sync0sync.c Fix the infinite spin on FreeBSD

os0thread.c	Use pthread_yield instead of os_thread_sleep(0)

BitKeeper/etc/logging_ok

-mwagner@evoq.mwagner.org
-jcole@abel.spaceapes.com
-monty@donna.mysql.fi
-sasha@mysql.sashanet.com
+heikki@donna.mysql.fi

innobase/os/os0thread.c

@@ -122,7 +122,7 @@ os_thread_yield(void)
 #ifdef __WIN__	
 	Sleep(0);
 #else
-	os_thread_sleep(0);
+	pthread_yield();
 #endif
 }
 

innobase/sync/sync0sync.c

@@ -367,6 +367,15 @@ spin_loop:
                 return;
    	}
 
+	/* We may end up with a situation where lock_word is
+	0 but the OS fast mutex is still reserved. On FreeBSD
+	the OS does not seem to schedule a thread which is constantly
+	calling pthread_mutex_trylock (in mutex_test_and_set
+	implementation). Then we could end up spinning here indefinitely.
+	The following 'i++' stops this infinite spin. */
+
+	i++;
+        
 	if (i < SYNC_SPIN_ROUNDS) {
 
 		goto spin_loop;