Initial Commit

database/perl/lib/Thread/Semaphore.pm

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+package Thread::Semaphore;
+
+use strict;
+use warnings;
+
+our $VERSION = '2.13';
+$VERSION = eval $VERSION;
+
+use threads::shared;
+use Scalar::Util 1.10 qw(looks_like_number);
+
+# Predeclarations for internal functions
+my ($validate_arg);
+
+# Create a new semaphore optionally with specified count (count defaults to 1)
+sub new {
+    my $class = shift;
+
+    my $val :shared = 1;
+    if (@_) {
+        $val = shift;
+        if (! defined($val) ||
+            ! looks_like_number($val) ||
+            (int($val) != $val))
+        {
+            require Carp;
+            $val = 'undef' if (! defined($val));
+            Carp::croak("Semaphore initializer is not an integer: $val");
+        }
+    }
+
+    return bless(\$val, $class);
+}
+
+# Decrement a semaphore's count (decrement amount defaults to 1)
+sub down {
+    my $sema = shift;
+    my $dec = @_ ? $validate_arg->(shift) : 1;
+
+    lock($$sema);
+    cond_wait($$sema) until ($$sema >= $dec);
+    $$sema -= $dec;
+}
+
+# Decrement a semaphore's count only if count >= decrement value
+#  (decrement amount defaults to 1)
+sub down_nb {
+    my $sema = shift;
+    my $dec = @_ ? $validate_arg->(shift) : 1;
+
+    lock($$sema);
+    my $ok = ($$sema >= $dec);
+    $$sema -= $dec if $ok;
+    return $ok;
+}
+
+# Decrement a semaphore's count even if the count goes below 0
+#  (decrement amount defaults to 1)
+sub down_force {
+    my $sema = shift;
+    my $dec = @_ ? $validate_arg->(shift) : 1;
+
+    lock($$sema);
+    $$sema -= $dec;
+}
+
+# Decrement a semaphore's count with timeout
+#  (timeout in seconds; decrement amount defaults to 1)
+sub down_timed {
+    my $sema = shift;
+    my $timeout = $validate_arg->(shift);
+    my $dec = @_ ? $validate_arg->(shift) : 1;
+
+    lock($$sema);
+    my $abs = time() + $timeout;
+    until ($$sema >= $dec) {
+        return if !cond_timedwait($$sema, $abs);
+    }
+    $$sema -= $dec;
+    return 1;
+}
+
+# Increment a semaphore's count (increment amount defaults to 1)
+sub up {
+    my $sema = shift;
+    my $inc = @_ ? $validate_arg->(shift) : 1;
+
+    lock($$sema);
+    ($$sema += $inc) > 0 and cond_broadcast($$sema);
+}
+
+### Internal Functions ###
+
+# Validate method argument
+$validate_arg = sub {
+    my $arg = shift;
+
+    if (! defined($arg) ||
+        ! looks_like_number($arg) ||
+        (int($arg) != $arg) ||
+        ($arg < 1))
+    {
+        require Carp;
+        my ($method) = (caller(1))[3];
+        $method =~ s/Thread::Semaphore:://;
+        $arg = 'undef' if (! defined($arg));
+        Carp::croak("Argument to semaphore method '$method' is not a positive integer: $arg");
+    }
+
+    return $arg;
+};
+
+1;
+
+=head1 NAME
+
+Thread::Semaphore - Thread-safe semaphores
+
+=head1 VERSION
+
+This document describes Thread::Semaphore version 2.13
+
+=head1 SYNOPSIS
+
+    use Thread::Semaphore;
+    my $s = Thread::Semaphore->new();
+    $s->down();   # Also known as the semaphore P operation.
+    # The guarded section is here
+    $s->up();     # Also known as the semaphore V operation.
+
+    # Decrement the semaphore only if it would immediately succeed.
+    if ($s->down_nb()) {
+        # The guarded section is here
+        $s->up();
+    }
+
+    # Forcefully decrement the semaphore even if its count goes below 0.
+    $s->down_force();
+
+    # The default value for semaphore operations is 1
+    my $s = Thread::Semaphore->new($initial_value);
+    $s->down($down_value);
+    $s->up($up_value);
+    if ($s->down_nb($down_value)) {
+        ...
