消息队列的实现

8.8 消息队列

队列是一种先进先出的结构，消息队列是进程(线程)常用的一种方法，实现消息队列常用的方法：

（1）阻塞队列 （2）无锁队列 （3）环形队列

值得注意的是：在pop 和push 一定要使用while循环，避免虚假唤醒

8.8.1 阻塞队列

(1）pthread

实现阻塞队列使用生产者-消费者模式，使用步骤：

#include 
#include 
//第一步，添加成员变量
std::queue queue_;
int max_size_;
pthread_mutex_t mutex_;
pthread_cond_t condition_var_;
//第二步，实现push函数
void Push(const T& item) {
    pthread_mutex_lock(&mutex_);

    while (queue_.size() >= max_size_) {
        pthread_cond_wait(&condition_var_, &mutex_);
    }

    queue_.push(item);
    pthread_cond_signal(&condition_var_);

    pthread_mutex_unlock(&mutex_);
}
//第三步，实现pop函数
 T Pop() 
 {
     pthread_mutex_lock(&mutex_);

     while (queue_.empty()) {
         pthread_cond_wait(&condition_var_, &mutex_);
     }

     T item = queue_.front();
     queue_.pop();
     pthread_cond_signal(&condition_var_);

     pthread_mutex_unlock(&mutex_);

     return item;
  }

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示例代码：

#include 
#include 

template 
class BlockingQueue {
public:
    BlockingQueue() : max_size_(100) {
        pthread_mutex_init(&mutex_, nullptr);
        pthread_cond_init(&condition_var_, nullptr);
    }

    ~BlockingQueue() {
        pthread_mutex_destroy(&mutex_);
        pthread_cond_destroy(&condition_var_);
    }

    void Push(const T& item) {
        pthread_mutex_lock(&mutex_);

        while (queue_.size() >= max_size_) {
            pthread_cond_wait(&condition_var_, &mutex_);
        }

        queue_.push(item);
        pthread_cond_signal(&condition_var_);

        pthread_mutex_unlock(&mutex_);
    }

    T Pop() {
        pthread_mutex_lock(&mutex_);

        while (queue_.empty()) {
            pthread_cond_wait(&condition_var_, &mutex_);
        }

        T item = queue_.front();
        queue_.pop();
        pthread_cond_signal(&condition_var_);

        pthread_mutex_unlock(&mutex_);

        return item;
    }

private:
    std::queue queue_;
    int max_size_;
    pthread_mutex_t mutex_;
    pthread_cond_t condition_var_;
};

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测试代码：

#include 
#include 
#include 
#include 

BlockingQueue queue;

void* ProducerThread(void* arg) {
    int thread_id = *static_cast(arg);
    for (int i = 1; i <= 5; ++i) {
        int item = thread_id * 10 + i;
        queue.Push(item);
        std::cout << "Producer " << thread_id << " produced: " << item << std::endl;
        sleep(1);
    }
    pthread_exit(nullptr);
}

void* ConsumerThread(void* arg) {
    int thread_id = *static_cast(arg);
    for (int i = 1; i <= 5; ++i) {
        int item = queue.Pop();
        std::cout << "Consumer " << thread_id << " consumed: " << item << std::endl;
        sleep(2);
    }
    pthread_exit(nullptr);
}

int main() {
    const int num_producers = 3;
    const int num_consumers = 2;

    std::vector producer_threads(num_producers);
    std::vector consumer_threads(num_consumers);

    for (int i = 0; i < num_producers; ++i) {
        int* thread_id = new int(i);
        pthread_create(&producer_threads[i], nullptr, ProducerThread, static_cast(thread_id));
    }

    for (int i = 0; i < num_consumers; ++i) {
        int* thread_id = new int(i);
        pthread_create(&consumer_threads[i], nullptr, ConsumerThread, static_cast(thread_id));
    }

    for (int i = 0; i < num_producers; ++i) {
        pthread_join(producer_threads[i], nullptr);
    }

    for (int i = 0; i < num_consumers; ++i) {
        pthread_join(consumer_threads[i], nullptr);
    }

    return 0;
}

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**（2）STD **

示例代码：

#include 
#include 
#include 

template 
class BlockingQueue {
public:
    BlockingQueue() = default;

    void Push(const T& item) {
        std::unique_lock lock(mutex_);

        while (queue_.size() >= max_size_) {
            condition_var_.wait(lock);
        }

        queue_.push(item);
        condition_var_.notify_one();
    }

    T Pop() {
        std::unique_lock lock(mutex_);

        while (queue_.empty()) {
            condition_var_.wait(lock);
        }

        T item = queue_.front();
        queue_.pop();
        condition_var_.notify_one();

        return item;
    }

private:
    std::queue queue_;
    std::mutex mutex_;
    std::condition_variable condition_var_;
    const size_t max_size_ = 100; // 最大容量
};

