Thread overview
Invoking writeln() from a lot of threads running concurrently --> crash
Dec 09
IM
Dec 09
Messenger
Dec 10
IM
Dec 10
Mengu
Dec 09
Seb
Dec 10
IM
December 09
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?
December 09
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)
December 09
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.
December 09
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.
December 10
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.
December 10
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!
December 10
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.