pthread_cond remove csection

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 <[email protected]>

include/pthread.h

@@ -269,6 +269,7 @@ struct pthread_cond_s
 {
   sem_t sem;
   clockid_t clockid;
+  volatile int16_t lock_count;
 };
 
 #ifndef __PTHREAD_COND_T_DEFINED

libs/libc/pthread/pthread_condinit.c

@@ -74,6 +74,7 @@ int pthread_cond_init(FAR pthread_cond_t *cond,
   else
     {
       cond->clockid = attr ? attr->clockid : CLOCK_REALTIME;
+      cond->lock_count = 0;
     }
 
   sinfo("Returning %d\n", ret);

sched/pthread/pthread_condclockwait.c

@@ -75,7 +75,6 @@ int pthread_cond_clockwait(FAR pthread_cond_t *cond,
                            clockid_t clockid,
                            FAR const struct timespec *abstime)
 {
-  irqstate_t flags;
   int ret = OK;
   int status;
 
@@ -114,14 +113,7 @@ int pthread_cond_clockwait(FAR pthread_cond_t *cond,
 
       sinfo("Give up mutex...\n");
 
-      /* We must disable pre-emption and interrupts here so that
-       * the time stays valid until the wait begins.   This adds
-       * complexity because we assure that interrupts and
-       * pre-emption are re-enabled correctly.
-       */
-
-      sched_lock();
-      flags = enter_critical_section();
+      cond->lock_count--;
 
       /* Give up the mutex */
 
@@ -136,12 +128,6 @@ int pthread_cond_clockwait(FAR pthread_cond_t *cond,
             }
         }
 
-      /* Restore interrupts  (pre-emption will be enabled
-       * when we fall through the if/then/else)
-       */
-
-      leave_critical_section(flags);
-
       /* Reacquire the mutex (retaining the ret). */
 
       sinfo("Re-locking...\n");
@@ -151,12 +137,6 @@ int pthread_cond_clockwait(FAR pthread_cond_t *cond,
         {
           ret = status;
         }
-
-      /* Re-enable pre-emption (It is expected that interrupts
-       * have already been re-enabled in the above logic)
-       */
-
-      sched_unlock();
     }
 
   leave_cancellation_point();

sched/pthread/pthread_condsignal.c

@@ -55,7 +55,6 @@
 int pthread_cond_signal(FAR pthread_cond_t *cond)
 {
   int ret = OK;
-  int sval;
 
   sinfo("cond=%p\n", cond);
 
@@ -65,36 +64,11 @@ int pthread_cond_signal(FAR pthread_cond_t *cond)
     }
   else
     {
-      /* Get the current value of the semaphore */
-
-      if (nxsem_get_value(&cond->sem, &sval) != OK)
-        {
-          ret = EINVAL;
-        }
-
-      /* If the value is less than zero (meaning that one or more
-       * thread is waiting), then post the condition semaphore.
-       * Only the highest priority waiting thread will get to execute
-       */
-
-      else
+      if (cond->lock_count < 0)
         {
-          /* One of my objectives in this design was to make
-           * pthread_cond_signal() usable from interrupt handlers.  However,
-           * from interrupt handlers, you cannot take the associated mutex
-           * before signaling the condition.  As a result, I think that
-           * there could be a race condition with the following logic which
-           * assumes that the if sval < 0 then the thread is waiting.
-           * Without the mutex, there is no atomic, protected operation that
-           * will guarantee this to be so.
-           */
-
-          sinfo("sval=%d\n", sval);
-          if (sval < 0)
-            {
-              sinfo("Signalling...\n");
-              ret = -nxsem_post(&cond->sem);
-            }
+          sinfo("Signalling...\n");
+          cond->lock_count++;
+          ret = -nxsem_post(&cond->sem);
         }
     }
 

sched/pthread/pthread_condwait.c

@@ -60,7 +60,6 @@ int pthread_cond_wait(FAR pthread_cond_t *cond, FAR pthread_mutex_t *mutex)
 {
   int status;
   int ret;
-  irqstate_t flags;
 
   sinfo("cond=%p mutex=%p\n", cond, mutex);
 
@@ -89,14 +88,9 @@ int pthread_cond_wait(FAR pthread_cond_t *cond, FAR pthread_mutex_t *mutex)
 
       sinfo("Give up mutex / take cond\n");
 
-      flags = enter_critical_section();
-      sched_lock();
+      cond->lock_count--;
       ret = pthread_mutex_breaklock(mutex, &nlocks);
 
-      /* Take the semaphore.  This may be awakened only be a signal (EINTR)
-       * or if the thread is canceled (ECANCELED)
-       */
-
       status = -nxsem_wait_uninterruptible(&cond->sem);
       if (ret == OK)
         {
@@ -105,9 +99,6 @@ int pthread_cond_wait(FAR pthread_cond_t *cond, FAR pthread_mutex_t *mutex)
           ret = status;
         }
 
-      sched_unlock();
-      leave_critical_section(flags);
-
       /* Reacquire the mutex.
        *
        * When cancellation points are enabled, we need to hold the mutex