Update.

2000-06-13  Kaz Kylheku  <kaz@ashi.footprints.net>

	A few optimizations.  Got rid of unnecessary wakeups of timer threads,
	tightened up some critical regions and micro-optimized some list
	manipulation code.

	* sysdeps/pthread/timer_routines.c (__timer_thread_queue_timer):
	Returns int value now to indicate whether timer was queued at head.
	* sysdeps/pthread/posix-timer.h: Likewise.
	* sysdeps/pthread/timer_settime.c (timer_settime): Takes advantage of
	new return value from __timer_thread_queue_timer to avoid waking
	up timer thread unnecessarily.

	* sysdeps/pthread/posix-timer.h (timer_id2ptr): No longer checks
	inuse flag, because this requires mutex to be held.  Callers updated
	to do the check when they have the mutex.
	* sysdeps/pthread/timer_getoverr.c: Add check for inuse here.

	* sysdeps/pthread/timer_settime.c (timer_settime): Tighter critical
	regions: avoids making system calls while holding timer mutex, and
	a few computations were moved outside of the mutex as well.
	* sysdeps/pthread/timer_gettime.c (timer_gettime): Likewise.

	* sysdeps/pthread/posix-timer.h (list_unlink_ip): Function name changed
	to list_unlink_ip, meaning idempotent.  Pointer manipulation
	changed to get better better code out of gcc.
	* sysdeps/pthread/timer_routines.c (list_unlink): Non-idempotent
	version of list_unlink added here.
	* sysdeps/pthread/timer_delete.c: Use appropriate list unlink
	function in all places: idempotent one for timers, non-idempotent
	one for thread nodes.
	* sysdeps/pthread/timer_settime: Likewise.
	* sysdeps/pthread/timer_routines.c: Likewise.

1 files changed, 38 insertions, 17 deletions

diff --git a/linuxthreads/sysdeps/pthread/timer_settime.c b/linuxthreads/sysdeps/pthread/timer_settime.c
index 63b117f797..858edc7657 100644
--- a/linuxthreads/sysdeps/pthread/timer_settime.c
+++ b/linuxthreads/sysdeps/pthread/timer_settime.c
@@ -35,11 +35,9 @@ timer_settime (timerid, flags, value, ovalue)
   struct timer_node *timer;
   struct thread_node *thread = NULL;
   struct timespec now;
-  int have_now = 0;
+  int have_now = 0, need_wakeup = 0;
   int retval = -1;
 
-  pthread_mutex_lock (&__timer_mutex);
-
   timer = timer_id2ptr (timerid);
   if (timer == NULL)
     {
@@ -56,14 +54,40 @@ timer_settime (timerid, flags, value, ovalue)
       goto bail;
     }
 
+  /* Will need to know current time since this is a relative timer;
+     might as well make the system call outside of the lock now! */
+
+  if ((flags & TIMER_ABSTIME) == 0)
+    {
+      clock_gettime (timer->clock, &now);
+      have_now = 1;
+    }
+
+  pthread_mutex_lock (&__timer_mutex);
+
+  /* One final check of timer validity; this one is possible only
+     until we have the mutex, which guards the inuse flag. */
+
+  if (!timer->inuse)
+    {
+      errno = EINVAL;
+      goto unlock_bail;
+    }
+
   if (ovalue != NULL)
     {
       ovalue->it_interval = timer->value.it_interval;
 
       if (timer->armed)
 	{
-	  clock_gettime (timer->clock, &now);
-	  have_now = 1;
+	  if (! have_now)
+	    {
+	      pthread_mutex_unlock (&__timer_mutex);
+	      clock_gettime (timer->clock, &now);
+	      have_now = 1;
+	      pthread_mutex_lock (&__timer_mutex);
+	    }
+
 	  timespec_sub (&ovalue->it_value, &timer->expirytime, &now);
 	}
       else
@@ -75,11 +99,12 @@ timer_settime (timerid, flags, value, ovalue)
 
   timer->value = *value;
 
-  list_unlink (&timer->links);
+  list_unlink_ip (&timer->links);
   timer->armed = 0;
 
   thread = timer->thread;
 
+  /* A value of { 0, 0 } causes the timer to be stopped. */
   if (value->it_value.tv_sec != 0
       || __builtin_expect (value->it_value.tv_nsec != 0, 1))
     {
@@ -87,25 +112,21 @@ timer_settime (timerid, flags, value, ovalue)
 	/* The user specified the expiration time.  */
 	timer->expirytime = value->it_value;
       else
-	{
-	  if (! have_now)
-	    clock_gettime (timer->clock, &now);
-
-	  timespec_add (&timer->expirytime, &now, &value->it_value);
-        }
+	timespec_add (&timer->expirytime, &now, &value->it_value);
 
-      __timer_thread_queue_timer (thread, timer);
+      /* Only need to wake up the thread if timer is inserted
+	 at the head of the queue. */
+      need_wakeup = __timer_thread_queue_timer (thread, timer);
       timer->armed = 1;
     }
 
   retval = 0;
 
-bail:
+unlock_bail:
   pthread_mutex_unlock (&__timer_mutex);
 
-  /* TODO: optimize this. Only need to wake up the thread if inserting
-     a new timer at the head of the queue.  */
-  if (thread != NULL)
+bail:
+  if (thread != NULL && need_wakeup)
     __timer_thread_wakeup (thread);
 
   return retval;