C++线程同步和互斥

news2024/12/28 5:43:22

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1、互斥锁基本使用

#include <mutex>
#include <thread>
#include <iostream>

class Counter {
private:
    int value = 0;
    std::mutex mtx;

public:
    // 使用互斥锁保护临界区
    void increment() {
        // 传统加锁方式
        mtx.lock();
        value++;
        mtx.unlock();
    }

    // 推荐使用RAII锁
    void incrementSafe() {
        std::lock_guard<std::mutex> lock(mtx);
        value++;
    }

    int getValue() {
        std::lock_guard<std::mutex> lock(mtx);
        return value;
    }
};

2、读写锁

#include <shared_mutex>

class ThreadSafeCache {
private:
    std::unordered_map<int, std::string> cache;
    mutable std::shared_mutex mtx;

public:
    // 写操作
    void put(int key, const std::string& value) {
        std::unique_lock<std::shared_mutex> lock(mtx);
        cache[key] = value;
    }

    // 读操作
    std::string get(int key) const {
        std::shared_lock<std::shared_mutex> lock(mtx);
        auto it = cache.find(key);
        return (it != cache.end()) ? it->second : "";
    }
};

3、条件变量

#include <condition_variable>
#include <queue>

class ThreadSafeQueue {
private:
    std::queue<int> queue;
    std::mutex mtx;
    std::condition_variable cv;

public:
    void push(int value) {
        {
            std::lock_guard<std::mutex> lock(mtx);
            queue.push(value);
        }
        cv.notify_one(); // 通知等待线程
    }

    int pop() {
        std::unique_lock<std::mutex> lock(mtx);
        
        // 等待直到队列非空
        cv.wait(lock, [this]() { 
            return !queue.empty(); 
        });

        int value = queue.front();
        queue.pop();
        return value;
    }
};

4、原子操作

#include <atomic>

class AtomicCounter {
private:
    std::atomic<int> counter{0};

public:
    void increment() {
        // 原子自增
        counter++;
    }

    int get() {
        return counter.load(); // 原子读取
    }

    // 复杂原子操作
    void complexOperation() {
        counter.compare_exchange_weak(
            expected,  // 期望值
            desired    // 新值
        );
    }
};

5、死锁预防

class DeadlockPrevention {
private:
    std::mutex mtx1, mtx2;

public:
    void safeOperation() {
        // 使用std::lock避免死锁
        std::lock(mtx1, mtx2);
        
        // RAII锁
        std::lock_guard<std::mutex> lock1(mtx1, std::adopt_lock);
        std::lock_guard<std::mutex> lock2(mtx2, std::adopt_lock);

        // 临界区代码
    }
};

6、信号量

class Semaphore {
private:
    std::mutex mtx;
    std::condition_variable cv;
    int count;

public:
    explicit Semaphore(int initial = 0) : count(initial) {}

    void wait() {
        std::unique_lock<std::mutex> lock(mtx);
        cv.wait(lock, [this] { return count > 0; });
        --count;
    }

    void signal() {
        std::unique_lock<std::mutex> lock(mtx);
        ++count;
        cv.notify_one();
    }
};

7、生产者、消费者模型

class ProducerConsumer {
private:
    std::queue<int> queue;
    std::mutex mtx;
    std::condition_variable not_full;
    std::condition_variable not_empty;
    const size_t CAPACITY = 10;

public:
    void produce(int value) {
        std::unique_lock<std::mutex> lock(mtx);
        
        // 等待队列不满
        not_full.wait(lock, [this]{ 
            return queue.size() < CAPACITY; 
        });

        queue.push(value);
        lock.unlock();
        not_empty.notify_one();
    }

    int consume() {
        std::unique_lock<std::mutex> lock(mtx);
        
        // 等待队列非空
        not_empty.wait(lock, [this]{ 
            return !queue.empty(); 
        });

        int value = queue.front();
        queue.pop();
        lock.unlock();
        not_full.notify_one();

        return value;
    }
};

8、性能优化

// 减少锁的粒度
class OptimizedCounter {
private:
    // 使用更细粒度的锁
    std::array<std::mutex, 16> locks;
    std::array<int, 16> counters = {0};

public:
    void increment(int index) {
        // 根据索引选择特定锁
        std::lock_guard<std::mutex> lock(locks[index % locks.size()]);
        counters[index % counters.size()]++;
    }
};