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#!/usr/bin/perl
# Simplified example illustrating event handling and callback threads
# Callback threads register their queues with the event handler thread.
# Events are passed to the event handler via a queue.
# The event handler then disseminates the event to the appropriately
# registered thread.
use strict;
use warnings;
use threads;
use Thread::Queue;
MAIN:
{
# Queue for registering callbacks
my $regis_q = Thread::Queue->new();
# Queue for disseminating events
my $event_q = Thread::Queue->new();
# Create callback threads
threads->create('CallBack', 'USR1', $regis_q)->detach();
threads->create('CallBack', 'USR2', $regis_q)->detach();
threads->create('CallBack', 'HUP', $regis_q)->detach();
threads->create('CallBack', 'ALRM', $regis_q)->detach();
# Create event handler thread
threads->create('EventHandler', $regis_q, $event_q)->detach();
# Capture SIGUSR1 events
$SIG{'USR1'} = sub {
$event_q->enqueue('USR1'); # Send to event handler
};
# Capture SIGUSR1 events
$SIG{'USR2'} = sub {
$event_q->enqueue('USR2'); # Send to event handler
};
# Capture SIGHUP events
$SIG{'HUP'} = sub {
$event_q->enqueue('HUP'); # Send to event handler
};
# Capture SIGHUP events
$SIG{'ALRM'} = sub {
$event_q->enqueue('ALRM'); # Send to event handler
alarm(5); # Reset alarm
};
# Ready
print(<<_MSG_);
Send signals to PID = $$
(e.g., 'kill -USR1 $$')
Use ^C (or 'kill -INT $$') to terminate
_MSG_
# Set initial alarm
alarm(5);
# Just hang around
while (1) {
sleep(10);
}
}
### Subroutines ###
sub EventHandler
{
my ($regis_q, $event_q) = @_;
my %callbacks; # Registered callback queues
while (1) {
# Check for any registrations
while (my ($event_type, $q) = $regis_q->dequeue_nb(2)) {
if ($q) {
$callbacks{$event_type} = $q;
} else {
warn("BUG: Bad callback registration for event type $event_type\n");
}
}
# Wait for event
if (my $event = $event_q->dequeue()) {
# Send event to appropriate queue
if (exists($callbacks{$event})) {
$callbacks{$event}->enqueue($event);
} else {
warn("WARNING: No callback for event type $event\n");
}
}
}
}
sub CallBack
{
my $event_type = shift; # The type of event I'm handling
my $regis_q = shift;
# Announce registration
my $tid = threads->tid();
print("Callback thread $tid registering for $event_type events\n");
# Register my queue for my type of event
my $q = Thread::Queue->new();
$regis_q->enqueue($event_type, $q);
# Process loop
while (1) {
# Wait for event callback
my $item = $q->dequeue();
# Process event
print("Callback thread $tid notified of $item event\n") if $item;
}
}
# EOF
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