python 读写锁（优化）

python 读写锁（优化）

# import system module

import threading

class ReadWriteLock:

    """A lock object that allows many simultaneous "read-locks",

    but only one "write-lock".

    """

   

    def __init__(self,index):

        self._read_ready = threading.Condition(threading.Lock())

        self._readers = 0

        self._index = index

    def acquire_read(self):

        """Acquire a read-lock.

       

        Blocks only if some thread has acquired write-lock.

        """

       

        self._read_ready.acquire()

        try:

            self._readers += 1

        finally:

            self._read_ready.release()

    def release_read(self):

        """Release a read-lock.

       

        """

       

        self._read_ready.acquire()

        try:

            self._readers -= 1

            if not self._readers:

                self._read_ready.notifyAll()

        finally:

            self._read_ready.release()

    def acquire_write(self):

        """Acquire a write lock. Blocks until there are no

       

        acquired read- or write-locks.

        """

        self._read_ready.acquire()

        while self._readers > 0:

            self._read_ready.wait()

    def release_write(self):

        """Release a write-lock.

        """

       

        self._read_ready.release()