Jonathan Gossage <jgoss...@gmail.com> added the comment:
This is a great example of abusing the multi-processing API and thus creating timing errors that lead to locks not being released. What is happening is that the example attempts to transmit data that is too big for the underlying pipe and this creates the timing errors since the pipe that returns the result of invoking apply_async does not have the capacity of transmitting the result of the worker process in a single operation and accordingly the worker process returns prematurely while still holding the pipe lock. This can be seen by testing the ready status of the result returned by apply_async which will show whether the complete result of the worker process has been received. The solution to this situation is simple, simply invoke get() on the asynchronous result returned by apply_async. Using this call has the effect of correctly synchronizing the pipe used by the low-level queues used by the Pool Manager and there will be no lock left active when it should'nt be. The script lock1.py contains code that implements this fix as well as verifying that everything has worked properly. The output from the script is found in the file lock1.result.txt. Because there is an API based solution to the problem plus the behavior of apply_async makes sense in that the process of transferring multi-buffer data is very CPU intensive and should be delegated to the worker process rather than to the main-line process, I do not recommend that any changes be made to the multiprocessing code in Python, rather the solution should use the available multiprocessing API correctly. ---------- nosy: +Jonathan.Gossage Added file: https://bugs.python.org/file47979/lock1.py _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue35267> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
