1#!/usr/bin/perl
2
3# Simplified example illustrating event handling and callback threads
4
5# Callback threads register their queues with the event handler thread.
6# Events are passed to the event handler via a queue.
7# The event handler then disseminates the event to the appropriately
8#   registered thread.
9
10use strict;
11use warnings;
12
13use threads;
14use Thread::Queue;
15
16MAIN:
17{
18    # Queue for registering callbacks
19    my $regis_q = Thread::Queue->new();
20
21    # Queue for disseminating events
22    my $event_q = Thread::Queue->new();
23
24    # Create callback threads
25    threads->create('CallBack', 'USR1', $regis_q)->detach();
26    threads->create('CallBack', 'USR2', $regis_q)->detach();
27    threads->create('CallBack', 'HUP', $regis_q)->detach();
28    threads->create('CallBack', 'ALRM', $regis_q)->detach();
29
30    # Create event handler thread
31    threads->create('EventHandler', $regis_q, $event_q)->detach();
32
33    # Capture SIGUSR1 events
34    $SIG{'USR1'} = sub {
35        $event_q->enqueue('USR1');  # Send to event handler
36    };
37
38    # Capture SIGUSR1 events
39    $SIG{'USR2'} = sub {
40        $event_q->enqueue('USR2');  # Send to event handler
41    };
42
43    # Capture SIGHUP events
44    $SIG{'HUP'} = sub {
45        $event_q->enqueue('HUP');  # Send to event handler
46    };
47
48    # Capture SIGHUP events
49    $SIG{'ALRM'} = sub {
50        $event_q->enqueue('ALRM');  # Send to event handler
51        alarm(5);                   # Reset alarm
52    };
53
54    # Ready
55    print(<<_MSG_);
56Send signals to PID = $$
57  (e.g., 'kill -USR1 $$')
58Use ^C (or 'kill -INT $$') to terminate
59_MSG_
60
61    # Set initial alarm
62    alarm(5);
63
64    # Just hang around
65    while (1) {
66        sleep(10);
67    }
68}
69
70### Subroutines ###
71
72sub EventHandler
73{
74    my ($regis_q, $event_q) = @_;
75
76    my %callbacks;   # Registered callback queues
77
78    while (1) {
79        # Check for any registrations
80        while (my ($event_type, $q) = $regis_q->dequeue_nb(2)) {
81            if ($q) {
82                $callbacks{$event_type} = $q;
83            } else {
84                warn("BUG: Bad callback registration for event type $event_type\n");
85            }
86        }
87
88        # Wait for event
89        if (my $event = $event_q->dequeue()) {
90            # Send event to appropriate queue
91            if (exists($callbacks{$event})) {
92                $callbacks{$event}->enqueue($event);
93            } else {
94                warn("WARNING: No callback for event type $event\n");
95            }
96        }
97    }
98}
99
100
101sub CallBack
102{
103    my $event_type = shift;   # The type of event I'm handling
104    my $regis_q    = shift;
105
106    # Announce registration
107    my $tid = threads->tid();
108    print("Callback thread $tid registering for $event_type events\n");
109
110    # Register my queue for my type of event
111    my $q = Thread::Queue->new();
112    $regis_q->enqueue($event_type, $q);
113
114    # Process loop
115    while (1) {
116        # Wait for event callback
117        my $item = $q->dequeue();
118        # Process event
119        print("Callback thread $tid notified of $item event\n") if $item;
120    }
121}
122
123# EOF
124