Linux线程互斥锁：核心机制与实战指南

Linux线程互斥的基本概念

线程互斥是多线程编程中防止数据竞争的核心机制。当多个线程访问共享资源时，互斥锁（Mutex）确保同一时间仅有一个线程能执行临界区代码，避免数据不一致问题。Linux通过POSIX线程库（pthread）提供互斥锁支持，核心操作包括初始化、加锁、解锁和销毁。

互斥锁的类型与特性

Linux中常见的互斥锁类型包括：

普通互斥锁（PTHREAD_MUTEX_NORMAL）：默认类型，重复加锁会导致死锁。
检错互斥锁（PTHREAD_MUTEX_ERRORCHECK）：检测重复加锁并返回错误码。
递归互斥锁（PTHREAD_MUTEX_RECURSIVE）：允许同一线程多次加锁，需对应次数的解锁。
自适应互斥锁（PTHREAD_MUTEX_ADAPTIVE_NP）：针对高竞争场景优化，减少线程切换开销。

互斥锁的API与使用示例

以下是关键API及典型用法：

初始化与销毁

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; // 静态初始化
// 或动态初始化
pthread_mutex_init(&mutex, NULL); 
pthread_mutex_destroy(&mutex); // 销毁

加锁与解锁

pthread_mutex_lock(&mutex);   // 阻塞式加锁
if (pthread_mutex_trylock(&mutex) == 0) { // 非阻塞尝试
    // 临界区操作
    pthread_mutex_unlock(&mutex);
}

互斥锁的注意事项

避免死锁：确保加锁顺序一致，或使用超时机制（如pthread_mutex_timedlock）。
性能优化：减少临界区代码量，缩短锁持有时间。高竞争场景可考虑读写锁（pthread_rwlock_t）。
错误处理：检查API返回值，如pthread_mutex_lock可能因线程终止或资源不足失败。

替代方案与高级特性

条件变量（Condition Variable）：结合互斥锁实现线程间同步，适用于生产者-消费者模型。
原子操作：对简单数据类型（如int）可使用GCC内置原子操作（__atomic_*）替代锁。
无锁编程：CAS（Compare-And-Swap）等机制适用于特定场景，但实现复杂度较高。

实际案例：线程安全队列

以下是一个使用互斥锁实现的线程安全队列片段：

typedef struct {
    int *buffer;
    int capacity;
    int head, tail;
    pthread_mutex_t lock;
} ThreadSafeQueue;

void enqueue(ThreadSafeQueue *q, int item) {
    pthread_mutex_lock(&q->lock);
    q->buffer[q->tail] = item;
    q->tail = (q->tail + 1) % q->capacity;
    pthread_mutex_unlock(&q->lock);
}

通过合理设计锁粒度（如分段锁）可进一步提升并发性能。

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