Re: Cannot print child process command during fork

Forking child process, only to run a brief system command seems pointless, because system already does a fork.

To answer your question, simultanious writing to the same file handle by so many child processes probably gets them to clobber each other occasionally.

I would recommend getting rid of the fork entirely - simply put 24 system calls in a loop.

"An undefined problem has an infinite number of solutions." - Robert A. Humphrey "If you're not part of the solution, you're part of the precipitate." - Henry J. Tillman

Comment on Re: Cannot print child process command during fork

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Re^2: Cannot print child process command during fork by BrowserUk (Patriarch) on Aug 02, 2007 at 05:31 UTC
If he did 24 system calls in a loop, wouldn't they all run serially rather than in parallel as now? Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re^3: Cannot print child process command during fork by NetWallah (Canon) on Aug 02, 2007 at 14:56 UTC
Since no useful work appears to be done at the conclusion of the forked child processes, and $proc and $cmd were unspecified, I assumed that $cmd was a brief command that started a remote process, and exited. If this is the case, the difference between serial and parallel processing would not be significant. So, point taken. I should have clarified my assumptions. "An undefined problem has an infinite number of solutions." - Robert A. Humphrey "If you're not part of the solution, you're part of the precipitate." - Henry J. Tillman	[reply]
Re^2: Cannot print child process command during fork by whatwhat (Novice) on Aug 02, 2007 at 07:50 UTC
In my code the system command calls another program to run on the remote node. The program on the remote node can take several hours to run. So I think I need the explicit perl 'fork' command, so that I can start, for example, 24 independent calculations on 24 different compute nodes (computers) all running at the same time. I think a loop through system calls would run them serially. Even if system exited without waiting for the program to finish this would be undersirable for my needs. I need the parent process to monitor when the child (the program on the remote node) is finished. Thanks for the explanation of 'clobbering'!	[reply]