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;

no warnings;

use Coro ();

$VERSION = 5.0;

=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.

=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 coroutine 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
coroutines, but is I<NOT> allowed to block (switch to other coroutines).

This is considered a rather experimental interface, and is subject to
change.

=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 coroutines 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;
   # double indirection because bless works on the referenced
   # object, not (only) on the reference itself.
   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]}});
}

=back

=head1 AUTHOR

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

=cut

1

Revision:	1.82
Committed:	Wed Nov 19 11:11:10 2008 UTC (15 years, 6 months ago) by root
Branch:	MAIN
Changes since 1.81:	+13 -0 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			Coro::Semaphore - non-binary semaphores
4
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			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	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	1.79	$VERSION = 5.0;
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			guaranteed to succeed without blocking, until the next coroutine switch
69			(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			coroutines, but is I<NOT> allowed to block (switch to other coroutines).
83
84			This is considered a rather experimental interface, and is subject to
85			change.
86
87	root	1.3	=cut
88
89	root	1.80	#=item $status = $sem->timed_down ($timeout)
90			#
91			#Like C<down>, but returns false if semaphore couldn't be acquired within
92			#$timeout seconds, otherwise true.
93
94			#sub timed_down {
95			# require Coro::Timer;
96			# my $timeout = Coro::Timer::timeout ($_[1]);
97			#
98			# while ($_[0][0] <= 0) {
99			# push @{$_[0][1]}, $Coro::current;
100			# &Coro::schedule;
101			# if ($timeout) {
102			# # ugly as hell. slow, too, btw!
103			# for (0..$#{$_[0][1]}) {
104			# if ($_[0][1][$_] == $Coro::current) {
105			# splice @{$_[0][1]}, $_, 1;
106			# return;
107			# }
108			# }
109			# die;
110			# }
111			# }
112			#
113			# --$_[0][0];
114			# return 1;
115			#}
116	root	1.1
117	root	1.3	=item $sem->up
118
119			Unlock the semaphore again.
120
121			=item $sem->try
122
123			Try to C<down> the semaphore. Returns true when this was possible,
124			otherwise return false and leave the semaphore unchanged.
125
126	root	1.15	=item $sem->waiters
127
128			In scalar context, returns the number of coroutines waiting for this
129			semaphore.
130
131	root	1.12	=item $guard = $sem->guard
132
133			This method calls C<down> and then creates a guard object. When the guard
134			object is destroyed it automatically calls C<up>.
135
136			=cut
137
138			sub guard {
139	root	1.16	&down;
140	root	1.13	# double indirection because bless works on the referenced
141			# object, not (only) on the reference itself.
142	root	1.26	bless \\$_[0], Coro::Semaphore::guard::;
143	root	1.25	}
144
145	root	1.80	#=item $guard = $sem->timed_guard ($timeout)
146			#
147			#Like C<guard>, but returns undef if semaphore couldn't be acquired within
148			#$timeout seconds, otherwise the guard object.
149
150			#sub timed_guard {
151			# &timed_down
152			# ? bless \\$_[0], Coro::Semaphore::guard::
153			# : ();
154			#}
155	root	1.12
156	root	1.25	sub Coro::Semaphore::guard::DESTROY {
157	root	1.16	&up(${${$_[0]}});
158	root	1.1	}
159
160			=back
161
162			=head1 AUTHOR
163
164	root	1.44	Marc Lehmann <schmorp@schmorp.de>
165	root	1.42	http://home.schmorp.de/
166	root	1.1
167			=cut
168
169	root	1.51	1
170