pthread: remove enter_critical_section in pthread_barrier_wait

reason:
We decouple semcount from business logic by using an independent counting variable,
which allows us to remove critical sections in many cases.

Signed-off-by: hujun5 <hujun5@xiaomi.com>

include/pthread.h

@@ -368,6 +368,8 @@ struct pthread_barrier_s
 {
   sem_t        sem;
   unsigned int count;
+  unsigned int wait_count;
+  mutex_t      mutex;
 };
 
 #ifndef __PTHREAD_BARRIER_T_DEFINED

libs/libc/pthread/pthread_barrierinit.c

@@ -87,6 +87,8 @@ int pthread_barrier_init(FAR pthread_barrier_t *barrier,
     {
       sem_init(&barrier->sem, 0, 0);
       barrier->count = count;
+      barrier->wait_count = 0;
+      nxmutex_init(&barrier->mutex);
     }
 
   return ret;

sched/pthread/pthread_barrierwait.c

@@ -82,67 +82,35 @@
 
 int pthread_barrier_wait(FAR pthread_barrier_t *barrier)
 {
-  irqstate_t flags;
-  int semcount;
-  int ret;
-
   if (barrier == NULL)
     {
       return EINVAL;
     }
 
-  /* Disable pre-emption throughout the following */
-
-  flags = enter_critical_section();
-
-  /* Find out how many threads are already waiting at the barrier */
-
-  ret = nxsem_get_value(&barrier->sem, &semcount);
-  if (ret != OK)
-    {
-      leave_critical_section(flags);
-      return -ret;
-    }
-
   /* If the number of waiters would be equal to the count, then we are done */
 
-  if ((1 - semcount) >= (int)barrier->count)
+  nxmutex_lock(&barrier->mutex);
+
+  if ((barrier->wait_count + 1) >= barrier->count)
     {
       /* Free all of the waiting threads */
 
-      while (semcount < 0)
+      while (barrier->wait_count > 0)
         {
+          barrier->wait_count--;
           nxsem_post(&barrier->sem);
-          nxsem_get_value(&barrier->sem, &semcount);
         }
 
       /* Then return PTHREAD_BARRIER_SERIAL_THREAD to the final thread */
 
-      leave_critical_section(flags);
+      nxmutex_unlock(&barrier->mutex);
+
       return PTHREAD_BARRIER_SERIAL_THREAD;
     }
 
-  /* Otherwise, this thread must wait as well */
+  barrier->wait_count++;
 
-  while ((ret = nxsem_wait(&barrier->sem)) != OK)
+  nxmutex_unlock(&barrier->mutex);
-    {
-      /* If the thread is awakened by a signal, just continue to wait */
 
-      if (ret != -EINTR)
+  return -nxsem_wait_uninterruptible(&barrier->sem);
-        {
-          /* If it is awakened by some other error, then there is a
-           * problem
-           */
-
-          break;
-        }
-    }
-
-  /* We will only get here when we are one of the N-1 threads that were
-   * waiting for the final thread at the barrier.  We just need to return
-   * zero.
-   */
-
-  leave_critical_section(flags);
-  return -ret;
 }