Re: Re: Background process using a system call

You've got the parent/child comments the wrong way round, you may as well use exec instead of the system/exit pair, and why not catch all of those return codes from rsh?

local (%rc, $running);

# turn off stdout buffering
$| = 1;

# catch return codes
local $SIG{CHLD} = sub { $rc{wait()} = $?; --$running; };

foreach my $wks (@wkslist) {
    if ( my $pid = fork() ) {
        # parent
        ++$running;
    } else {
        # child
        print "rshing to $wks\n";
        exec($rsh_cmd, $wks, "ls");
    }
}

sleep while ($running);
[download]

I have an old snippet which you may find useful at Run some commands in parallel

Are you writing a program to execute arbitrary commands on multiple hosts at the same time? If so, check back in a day or two and I'll have the script I use posted that packs in a few features.

Comment on Re: Re: Background process using a system call Download Code

Replies are listed 'Best First'.
Re: Re: Re: Background process using a system call by maverick (Curate) on Aug 21, 2001 at 05:09 UTC
ummm...according to "perldoc perlfunc" my parent/child comments aren't backwards. Fork Does a fork(2) system call to create a new process running the same program at the same point. It returns the child pid to the parent process, `0' to the child process, or `undef' if the fork is unsuccessful. In your code example you have `if (my $pid = fork()) { # a true or non-zero value for the parent # stuff } else { # a false value or 0 for the child # stuff }` [download] Your logic is the same as mine. I used system because that is what he was using, it makes it clearer (at least to me) how his example correlated to my solution. I also tend to leave out the extra error checking because it can cause one to miss the point of the example...and by that token, you're not checking to see if your fork failed. :) To error test everything I guess the code would look like `foreach my $wks (@wkslist) { my $pid = fork; if (!defined($pid)) { die "fork failed: $!"; } elsif ($pid == 0) { # child print "rshing to $wks\n"; exec("$rsh_cmd $wks ls") \|\| die "exec failed for $wks: $!"; } else { push(@pids,$pid); } } foreach my $pid (@pids) { waitpid($pid,0); if ($? != 0) { print "non zero exit from $pid: $?"; } }` [download] give me a bit and I'll figure out how to make $? look pretty :) /\/\averick perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re: Re: Re: Background process using a system call
by maverick (Curate) on Aug 21, 2001 at 05:09 UTC

Fork Does a fork(2) system call to create a new process running the same program at the same point. It returns the child pid to the parent process, `0' to the child process, or `undef' if the fork is unsuccessful.

In your code example you have

if (my $pid = fork()) {  # a true or non-zero value for the parent
    # stuff
}
else {                   # a false value or 0 for the child
    # stuff
}
[download]

I used system because that is what he was using, it makes it clearer (at least to me) how his example correlated to my solution. I also tend to leave out the extra error checking because it can cause one to miss the point of the example...and by that token, you're not checking to see if your fork failed. :)

To error test everything I guess the code would look like

foreach my $wks (@wkslist) {
    my $pid = fork;

    if (!defined($pid)) {
        die "fork failed: $!";
    }
    elsif ($pid == 0) {
        # child
        print "rshing to $wks\n";
        exec("$rsh_cmd $wks ls") || die "exec failed for $wks: $!";
    }
    else {
        push(@pids,$pid);
    }
}

foreach my $pid (@pids) {
    waitpid($pid,0);
    if ($? != 0) {
       print "non zero exit from $pid: $?";
    }
}
[download]

/\/\averick
perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"

[reply]
[d/l]
[select]