System Programming in Perl

36

Signal Handling

Related to signal handling is the alarm clock

Every process has an alarm clock

When the alarm clock goes off, the kernel sends the process an ALRM signal

The alarm clock is preserved across exec, but not copied on fork

We can use it to make a useful utility, stopafter:

        #!/usr/bin/perl
        my ($limit, $command, @args) = @ARGV;
        $SIG{ALARM} = 'DEFAULT';
        alarm $limit;
        exec $command, @args;
        die "Couldn't run '$command': $!";

To use:

        stopafter 30 command arg arg arg...

stopafter just sets up an alarm clock and then execs the program you asked for

30 seconds later, the alarm clock goes off

The ALRM signal is delivered

The process dies

(Unless the command cancelled the alarm clock or caught or ignored the ALRM signal)

36