How to pause and resume a multithread perl script? - multithreading

Question

I have written the perl script to pause and resume.When the user enters Ctrl+c it has to pause and on pressing c it should resume. But is not working properly as expected. Can anyone help me on this what mistake i am making:
use strict;
use threads;
use threads::shared;
use Thread::Suspend;
use Lens;
$SIG{'INT'} = 'Pause';
#$| = 1;
print chr(7);
my $nthreads = 64;
my #thrs;
for(1..$nthreads)
{
print "START $_ \n";
my ($thr) = threads->create(\&worker, $_);
push #thrs ,$thr;
}
$_->join for #thrs;
exit;
sub worker
{
my $id = shift;
my $tmp;
my $lens = Lens->new("172.16.1.65:2000");
die "cannot create object" unless defined $lens;
die "cannot connect to XRay at " unless defined $lens->open("172.16.1.65:2000");
for(1..100000)
{
print "Thread $id \n";
}
print "$id>LOAD EXIT\n";
}
sub Pause
{
sleep(1);
print "\nCaught ^C\n";
print "Press \"c\" to continue, \"e\" to exit: ";
$_->suspend() for #thrs;
while (1)
{
my $input = lc(getc());
chomp ($input);
if ($input eq 'c') {
#clock($hour,$min,$sec);
$_->resume() for #thrs;
return;
}
elsif ($input eq 'e') {
exit 1;
}
}
}

Answer 1

Well, you haven't been too specific as to how it's "not working properly". But I would suggest looking at using Thread::Semaphore for a 'suspend' mechanism.
I would also suggest not using signal and instead doing something like:
#!/usr/bin/perl
use strict;
use warnings;
use threads;
use Thread::Semaphore;
use Term::ReadKey;
my $nthreads = 64;
my $thread_semaphore = Thread::Semaphore->new($nthreads);
sub worker {
for ( 1 .. 10 ) {
$thread_semaphore->down();
print threads->self->tid(), "\n";
sleep 1;
$thread_semaphore->up();
}
}
for ( 1 .. $nthreads ) {
threads->create( \&worker );
}
my $keypress;
ReadMode 4;
while ( threads->list(threads::running) ) {
while ( not defined( $keypress = ReadKey(-1) )
and threads->list(threads::running) )
{
print "Waiting\nRunning:". threads->list(threads::running) . "\n";
sleep 1;
}
print "Got $keypress\n";
if ( $keypress eq "p" ) {
print "Pausing...";
$thread_semaphore -> down_force($nthreads);
print "All paused\n";
}
if ( $keypress eq "c" ) {
print "Resuming...";
$thread_semaphore -> up ( $nthreads );
}
}
ReadMode 0;
foreach my $thr ( threads->list ) {
$thr->join();
}
It'll 'suspend' by setting the semaphores to zero (or negative) and relies on the threads checking if they should be stopping here or not.
I think the root of your problem though, will probably be signal propagation - your signal handler is global across your threads. You might find configuring $SIG{'INT'} for your threads separately will yield better results. (E.g. set the signal handler to 'IGNORE' at the start of your code, and set specific ones in the thread/main once the threads have been spawned).