NAME
MCE::Shared::Condvar - Condvar helper class
VERSION
This document describes MCE::Shared::Condvar version 1.881
DESCRIPTION
This helper class for MCE::Shared provides a Scalar, Mutex, and primitives for conditional locking.
SYNOPSIS
use MCE::Shared;
my $cv = MCE::Shared->condvar( 0 );
# OO interface
$val = $cv->set( $val );
$val = $cv->get();
$len = $cv->len();
# conditional locking primitives
$cv->lock();
$cv->unlock();
$cv->broadcast(0.05); # delay before broadcasting
$cv->broadcast();
$cv->signal(0.05); # delay before signaling
$cv->signal();
$cv->timedwait(2.5);
$cv->wait();
# included, sugar methods without having to call set/get explicitly
$val = $cv->append( $string ); # $val .= $string
$val = $cv->decr(); # --$val
$val = $cv->decrby( $number ); # $val -= $number
$val = $cv->getdecr(); # $val--
$val = $cv->getincr(); # $val++
$val = $cv->incr(); # ++$val
$val = $cv->incrby( $number ); # $val += $number
$old = $cv->getset( $new ); # $o = $v, $v = $n, $oEXAMPLE
The following example demonstrates barrier synchronization.
use MCE;
use MCE::Shared;
use Time::HiRes qw(usleep);
my $num_workers = 8;
my $count = MCE::Shared->condvar(0);
my $state = MCE::Shared->scalar('ready');
my $microsecs = ( $^O =~ /mswin|mingw|msys|cygwin/i ) ? 0 : 200;
# The lock is released upon entering ->broadcast, ->signal, ->timedwait,
# and ->wait. For performance reasons, the condition variable is *not*
# re-locked prior to exiting the call. Therefore, obtain the lock when
# synchronization is desired subsequently.
sub barrier_sync {
usleep($microsecs) while $state->get eq 'down';
$count->lock;
$state->set('up'), $count->incr;
if ($count->get == $num_workers) {
$count->decr, $state->set('down');
$count->broadcast;
}
else {
$count->wait while $state->get eq 'up';
$count->lock;
$state->set('ready') if $count->decr == 0;
$count->unlock;
}
}
sub user_func {
my $id = MCE->wid;
for (1 .. 400) {
MCE->print("$_: $id\n");
barrier_sync(); # made possible by MCE::Shared::Condvar
# MCE->sync(); # same thing via the MCE-Core API
}
}
my $mce = MCE->new(
max_workers => $num_workers,
user_func => \&user_func
)->run;
# Time taken from a 2.6 GHz machine running Mac OS X.
# threads::shared: 0.207s Perl threads
# forks::shared: 36.426s child processes
# MCE::Shared: 0.353s child processes
# MCE Sync: 0.062s child processesAPI DOCUMENTATION
MCE::Shared::Condvar->new ( )
Called by MCE::Shared for constructing a shared-condvar object.
MCE::Shared->condvar ( [ value ] )
Constructs a new condition variable. Its value defaults to 0 when value is not specified.
use MCE::Shared;
$cv = MCE::Shared->condvar( 100 );
$cv = MCE::Shared->condvar;set ( value )
Sets the value associated with the cv object. The new value is returned in scalar context.
$val = $cv->set( 10 );
$cv->set( 10 );get
Returns the value associated with the cv object.
$val = $cv->get;len
Returns the length of the value. It returns the undef value if the value is not defined.
$len = $var->len;lock
Attempts to grab the lock and waits if not available. Multiple calls to $cv->lock by the same process or thread is safe. The mutex will remain locked until $cv->unlock is called.
$cv->lock;unlock
Releases the lock. A held lock by an exiting process or thread is released automatically.
$cv->unlock;signal ( [ floating_seconds ] )
Releases a held lock on the variable. Then, unblocks one process or thread that's waiting on that variable. The variable is *not* locked upon return.
Optionally, delay floating_seconds before signaling.
$count->signal;
$count->signal( 0.5 );broadcast ( [ floating_seconds ] )
The broadcast method works similarly to signal. It releases a held lock on the variable. Then, unblocks all the processes or threads that are blocked in a condition wait on the variable, rather than only one. The variable is *not* locked upon return.
Optionally, delay floating_seconds before broadcasting.
$count->broadcast;
$count->broadcast( 0.5 );wait
Releases a held lock on the variable. Then, waits until another thread does a signal or broadcast for the same variable. The variable is *not* locked upon return.
$count->wait() while $state->get() eq "bar";timedwait ( floating_seconds )
Releases a held lock on the variable. Then, waits until another thread does a signal or broadcast for the same variable or if the timeout exceeds floating_seconds.
A false value is returned if the timeout is reached, and a true value otherwise. In either case, the variable is *not* locked upon return.
$count->timedwait( 10 ) while $state->get() eq "foo";SUGAR METHODS
This module is equipped with sugar methods to not have to call set and get explicitly. In shared context, the benefit is atomicity and reduction in inter-process communication.
The API resembles a subset of the Redis primitives https://redis.io/commands#strings without the key argument.
append ( value )
Appends a value at the end of the current value and returns its new length.
$len = $cv->append( "foo" );decr
Decrements the value by one and returns its new value.
$num = $cv->decr;decrby ( number )
Decrements the value by the given number and returns its new value.
