According to multiprocessing documentation for Value
(https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Value)
reads and writes are protected with lock when the lock argument is True
(the default) or the lock argument is an instance of Lock or RLock. The
documentation states that operations like += are not atomic as that
involves reading and writing.
On the worker side the critical section includes also storing finished task
result because the timeout could happen after the task function has
finished but before the result has been stored and timer.value has been
updated to tell the guard process that the task has been finished.
On the guard side the critical section includes all checks done to see
if the worker has timed out or died and the actual reincarnation function
because the worker could update timer value to -1 (idle) or -2 (recycle)
after the guard has seen timer value 0 (timeout) and is going to terminate
the worker.
The cluster timeout configuration default value None is documented to mean
tasks never timeout out. Also the documentation states that the timeout
can be overridden for individual tasks.
With the old implementation the timeout parameter given to async_task was
not honored if the cluster timeout was set to None.
Fixes: #335
The old implementation used count_forever test task that never finishes.
If the timeout implementation does not work in the test, the test never
end and you was required to kill the test runner.
Janne Rönkkö