Bug#1093776: perl: occasionally hangs and no longer responds to trapped signals

[Vincent Lefevre]

Control: retitle -1 perl: occasionally stuck in Perl_pp_lock and no longer responds to trapped signals

As this occurred again... The backtrace obtained with gdb on the
running process for the main thread:

#0  __futex_abstimed_wait_common64 (private=0, cancel=true, abstime=0x0,
    op=393, expected=0, futex_word=0x7ff580000c74)
    at ./nptl/futex-internal.c:57
#1  __futex_abstimed_wait_common (futex_word=futex_word at entry=0x7ff580000c74,
    expected=expected at entry=0, clockid=clockid at entry=0,
    abstime=abstime at entry=0x0, private=private at entry=0,
    cancel=cancel at entry=true) at ./nptl/futex-internal.c:87
#2  0x00007ff584db8f7b in __GI___futex_abstimed_wait_cancelable64 (
    futex_word=futex_word at entry=0x7ff580000c74, expected=expected at entry=0,
    clockid=clockid at entry=0, abstime=abstime at entry=0x0,
    private=private at entry=0) at ./nptl/futex-internal.c:139
#3  0x00007ff584dbb5d8 in __pthread_cond_wait_common (abstime=0x0, clockid=0,
    mutex=0x7ff580000c10, cond=0x7ff580000c48)
    at ./nptl/pthread_cond_wait.c:503
#4  ___pthread_cond_wait (cond=0x7ff580000c48, mutex=0x7ff580000c10)
    at ./nptl/pthread_cond_wait.c:618
#5  0x00007ff584ac8ac3 in ?? ()
   from /usr/lib/x86_64-linux-gnu/perl/5.36/auto/threads/shared/shared.so
#6  0x0000560ec5063377 in Perl_pp_lock ()
#7  0x0000560ec5022f26 in Perl_runops_standard ()
#8  0x0000560ec4f81779 in perl_run ()
#9  0x0000560ec4f534b2 in main ()

This is a script with worker threads, and there is nothing that
could make the main thread hang. In particular, according to
logging messages, no locks are involved here. The only thing
related to threading in this part of the code is

  $queue->enqueue($_[0]);

where $queue has been created with

  my $queue = Thread::Queue->new();

(note that there is no limit of the size of the queue, and even
if there had been one, this should not have been an issue).

So perhaps there's something wrong in the Thread::Queue
implementation.

-- 
Vincent Lefèvre <vincent at vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / Pascaline project (LIP, ENS-Lyon)