leetcode & c++多线程刷题日志

1.按序打印

按序打印
解法

• 1. 互斥锁

class Foo {
    mutex mtx1, mtx2;
public:
    Foo() {
        mtx1.lock(), mtx2.lock();
    }

    void first(function<void()> printFirst) {
        printFirst();
        mtx1.unlock();
    }

    void second(function<void()> printSecond) {
        mtx1.lock();
        printSecond();
        mtx1.unlock();
        mtx2.unlock();
    }

    void third(function<void()> printThird) {
        mtx2.lock();
        printThird();
        mtx2.unlock();
    }
};

• 2. 条件变量

class Foo {
    condition_variable cv;
    mutex mtx;
    int k = 0;
public:
    void first(function<void()> printFirst) {
        printFirst();
        k = 1;
        cv.notify_all();    // 通知其他所有在等待唤醒队列中的线程
    }

    void second(function<void()> printSecond) {
        unique_lock<mutex> lock(mtx);   // lock mtx
        cv.wait(lock, [this](){ return k == 1; });  // unlock mtx，并阻塞等待唤醒通知，需要满足 k == 1 才能继续运行
        printSecond();
        k = 2;
        cv.notify_one();    // 随机通知一个（unspecified）在等待唤醒队列中的线程
    }

    void third(function<void()> printThird) {
        unique_lock<mutex> lock(mtx);   // lock mtx
        cv.wait(lock, [this](){ return k == 2; });  // unlock mtx，并阻塞等待唤醒通知，需要满足 k == 2 才能继续运行
        printThird();
    }
};

• 3. <sempahore.h>

class Foo {
private:
    sem_t sem_1, sem_2;

public:
    Foo() {
        sem_init(&sem_1, 0, 0), sem_init(&sem_2, 0, 0);
    }

    void first(function<void()> printFirst) {
        printFirst();
        sem_post(&sem_1);
    }

    void second(function<void()> printSecond) {
        sem_wait(&sem_1);
        printSecond();
        sem_post(&sem_2);
    }

    void third(function<void()> printThird) {
        sem_wait(&sem_2);
        printThird();
    }
};

• 4. std::future 异步操作

class Foo {
    promise<void> pro1, pro2;

public:
    void first(function<void()> printFirst) {
        printFirst();
        pro1.set_value();
    }

    void second(function<void()> printSecond) {
        pro1.get_future().wait();
        printSecond();
        pro2.set_value();
    }

    void third(function<void()> printThird) {
        pro2.get_future().wait();
        printThird();
    }
};

• 原子操作

class Foo {
    std::atomic<bool> a{ false };
    std::atomic<bool> b{ false };
public:
    void first(function<void()> printFirst) {
        printFirst();
        a = true;
    }

    void second(function<void()> printSecond) {
        while (!a)
            this_thread::sleep_for(chrono::milliseconds(1));
        printSecond();
        b = true;
    }

    void third(function<void()> printThird) {
        while (!b)
            this_thread::sleep_for(chrono::milliseconds(1));
        printThird();
    }
};

2 交替打印 FooBar

交替打印 FooBar
解法

• <semaphore.h>

#include<semaphore.h>
class FooBar {
private:
    int n;
    sem_t m1, m2;
public:
    FooBar(int n) {
        this->n = n;
        sem_init(&m1, 0, 0);
        sem_init(&m2, 0, 0);
        sem_post(&m2);
    }

    void foo(function<void()> printFoo) {
        
        for (int i = 0; i < n; i++) {
            sem_wait(&m2);
        	// printFoo() outputs "foo". Do not change or remove this line.
        	printFoo();
            sem_post(&m1);
        }
    }

    void bar(function<void()> printBar) {
        
        for (int i = 0; i < n; i++) {
            sem_wait(&m1);
        	// printBar() outputs "bar". Do not change or remove this line.
        	printBar();
            sem_post(&m2);
        }
    }
};