$num = $cv->decrby( 2 );getdecr
Decrements the value by one and returns its old value.
$old = $cv->getdecr;getincr
Increments the value by one and returns its old value.
$old = $cv->getincr;getset ( value )
Sets the value and returns its old value.
$old = $cv->getset( "baz" );incr
Increments the value by one and returns its new value.
$num = $cv->incr;incrby ( number )
Increments the value by the given number and returns its new value.
$num = $cv->incrby( 2 );CHAMENEOS DEMONSTRATION
The MCE example is derived from the chameneos example by Jonathan DePeri and Andrew Rodland.
use 5.010;
use strict;
use warnings;
use MCE::Hobo;
use MCE::Shared;
use Time::HiRes 'time';
die 'No argument given' if not @ARGV;
my $start = time;
my %color = ( blue => 1, red => 2, yellow => 4 );
my ( @colors, @complement );
@colors[values %color] = keys %color;
for my $triple (
[qw(blue blue blue)],
[qw(red red red)],
[qw(yellow yellow yellow)],
[qw(blue red yellow)],
[qw(blue yellow red)],
[qw(red blue yellow)],
[qw(red yellow blue)],
[qw(yellow red blue)],
[qw(yellow blue red)],
) {
$complement[ $color{$triple->[0]} | $color{$triple->[1]} ] =
$color{$triple->[2]};
}
my @numbers = qw(zero one two three four five six seven eight nine);
sub display_complements
{
for my $i (1, 2, 4) {
for my $j (1, 2, 4) {
print "$colors[$i] + $colors[$j] -> $colors[ $complement[$i | $j] ]\n";
}
}
print "\n";
}
sub num2words
{
join ' ', '', map $numbers[$_], split //, shift;
}
# Construct condvars and queues first before other shared objects or in
# any order when IO::FDPass is installed, used by MCE::Shared::Server.
my $meetings = MCE::Shared->condvar();
tie my @creatures, 'MCE::Shared';
tie my $first, 'MCE::Shared', undef;
tie my @met, 'MCE::Shared';
tie my @met_self, 'MCE::Shared';
sub chameneos
{
my $id = shift;
while (1) {
$meetings->lock();
unless ($meetings->get()) {
$meetings->unlock();
last;
}
if (defined $first) {
$creatures[$first] = $creatures[$id] =
$complement[$creatures[$first] | $creatures[$id]];
$met_self[$first]++ if ($first == $id);
$met[$first]++; $met[$id]++;
$meetings->decr();
$first = undef;
# Unlike threads::shared (condvar) which retains the lock
# while in the scope, MCE::Shared signal and wait methods
# must be called prior to leaving the block, due to lock
# being released upon return.
$meetings->signal();
}
else {
$first = $id;
$meetings->wait(); # ditto ^^
}
}
}
sub pall_mall
{
my $N = shift;
@creatures = map $color{$_}, @_;
my @threads;
print " ", join(" ", @_);
$meetings->set($N);
for (0 .. $#creatures) {
$met[$_] = $met_self[$_] = 0;
push @threads, MCE::Hobo->create(\&chameneos, $_);
}
for (@threads) {
$_->join();
}
$meetings->set(0);
for (0 .. $#creatures) {
print "\n$met[$_]", num2words($met_self[$_]);
$meetings->incrby($met[$_]);
}
print "\n", num2words($meetings->get()), "\n\n";
}
display_complements();
pall_mall($ARGV[0], qw(blue red yellow));
pall_mall($ARGV[0], qw(blue red yellow red yellow blue red yellow red blue));
printf "duration: %0.03f\n", time - $start;CREDITS
The conditional locking feature is inspired by threads::shared.
LIMITATIONS
Perl must have IO::FDPass for constructing a shared condvar or queue while the shared-manager process is running. For platforms where IO::FDPass isn't possible, construct condvar and queue before other classes. On systems without IO::FDPass, the manager process is delayed until sharing other classes or started explicitly.
use MCE::Shared;
my $has_IO_FDPass = $INC{'IO/FDPass.pm'} ? 1 : 0;
my $cv = MCE::Shared->condvar();
my $que = MCE::Shared->queue();
MCE::Shared->start() unless $has_IO_FDPass;Regarding mce_open, IO::FDPass is needed for constructing a shared-handle from a non-shared handle not yet available inside the shared-manager process. The workaround is to have the non-shared handle made before the shared-manager is started. Passing a file by reference is fine for the three STD* handles.
# The shared-manager knows of \*STDIN, \*STDOUT, \*STDERR.
mce_open my $shared_in, "<", \*STDIN; # ok
mce_open my $shared_out, ">>", \*STDOUT; # ok
mce_open my $shared_err, ">>", \*STDERR; # ok
mce_open my $shared_fh1, "<", "/path/to/sequence.fasta"; # ok
mce_open my $shared_fh2, ">>", "/path/to/results.log"; # ok
mce_open my $shared_fh, ">>", \*NON_SHARED_FH; # requires IO::FDPassThe IO::FDPass module is known to work reliably on most platforms. Install 1.1 or later to rid of limitations described above.
perl -MIO::FDPass -le "print 'Cheers! Perl has IO::FDPass.'"INDEX
AUTHOR
Mario E. Roy, <marioeroy AT gmail DOT com>