Python 3 Implementation of prioritized Lock objects

prioritylock.py

"""
This module implements a set of prioritized locks.

Implemented:
    * PriorityLock
    * FIFOPriorityLock

License: MIT <tuxtimo@gmail.com>
"""

import time
import queue
import threading


class PriorityLock:
    """Lock object which prioritizes each acquire

    >>> import random

    >>> thread_exec_order = []
    >>> lock = PriorityLock()

    >>> def worker(priority):
    ...     with lock(priority):
    ...         time.sleep(0.2)
    ...         thread_exec_order.append(priority)

    >>> threads = [
    ...     threading.Thread(target=worker, args=(p,))
    ...     for p in range(10)
    ... ]

    >>> random.shuffle(threads)
    >>> for thread in threads:
    ...     thread.start()
    >>> for thread in threads:
    ...     thread.join()

    >>> # the first thread to be executed is non-deterministic
    >>> assert thread_exec_order[1:] == list(sorted(thread_exec_order[1:]))
    """
    class _Context:
        def __init__(self, lock, priority):
            self._lock = lock
            self._priority = priority

        def __enter__(self):
            self._lock.acquire(self._priority)

        def __exit__(self, exc_type, exc_val, exc_tb):
            self._lock.release()

    def __init__(self):
        self._lock = threading.Lock()
        self._acquire_queue = queue.PriorityQueue()
        self._need_to_wait = False

    def acquire(self, priority):
        with self._lock:
            if not self._need_to_wait:
                self._need_to_wait = True
                return True

            event = threading.Event()
            self._acquire_queue.put((priority, event))
        event.wait()
        return True

    def release(self):
        with self._lock:
            try:
                _, event = self._acquire_queue.get_nowait()
            except queue.Empty:
                self._need_to_wait = False
            else:
                event.set()

    def __call__(self, priority):
        return self._Context(self, priority)


class FIFOPriorityLock(PriorityLock):
    """Lock object which prioritizes acquires by first-comes-first-serves

    >>> import random

    >>> thread_exec_order = []
    >>> lock = FIFOPriorityLock()

    >>> def worker():
    ...     with lock:
    ...         time.sleep(0.2)
    ...         thread_exec_order.append(threading.current_thread())

    >>> threads = [
    ...     threading.Thread(target=worker, name=str(x))
    ...     for x in range(10)
    ... ]

    >>> random.shuffle(threads)
    >>> for thread in threads:
    ...     thread.start()
    >>> for thread in threads:
    ...     thread.join()

    >>> assert thread_exec_order == threads
    """
    def acquire(self):
        acquiring_time = time.time()
        super().acquire(priority=acquiring_time)

    def __enter__(self):
        self.acquire()

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.release()