理解MultiThreading和Locks Python

Question

我试图理解以下代码:线程(例如Thread1)获取锁意味着什么，这是否意味着在Thread1释放其锁之前没有其他方法可以运行？

import threading
import time

class myThread (threading.Thread):
    def __init__(self, threadID, name, counter):
        threading.Thread.__init__(self)
        self.threadID = threadID
        self.name = name
        self.counter = counter
    def run(self):
        print "Starting " + self.name
        # Get lock to synchronize threads
        threadLock.acquire()
        print_time(self.name, self.counter, 3)
        # Free lock to release next thread
        threadLock.release()

def print_time(threadName, delay, counter):
    while counter:
        time.sleep(delay)
        print "%s: %s" % (threadName, time.ctime(time.time()))
        counter -= 1

threadLock = threading.Lock()
threads = []

# Create new threads
thread1 = myThread(1, "Thread-1", 1)
thread2 = myThread(2, "Thread-2", 2)

# Start new Threads
thread1.start()
thread2.start()

# Add threads to thread list
threads.append(thread1)
threads.append(thread2)

# Wait for all threads to complete
for t in threads:
    t.join()

打印“退出主线程”

Answer 1

锁是一种确保一次最多只执行一个线程的方法。它是一个有两种状态的对象，被锁定和未锁定。如果它被解锁，对其acquire()方法的调用将锁定它。如果对acquire()进行第二次调用(通常由另一个线程进行)，则此调用将阻塞调用线程，直到某个人(通常是第一个线程)用release()方法释放锁为止。只有这样，第二个线程才能继续。

在您的示例中，锁确保“先获得它”的线程将在第二个线程打印任何内容之前打印print_time()函数中的所有行。如果删除/注释acquire()和release()调用，两者之间的区别应该是显而易见的。

https://docs.python.org/2/library/threading.html#lock-objects