Perl how to join all threads - perl

Question

My code is like below:
use threads;
use threads::shared;
use Thread::Queue;
my $q = Thread::Queue->new();
my #threads = ();
my $run :shared = 1;
$SIG{'TERM'} = sub {
$run = 0;
$q->enqueue('exit');
foreach(#threads){
$_->join();
}
};
push #threads, threads->create(proc1);
push #threads, threads->create(proc2);
sub proc1 {
while($p = $q->dequeue()){
if($p eq 'exit'){
last;
}
.....
}
$q->end();
threads->exit();
}
sub proc2 {
while($run){
.....
}
}
On TERM signal im trying to wait till all threads are ended. However, whenever I pass TERM signal my program gets terminated with an error
Segmentation fault
How to fix this ?

Answer 1

Assuming threads->create(proc1) even works (and that would only be because you didn't use use strict; as you should), then your program exits immediately after creating the threads. You need to have your main thread wait for the children threads to finish.
Fixing that problem (and applying some simplifications) results in the following:
use strict;
use warnings;
use threads;
use threads::shared;
use Thread::Queue 3.01 qw( );
my $q = Thread::Queue->new();
my $run :shared = 1;
$SIG{TERM} = sub {
print("Received SIGTERM. Shutting down...\n");
$run = 0;
$q->end();
};
print("$$\n");
threads->create(\&proc1);
threads->create(\&proc2);
$_->join() for threads->list();
sub proc1 {
while(my $p = $q->dequeue()) {
sleep 1; # Placeholder
}
}
sub proc2 {
while($run){
sleep 1; # Placeholder
}
}
I don't get a seg fault, but the program doesn't exit either. The signal handler is simply not called. It's because Perl is waiting for join to return before calling the signal handler. You can solve that by polling the list of joinable threads. In other words, replace
$_->join() for threads->list();
with
my $running_threads = 2;
while ($running_threads) {
for my $thread (threads->list(threads::joinable)) {
$thread->join();
$running_threads--;
}
sleep 1;
}