python 读写锁

读写锁是一种用于多线程编程的同步机制，它允许多个线程同时读取共享资源，但只允许一个线程写入共享资源。在Python中，可以使用threading模块中的RLock类来实现读写锁。

下面是一个使用Python实现读写锁的例子：

import threading

class RWLock:
    def __init__(self):
        self._lock = threading.Lock()
        self._read_lock = threading.Lock()
        self._write_lock = threading.Lock()
        self._read_count = 0

    def acquire_read(self):
        with self._lock:
            self._read_count += 1
            if self._read_count == 1:
                self._write_lock.acquire()
        self._read_lock.acquire()
        self._read_lock.release()

    def release_read(self):
        with self._lock:
            self._read_count -= 1
            if self._read_count == 0:
                self._write_lock.release()

    def acquire_write(self):
        self._write_lock.acquire()

    def release_write(self):
        self._write_lock.release()

在上面的代码中，我们定义了一个RWLock类，它包含了acquire_read、release_read、acquire_write和release_write等方法。acquire_read方法用于获取读锁，release_read方法用于释放读锁，acquire_write方法用于获取写锁，release_write方法用于释放写锁。

使用读写锁的示例代码如下：

lock = RWLock()

def read_func():
    lock.acquire_read()
    # 读取共享资源的操作
    lock.release_read()

def write_func():
    lock.acquire_write()
    # 写入共享资源的操作
    lock.release_write()

# 创建多个读线程和写线程
read_threads = [threading.Thread(target=read_func) for _ in range(5)]
write_threads = [threading.Thread(target=write_func) for _ in range(2)]

# 启动线程
for thread in read_threads + write_threads:
    thread.start()

# 等待线程结束
for thread in read_threads + write_threads:
    thread.join()

上面的代码中，我们创建了5个读线程和2个写线程，并通过调用start方法启动线程。然后，我们使用join方法等待所有线程执行完毕。