# 1114. Print in Order

### 題目敘述

Suppose we have a class:

``````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()`.

Note:

We do not know how the threads will be scheduled in the operating system, even though the numbers in the input seem to imply the ordering. The input format you see is mainly to ensure our tests' comprehensiveness.

Example 1:

``````Input: [1,2,3]
Output: "firstsecondthird"
Explanation: There are three threads being fired asynchronously. The input [1,2,3] means thread A calls first(), thread B calls second(), and thread C calls third(). "firstsecondthird" is the correct output.
``````

Example 2:

``````Input: [1,3,2]
Output: "firstsecondthird"
Explanation: The input [1,3,2] means thread A calls first(), thread B calls third(), and thread C calls second(). "firstsecondthird" is the correct output.
``````

Constraints:

• `nums` is a permutation of `[1, 2, 3]`.

### 解法解析

#### 程式範例

##### Python
``````from threading import Lock

class Foo:
def __init__(self):
self.firstJobDone = Lock()
self.secondJobDone = Lock()
self.firstJobDone.acquire()
self.secondJobDone.acquire()

def first(self, printFirst: 'Callable[[], None]') -> None:
# printFirst() outputs "first".
printFirst()
# Notify the thread that is waiting for the first job to be done.
self.firstJobDone.release()

def second(self, printSecond: 'Callable[[], None]') -> None:
# Wait for the first job to be done
with self.firstJobDone:
# printSecond() outputs "second".
printSecond()
# Notify the thread that is waiting for the second job to be done.
self.secondJobDone.release()

def third(self, printThird: 'Callable[[], None]') -> None:

# Wait for the second job to be done.
with self.secondJobDone:
# printThird() outputs "third".
printThird()
``````