使用线程和队列时格式不正确

Question

我在下面写的代码应该输出类似这样的东西：

<Floor(Thread-3, started 44660)> <Bank(Thread-1, started 43356)> shutting down
<Floor(Thread-4, started 44108)> received a message: shutting down (0, 'UP')
<Bank(Thread-1, started 43356)> received a message: (1, 'DOWN')
<Bank(Thread-1, started 43356)> shutting down
<Bank(Thread-2, started 27800)> shutting down

但是，输出的格式有时似乎不一致。例如：

<Floor(Thread-3, started 27076)> <Bank(Thread-1, started 44608)>shutting down
<Floor(Thread-4, started 28772)>received a message:  (shutting down0, 'UP')

<Bank(Thread-1, started 44608)> received a message: (1, 'DOWN')
<Bank(Thread-1, started 44608)> shutting down
<Bank(Thread-2, started 41480)> shutting down

在大多数程序中，一致的数据很重要。为什么这个输出不一致，我该如何防止它？

import threading
import Queue

banks = []
floors = []

class Bank(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.mailbox = Queue.Queue()
        banks.append(self.mailbox)

    def run(self):
        while True:
            data = self.mailbox.get()
            if data == 'shutdown':
                print self, 'shutting down'
                return
            print self, 'received a message:', data

    def stop(self):
        banks.remove(self.mailbox)
        self.mailbox.put('shutdown')
        self.join()

class Floor(threading.Thread):
    def __init__(self, number = 0):
        threading.Thread.__init__(self)
        self.mailbox = Queue.Queue()
        floors.append(self.mailbox)
        self.number = number

    def run(self):
        while True:
            data = self.mailbox.get()
            if data == 'shutdown':
                print self, 'shutting down'
                return
            print self, 'received a message:', data

    def stop(self):
        floors.remove(self.mailbox)
        self.mailbox.put('shutdown')
        self.join()

    def call(self, data):
        banks[0].put((self.number, data))

b0 = Bank()
b1 = Bank()
b0.start()
b1.start()
f0 = Floor(0)
f1 = Floor(1)
f0.start()
f1.start()
f0.call('UP')
f1.call('DOWN')
f0.stop()
f1.stop()
b0.stop()
b1.stop()

Answer 1

最终，由于您的 call() 调用现在在不同的线程中执行，因此无法保证它们将同步执行（和输出）。如果你想保证输出不交错，你需要在你的打印调用周围放置一个大的全局锁（互斥锁）。

即使这样也不能保证它们的顺序一致 - 例如上面的不同线路可以很容易地切换 - 在这种情况下你需要锁定你的电话。顺便说一句，这首先会抵消多线程的几乎所有性能优势。

Answer 2

print 不是线程安全的。然而，sys.stdout.write是。

这确实解决了交织的直接问题，但我怀疑这是最合适的方法。

使用线程和队列时格式不正确

Improper formatting while using threading and queues

queue

formatting

multithreading

python-2.7