title: pthread_mutex_t struct: What does lock stand for?
body: <p>I am looking at the pthread_mutex_t structure in the pthreadtypes.h file. What does the "__lock" stand for? Is it like a lock number assigned to the mutex?</p>
  
  <pre><code>typedef union
  {
    struct __pthread_mutex_s
    {
       int __lock;
       unsigned int __count;
       int __owner;
       #if __WORDSIZE == 64
       unsigned int __nusers;
       #endif
      /* KIND must stay at this position in the structure to maintain
       binary compatibility.  */
       int __kind;
       #if __WORDSIZE == 64
       int __spins;
       __pthread_list_t __list;
       # define __PTHREAD_MUTEX_HAVE_PREV 1
       #else
       unsigned int __nusers;
       __extension__ union
      {
        int __spins;
        __pthread_slist_t __list;
      };
      #endif
    } __data;
   char __size[__SIZEOF_PTHREAD_MUTEX_T];
   long int __align;
  </code></pre>
  
  <p>} pthread_mutex_t;</p>