From: Marc Alff
Date: December 1 2010 8:33am
Subject: bzr commit into mysql-trunk-bugfixing branch (marc.alff:3401) Bug#58620
List-Archive: http://lists.mysql.com/commits/125614
X-Bug: 58620
Message-Id: <201012010834.oAUHIODr011368@acsinet15.oracle.com>
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#At file:///Users/malff/BZR_TREE/mysql-trunk-bugfixing-58620/ based on revid:nirbhay.choubey@stripped

 3401 Marc Alff	2010-12-01
      Bug#58620 Performance schema failed assert, pfs_instr_class.cc, line 956
      
      Before this fix, the member PFS_table_share::m_refcount was maintained
      with ++ and -- operations.
      
      This is not thread safe, since two threads may open or close table
      handles on the same table share, and compete when updating m_refcount.
      
      This fix uses atomic operations to maintain this reference counter,
      making the counter safe.

    modified:
      storage/perfschema/pfs_instr.cc
      storage/perfschema/pfs_instr_class.cc
      storage/perfschema/pfs_instr_class.h
=== modified file 'storage/perfschema/pfs_instr.cc'
--- a/storage/perfschema/pfs_instr.cc	2010-11-16 06:27:18 +0000
+++ b/storage/perfschema/pfs_instr.cc	2010-12-01 08:33:53 +0000
@@ -1057,7 +1057,7 @@ PFS_table* create_table(PFS_table_share 
         {
           pfs->m_identity= identity;
           pfs->m_share= share;
-          share->m_refcount++;
+          share->inc_refcount();
           pfs->m_wait_stat.m_control_flag=
             &flag_events_waits_summary_by_instance;
           pfs->m_wait_stat.m_parent= &share->m_wait_stat;

=== modified file 'storage/perfschema/pfs_instr_class.cc'
--- a/storage/perfschema/pfs_instr_class.cc	2010-11-16 06:27:18 +0000
+++ b/storage/perfschema/pfs_instr_class.cc	2010-12-01 08:33:53 +0000
@@ -788,7 +788,7 @@ search:
   {
     PFS_table_share *pfs;
     pfs= *entry;
-    pfs->m_refcount++ ;
+    pfs->inc_refcount() ;
     lf_hash_search_unpin(pins);
     return pfs;
   }
@@ -835,7 +835,7 @@ search:
           reset_single_stat_link(&pfs->m_wait_stat);
           pfs->m_enabled= enabled;
           pfs->m_timed= timed;
-          pfs->m_refcount= 1;
+          pfs->init_refcount();
 
           int res;
           res= lf_hash_insert(&table_share_hash, pins, &pfs);
@@ -879,7 +879,7 @@ search:
 */
 void purge_table_share(PFS_thread *thread, PFS_table_share *pfs)
 {
-  if (pfs->m_refcount == 1)
+  if (pfs->get_refcount() == 1)
   {
     LF_PINS* pins= get_table_share_hash_pins(thread);
     if (likely(pins != NULL))

=== modified file 'storage/perfschema/pfs_instr_class.h'
--- a/storage/perfschema/pfs_instr_class.h	2010-11-16 06:27:18 +0000
+++ b/storage/perfschema/pfs_instr_class.h	2010-12-01 08:33:53 +0000
@@ -146,11 +146,32 @@ struct PFS_table_share_key
 /** Instrumentation metadata for a table share. */
 struct PFS_table_share
 {
+public:
   enum_object_type get_object_type()
   {
     return (enum_object_type) m_key.m_hash_key[0];
   }
 
+  inline void init_refcount(void)
+  {
+    PFS_atomic::store_32(& m_refcount, 1);
+  }
+
+  inline int get_refcount(void)
+  {
+    return PFS_atomic::load_32(& m_refcount);
+  }
+
+  inline void inc_refcount(void)
+  {
+    PFS_atomic::add_32(& m_refcount, 1);
+  }
+
+  inline void dec_refcount(void)
+  {
+    PFS_atomic::add_32(& m_refcount, -1);
+  }
+
   /** Internal lock. */
   pfs_lock m_lock;
   /** Search key. */
@@ -170,8 +191,10 @@ struct PFS_table_share
   /** True if this table instrument is timed. */
   bool m_timed;
   bool m_purge;
+
+private:
   /** Number of opened table handles. */
-  uint m_refcount;
+  int m_refcount;
 };
 
 /**


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