From 61cc839253bdc403a4da1ad638c20334d94fc9c0 Mon Sep 17 00:00:00 2001
From: Mikael Ronstrom <mikael@mysql.com>
Date: Mon, 17 Nov 2008 23:04:36 +0100
Subject: [PATCH] Fix for Percona reported bug with manual merge and fix of bug
 in patch (changed to use of UNIV_SYNC_ATOMIC from faulty
 HAVE_ATOMIC_BUILTINS).

---
 storage/innobase/include/sync0rw.ic | 29 ++++++++++++++++++++++-------
 storage/innobase/sync/sync0arr.c    |  7 ++++++-
 storage/innobase/sync/sync0rw.c     |  6 +++---
 3 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/storage/innobase/include/sync0rw.ic b/storage/innobase/include/sync0rw.ic
index d5d3ee954be..ce25ae0e6a8 100644
--- a/storage/innobase/include/sync0rw.ic
+++ b/storage/innobase/include/sync0rw.ic
@@ -57,10 +57,25 @@ UNIV_INLINE
 void
 rw_lock_set_waiters(
 /*================*/
-	rw_lock_t*	lock,
-	ulint		flag)
+	rw_lock_t*	lock)
 {
-	lock->waiters = flag;
+#ifdef UNIV_SYNC_ATOMIC
+	os_compare_and_swap(&(lock->waiters), 0, 1);
+#else /* UNIV_SYNC_ATOMIC */
+	lock->waiters = 1;
+#endif /* UNIV_SYNC_ATOMIC */
+}
+UNIV_INLINE
+void
+rw_lock_reset_waiters(
+/*================*/
+	rw_lock_t*	lock)
+{
+#ifdef UNIV_SYNC_ATOMIC
+	os_compare_and_swap(&(lock->waiters), 1, 0);
+#else /* UNIV_SYNC_ATOMIC */
+	lock->waiters = 0;
+#endif /* UNIV_SYNC_ATOMIC */
 }
 
 /**********************************************************************
@@ -454,7 +469,7 @@ rw_lock_s_unlock_direct(
 	/* Decrease reader count by incrementing lock_word */
 	lock->lock_word++;
 
-	ut_ad(!lock->waiters);
+	ut_ad(!rw_lock_get_waiters(lock));
 	ut_ad(rw_lock_validate(lock));
 #ifdef UNIV_SYNC_PERF_STAT
 	rw_s_exit_count++;
@@ -494,8 +509,8 @@ rw_lock_x_unlock_func(
 		/* Lock is now free. May have to signal read/write waiters.
                 We do not need to signal wait_ex waiters, since they cannot
                 exist when there is a writer. */
-		if(lock->waiters) {
-			rw_lock_set_waiters(lock, 0);
+		if(rw_lock_get_waiters(lock)) {
+			rw_lock_reset_waiters(lock);
 			os_event_set(lock->event);
 			sync_array_object_signalled(sync_primary_wait_array);
 		}
@@ -532,7 +547,7 @@ rw_lock_x_unlock_direct(
 
 	lock->lock_word += X_LOCK_DECR;
 
-	ut_ad(!lock->waiters);
+	ut_ad(!rw_lock_get_waiters(lock));
 	ut_ad(rw_lock_validate(lock));
 
 #ifdef UNIV_SYNC_PERF_STAT
diff --git a/storage/innobase/sync/sync0arr.c b/storage/innobase/sync/sync0arr.c
index a03d6d13502..bb64ac07342 100644
--- a/storage/innobase/sync/sync0arr.c
+++ b/storage/innobase/sync/sync0arr.c
@@ -549,7 +549,8 @@ sync_array_find_thread(
 		cell = sync_array_get_nth_cell(arr, i);
 
 		if (cell->wait_object != NULL
-		    && os_thread_eq(cell->thread, thread)) {
+		    && os_thread_eq(cell->thread, thread)
+		    && cell->waiting)) {
 
 			return(cell);	/* Found */
 		}
@@ -887,6 +888,10 @@ sync_arr_wake_threads_if_sema_free(void)
 		}
 			count++;
 
+		if (!cell->waiting) {
+			continue;
+		}
+
 			if (sync_arr_cell_can_wake_up(cell)) {
 
 			event = sync_cell_get_event(cell);
diff --git a/storage/innobase/sync/sync0rw.c b/storage/innobase/sync/sync0rw.c
index ced2f72187a..e178606cef5 100644
--- a/storage/innobase/sync/sync0rw.c
+++ b/storage/innobase/sync/sync0rw.c
@@ -209,7 +209,7 @@ rw_lock_create_func(
 #endif /* UNIV_SYNC_ATOMIC */
 
 	lock->lock_word = X_LOCK_DECR;
-	rw_lock_set_waiters(lock, 0);
+	lock->waiters = 0;
 	lock->writer_thread = -1;
 	lock->pass = 0;
 
@@ -369,7 +369,7 @@ lock_loop:
 
 		/* Set waiters before checking lock_word to ensure wake-up
                 signal is sent. This may lead to some unnecessary signals. */
-		rw_lock_set_waiters(lock, 1);
+		rw_lock_set_waiters(lock);
 
 		if (TRUE == rw_lock_s_lock_low(lock, pass, file_name, line)) {
 			sync_array_free_cell(sync_primary_wait_array, index);
@@ -634,7 +634,7 @@ lock_loop:
 
 	/* Waiters must be set before checking lock_word, to ensure signal
 	is sent. This could lead to a few unnecessary wake-up signals. */
-	rw_lock_set_waiters(lock, 1);
+	rw_lock_set_waiters(lock);
 
 	if (rw_lock_x_lock_low(lock, pass, file_name, line)) {
 		sync_array_free_cell(sync_primary_wait_array, index);