python 多線程編程

python 多線程編程

使用回調方式

import time
def countdown(n):
    while n > 0:
        print('T-minus', n)
        n -= 1
        time.sleep(5)

# Create and launch a thread
from threading import Thread
t = Thread(target=countdown, args=(10,))
t.start()

把線程放入一個類

from threading import Thread

class CountdownTask:
    def __init__(self):
        self._running = True

    def terminate(self):
        self._running = False

    def run(self, n):
        while self._running and n > 0:
            print('T-minus', n)
            n -= 1
            time.sleep(5)

c = CountdownTask()
t = Thread(target=c.run, args=(10,))
t.start()
c.terminate() # Signal termination
t.join()      # Wait for actual termination (if needed)

注意使用變量 self._running 退出線程的方式

使用繼承方式

from threading import Thread

class CountdownThread(Thread):

def __init__(self, n):
    super().__init__()
    self.n = n
def run(self):
    while self.n > 0:

        print('T-minus', self.n)
        self.n -= 1
        time.sleep(5)

c = CountdownThread(5)
c.start()

使用 Queue 進行線程間通訊

import Queue
import threading
import time

task_queue = Queue.Queue()


class ThreadTest(threading.Thread):
    def __init__(self, queue):
        threading.Thread.__init__(self)
        self.queue = queue

    def run(self):
        while True:
            msg = self.queue.get()
            print(msg)
            time.sleep(0.1)
            self.queue.task_done()


def main():
    start = time.time()
    # populate queue with data
    for i in range(100):
        task_queue.put("message")

    # spawn a pool of threads, and pass them queue instance
    for i in range(5):
        t = ThreadTest(task_queue)
        t.setDaemon(True)
        t.start()

    # wait on the queue until everything has been processed
    task_queue.join()
    print "Elapsed Time: {}".format(time.time() - start)


if __name__ == "__main__":
    main()

setDaemon 設置爲 True, run 函數中不須要退出，主線程結束後全部子線程退出
若是 setDaemon 設置爲 False,則改成

def run(self):
    while not self.queue.empty():
        msg = self.queue.get()
        print(msg)
        time.sleep(0.1)
        self.queue.task_done()

而且在主函數結束前 join 全部線程

注意

• 向隊列中添加數據項時並不會複製此數據項，線程間通訊其實是在線程間傳遞對象引用。若是你擔憂對象的共享狀態，那你最好只傳遞不可修改的數據結構（如：整型、字符串或者元組）或者一個對象的深拷貝。

  from queue import Queue
    from threading import Thread
    import copy
  
    # A thread that produces data
    def producer(out_q):
        while True:
            # Produce some data
            ...
            out_q.put(copy.deepcopy(data))
  
    # A thread that consumes data
    def consumer(in_q):
        while True:
            # Get some data
            data = in_q.get()
            # Process the data
            ...

• q.qsize() ， q.full() ， q.empty() 等實用方法能夠獲取一個隊列的當前大小和狀態。但要注意，這些方法都不是線程安全的。可能你對一個隊列使用 empty() 判斷出這個隊列爲空，但同時另一個線程可能已經向這個隊列中插入一個數據項。

參考

• python3-cookbook Chapter 12 'Concurrency-Starting and Stopping Threads'
• Practical threaded programming with Python