Coro/Coro/Semaphore.pm

=head1 NAME

Coro::Semaphore - non-binary semaphores

=head1 SYNOPSIS

 use Coro::Semaphore;

 $sig = new Coro::Semaphore [initial value];

 $sig->down; # wait for signal

 # ... some other "thread"

 $sig->up;

=head1 DESCRIPTION

This module implements counting semaphores. You can initialize a mutex
with any level of parallel users, that is, you can intialize a sempahore
that can be C<down>ed more than once until it blocks. There is no owner
associated with semaphores, so one coroutine can C<down> it while another
can C<up> it.

Counting semaphores are typically used to coordinate access to
resources, with the semaphore count initialized to the number of free
resources. Coroutines then increment the count when resources are added
and decrement the count when resources are removed.

=over 4

=cut

package Coro::Semaphore;

BEGIN { eval { require warnings } && warnings->unimport ("uninitialized") }

use Coro ();

$VERSION = 1.0;

=item new [inital count]

Creates a new sempahore object with the given initial lock count. The
default lock count is 1, which means it is unlocked by default. Zero (or
negative values) are also allowed, in which case the semaphore is locked
by default.

=cut

sub new {
   bless [defined $_[1] ? $_[1] : 1], $_[0];
}

=item $sem->down

Decrement the counter, therefore "locking" the semaphore. This method
waits until the semaphore is available if the counter is zero.

=item $status = $sem->timed_down($timeout)

Like C<down>, but returns false if semaphore couldn't be acquired within
$timeout seconds, otherwise true.

=cut

sub down {
   while ($_[0][0] <= 0) {
      push @{$_[0][1]}, $Coro::current;
      Coro::schedule;
   }
   --$_[0][0];
}

sub timed_down {
   require Coro::Timer;
   my $timeout = Coro::Timer::timeout($_[1]);

   while ($_[0][0] <= 0) {
      push @{$_[0][1]}, $Coro::current;
      Coro::schedule;
      if ($timeout) {
         # ugly as hell. slow, too, btw!
         for (0..$#{$_[0][1]}) {
            if ($_[0][1][$_] == $Coro::current) {
               splice @{$_[0][1]}, $_, 1;
               return;
            }
         }
         die;
      }
   }

   --$_[0][0];
   return 1;
}

=item $sem->up

Unlock the semaphore again.

=cut

sub up {
   if (++$_[0][0] > 0) {
      (shift @{$_[0][1]})->ready if @{$_[0][1]};
   }
}

=item $sem->try

Try to C<down> the semaphore. Returns true when this was possible,
otherwise return false and leave the semaphore unchanged.

=cut

sub try {
   if ($_[0][0] > 0) {
      --$_[0][0];
      return 1;
   } else {
      return 0;
   }
}

=item $sem->waiters

In scalar context, returns the number of coroutines waiting for this
semaphore.

=cut

sub waiters {
   @{$_[0][1]};
}

=item $guard = $sem->guard

This method calls C<down> and then creates a guard object. When the guard
object is destroyed it automatically calls C<up>.

=item $guard = $sem->timed_guard($timeout)

Like C<guard>, but returns undef if semaphore couldn't be acquired within
$timeout seconds, otherwise the guard object.

=cut

sub guard {
   &down;
   # double indirection because bless works on the referenced
   # object, not (only) on the reference itself.
   bless \\$_[0], Coro::Semaphore::guard::;
}

sub timed_guard {
   &timed_down
      ? bless \\$_[0], Coro::Semaphore::guard::
      : ();
}

sub Coro::Semaphore::guard::DESTROY {
   &up(${${$_[0]}});
}

1;

