| 1 |
=head1 NAME |
| 2 |
|
| 3 |
Coro::Semaphore - counting semaphores |
| 4 |
|
| 5 |
=head1 SYNOPSIS |
| 6 |
|
| 7 |
use Coro; |
| 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 thread can C<down> it while another can |
| 23 |
C<up> it (or vice versa), C<up> can be called before C<down> and so on: |
| 24 |
the semaphore is really just an integer counter that optionally blocks |
| 25 |
when it is 0. |
| 26 |
|
| 27 |
Counting semaphores are typically used to coordinate access to |
| 28 |
resources, with the semaphore count initialized to the number of free |
| 29 |
resources. Threads then increment the count when resources are added |
| 30 |
and decrement the count when resources are removed. |
| 31 |
|
| 32 |
You don't have to load C<Coro::Semaphore> manually, it will be loaded |
| 33 |
automatically when you C<use Coro> and call the C<new> constructor. |
| 34 |
|
| 35 |
=over 4 |
| 36 |
|
| 37 |
=cut |
| 38 |
|
| 39 |
package Coro::Semaphore; |
| 40 |
|
| 41 |
use common::sense; |
| 42 |
|
| 43 |
use Coro (); |
| 44 |
|
| 45 |
our $VERSION = 6.23; |
| 46 |
|
| 47 |
=item new [inital count] |
| 48 |
|
| 49 |
Creates a new sempahore object with the given initial lock count. The |
| 50 |
default lock count is 1, which means it is unlocked by default. Zero (or |
| 51 |
negative values) are also allowed, in which case the semaphore is locked |
| 52 |
by default. |
| 53 |
|
| 54 |
=item $sem->count |
| 55 |
|
| 56 |
Returns the current semaphore count. |
| 57 |
|
| 58 |
=item $sem->adjust ($diff) |
| 59 |
|
| 60 |
Atomically adds the amount given to the current semaphore count. If the |
| 61 |
count becomes positive, wakes up any waiters. Does not block if the count |
| 62 |
becomes negative, however. |
| 63 |
|
| 64 |
=item $sem->down |
| 65 |
|
| 66 |
Decrement the counter, therefore "locking" the semaphore. This method |
| 67 |
waits until the semaphore is available if the counter is zero. |
| 68 |
|
| 69 |
=item $sem->wait |
| 70 |
|
| 71 |
Similar to C<down>, but does not actually decrement the counter. Instead, |
| 72 |
when this function returns, a following call to C<down> or C<try> is |
| 73 |
guaranteed to succeed without blocking, until the next thread switch |
| 74 |
(C<cede> etc.). |
| 75 |
|
| 76 |
Note that using C<wait> is much less efficient than using C<down>, so try |
| 77 |
to prefer C<down> whenever possible. |
| 78 |
|
| 79 |
=item $sem->wait ($callback) |
| 80 |
|
| 81 |
If you pass a callback argument to C<wait>, it will not wait, but |
| 82 |
immediately return. The callback will be called as soon as the semaphore |
| 83 |
becomes available (which might be instantly), and gets passed the |
| 84 |
semaphore as first argument. |
| 85 |
|
| 86 |
The callback might C<down> the semaphore exactly once, might wake up other |
| 87 |
threads, but is I<NOT> allowed to block (switch to other threads). |
| 88 |
|
| 89 |
=cut |
| 90 |
|
| 91 |
#=item $status = $sem->timed_down ($timeout) |
| 92 |
# |
| 93 |
#Like C<down>, but returns false if semaphore couldn't be acquired within |
| 94 |
#$timeout seconds, otherwise true. |
| 95 |
|
| 96 |
#sub timed_down { |
| 97 |
# require Coro::Timer; |
| 98 |
# my $timeout = Coro::Timer::timeout ($_[1]); |
| 99 |
# |
| 100 |
# while ($_[0][0] <= 0) { |
| 101 |
# push @{$_[0][1]}, $Coro::current; |
| 102 |
# &Coro::schedule; |
| 103 |
# if ($timeout) { |
| 104 |
# # ugly as hell. slow, too, btw! |
| 105 |
# for (0..$#{$_[0][1]}) { |
| 106 |
# if ($_[0][1][$_] == $Coro::current) { |
| 107 |
# splice @{$_[0][1]}, $_, 1; |
| 108 |
# return; |
| 109 |
# } |
| 110 |
# } |
| 111 |
# die; |
| 112 |
# } |
| 113 |
# } |
| 114 |
# |
| 115 |
# --$_[0][0]; |
| 116 |
# return 1; |
| 117 |
#} |
| 118 |
|
| 119 |
=item $sem->up |
| 120 |
|
| 121 |
Unlock the semaphore again. |
| 122 |
|
| 123 |
=item $sem->try |
| 124 |
|
| 125 |
Try to C<down> the semaphore. Returns true when this was possible, |
| 126 |
otherwise return false and leave the semaphore unchanged. |
| 127 |
|
| 128 |
=item $sem->waiters |
| 129 |
|
| 130 |
In scalar context, returns the number of threads waiting for this |
| 131 |
semaphore. |
| 132 |
|
| 133 |
=item $guard = $sem->guard |
| 134 |
|
| 135 |
This method calls C<down> and then creates a guard object. When the guard |
| 136 |
object is destroyed it automatically calls C<up>. |
| 137 |
|
| 138 |
=cut |
| 139 |
|
| 140 |
sub guard { |
| 141 |
&down; |
| 142 |
bless [$_[0]], Coro::Semaphore::guard:: |
| 143 |
} |
| 144 |
|
| 145 |
#=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 |
|
| 156 |
sub Coro::Semaphore::guard::DESTROY { |
| 157 |
&up($_[0][0]); |
| 158 |
} |
| 159 |
|
| 160 |
=back |
| 161 |
|
| 162 |
=head1 AUTHOR |
| 163 |
|
| 164 |
Marc Lehmann <schmorp@schmorp.de> |
| 165 |
http://home.schmorp.de/ |
| 166 |
|
| 167 |
=cut |
| 168 |
|
| 169 |
1 |
| 170 |
|
