For purposes of debugging, I'm using writeln() to print stuff out from tasks running concurrently on many threads. At some point it crashes with the following stack trace:

Thread 4 received signal SIGUSR1, User defined signal 1.
[Switching to Thread 0x7ffff5ec2700 (LWP 19267)]
__lll_lock_wait_private () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95
95	../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S: No such file or directory.
(gdb) bt
#0  __lll_lock_wait_private () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95
#1  0x00007ffff7bcb2d5 in __flockfile (stream=0x7ffff728b780 <_IO_stdfile_1_lock>) at ../sysdeps/pthread/flockfile.c:28
#2  0x000000000045f5b0 in _D3std5stdio4File17LockingTextWriter6__ctorMFNcNeKSQBxQBwQBtZSQCiQChQCeQCc ()
#3  0x000000000045f670 in _D3std5stdio4File17lockingTextWriterMFNfZSQBoQBnQBk17LockingTextWriter ()
#4  0x000000000044a1e0 in _D3std5stdio4File__T5writeTAyaTyiTaZQqMFNfQpyiaZv (this=..., _param_2=10 '\n', _param_1=12, _param_0=...)
    at /usr/include/dmd/phobos/std/stdio.d:1399

Note that I didn't add any synchronizations around the writeln() calls, should I? I assume the implementation *should* synchronize access to std_out, no?

Bug in phobos?

On Saturday, 9 December 2017 at 09:38:05 UTC, IM wrote:
> For purposes of debugging, I'm using writeln() to print stuff out from tasks running concurrently on many threads. At some point it crashes with the following stack trace:
>
> Thread 4 received signal SIGUSR1, User defined signal 1.
[...]
> Bug in phobos?

Is that a crash or just thread 4 receiving SIGUSR1? (GC signal)

If so you just need to tell gdb not to stop on that. ("handle SIGUR1 SIGUSR2 nostop", place it in ~/.gdbinit)

On Saturday, 9 December 2017 at 09:38:05 UTC, IM wrote:
> Note that I didn't add any synchronizations around the writeln() calls, should I? I assume the implementation *should* synchronize access to std_out, no?
>
> Bug in phobos?

Yes, try using synchronized access. IIRC the implementation of LockingTextWriter isn't thread-safe.

On 12/9/2017 5:56 AM, Seb wrote:
> IIRC the implementation of LockingTextWriter isn't thread-safe.

There's no bugzilla issue on this. So I added one:

  https://issues.dlang.org/show_bug.cgi?id=18052

Please, folks, I can't emphasize this enough. When you find a bug, POST IT ON BUGZILLA! Otherwise, it will NEVER get fixed.

On Sunday, 10 December 2017 at 01:12:37 UTC, Walter Bright wrote:
> On 12/9/2017 5:56 AM, Seb wrote:
>> IIRC the implementation of LockingTextWriter isn't thread-safe.
>
> There's no bugzilla issue on this. So I added one:
>
>   https://issues.dlang.org/show_bug.cgi?id=18052
>
> Please, folks, I can't emphasize this enough. When you find a bug, POST IT ON BUGZILLA! Otherwise, it will NEVER get fixed.

I was going to file one, but I wanted to verify first that it's actually a bug. According to comment #2 by Messenger, it doesn't seem to be one if SIGUSR1 is a GC signal. I was trying to debug a crash in gdb and that one kept showing up. After adding handle SIGUSR1 SIGUSR2 nostop I was able to capture the real issue.

Sorry for the false positive --- still learning about D! :( I think we can probably close that bug.

On Saturday, 9 December 2017 at 10:36:08 UTC, Messenger wrote:
> On Saturday, 9 December 2017 at 09:38:05 UTC, IM wrote:
>> For purposes of debugging, I'm using writeln() to print stuff out from tasks running concurrently on many threads. At some point it crashes with the following stack trace:
>>
>> Thread 4 received signal SIGUSR1, User defined signal 1.
> [...]
>> Bug in phobos?
>
> Is that a crash or just thread 4 receiving SIGUSR1? (GC signal)
>
> If so you just need to tell gdb not to stop on that. ("handle SIGUR1 SIGUSR2 nostop", place it in ~/.gdbinit)

Thanks! That works!

On Saturday, 9 December 2017 at 10:36:08 UTC, Messenger wrote:
> On Saturday, 9 December 2017 at 09:38:05 UTC, IM wrote:
>> For purposes of debugging, I'm using writeln() to print stuff out from tasks running concurrently on many threads. At some point it crashes with the following stack trace:
>>
>> Thread 4 received signal SIGUSR1, User defined signal 1.
> [...]
>> Bug in phobos?
>
> Is that a crash or just thread 4 receiving SIGUSR1? (GC signal)
>
> If so you just need to tell gdb not to stop on that. ("handle SIGUR1 SIGUSR2 nostop", place it in ~/.gdbinit)

i've been bitten many times by this. thanks to the folks on irc, it now lives in gdbinit.