=back

=head1 AUTHOR

 Marc Lehmann <pcg@goof.com>
 http://home.schmorp.de/

=cut

Revision:	1.42
Committed:	Wed Jan 12 20:35:35 2005 UTC (19 years, 4 months ago) by root
Branch:	MAIN
Changes since 1.41:	+1 -1 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	Coro::Semaphore - non-binary semaphores
4
5	=head1 SYNOPSIS
6
7	use Coro::Semaphore;
8
9	$sig = new Coro::Semaphore [initial value];
10
11	$sig->down; # wait for signal
12
13	# ... some other "thread"
14
15	$sig->up;
16
17	=head1 DESCRIPTION
18
19	This module implements counting semaphores. You can initialize a mutex
20	with any level of parallel users, that is, you can intialize a sempahore
21	that can be C<down>ed more than once until it blocks. There is no owner
22	associated with semaphores, so one coroutine can C<down> it while another
23	can C<up> it.
24
25	Counting semaphores are typically used to coordinate access to
26	resources, with the semaphore count initialized to the number of free
27	resources. Coroutines then increment the count when resources are added
28	and decrement the count when resources are removed.
29
30	=over 4
31
32	=cut
33
34	package Coro::Semaphore;
35
36	BEGIN { eval { require warnings } && warnings->unimport ("uninitialized") }
37
38	use Coro ();
39
40	$VERSION = 1.0;
41
42	=item new [inital count]
43
44	Creates a new sempahore object with the given initial lock count. The
45	default lock count is 1, which means it is unlocked by default. Zero (or
46	negative values) are also allowed, in which case the semaphore is locked
47	by default.
48
49	=cut
50
51	sub new {
52	bless [defined $_[1] ? $_[1] : 1], $_[0];
53	}
54
55	=item $sem->down
56
57	Decrement the counter, therefore "locking" the semaphore. This method
58	waits until the semaphore is available if the counter is zero.
59
60	=item $status = $sem->timed_down($timeout)
61
62	Like C<down>, but returns false if semaphore couldn't be acquired within
63	$timeout seconds, otherwise true.
64
65	=cut
66
67	sub down {
68	while ($_[0][0] <= 0) {
69	push @{$_[0][1]}, $Coro::current;
70	Coro::schedule;
71	}
72	--$_[0][0];
73	}
74
75	sub timed_down {
76	require Coro::Timer;
77	my $timeout = Coro::Timer::timeout($_[1]);
78
79	while ($_[0][0] <= 0) {
80	push @{$_[0][1]}, $Coro::current;
81	Coro::schedule;
82	if ($timeout) {
83	# ugly as hell. slow, too, btw!
84	for (0..$#{$_[0][1]}) {
85	if ($_[0][1][$_] == $Coro::current) {
86	splice @{$_[0][1]}, $_, 1;
87	return;
88	}
89	}
90	die;
91	}
92	}
93
94	--$_[0][0];
95	return 1;
96	}
97
98	=item $sem->up
99
100	Unlock the semaphore again.
101
102	=cut
103
104	sub up {
105	if (++$_[0][0] > 0) {
106	(shift @{$_[0][1]})->ready if @{$_[0][1]};
107	}
108	}
109
110	=item $sem->try
111
112	Try to C<down> the semaphore. Returns true when this was possible,
113	otherwise return false and leave the semaphore unchanged.
114
115	=cut
116
117	sub try {
118	if ($_[0][0] > 0) {
119	--$_[0][0];
120	return 1;
121	} else {
122	return 0;
123	}
124	}
125
126	=item $sem->waiters
127
128	In scalar context, returns the number of coroutines waiting for this
129	semaphore.
130
131	=cut
132
133	sub waiters {
134	@{$_[0][1]};
135	}
136
137	=item $guard = $sem->guard
138
139	This method calls C<down> and then creates a guard object. When the guard
140	object is destroyed it automatically calls C<up>.
141
142	=item $guard = $sem->timed_guard($timeout)
143
144	Like C<guard>, but returns undef if semaphore couldn't be acquired within
145	$timeout seconds, otherwise the guard object.
146
147	=cut
148
149	sub guard {
150	&down;
151	# double indirection because bless works on the referenced
152	# object, not (only) on the reference itself.
153	bless \\$_[0], Coro::Semaphore::guard::;
154	}
155
156	sub timed_guard {
157	&timed_down
158	? bless \\$_[0], Coro::Semaphore::guard::
159	: ();
160	}
161
162	sub Coro::Semaphore::guard::DESTROY {
163	&up(${${$_[0]}});
164	}
165
166	1;
167
168	=back
169
170	=head1 AUTHOR
171
172	Marc Lehmann <pcg@goof.com>
173	http://home.schmorp.de/
174
175	=cut
176