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=head1 NAME |
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Coro::Semaphore - counting semaphores |
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=head1 SYNOPSIS |
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use Coro; |
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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 thread can C<down> it while another can |
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C<up> it (or vice versa), C<up> can be called before C<down> and so on: |
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the semaphore is really just an integer counter that optionally blocks |
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when it is 0. |
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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. Threads then increment the count when resources are added |
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and decrement the count when resources are removed. |
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You don't have to load C<Coro::Semaphore> manually, it will be loaded |
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automatically when you C<use Coro> and call the C<new> constructor. |
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=over 4 |
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=cut |
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package Coro::Semaphore; |
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use common::sense; |
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use Coro (); |
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our $VERSION = 6.29; |
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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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=item $sem->count |
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Returns the current semaphore count. |
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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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=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 $sem->wait |
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Similar to C<down>, but does not actually decrement the counter. Instead, |
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when this function returns, a following call to C<down> or C<try> is |
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guaranteed to succeed without blocking, until the next thread switch |
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(C<cede> etc.). |
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Note that using C<wait> is much less efficient than using C<down>, so try |
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to prefer C<down> whenever possible. |
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=item $sem->wait ($callback) |
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If you pass a callback argument to C<wait>, it will not wait, but |
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immediately return. The callback will be called as soon as the semaphore |
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becomes available (which might be instantly), and gets passed the |
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semaphore as first argument. |
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The callback might C<down> the semaphore exactly once, might wake up other |
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threads, but is I<NOT> allowed to block (switch to other threads). |
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=cut |
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#=item $status = $sem->timed_down ($timeout) |
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# |
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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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#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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=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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=item $sem->waiters |
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In scalar context, returns the number of threads waiting for this |
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semaphore. Might accidentally cause WW3 if called in other contexts, so |
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don't use these. |
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=item $guard = $sem->guard |
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This method calls C<down> and then creates a guard object. When the guard |
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object is destroyed it automatically calls C<up>. |
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=cut |
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sub guard { |
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&down; |
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bless [$_[0]], Coro::Semaphore::guard:: |
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} |
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#=item $guard = $sem->timed_guard ($timeout) |
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# |
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#Like C<guard>, but returns undef if semaphore couldn't be acquired within |
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#$timeout seconds, otherwise the guard object. |
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#sub timed_guard { |
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# &timed_down |
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# ? bless \\$_[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][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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