Python Thread join()用法及代碼示例

Python Thread.join() 方法

Thread.join() 方法是 Python 中線程模塊的 Thread 類的內置方法。每當為任何 Thread 對象調用此方法時，它都會阻塞調用線程，直到調用其 join() 方法的線程終止(正常或通過未處理的異常)。

模塊：

    from threading import Thread

用法:

    join(timeout=None)

參數：

• timeout:它是一個可選參數，它以秒為單位指定操作的超時時間。它應該是一個浮點數。當超時參數丟失時，操作將阻塞，直到線程終止。

返回值：

這個方法的返回類型是<class 'NoneType'>，它什麽都不返回。

例：

# Python program to explain the
# use of join() method in Thread class

import time
import threading

def thread_1(i):
    time.sleep(2)
    print('Value by Thread 1:', i)

def thread_2(i):
    time.sleep(5)
    print('Value by Thread 2:', i)

def thread_3(i):
    print('Value by Thread 3:', i)    

    
# Creating three sample threads 
thread1 = threading.Thread(target=thread_1, args=(1,))
thread2 = threading.Thread(target=thread_2, args=(2,))
thread3 = threading.Thread(target=thread_3, args=(3,))

# Running three thread object
thread1.start()
thread1.join()
thread2.start()
thread2.join()
thread3.start()
thread3.join()

print()
# Creating another 3 threads
thread4 = threading.Thread(target=thread_1, args=(1,))
thread5 = threading.Thread(target=thread_2, args=(2,))
thread6 = threading.Thread(target=thread_3, args=(3,))

thread4.start()
thread5.start()
thread6.start()
thread4.join()
thread5.join()
thread6.join()

輸出

Value by Thread 1:1
Value by Thread 2:2
Value by Thread 3:3

Value by Thread 3:3
Value by Thread 1:1
Value by Thread 2:2

在最初的三個 Thread 對象中，我們首先創建了一個線程並等待它執行，然後加入到主線程中。因此，它們的打印順序與調用順序相同。

在接下來的三個 Thread 對象中，它們同時運行，因此根據它們應該執行的時間打印出來，

    time(thread3)<time(thread2)<time(thread1)

例：

# Python program to explain the
# use of join() method in Thread class 
# with timeout parameter defined

import time
import threading

def thread_1(i):
    time.sleep(2)
    print('Value by Thread 1:', i)

def thread_2(i):
    time.sleep(5)
    print('Value by Thread 2:', i)
    
# Creating three sample threads 
thread1 = threading.Thread(target=thread_1, args=(1,))
thread2 = threading.Thread(target=thread_2, args=(2,))

# Running three thread object
thread1.start()
thread1.join(timeout=5)
thread2.start()
thread2.join()

輸出

Value by Thread 1:1
Value by Thread 2:2