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8.8.2 环形队列

环形队列的特点：（1）固定容量 （2）前后指针 （3）循环存储

(1)pthread

示例代码：

#include 
#include 
#include 

template 
class CircularQueue {
public:
    CircularQueue(int capacity) : capacity_(capacity), front_(0), rear_(0), size_(0) {
        queue_.resize(capacity_);
        pthread_mutex_init(&mutex_, nullptr);
        pthread_cond_init(&condition_var_, nullptr);
    }

    ~CircularQueue() {
        pthread_mutex_destroy(&mutex_);
        pthread_cond_destroy(&condition_var_);
    }

    void Push(const T& item) {
        pthread_mutex_lock(&mutex_);

        while (size_ >= capacity_) {
            pthread_cond_wait(&condition_var_, &mutex_);
        }

        queue_[rear_] = item;
        rear_ = (rear_ + 1) % capacity_;
        ++size_;

        pthread_cond_signal(&condition_var_);

        pthread_mutex_unlock(&mutex_);
    }

    T Pop() {
        pthread_mutex_lock(&mutex_);

        while (size_ <= 0) {
            pthread_cond_wait(&condition_var_, &mutex_);
        }

        T item = queue_[front_];
        front_ = (front_ + 1) % capacity_;
        --size_;

        pthread_cond_signal(&condition_var_);

        pthread_mutex_unlock(&mutex_);

        return item;
    }

private:
    std::vector queue_;
    int capacity_;
    int front_;
    int rear_;
    int size_;
    pthread_mutex_t mutex_;
    pthread_cond_t condition_var_;
};

void* ProducerThread(void* arg) {
    CircularQueue* queue = static_cast*>(arg);

    for (int i = 1; i <= 10; ++i) {
        queue->Push(i);
        std::cout << "Produced: " << i << std::endl;
        sleep(1);
    }

    return nullptr;
}

void* ConsumerThread(void* arg) {
    CircularQueue* queue = static_cast*>(arg);

    for (int i = 1; i <= 10; ++i) {
        int item = queue->Pop();
        std::cout << "Consumed: " << item << std::endl;
        sleep(2);
    }

    return nullptr;
}

int main() {
    CircularQueue queue(5);

    pthread_t producer_thread;
    pthread_create(&producer_thread, nullptr, ProducerThread, static_cast(&queue));

    pthread_t consumer_thread;
    pthread_create(&consumer_thread, nullptr, ConsumerThread, static_cast(&queue));

    pthread_join(producer_thread, nullptr);
    pthread_join(consumer_thread, nullptr);

    return 0;
}

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（2）STD

示例代码：

#include 
#include 
#include 

template 
class CircularQueue {
public:
    CircularQueue(int capacity) : capacity_(capacity), front_(0), rear_(0), size_(0), queue_(capacity_) {}

    void Push(const T& item) {
        std::unique_lock lock(mutex_);

        while (IsFull()) {
            condition_var_.wait(lock);
        }

        queue_[rear_] = item;
        rear_ = (rear_ + 1) % capacity_;
        ++size_;

        condition_var_.notify_one();
    }

    T Pop() {
        std::unique_lock lock(mutex_);

        while (IsEmpty()) {
            condition_var_.wait(lock);
        }

        T item = queue_[front_];
        front_ = (front_ + 1) % capacity_;
        --size_;

        condition_var_.notify_one();

        return item;
    }

    bool IsEmpty() const {
        return size_ == 0;
    }

    bool IsFull() const {
        return size_ == capacity_;
    }

private:
    int capacity_;
    int front_;
    int rear_;
    int size_;
    std::vector queue_;
    std::mutex mutex_;
    std::condition_variable condition_var_;
};

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