pthread_mutex_errorcheck_np初始化错误

Question

Below code gives me compilation error:

#include<pthread.h>
#include<stdio.h>

pthread_mutex_t mutex= PTHREAD_MUTEX_ERRORCHECK_NP;
int i=0;
void *func(void *a)
{
    pthread_mutex_lock(&mutex);
    i++;
    printf("The value of thread is: %d\n",i);
    pthread_mutex_unlock(&mutex);
    pthread_exit(NULL); 
}

int main()
{
    pthread_t id1,id2;
    if(pthread_create(&id1,NULL,func,NULL)<0)
    perror("pthread_create error\n");
    pthread_join(id1,NULL);
    pthread_join(id2,NULL);

}

The error is:

 error: invalid initializer
 pthread_mutex_t mutex= PTHREAD_MUTEX_ERRORCHECK_NP;

related content of my pthread.h is:

enum
{
  PTHREAD_MUTEX_TIMED_NP,
  PTHREAD_MUTEX_RECURSIVE_NP,
  PTHREAD_MUTEX_ERRORCHECK_NP,
  PTHREAD_MUTEX_ADAPTIVE_NP
#if defined __USE_UNIX98 || defined __USE_XOPEN2K8
  ,
  PTHREAD_MUTEX_NORMAL = PTHREAD_MUTEX_TIMED_NP,
  PTHREAD_MUTEX_RECURSIVE = PTHREAD_MUTEX_RECURSIVE_NP,
  PTHREAD_MUTEX_ERRORCHECK = PTHREAD_MUTEX_ERRORCHECK_NP,
  PTHREAD_MUTEX_DEFAULT = PTHREAD_MUTEX_NORMAL
#endif
#ifdef __USE_GNU
  /* For compatibility.  */
  , PTHREAD_MUTEX_FAST_NP = PTHREAD_MUTEX_TIMED_NP
#endif
};

Why this compilation error is occuring? I am not able to get any definite answer googling it. I am using gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1)

The command I used for compilation : gcc prog.c -lpthread

Answer 1

You need to use PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP when initializing the mutex statically with '=' (note the extra _INITIALIZER ). PTHREAD_MUTEX_ERRORCHECK_NP is for when you're initializing it at runtime using pthread_mutex_init(3) .

It is better to use -pthread than -lpthread by the way. It sets preprocessor flags to make some functions reentrant for example.