WL#2360 Performance schema

Part V: performance schema implementation

1 files changed, 78 insertions, 0 deletions

diff --git a/storage/perfschema/pfs_atomic.cc b/storage/perfschema/pfs_atomic.cc
new file mode 100644
index 00000000000..c33bb251767
--- /dev/null
+++ b/storage/perfschema/pfs_atomic.cc
@@ -0,0 +1,78 @@
+/* Copyright (C) 2009 Sun Microsystems, Inc
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; version 2 of the License.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+/**
+  @file storage/perfschema/pfs_atomic.cc
+  Atomic operations (implementation).
+*/
+
+#include <my_global.h>
+#include <my_pthread.h>
+#include "pfs_atomic.h"
+
+/*
+  Using SAFE_MUTEX is impossible, because of recursion.
+  - code locks mutex X
+    - P_S records the event
+      - P_S needs an atomic counter A
+        - safe mutex called for m_mutex[hash(A)]
+          - safe mutex allocates/free memory
+            - safe mutex locks THR_LOCK_malloc
+              - P_S records the event
+                - P_S needs an atomic counter B
+                  - safe mutex called for m_mutex[hash(B)]
+
+  When hash(A) == hash(B), safe_mutex complains rightly that
+  the mutex is already locked.
+  In some cases, A == B, in particular for events_waits_history_long_index.
+
+  In short, the implementation of PFS_atomic should not cause events
+  to be recorded in the performance schema.
+
+  Also, because SAFE_MUTEX redefines pthread_mutex_t, etc,
+  this code is not inlined in pfs_atomic.h, but located here in pfs_atomic.cc.
+
+  What is needed is a plain, unmodified, pthread_mutex_t.
+  This is provided by my_atomic_rwlock_t.
+*/
+
+/**
+  Internal rwlock array.
+  Using a single rwlock for all atomic operations would be a bottleneck.
+  Using a rwlock per performance schema structure would be too costly in
+  memory, and use too many rwlock.
+  The PFS_atomic implementation computes a hash value from the
+  atomic variable, to spread the bottleneck across 256 buckets,
+  while still providing --transparently for the caller-- an atomic
+  operation.
+*/
+my_atomic_rwlock_t PFS_atomic::m_rwlock_array[256];
+
+void PFS_atomic::init(void)
+{
+  uint i;
+
+  for (i=0; i< array_elements(m_rwlock_array); i++)
+    my_atomic_rwlock_init(&m_rwlock_array[i]);
+}
+
+void PFS_atomic::cleanup(void)
+{
+  uint i;
+
+  for (i=0; i< array_elements(m_rwlock_array); i++)
+    my_atomic_rwlock_destroy(&m_rwlock_array[i]);
+}
+