in reply to Setting an alarm

Signals are checked after each Perl opcode is executed, and only then. Perl won't check until if a signal was received until the create_thumbnail XS functions call ends (or until it calls some Perl code, which it probably doesn't do). I'm not sure why Ctrl-C works. (Are you on Windows or unix?)

One solution is to create the thumbnails in a child process, and kill the process if it hasn't finished in the desired amount of time. Bonus: It'll provide a cleaner shutdown when a problem occurs. Bonus: It'll allow you to parallelize the process if you so desire.

You could also turn off safe signals.

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Re^2: Setting an alarm
by Rodster001 (Pilgrim) on Mar 10, 2010 at 17:10 UTC
    I am on UNIX.

    Forking kids is new to me. After looking around, I came up with this: 

        my $pid;

    ...

    if (!stat($png)) {

            $SIG{'CHLD'} = "wait_for_child";
            $pid = fork();
            if ($pid) {
                    "Creating thumbnail for: $pdf (pid $pid)\n";

            } else {
                    create_thumbnail($pdf,$png);
                    exit(0);
            }
    }

    sub wait_for_child {
            print "Waiting on $pid...";
            sleep(1);
    }

    [download]

    I haven't actually run the code yet for two reasons. This will generate all of them at the same time (forking a child for each PDF). And I don't have anything to check how long they are taking.

    Can you add some pseudo code that would point me in the right direction?

    Thanks!

[reply]
[d/l]

      The $SIG{CHLD} + sleep approach you took (instead of wait/waitpid) is interesting, since it saves you from using alarm. While an alarm would interrupt wait/waitpid, why use signals when they're not needed. 

      use POSIX qw( _exit );

if (!stat($png)) {
    my $child_code;

    local $SIG{CHLD} = sub {
        wait();  # Reap child
        $child_code = $?;
    };

    defined( my $pid = fork() )
        or die("Can't fork: $!\n");

    if (!$pid) {  # Child
        if (eval { create_thumbnail($pdf,$png); 1 }) {
            _exit(0);
        } else {
            # Especially deadly version of die()
            print STDERR $@;
            _exit($! || $?>>8 || 255);
        }
    }

    print "Waiting on $pid...\n";
    sleep($timeout);  # Interrupted by SIGCHLD since we have a handler
    if (defined($child_code)) {
        die("Child failure\n") if $child_code;
    } else {
        $SIG{CHLD} = 'DEFAULT';
        kill KILL => $pid;
        wait();  # Reap child
        die("Child timeout\n");
    }
}

      [download]
[reply]
[d/l]
[select]
        Thanks for taking the time to write this, clears a lot of things up too! I've got it working nicely.
[reply]

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