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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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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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$sig->up; |
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=head1 DESCRIPTION |
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This module implements counting semaphores. You can initialize a mutex |
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with any level of parallel users, that is, you can intialize a sempahore |
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that can be C<down>ed more than once until it blocks. There is no owner |
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associated with semaphores, so one coroutine can C<down> it while another |
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can C<up> it. |
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|
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Counting semaphores are typically used to coordinate access to |
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resources, with the semaphore count initialized to the number of free |
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resources. Coroutines then increment the count when resources are added |
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and decrement the count when resources are removed. |
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=over 4 |
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=cut |
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|
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package Coro::Semaphore; |
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no warnings; |
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|
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use Coro (); |
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$VERSION = 4.9; |
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=item new [inital count] |
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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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|
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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 $sem->count |
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Returns the current semaphore count. |
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=cut |
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sub count { |
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$_[0][0] |
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} |
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=item $sem->adjust ($diff) |
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Atomically adds the amount given to the current semaphore count. If the |
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count becomes positive, wakes up any waiters. Does not block if the count |
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becomes negative, however. |
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=cut |
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|
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sub adjust { |
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# basically a weird copy of up |
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if (($_[0][0] += $_[1]) > 0) { |
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(shift @{$_[0][1]})->ready if @{$_[0][1]}; |
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} |
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} |
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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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=item $status = $sem->timed_down ($timeout) |
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Like C<down>, but returns false if semaphore couldn't be acquired within |
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$timeout seconds, otherwise true. |
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=cut |
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sub down { |
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while ($_[0][0] <= 0) { |
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push @{$_[0][1]}, $Coro::current; |
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&Coro::schedule; |
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} |
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--$_[0][0]; |
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} |
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sub timed_down { |
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require Coro::Timer; |
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my $timeout = Coro::Timer::timeout ($_[1]); |
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|
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while ($_[0][0] <= 0) { |
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push @{$_[0][1]}, $Coro::current; |
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&Coro::schedule; |
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if ($timeout) { |
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# ugly as hell. slow, too, btw! |
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for (0..$#{$_[0][1]}) { |
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if ($_[0][1][$_] == $Coro::current) { |
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splice @{$_[0][1]}, $_, 1; |
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return; |
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} |
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} |
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die; |
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} |
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} |
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|
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--$_[0][0]; |
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return 1; |
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} |
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=item $sem->up |
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Unlock the semaphore again. |
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=cut |
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sub up { |
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if (++$_[0][0] > 0) { |
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(shift @{$_[0][1]})->ready if @{$_[0][1]}; |
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} |
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} |
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=item $sem->try |
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Try to C<down> the semaphore. Returns true when this was possible, |
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otherwise return false and leave the semaphore unchanged. |
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=cut |
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sub try { |
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if ($_[0][0] > 0) { |
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--$_[0][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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=item $sem->waiters |
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In scalar context, returns the number of coroutines waiting for this |
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semaphore. |
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=cut |
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sub waiters { |
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@{$_[0][1]}; |
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} |
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=item $guard = $sem->guard |
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This method calls C<down> and then creates a guard object. When the guard |
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object is destroyed it automatically calls C<up>. |
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=item $guard = $sem->timed_guard ($timeout) |
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Like C<guard>, but returns undef if semaphore couldn't be acquired within |
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$timeout seconds, otherwise the guard object. |
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=cut |
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|
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sub guard { |
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&down; |
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# double indirection because bless works on the referenced |
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# object, not (only) on the reference itself. |
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bless \\$_[0], Coro::Semaphore::guard::; |
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} |
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sub timed_guard { |
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&timed_down |
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? bless \\$_[0], Coro::Semaphore::guard:: |
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: (); |
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} |
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sub Coro::Semaphore::guard::DESTROY { |
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&up(${${$_[0]}}); |
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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 <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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=cut |
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1 |
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