
|
| 84 |
Free portability pro-tip: it seems native win32 perls ignore $^F and |
| 85 |
set all file handles to be inherited by default - but this function |
| 86 |
can switch it off. |
| 87 |
|
| 88 |
PORTABILITY NOTES |
| 89 |
On POSIX systems, this module currently calls vfork+exec, spawn, or |
| 90 |
fork+exec, depending on the platform. If your platform has a good vfork |
| 91 |
or spawn but is misdetected and falls back to slow fork+exec, drop me a |
| 92 |
note. |
| 93 |
|
| 94 |
On win32, the "_spawn" family of functions is used, and the module tries |
| 95 |
hard to patch the new process into perl's internal pid table, so the pid |
| 96 |
returned should work with other Perl functions such as waitpid. Also, |
| 97 |
win32 doesn't have a meaningful way to quote arguments containing |
| 98 |
"special" characters, so this module tries it's best to quote those |
| 99 |
strings itself. Other typical platform limitations (such as being able |
| 100 |
to only have 64 or so subprocesses) are not worked around. |
| 101 |
|
| 102 |
AUTHOR |
| 103 |
Marc Lehmann <schmorp@schmorp.de> |
| 104 |
http://home.schmorp.de/ |
| 105 |
|
