006Python-threading__1

In CPython, due to the Global Interpreter Lock, only one thread can execute Python code at once(even though certain performance-oriented libraries might overcome this limitation).

But now,threading is still an appropriate model if you want to run multiple I/O-bound tasks simultaneously.

Python通过threading模块来实现多线程，内部核心类是threading.Thread

参考链接:

官方文档

Runoob参考

The Thread class represents an activity that is run in a separate thread of control.

There are two ways to specify the activity:

• by passing a callable object to the constructor;

• by overriding the run() method in a subclass.

  No other methods (except for the constructor) should be overridden in a subclass.

  In other words, only override the __init__() and run() methods of this class.

Once a thread object is created, its activity must be started by calling the thread’s start() method. This invokes the run() method in a separate thread of control.

Once the thread’s activity is started, the thread is considered ‘alive’. It stops being alive when its run() method terminates – either normally, or by raising an unhandled exception.

The is_alive() method tests whether the thread is alive.

Other threads can call a thread’s join() method. This blocks the calling thread until the thread whose join() method is called is terminated.

多线程基础

创建线程的两种方式

1. 根据Thread构造函数直接实例化

   import threading
   import time
   
   def print_numbers():
       for i in range(5):
           print(i)
           time.sleep(1)
   
   
   
   def test001():
       print("---1")
       thread = threading.Thread(target=print_numbers)
       print("---2")
       thread.start()
       print("---3")
       thread.join()  ## 等待线程终止。默认情况下，join()会一直阻塞，直到被调用线程终止。如果指定了timeout参数，则最多等待timeout秒。
       print("---4")

   其输出如下:

   —1
   —2
   0
   —3
   1
   2
   3
   4
   —4

   从上可知，start方法之后，thread就会去处理其内部的任务；join会阻塞当前线程，知道我们创建的thread调用终止，才会继续执行当前线程(主线程)；

   threading模块里有很多好用的方法，比如查看当前线程threading.current_thread()，具体可以查看官方文档。

2. 继承Thread并重写__init__(如果需要额外参数) 和 run() 方法.

   exit_flag = False
   
   class MyThread(threading.Thread):
       def __init__(self, thread_id, name, delay):
           super().__init__()
           self.thread_id = thread_id
           self.name = name
           self.delay = delay
   
       def run(self):
           print(f"Starting {self.name}")
           print_time(self.name, self.delay, 5)
           print(f"Exiting {self.name}")
   
   
   def print_time(thread_name, delay, counter):
       while counter:
           if exit_flag:
               thread_name.exit()
           time.sleep(delay)
           print(f"{thread_name} : {time.ctime(time.time())}")
           counter -= 1
   
   
   def test002():
       thread1 = MyThread(1, "Thread-1", 1)
       thread2 = MyThread(2, "Thread-2", 2)
       thread1.start()
       thread2.start()
       thread1.join()
       thread2.join()

   运行上述代码输出如下:

   Starting Thread-1
   Starting Thread-2
   Thread-1 : Wed Mar 19 13:11:45 2025
   Thread-2 : Wed Mar 19 13:11:46 2025
   Thread-1 : Wed Mar 19 13:11:46 2025
   Thread-1 : Wed Mar 19 13:11:47 2025
   Thread-2 : Wed Mar 19 13:11:48 2025
   Thread-1 : Wed Mar 19 13:11:48 2025
   Thread-1 : Wed Mar 19 13:11:49 2025
   Exiting Thread-1
   Thread-2 : Wed Mar 19 13:11:50 2025
   Thread-2 : Wed Mar 19 13:11:52 2025
   Thread-2 : Wed Mar 19 13:11:54 2025
   Exiting Thread-2