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Top Forums Shell Programming and Scripting Waiting for an arbitrary background process (limiting number of jobs running) Post 302390849 by p.f.moore on Friday 29th of January 2010 07:58:56 AM
Old 01-29-2010
I tried seeing what I could do with Perl, and I got this, which seems to work:
Code:
#!/usr/bin/perl
sub spawn {
    $pid = fork;
    unless ($pid) {
        exec "@_";
    }
    $pid
}
@pids = ();
for $i (1..20) {
    $cmd = "sleep $i; echo \$\$";
    $pid = spawn $cmd;
    print "$pid: '$cmd'\n";
    push @pids, $pid;
    if ($i > 10) {
        $pid = shift @pids;
        waitpid $pid, 0;
        printf "Process $pid ended\n";
    }
}
while (@pids) {
    $pid = shift @pids;
    waitpid $pid, 0;
    printf "Process $pid ended\n";
}

Does that look like a reasonable approach? It seems reasonably clean - although not as nice as my original ksh attempt (which had the disadvantage that it didn't work, of course Smilie)
 

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ptree(1)						      General Commands Manual							  ptree(1)

NAME
ptree - prints the process tree hierarchy SYNOPSIS
[pid1|username1 [pid2|username2]...] DESCRIPTION
prints the process tree of all processes that match the specified arguments. While printing the tree, the child processes are indented to the right from their respective parent processes. Options Prints the tree starting from the children of (usually pid 0). The default is to print the tree starting from the children of (pid 1). Operands pid Print the process tree for the process ID number specified by pid. username Print the process tree for all the processes from the user specified by username. Note that only username (and not user ID) can be specified for this instance. If no operands are specified, then prints the process tree of all processes starting from the children of or (if is specified). EXTERNAL INFLUENCES
Environment Variables If is not specified or is null, it defaults to (see lang(5)). EXAMPLES
Print the process tree for pid 100 and for all processes owned by WARNINGS
Process information can change while is running; the tree displayed by is only a snapshot in time. Some data printed for defunct processes is irrelevant. Users of must not rely on the exact field widths and spacing of its output, as these will vary depending on the system and the release of HP-UX. SEE ALSO
pgrep(1), pkill(1), ps(1), fork(2). ptree(1)
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