MWL#116: Replace atomic queue with simple mutex locking for non-transactional binlog writes.

Also add missing destroy of pthread_cond.

sql/log.cc

@@ -158,15 +158,15 @@ class binlog_trx_data {
     before_stmt_pos(MY_OFF_T_UNDEF), using_xa(0), commit_bin_log_file_pos(0)
   {
     trans_log.end_of_file= max_binlog_cache_size;
-    (void) my_pthread_mutex_init(&LOCK_group_commit, MY_MUTEX_INIT_SLOW,
-                                 "LOCK_group_commit", MYF(0));
+    (void) my_pthread_mutex_init(&LOCK_binlog_participant, MY_MUTEX_INIT_SLOW,
+                                 "LOCK_binlog_participant", MYF(0));
     (void) pthread_cond_init(&COND_group_commit, 0);
   }
 
   ~binlog_trx_data()
   {
     DBUG_ASSERT(pending() == NULL);
-    (void) pthread_mutex_destroy(&LOCK_group_commit);
+    (void) pthread_mutex_destroy(&LOCK_binlog_participant);
     close_cached_file(&trans_log);
   }
 
@@ -274,13 +274,13 @@ class binlog_trx_data {
   /*
     Flag set true when group commit for this transaction is finished; used
     with pthread_cond_wait() to wait until commit is done.
-    This flag is protected by LOCK_group_commit.
+    This flag is protected by LOCK_binlog_participant.
   */
   bool done;
   /*
     Flag set if this transaction is the group commit leader that will handle
     the actual writing to the binlog.
-    This flag is protected by LOCK_group_commit.
+    This flag is protected by LOCK_binlog_participant.
   */
   bool group_commit_leader;
   /*
@@ -297,7 +297,7 @@ class binlog_trx_data {
   Log_event *end_event;
   Log_event *incident_event;
   /* Mutex and condition for wakeup after group commit. */
-  pthread_mutex_t LOCK_group_commit;
+  pthread_mutex_t LOCK_binlog_participant;
   pthread_cond_t COND_group_commit;
   /*
     Binlog position after current commit, available to storage engines during
@@ -4994,8 +4994,13 @@ MYSQL_BIN_LOG::write_transaction_to_binlog_events(binlog_trx_data *trx_data)
     the commit and wake them up.
   */
 
-  pthread_mutex_lock(&trx_data->LOCK_group_commit);
-  const binlog_trx_data *orig_queue= atomic_enqueue_trx(trx_data);
+  pthread_mutex_lock(&trx_data->LOCK_binlog_participant);
+
+  pthread_mutex_lock(&LOCK_queue);
+  binlog_trx_data *orig_queue= group_commit_queue;
+  trx_data->next= orig_queue;
+  group_commit_queue= trx_data;
+  pthread_mutex_unlock(&LOCK_queue);
 
   if (orig_queue != NULL)
   {
@@ -5006,7 +5011,7 @@ MYSQL_BIN_LOG::write_transaction_to_binlog_events(binlog_trx_data *trx_data)
   else
   {
     trx_data->group_commit_leader= TRUE;
-    pthread_mutex_unlock(&trx_data->LOCK_group_commit);
+    pthread_mutex_unlock(&trx_data->LOCK_binlog_participant);
     trx_group_commit_leader(NULL);
   }
 
@@ -5020,19 +5025,19 @@ MYSQL_BIN_LOG::write_transaction_to_binlog_events(binlog_trx_data *trx_data)
   this thread in the group commit once the log is obtained. So here we put
   ourself in the queue and wait to be signalled that the group commit is done.
 
