SQLite

static void pthreadMutexFree(sqlite3_mutex *p){
  assert( p->nRef==0 );
  assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
  pthread_mutex_destroy(&p->mutex);
  sqlite3_free(p);
}

#include <sys/time.h>
#ifdef SQLITE_MUTEX_NREF
# define MUTEX_ID(p)  (p->id)
#else
# define MUTEX_ID(p)  0
#endif

/*
** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
** to enter a mutex.  If another thread is already within the mutex,
** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
** be entered multiple times by the same thread.  In such cases the,
** mutex must be exited an equal number of times before another thread
** can enter.  If the same thread tries to enter any other kind of mutex
** more than once, the behavior is undefined.
*/
static void pthreadMutexEnter(sqlite3_mutex *p){
  struct timeval x;
  sqlite3_uint64 iBegin, iEnd;
  assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );

  gettimeofday(&x, 0);
  iBegin = 1000000*(sqlite3_uint64)x.tv_sec + x.tv_usec;
#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
  /* If recursive mutexes are not available, then we have to grow
  ** our own.  This implementation assumes that pthread_equal()
  ** is atomic - that it cannot be deceived into thinking self
  ** and p->owner are equal if p->owner changes between two values
  ** that are not equal to self while the comparison is taking place.
  ** This implementation also assumes a coherent cache - that 

  */
  pthread_mutex_lock(&p->mutex);
#if SQLITE_MUTEX_NREF
  assert( p->nRef>0 || p->owner==0 );
  p->owner = pthread_self();
  p->nRef++;
#endif
  gettimeofday(&x, 0);
  iEnd = 1000000*(sqlite3_uint64)x.tv_sec + x.tv_usec;
  if( iEnd > iBegin+500 ){
    sqlite3_mutex *pMaster = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER);
    int id = -1;
    if( p>=pMaster && p<=&pMaster[SQLITE_MUTEX_STATIC_APP3-2] ){
      id = (int)(p - pMaster) + 2;
    }
    sqlite3_log(SQLITE_NOTICE, "slow mutex: %llu uS on %d/%p",
                iEnd - iBegin, id, p);
  }
#endif

#ifdef SQLITE_DEBUG
  if( p->trace ){
    printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
  }