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=head1 NAME |
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Coro::Semaphore - non-binary semaphores |
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=head1 SYNOPSIS |
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|
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use Coro::Semaphore; |
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$sig = new Coro::Semaphore [initial value]; |
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$sig->down; # wait for signal |
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# ... some other "thread" |
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|
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$sig->up; |
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|
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=head1 DESCRIPTION |
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|
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This module implements counted semaphores. You can initialize a mutex |
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with any level of parallel users, that is, you can intialize a sempahore |
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that can be C<down>ed more than once until it blocks. There is no owner |
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associated with semaphores, so one coroutine can C<down> it while another |
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can C<up> it. |
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|
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Counting semaphores are typically used to coordinate access to |
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resources, with the semaphore count initialized to the number of free |
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resources. Coroutines then increment the count when resources are added |
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and decrement the count when resources are removed. |
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|
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=over 4 |
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=cut |
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|
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package Coro::Semaphore; |
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use Coro (); |
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$VERSION = 0.12; |
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=item new [inital count, default one] |
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Creates a new sempahore object with the given initial lock count. The |
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default lock count is 1, which means it is unlocked by default. Zero (or |
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negative values) are also allowed, in which case the semaphore is locked |
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by default. |
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|
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=cut |
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sub new { |
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bless [defined $_[1] ? $_[1] : 1], $_[0]; |
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} |
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=item $sem->down |
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Decrement the counter, therefore "locking" the semaphore. This method |
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waits until the semaphore is available if the counter is zero. |
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|
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=cut |
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|
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sub down { |
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my $self = shift; |
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while ($self->[0] <= 0) { |
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push @{$self->[1]}, $Coro::current; |
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Coro::schedule; |
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} |
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--$self->[0]; |
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} |
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|
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=item $sem->up |
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Unlock the semaphore again. |
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|
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=cut |
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|
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sub up { |
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my $self = shift; |
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if (++$self->[0] > 0) { |
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(shift @{$self->[1]})->ready if @{$self->[1]}; |
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} |
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} |
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|
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=item $sem->try |
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Try to C<down> the semaphore. Returns true when this was possible, |
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otherwise return false and leave the semaphore unchanged. |
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=cut |
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|
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sub try { |
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my $self = shift; |
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if ($self->[0] > 0) { |
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--$self->[0]; |
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return 1; |
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} else { |
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return 0; |
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} |
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} |
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1; |
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|
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=back |
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=head1 AUTHOR |
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|
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Marc Lehmann <pcg@goof.com> |
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http://www.goof.com/pcg/marc/ |
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=cut |
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