c++正确使用互斥

我有一个多线程项目，我用--tool=helgrind运行了valgrind，它显示了一些错误。我在那里使用互斥，我在网上找到了如何使用它，你能告诉我怎么了吗？

#include <iostream>
#include <pthread.h>
#define MAX_THREADS     100
#define MAX_SESSIONS    100
static pthread_mutex_t  M_CREATE_SESSION_LOCK= PTHREAD_MUTEX_INITIALIZER;

.....

void connection::proccess(threadVarsType &THREAD) {
    ....
    pthread_mutex_lock(&M_CREATE_SESSION_LOCK);
    unsigned int ii;
    for (ii=0; ii<MAX_SESSIONS; ii++) {
        if (SESSION[ii]==NULL) {
            break;
        }
    }
    if (ii==MAX_SESSIONS-1) {
        ....
        pthread_mutex_unlock(&M_CREATE_SESSION_LOCK);                       // unlock session mutex
        ....
        return;
    } else {
        ....
        pthread_mutex_unlock(&M_CREATE_SESSION_LOCK);                       // unlock session mutex
        ....
    }
    ....
}

以及错误消息：

==4985== Thread #1's call to pthread_mutex_lock failed
==4985==    with error code 22 (EINVAL: Invalid argument)
    ....
==4985== Thread #1 unlocked an invalid lock at 0x4E7B40
==4985==    at 0x32CD8: pthread_mutex_unlock (hg_intercepts.c:610)
    ....
==4985== Thread #1's call to pthread_mutex_unlock failed
==4985==    with error code 22 (EINVAL: Invalid argument)
    ....
==4985== Thread #1's call to pthread_mutex_lock failed
==4985==    with error code 22 (EINVAL: Invalid argument)
    ....
==4985== Thread #1 unlocked an invalid lock at 0x4E7B40
==4985==    at 0x32CD8: pthread_mutex_unlock (hg_intercepts.c:610)
    ....
==4985== Thread #1's call to pthread_mutex_unlock failed
==4985==    with error code 22 (EINVAL: Invalid argument)