Daniel Birnstiel added the comment:
Currently using
Python 3.6.0 (default, Mar 4 2017, 12:32:34)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)] on darwin
> So, somehow the print() statement is blocking, which I have /no/ idea how to
> go about debugging. I assume there's a lock /in/ the print statement function
> call, and I'm probably going to look into wrapping both the print() call and
> the multiprocessing.Process() call execution in a single, shared
> multiprocessing lock, but that
> seems like a very patchwork solution to something that should just work.
I am currently having a similar issue where I get a deadlock to a stdout.flush
call (which I assume is called when printing). Flush internally appears to
acquire a lock which is getting stuck in the subprocess.
This is the backtrace I was able to obtain through lldb, showing the waiting
for a lock after the flush-call:
* thread #1: tid = 0x77c27d, 0x00007fffe33c9c86
libsystem_kernel.dylib`__psynch_cvwait + 10, stop reason = signal SIGSTOP
frame #0: 0x00007fffe33c9c86 libsystem_kernel.dylib`__psynch_cvwait + 10
frame #1: 0x00007fffe34b396a libsystem_pthread.dylib`_pthread_cond_wait +
712
frame #2: 0x00000001021ecad8 Python`PyThread_acquire_lock_timed + 256
frame #3: 0x000000010221cc2f Python`_enter_buffered_busy + 169
frame #4: 0x000000010221ed36 Python`_io_BufferedWriter_write + 203
frame #5: 0x000000010215448b Python`_PyCFunction_FastCallDict + 529
frame #6: 0x000000010211b3f0 Python`_PyObject_FastCallDict + 237
frame #7: 0x000000010211be9e Python`PyObject_CallMethodObjArgs + 240
frame #8: 0x000000010222171a Python`_textiowrapper_writeflush + 150
* frame #9: 0x00000001022224a8 Python`_io_TextIOWrapper_flush + 239
Is there any update on this issue or any solution to avoid deadlocking without
wrapping every fork/print/logging call with a multiprocessing (or billiard in
my case) lock?
----------
nosy: +Birne94
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue6721>
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