Capture PID from child process on Windows.

stmast has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, I'm trying to capture the PID of a child process from SYSTEM or EXEC. I have tried using FORK with EXEC which returns a PID, but not the PID listed in TaskMgr for Windows. I need to capture the PID in order to kill the process if it hangs. Here is a copy of the code I'm using to get the non-matching PID. Thanks!


#!/bin/perl 
use strict; 
use warnings; 

my $prog = 'some_executable';

defined( my $pid = fork ) or die "Cannot fork: $!"; 
print "pid:$pid\n"; 
unless( $pid ) { 
  exec "$prog"; 
  die "cannot exec date: $!"; 
}
[download]

Comment on Capture PID from child process on Windows. Download Code

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Re: Capture PID from child process on Windows. by BrowserUk (Patriarch) on Nov 08, 2005 at 22:11 UTC
The problem you are encountering is that fork creates a pseudo-process (a thread) and the "pid" returned is a (negative) threadid, not a process id. The simplest way is to use the piped open, which spawns a real process and returns a real pid: `perl> $pid = open KID, 'perl -e"1 while sleep 1 \|' or die $!;; perl> kill 21, $pid;; Terminating on signal SIGBREAK(21) perl> close KID;;` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal? "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re: Capture PID from child process on Windows. by GrandFather (Saint) on Nov 08, 2005 at 22:12 UTC
Take a look at `Win32::Spawn(COMMAND, ARGS, PID)` in the Win32::Process module docs in the ActiveState documentation. `Kill($exitcode)` and `GetExitCode($exitcode)` may also be of interest. Perl is Huffman encoded by design.	[reply] [d/l] [select]
Re: Capture PID from child process on Windows. by antirice (Priest) on Nov 08, 2005 at 22:04 UTC
Since it's windows, perhaps you should look at Win32::Process.	[reply]
Re: Capture PID from child process on Windows. by ikegami (Patriarch) on Nov 08, 2005 at 22:05 UTC
Your command probably required a shell to execute, so you have the PID of the shell, the true child. Use `exec PROGRAM LIST` instead of `exec LIST`. In other words, use nothing but a (fully qualified???) file name in `$prog`. By the way, `fork` is not particulary strong in Windows since the non-native system call is emulated using threads. `$pid = system(-1, ...)` (undocumented), Win32::Process, IPC::Open2, IPC::Open3 and IPC::Run are more appropriate than `fork`+`exec`. In this case, I'd use Win32::Process unless portability is desired.	[reply] [d/l] [select]
Re: Capture PID from child process on Windows. by Amar (Sexton) on Nov 09, 2005 at 12:42 UTC
As u need to kill the process if it hangs(meaning u need to control process), the process you create must be an asynchronous process. The following is a code snipet of the same under windows `use strict; use Win32::Process; my ($processObj, $pid); Win32::Process::Create($ProcessObj, "C:\\foo\\Setup.exe", "Setup.exe", 0, NORMAL_PRIORITY_CLASS,".")\|\| die "$!\n"; $pid = $ProcessObj->GetProcessID();` [download] Using the pid you can control the process. To kill the process say, `$ProcessObj->Kill($exitcode);` [download] Amar	[reply] [d/l] [select]