perl function alarm

In Perl, the alarm function is used to schedule an alarm signal to be sent to the current process after a specified number of seconds. The alarm function takes a single argument, which is the number of seconds until the alarm should be triggered.

Here is an example that demonstrates the use of the alarm function:

use strict;
use warnings;

# set an alarm for 5 seconds from now
my $seconds = 5;
print "Setting alarm for $seconds seconds...\n";
alarm $seconds;

# do some work that might take more than 5 seconds
my $count = 0;
while ($count < 10) {
    print "$count\n";
    sleep 1;
    $count++;
}

# cancel the alarm (if it hasn't already triggered)
print "Cancelling alarm...\n";
alarm 0;

In the above example, we set an alarm for 5 seconds from now using the alarm function. We then enter a loop that prints a number and sleeps for one second, repeating 10 times. This simulates some work that might take longer than 5 seconds to complete.

If the work completes before the alarm is triggered, we cancel the alarm using the alarm function again.

Note that the alarm function sends a signal to the current process when the specified number of seconds has elapsed. By default, this signal is the SIGALRM signal, but you can specify a different signal using the %SIG hash. For example:

$SIG{USR1} = sub {
    print "Received USR1 signal.\n";
};

alarm 5;
print "Waiting for signal...\n";
sleep 10;

In the above example, we set up a signal handler for the USR1 signal using the %SIG hash. We then set an alarm for 5 seconds and enter a sleep loop for 10 seconds. If the USR1 signal is received during that time, the signal handler will be executed.