Re: seg faults when i use thread->new from a thread - am i using threads incorrectly?

On onsdag, apr 2, 2003, at 03:19 Europe/Stockholm, Bradley W. Langhorst 
wrote:

>
> I just found this newsgroup - so I hope no one is annoyed that I'm
> posting
> something very similar to what i posted on c.l.p.m
>

Not at all, :)

>
> I'm seeing unusual problems when i try to start a new thread from a
> previously created thread.
>

This has been known to be a bit wonky on Win32, but not under unix 
(which I assume you are using because you like forks.pm)

> I've written a INET socket program to respond to incoming messages with
> new
> messages sent out on a different socket.
>
> I start a new thread for every incoming request .
> When I don't need to spawn new threads the program works reliably.
> However, some incoming requests have to create multiple responses so 
> I'm
> creating new threads...
>
> I get seg faults when that happens with some of my tests
>
> ./agent.pl
> Segmentation fault
>  ./agent.pl
> Segmentation fault
>

A backtrace would be nice,,

gdb perl
run ./agent.pl
bt

> I also see leaked scalars when when it my test doesn't induce a seg
> fault
>

Probably the same thing.

> here's the code that creates the inner threads:
> Is there something wrong with this?
> (I was surprised to find that I could not return multiple values from a
> join
> - thus the array_ref and splice)
>

Because of some unknown reason the thread runs with the context of when 
it is created, so to return an array you need to do
($thread) = threads->new(....
so the thread gets a list context

>     foreach $subtask (@$ra_tasks) {
>         log_msg("Trying to schedule $subtask asynchronously\n",10);
>         #thread so these can occur simultaneously
>         $thr = threads->new(\&schedule_task,
>                             $subtask,
>                             $earliest_start,
>                             $bid_by,
>                             $req_id);
>         log_msg("adding thread $thr to list of workers\n", 12);
>         push @workers, $thr;
>     }
>
>     #now gather the results from the workers
>
>     foreach $thr (@workers) {
>
>         eval {
>             $ra_ret = $thr->join();
>         };
>         if ($@) {
>             die("subcontracing failed: $@\n");
>         } else {
>             ($start_time,$end_time, $ra_bids) = splice(@$ra_ret,0,3);
>
>             push @subtasks, {'first_start' => $start_time,
>                              'last_end' => $end_time,
>                              'bids' => $ra_bids};
>         }
>     }
>

Do you know when you are getting the coredump, in new() or in join?

Also, what modules are you using?

Arthur