-  Note that this function must be called with the trs_data->LOCK_group_commit
+  Note that this function must be called with trx_data->LOCK_binlog_participant
   locked; the mutex will be released before return.
 */
 void
 MYSQL_BIN_LOG::trx_group_commit_participant(binlog_trx_data *trx_data)
 {
-  safe_mutex_assert_owner(&trx_data->LOCK_group_commit);
+  safe_mutex_assert_owner(&trx_data->LOCK_binlog_participant);
 
   /* Wait until trx_data.done == true and woken up by the leader. */
   while (!trx_data->done)
     pthread_cond_wait(&trx_data->COND_group_commit,
-                      &trx_data->LOCK_group_commit);
-  pthread_mutex_unlock(&trx_data->LOCK_group_commit);
+                      &trx_data->LOCK_binlog_participant);
+  pthread_mutex_unlock(&trx_data->LOCK_binlog_participant);
 }
 
 bool
@@ -5131,7 +5136,10 @@ MYSQL_BIN_LOG::trx_group_commit_leader(TC_group_commit_entry *first)
     it to the existing one. Note that there is no ordering defined between
     transactional and non-transactional commits.
   */
-  binlog_trx_data *current= atomic_grab_trx_queue();
+  pthread_mutex_lock(&LOCK_queue);
+  binlog_trx_data *current= group_commit_queue;
+  group_commit_queue= NULL;
+  pthread_mutex_unlock(&LOCK_queue);
   binlog_trx_data *xtra_queue= NULL;
   while (current)
   {
@@ -5230,18 +5238,19 @@ MYSQL_BIN_LOG::trx_group_commit_leader(TC_group_commit_entry *first)
   for (current= xtra_queue; current != NULL; current= current->next)
   {
     /*
-      Note that we need to take LOCK_group_commit even in the case of a leader!
+      Note that we need to take LOCK_binlog_participant even in the case of a
+      leader!
 
       Otherwise there is a race between setting and testing the
       group_commit_leader flag.
     */
-    pthread_mutex_lock(&current->LOCK_group_commit);
+    pthread_mutex_lock(&current->LOCK_binlog_participant);
     if (!current->group_commit_leader)
     {
       current->done= true;
       pthread_cond_signal(&current->COND_group_commit);
     }
-    pthread_mutex_unlock(&current->LOCK_group_commit);
+    pthread_mutex_unlock(&current->LOCK_binlog_participant);
   }
 }
 
@@ -5291,32 +5300,6 @@ MYSQL_BIN_LOG::write_transaction(binlog_trx_data *trx_data)
   return 0;
 }
 
-binlog_trx_data *
-MYSQL_BIN_LOG::atomic_enqueue_trx(binlog_trx_data *trx_data)
-{
-  my_atomic_rwlock_wrlock(&LOCK_queue);
-  trx_data->next= group_commit_queue;
-  while (!my_atomic_casptr((void **)(&group_commit_queue),
-                           (void **)(&trx_data->next),
-                           trx_data))
-    ;
-  my_atomic_rwlock_wrunlock(&LOCK_queue);
-  return trx_data->next;
-}
-
-binlog_trx_data *
-MYSQL_BIN_LOG::atomic_grab_trx_queue()
-{
-  my_atomic_rwlock_wrlock(&LOCK_queue);
-  binlog_trx_data *queue= group_commit_queue;
-  while (!my_atomic_casptr((void **)(&group_commit_queue),
-                           (void **)(&queue),
-                           NULL))
-    ;
-  my_atomic_rwlock_wrunlock(&LOCK_queue);
-  return queue;
-}
-
 /**
   Wait until we get a signal that the binary log has been updated.
 

sql/log.h

@@ -404,8 +404,8 @@ class MYSQL_BIN_LOG: public TC_LOG_group_commit, private MYSQL_LOG
   pthread_mutex_t LOCK_index;
   pthread_mutex_t LOCK_prep_xids;
   /*
-    Mutex to protect the queue of transactions waiting to participate in group
-    commit. (Only used on platforms without native atomic operations).
+    Mutex to protect the queue of non-transactional binlog writes waiting to
+    participate in group commit.
   */
   pthread_mutex_t LOCK_queue;
 
@@ -462,8 +462,6 @@ class MYSQL_BIN_LOG: public TC_LOG_group_commit, private MYSQL_LOG
   bool write_transaction_to_binlog_events(binlog_trx_data *trx_data);
   void trx_group_commit_participant(binlog_trx_data *trx_data);
   void trx_group_commit_leader(TC_group_commit_entry *first);
-  binlog_trx_data *atomic_enqueue_trx(binlog_trx_data *trx_data);
-  binlog_trx_data *atomic_grab_trx_queue();
   void mark_xid_done();
   void mark_xids_active(uint xid_count);