A portable implementation of multiprocessing.Queue.
Because of multithreading / multiprocessing semantics, Queue.qsize() may raise the NotImplementedError exception on Unix platforms like Mac OS X where sem_getvalue() is not implemented. This subclass addresses this problem by using a synchronized shared counter (initialized to zero) and increasing / decreasing its value every time the put() and get() methods are called, respectively. This not only prevents NotImplementedError from being raised, but also allows us to implement a reliable version of both qsize() and empty().
empty() → bool¶
Reliable implementation of multiprocessing.Queue.empty().
get(*args, **kwargs) → object¶
put(*args, **kwargs) → None¶
qsize() → int¶
Reliable implementation of multiprocessing.Queue.qsize().
A synchronized shared counter.
The locking done by multiprocessing.Value ensures that only a single process or thread may read or write the in-memory ctypes object. However, in order to do n += 1, Python performs a read followed by a write, so a second process may read the old value before the new one is written by the first process. The solution is to use a multiprocessing.Lock to guarantee the atomicity of the modifications to Value.
Parameters: n (int) – The count to start at.
Increment the counter by n.
Parameters: n (int) – The amount to increment the counter by.
The value of the counter. (int, read-only)