Coro/Coro/Semaphore.pm

=head1 NAME

Coro::Semaphore - counting 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 thread 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. Threads then increment the count when resources are added
and decrement the count when resources are removed.

=over 4

=cut

package Coro::Semaphore;

no warnings;

use Coro ();

$VERSION = 5.16;

=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.

=item $sem->count

Returns the current semaphore count.

=item $sem->adjust ($diff)

Atomically adds the amount given to the current semaphore count. If the
count becomes positive, wakes up any waiters. Does not block if the count
becomes negative, however.

=item $sem->down

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

=item $sem->wait

Similar to C<down>, but does not actually decrement the counter. Instead,
when this function returns, a following call to C<down> or C<try> is
guaranteed to succeed without blocking, until the next thread switch
(C<cede> etc.).

Note that using C<wait> is much less efficient than using C<down>, so try
to prefer C<down> whenever possible.

=item $sem->wait ($callback)

If you pass a callback argument to C<wait>, it will not wait, but
immediately return. The callback will be called as soon as the semaphore
becomes available (which might be instantly), and gets passed the
semaphore as first argument.

The callback might C<down> the semaphore exactly once, might wake up other
threads, but is I<NOT> allowed to block (switch to other threads).

=cut

#=item $status = $sem->timed_down ($timeout)
#
#Like C<down>, but returns false if semaphore couldn't be acquired within
#$timeout seconds, otherwise true.

#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.

=item $sem->try

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

=item $sem->waiters

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

=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>.

=cut

sub guard {
   &down;
   bless [$_[0]], Coro::Semaphore::guard::
}

#=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.

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

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

=back

=head1 AUTHOR

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

=cut

1

Revision:	1.98
Committed:	Mon Jul 20 23:46:28 2009 UTC (14 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-5_16
Changes since 1.97:	+1 -1 lines
Log Message:	5.16
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3	root	1.84	Coro::Semaphore - counting semaphores
4	root	1.1
5			=head1 SYNOPSIS
6
7			use Coro::Semaphore;
8
9	root	1.3	$sig = new Coro::Semaphore [initial value];
10	root	1.1
11			$sig->down; # wait for signal
12
13			# ... some other "thread"
14
15			$sig->up;
16
17			=head1 DESCRIPTION
18
19	root	1.16	This module implements counting semaphores. You can initialize a mutex
20	root	1.11	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	root	1.95	associated with semaphores, so one thread can C<down> it while another
23	root	1.11	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	root	1.95	resources. Threads then increment the count when resources are added
28	root	1.11	and decrement the count when resources are removed.
29
30	root	1.1	=over 4
31
32			=cut
33
34			package Coro::Semaphore;
35
36	root	1.61	no warnings;
37	root	1.20
38	root	1.5	use Coro ();
39	root	1.1
40	root	1.98	$VERSION = 5.16;
41	root	1.1
42	root	1.16	=item new [inital count]
43	root	1.3
44			Creates a new sempahore object with the given initial lock count. The
45	root	1.11	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	root	1.3
49	root	1.55	=item $sem->count
50
51			Returns the current semaphore count.
52
53	root	1.56	=item $sem->adjust ($diff)
54
55			Atomically adds the amount given to the current semaphore count. If the
56			count becomes positive, wakes up any waiters. Does not block if the count
57			becomes negative, however.
58
59	root	1.3	=item $sem->down
60
61			Decrement the counter, therefore "locking" the semaphore. This method
62			waits until the semaphore is available if the counter is zero.
63
64	root	1.81	=item $sem->wait
65
66			Similar to C<down>, but does not actually decrement the counter. Instead,
67			when this function returns, a following call to C<down> or C<try> is
68	root	1.95	guaranteed to succeed without blocking, until the next thread switch
69	root	1.81	(C<cede> etc.).
70
71			Note that using C<wait> is much less efficient than using C<down>, so try
72			to prefer C<down> whenever possible.
73
74	root	1.82	=item $sem->wait ($callback)
75
76			If you pass a callback argument to C<wait>, it will not wait, but
77			immediately return. The callback will be called as soon as the semaphore
78			becomes available (which might be instantly), and gets passed the
79			semaphore as first argument.
80
81			The callback might C<down> the semaphore exactly once, might wake up other
82	root	1.95	threads, but is I<NOT> allowed to block (switch to other threads).
83	root	1.82
84	root	1.3	=cut
85
86	root	1.80	#=item $status = $sem->timed_down ($timeout)
87			#
88			#Like C<down>, but returns false if semaphore couldn't be acquired within
89			#$timeout seconds, otherwise true.
90
91			#sub timed_down {
92			# require Coro::Timer;
93			# my $timeout = Coro::Timer::timeout ($_[1]);
94			#
95			# while ($_[0][0] <= 0) {
96			# push @{$_[0][1]}, $Coro::current;
97			# &Coro::schedule;
98			# if ($timeout) {
99			# # ugly as hell. slow, too, btw!
100			# for (0..$#{$_[0][1]}) {
101			# if ($_[0][1][$_] == $Coro::current) {
102			# splice @{$_[0][1]}, $_, 1;
103			# return;
104			# }
105			# }
106			# die;
107			# }
108			# }
109			#
110			# --$_[0][0];
111			# return 1;
112			#}
113	root	1.1
114	root	1.3	=item $sem->up
115
116			Unlock the semaphore again.
117
118			=item $sem->try
119
120			Try to C<down> the semaphore. Returns true when this was possible,
121			otherwise return false and leave the semaphore unchanged.
122
123	root	1.15	=item $sem->waiters
124
125	root	1.95	In scalar context, returns the number of threads waiting for this
126	root	1.15	semaphore.
127
128	root	1.12	=item $guard = $sem->guard
129
130			This method calls C<down> and then creates a guard object. When the guard
131			object is destroyed it automatically calls C<up>.
132
133			=cut
134
135			sub guard {
136	root	1.16	&down;
137	root	1.90	bless [$_[0]], Coro::Semaphore::guard::
138	root	1.25	}
139
140	root	1.80	#=item $guard = $sem->timed_guard ($timeout)
141			#
142			#Like C<guard>, but returns undef if semaphore couldn't be acquired within
143			#$timeout seconds, otherwise the guard object.
144
145			#sub timed_guard {
146			# &timed_down
147			# ? bless \\$_[0], Coro::Semaphore::guard::
148			# : ();
149			#}
150	root	1.12
151	root	1.25	sub Coro::Semaphore::guard::DESTROY {
152	root	1.90	&up($_[0][0]);
153	root	1.1	}
154
155			=back
156
157			=head1 AUTHOR
158
159	root	1.44	Marc Lehmann <schmorp@schmorp.de>
160	root	1.42	http://home.schmorp.de/
161	root	1.1
162			=cut
163
164	root	1.51	1
165