Invoking writeln() from a lot of threads running concurrently --> crash

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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)