Race Condition in Python.

A race condition in Python refers to what happens when two or more threads or processes try to access and modify the same shared resource at the same time. The behavior of the program depends on their execution timing.

Key points:

1. Cause: Lack of proper synchronization mechanism.

2. Impact: Causes unpredictable or incorrect results as threads "race" to complete their operations first.

3. Example:

   • Two threads try to update the shared counter:

   counter = 0
   
   def increment():
       global counter
       for _ in range(1000):
           counter += 1  # 此处不是线程安全的
   
   thread1 = threading.Thread(target=increment)
   thread2 = threading.Thread(target=increment)
   
   thread1.start()
   thread2.start()
   thread1.join()
   thread2.join()
   
   print(counter)  # 输出可能会有所不同，并且小于 2000

   • Due to the lack of proper synchronization, the results are unpredictable as threads interfere with each other.

How to prevent:

• Use a lock (for example, Lock or RLock) to ensure that only one thread accesses the critical section at a time.
• Example of using lock:

import threading

counter = 0
lock = threading.Lock()

def increment():
    global counter
    for _ in range(1000):
        with lock:  # 确保一次只有一个线程访问此代码块
            counter += 1

thread1 = threading.Thread(target=increment)
thread2 = threading.Thread(target=increment)

thread1.start()
thread2.start()
thread1.join()
thread2.join()

print(counter)  # 输出将始终为 2000

Interview skills:

• It is caused by asynchronous access to a shared resource.
• Always mention the lock or synchronization mechanism to prevent it.

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