[issue35627] multiprocessing.queue in 3.7.2 doesn't behave as it was in 3.7.1

[Tom Wilson]

Tom Wilson  added the comment:

Hi there. I get this behavior as well, although only in a venv.

  Main   Virtual  
v3.7.1:260ec2c36a  CompletesCompletes
v3.7.2:9a3ffc0492  Completes  Hangs

Some other details of my setup:
 - Windows 10 Pro, Version 1803 (OS Build 17134.472)
 - Python platform is AMD64 on win32
 - Running from the command line (cmd.exe)
 - The virtual environment was created from the command line like this: 
 .\python -m venv c:\temp\Py-3.7.2b-Venv

--
nosy: +tom.wilson

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[issue35627] multiprocessing.queue in 3.7.2 doesn't behave as it was in 3.7.1

[Tom Wilson]

Tom Wilson  added the comment:

In case this is a clue - the attached script "mp_hang2.py" adds a call to 
qsize() and uses only a single consumer. When I run it from the command line it 
does one of two things:


Option 1:

C:\TEMP\Py-3.7.2b-Venv\Scripts>.\python.exe 
"C:\Users\Tom.Wilson\Documents\Python-Bugs\mp_hang2.py"
Creating 1 consumers
Putting
Poisoning
Joining
Process Consumer-1:
Traceback (most recent call last):
  File 
"C:\Users\Tom.Wilson\AppData\Local\Programs\Python\Python37\lib\multiprocessing\process.py",
 line 297, in _bootstrap
self.run()
  File "C:\Users\Tom.Wilson\Documents\Python-Bugs\mp_hang2.py", line 18, in run
print(f'Queue size: {self.task_queue.qsize()}')
  File 
"C:\Users\Tom.Wilson\AppData\Local\Programs\Python\Python37\lib\multiprocessing\queues.py",
 line 117, in qsize
return self._maxsize - self._sem._semlock._get_value()
PermissionError: [WinError 5] Access is denied


Option 2:

C:\TEMP\Py-3.7.2b-Venv\Scripts>.\python.exe 
"C:\Users\Tom.Wilson\Documents\Python-Bugs\mp_hang2.py"
Creating 1 consumers
Putting
Poisoning
Joining
Queue size: 2147483647
Getting task
 <<< Hangs here >>>


If I can provide anything else please let me know.

--
Added file: https://bugs.python.org/file48070/mp_hang2.py

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