+        $s->up($up_value);
+    }
+    $s->down_force($down_value);
+
+=head1 DESCRIPTION
+
+Semaphores provide a mechanism to regulate access to resources.  Unlike
+locks, semaphores aren't tied to particular scalars, and so may be used to
+control access to anything you care to use them for.
+
+Semaphores don't limit their values to zero and one, so they can be used to
+control access to some resource that there may be more than one of (e.g.,
+filehandles).  Increment and decrement amounts aren't fixed at one either,
+so threads can reserve or return multiple resources at once.
+
+=head1 METHODS
+
+=over 8
+
+=item ->new()
+
+=item ->new(NUMBER)
+
+C<new> creates a new semaphore, and initializes its count to the specified
+number (which must be an integer).  If no number is specified, the
+semaphore's count defaults to 1.
+
+=item ->down()
+
+=item ->down(NUMBER)
+
+The C<down> method decreases the semaphore's count by the specified number
+(which must be an integer >= 1), or by one if no number is specified.
+
+If the semaphore's count would drop below zero, this method will block
+until such time as the semaphore's count is greater than or equal to the
+amount you're C<down>ing the semaphore's count by.
+
+This is the semaphore "P operation" (the name derives from the Dutch
+word "pak", which means "capture" -- the semaphore operations were
+named by the late Dijkstra, who was Dutch).
+
+=item ->down_nb()
+
+=item ->down_nb(NUMBER)
+
+The C<down_nb> method attempts to decrease the semaphore's count by the
+specified number (which must be an integer >= 1), or by one if no number
+is specified.
+
+If the semaphore's count would drop below zero, this method will return
+I<false>, and the semaphore's count remains unchanged.  Otherwise, the
+semaphore's count is decremented and this method returns I<true>.
+
+=item ->down_force()
+
+=item ->down_force(NUMBER)
+
+The C<down_force> method decreases the semaphore's count by the specified
+number (which must be an integer >= 1), or by one if no number is specified.
+This method does not block, and may cause the semaphore's count to drop
+below zero.
+
+=item ->down_timed(TIMEOUT)
+
+=item ->down_timed(TIMEOUT, NUMBER)
+
+The C<down_timed> method attempts to decrease the semaphore's count by 1
+or by the specified number within the specified timeout period given in
+seconds (which must be an integer >= 0).
+
+If the semaphore's count would drop below zero, this method will block
+until either the semaphore's count is greater than or equal to the
+amount you're C<down>ing the semaphore's count by, or until the timeout is
+reached.
+
+If the timeout is reached, this method will return I<false>, and the
+semaphore's count remains unchanged.  Otherwise, the semaphore's count is
+decremented and this method returns I<true>.
+
+=item ->up()
+
+=item ->up(NUMBER)
+
+The C<up> method increases the semaphore's count by the number specified
+(which must be an integer >= 1), or by one if no number is specified.
+
+This will unblock any thread that is blocked trying to C<down> the
+semaphore if the C<up> raises the semaphore's count above the amount that
+the C<down> is trying to decrement it by.  For example, if three threads
+are blocked trying to C<down> a semaphore by one, and another thread C<up>s
+the semaphore by two, then two of the blocked threads (which two is
+indeterminate) will become unblocked.
+
+This is the semaphore "V operation" (the name derives from the Dutch
+word "vrij", which means "release").
+
+=back
+
+=head1 NOTES
+
+Semaphores created by L<Thread::Semaphore> can be used in both threaded and
+non-threaded applications.  This allows you to write modules and packages
+that potentially make use of semaphores, and that will function in either
+environment.
+
+=head1 SEE ALSO
+
+Thread::Semaphore on MetaCPAN:
+L<https://metacpan.org/release/Thread-Semaphore>
+
+Code repository for CPAN distribution:
+L<https://github.com/Dual-Life/Thread-Semaphore>
+
+L<threads>, L<threads::shared>
+
+Sample code in the I<examples> directory of this distribution on CPAN.
+
+=head1 MAINTAINER
+
+Jerry D. Hedden, S<E<lt>jdhedden AT cpan DOT orgE<gt>>
+
+=head1 LICENSE
+
+This program is free software; you can redistribute it and/or modify it under
+the same terms as Perl itself.
+
+=cut