释放包含 pthread_mutex_t 的结构 memory 时是否需要调用 pthread_mutex_destroy

Question

Let's say I have a sruct:

typedef struct peer_info {
        int ip;
        int port;
        int offset;
        pthread_mutex_t mutex;
} peer_info;

and then I use the struct and free the struct like below:

peer_info* p_info = (peer_info*)malloc(sizeof(peer_info));
pthread_mutex_init(&p_info->mutex, NULL);

/* do some work on the p_info */


// need I call the pthread_mutex_destory(&p_info->mutex); ?
free(p_info);

I checke the glibc ntpl souce code, it seems i don't need to explictly call pthread_mutex_destory() since there is not memroy allocted on the pthread_mutex_t , which is a union type.

Answer 1

Yes. If you've initialised the mutex with pthread_mutex_init() , it should be destroyed with pthread_mutex_destroy() before freeing the memory.

The POSIX standard contemplates both implementations where the mutex entirely resides in the pthread_mutex_t type, and implementations where the type includes only a reference to some externally-allocated mutex object. This is reinforced by the fact that pthread_mutex_init() is allowed to fail due to various resource-exhaustion reasons.

Calling pthread_mutex_destroy() where appropriate ensures your code is portable to the latter kinds of implementations.

Answer 2

I find the answer on Richard's APUE book.

A mutex variable is represented by the pthread_mutex_t data type. Before we can use a mutex variable, we must first initialize it by either setting it to the constant PTHREAD_MUTEX_INITIALIZER (for statically allocated mutexes only) or calling pthread_mutex_init. If we allocate the mutex dynamically (by calling malloc, for example), then we need to call pthread_mutex_destroy before freeing the memory.