leetcode 1114 Print in Order, sample concurrency in Python

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leetcode 1114 Print in Order, sample concurrency in Python

Problem

Suppose we have a class:

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public class Foo {
  public void first() { print("first"); }
  public void second() { print("second"); }
  public void third() { print("third"); }
}

The same instance of Foo will be passed to three different threads. Thread A will call first(), thread B will call second(), and thread C will call third(). Design a mechanism and modify the program to ensure that second() is executed after first(), and third() is executed after second().

Print in order is a simple concurrency programming problem, especially in Python. But it’s my first concurrency program in Python, so record in here.

Solution

I simply use two locks to achieve synchoronization.

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import threading
class Foo:
    lock1 = threading.Lock()
    lock2 = threading.Lock()
    def __init__(self):
        self.lock1.acquire()
        self.lock2.acquire()
        pass


    def first(self, printFirst: 'Callable[[], None]') -> None:
        
        # printFirst() outputs "first". Do not change or remove this line.
        printFirst()
        self.lock1.release()


    def second(self, printSecond: 'Callable[[], None]') -> None:
        self.lock1.acquire()
        # printSecond() outputs "second". Do not change or remove this line.
        printSecond()
        self.lock1.release()
        self.lock2.release()


    def third(self, printThird: 'Callable[[], None]') -> None:
        self.lock2.acquire()
        # printThird() outputs "third". Do not change or remove this line.
        printThird()
        self.lock2.release()