# 1115.Print FooBar Alternately

**1115.Print FooBar Alternately**

难度:Medium

> Suppose you are given the following code:

class FooBar { public void foo() { for (int i = 0; i < n; i++) { print("foo"); } }

public void bar() { for (int i = 0; i < n; i++) { print("bar"); } } } The same instance of FooBar will be passed to two different threads. Thread A will call foo() while thread B will call bar(). Modify the given program to output "foobar" n times.

```
Example 1:

Input: n = 1
Output: "foobar"
Explanation: There are two threads being fired asynchronously. One of them calls foo(), while the other calls bar(). "foobar" is being output 1 time.
Example 2:

Input: n = 2
Output: "foobarfoobar"
Explanation: "foobar" is being output 2 times.
```

要交替输出foo和bar，在每个函数中，每次循环结束将当前线程锁起来，令下一个循环处于阻塞状态，待另一个函数的当前循环结束后，解锁，交替进行输出。

```
class FooBar {
private:
    int n;
    pthread_mutex_t t1=PTHREAD_MUTEX_INITIALIZER;
    pthread_mutex_t t2=PTHREAD_MUTEX_INITIALIZER;
public:
    FooBar(int n) {
        this->n = n;
        pthread_mutex_lock(&t1);

        
    }

    void foo(function<void()> printFoo) {
        
        for (int i = 0; i < n; i++) {
            pthread_mutex_lock(&t2);

        	// printFoo() outputs "foo". Do not change or remove this line.
        	printFoo();
            pthread_mutex_unlock(&t1);
        }
    }

    void bar(function<void()> printBar) {
        for (int i = 0; i < n; i++) {
            pthread_mutex_lock(&t1);

        	// printBar() outputs "bar". Do not change or remove this line.
        	printBar();
            pthread_mutex_unlock(&t2);

        }
    }
};
```

> 执行用时 :52 ms, 在所有 C++ 提交中击败了50.00%的用户\
> 内存消耗 :10.3 MB, 在所有 C++ 提交中击败了100.00%的用户


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://dfine.gitbook.io/leetcode/1115.print_foobar_alternately.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.