thread ids stringifying wrong in v5.12.4?

[samwyse]

I want to fire off a dozen threads, and keep track of which one is doing what in case one of them hangs. (They are all running diagnostic commands on networking equipment.) Unfortunately, I can't seem to save the thread ids in any useful way. Here's sample code:

#! perl -slw

use 5.012_000;
use strict;
use threads;

use Data::Dumper;

my %toc;
for my $i (1..3) {
    my $id = async { sleep 3*$i+5; $i };
    print Dumper($id);
    $toc{$id} = "starting thread $id, with \$i = $i";
}
print Dumper(\%toc);

sub joinable { threads->list( threads::joinable ) };
sub running { threads->list( threads::running ) };

while (my $count = scalar running) {
    sleep 1 until joinable;
    print "$toc{$_} => ", $_->join, "\n" for joinable;
}
print "all post-commands are complete\n";

When I run the above, I get back this, which looks like my thread ids are getting converted to "threads=XXX" when I try to use them as hash keys:

$VAR1 = bless( do{\(my $o = '25730180')}, 'threads' );

$VAR1 = bless( do{\(my $o = '26709332')}, 'threads' );

$VAR1 = bless( do{\(my $o = '27250780')}, 'threads' );

$VAR1 = {
          'threads=SCALAR(0x187b454)' => 'starting thread threads=SCAL
+AR(0x187b4
54), with $i = 3',
          'threads=SCALAR(0x193d404)' => 'starting thread threads=SCAL
+AR(0x193d4
04), with $i = 1',
          'threads=SCALAR(0x193d5b4)' => 'starting thread threads=SCAL
+AR(0x193d5
b4), with $i = 2'
        };

Use of uninitialized value within %toc in concatenation (.) or string 
+at test.pl line 25.
 => 1

Use of uninitialized value within %toc in concatenation (.) or string 
+at test.pl line 25.
 => 2

Use of uninitialized value within %toc in concatenation (.) or string 
+at test.pl line 25.
 => 3

all post-commands are complete

Anyone got any ideas? Thanks!

[BrowserUk]

async does not return a "thread id", it returns a blessed thread handle. To get a thread id from a thread handle, use $threadHandle->tid;

Thus, there is no perpose in storing your thread handles in a hash -- where they will get stringified -- because you can (and do) obtain those handles from your joinable() sub.

Your while loop for joining the threads is horrible -- it obtains the same list over and over. It can be replaced by a simple:

printf "%d => %d\n", $_->tid, $_->join for @threads;

Provided you store your thread handles in the array @threads so:

push @threads, async { sleep 3*$i+5; $i };

[samwyse]

Strictly speaking, I wasn't storing the thread handles in a hash, I was wanting to use them as keys. This is because I wanted to associate information for each thread (i.e. the parameters used when started). Using the tid() method solved that problem.

I'm unsure that your code for joining the threads is useful to me, as it seems that it would wait for the first thread to finish before checking any others. Since some of the threads may hang, this would not solve my stated problem. I do agree that using a sleep loop isn't optimal, and I should look for a better way to wait for threads to exit.

[BrowserUk]

some of the threads may hang

How do you handle not getting the return value from those threads that hang?

How will you clean those threads up when your program ends?