bk commit into 5.1 tree (bar:1.2205)

[bar]

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ChangeSet
  1.2205 06/06/22 18:38:26 bar@stripped +1 -0
  Merge mysql.com:/usr/home/bar/mysql-5.1-new.19392
  into  mysql.com:/usr/home/bar/mysql-5.1-kt

  sql/sql_db.cc
    1.136 06/06/22 18:38:15 bar@stripped +0 -0
    Auto merged

# This is a BitKeeper patch.  What follows are the unified diffs for the
# set of deltas contained in the patch.  The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User:	bar
# Host:	bar.intranet.mysql.r18.ru
# Root:	/usr/home/bar/mysql-5.1-kt/RESYNC

--- 1.135/sql/sql_db.cc	2006-05-18 12:26:11 +05:00
+++ 1.136/sql/sql_db.cc	2006-06-22 18:38:15 +05:00
@@ -538,16 +538,27 @@ bool mysql_create_db(THD *thd, char *db,
     my_error(ER_DB_CREATE_EXISTS, MYF(0), db);
     DBUG_RETURN(-1);
   }
-  
-  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
 
-  /* do not create database if another thread is holding read lock */
+  /*
+    Do not create database if another thread is holding read lock.
+    Wait for global read lock before acquiring LOCK_mysql_create_db.
+    After wait_if_global_read_lock() we have protection against another
+    global read lock. If we would acquire LOCK_mysql_create_db first,
+    another thread could step in and get the global read lock before we
+    reach wait_if_global_read_lock(). If this thread tries the same as we
+    (admin a db), it would then go and wait on LOCK_mysql_create_db...
+    Furthermore wait_if_global_read_lock() checks if the current thread
+    has the global read lock and refuses the operation with
+    ER_CANT_UPDATE_WITH_READLOCK if applicable.
+  */
   if (wait_if_global_read_lock(thd, 0, 1))
   {
     error= -1;
     goto exit2;
   }
 
+  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
+
   /* Check directory */
   path_len= build_table_filename(path, sizeof(path), db, "", "");
   path[path_len-1]= 0;                    // Remove last '/' from path
@@ -655,9 +666,9 @@ bool mysql_create_db(THD *thd, char *db,
   }
 
 exit:
+  VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
   start_waiting_global_read_lock(thd);
 exit2:
-  VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
   DBUG_RETURN(error);
 }
 
@@ -671,12 +682,23 @@ bool mysql_alter_db(THD *thd, const char
   int error= 0;
   DBUG_ENTER("mysql_alter_db");
 
-  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
-
-  /* do not alter database if another thread is holding read lock */
+  /*
+    Do not alter database if another thread is holding read lock.
+    Wait for global read lock before acquiring LOCK_mysql_create_db.
+    After wait_if_global_read_lock() we have protection against another
+    global read lock. If we would acquire LOCK_mysql_create_db first,
+    another thread could step in and get the global read lock before we
+    reach wait_if_global_read_lock(). If this thread tries the same as we
+    (admin a db), it would then go and wait on LOCK_mysql_create_db...
+    Furthermore wait_if_global_read_lock() checks if the current thread
+    has the global read lock and refuses the operation with
+    ER_CANT_UPDATE_WITH_READLOCK if applicable.
+  */
   if ((error=wait_if_global_read_lock(thd,0,1)))
     goto exit2;
 
+  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
+
   /* 
      Recreate db options file: /dbpath/.db.opt
      We pass MY_DB_OPT_FILE as "extension" to avoid
@@ -721,9 +743,9 @@ bool mysql_alter_db(THD *thd, const char
   send_ok(thd, result);
 
 exit:
+  VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
   start_waiting_global_read_lock(thd);
 exit2:
-  VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
   DBUG_RETURN(error);
 }
 
@@ -755,15 +777,26 @@ bool mysql_rm_db(THD *thd,char *db,bool 
   TABLE_LIST* dropped_tables= 0;
   DBUG_ENTER("mysql_rm_db");
 
-  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
-
-  /* do not drop database if another thread is holding read lock */
+  /*
+    Do not drop database if another thread is holding read lock.
+    Wait for global read lock before acquiring LOCK_mysql_create_db.
+    After wait_if_global_read_lock() we have protection against another
+    global read lock. If we would acquire LOCK_mysql_create_db first,
+    another thread could step in and get the global read lock before we
+    reach wait_if_global_read_lock(). If this thread tries the same as we
+    (admin a db), it would then go and wait on LOCK_mysql_create_db...
+    Furthermore wait_if_global_read_lock() checks if the current thread
+    has the global read lock and refuses the operation with
+    ER_CANT_UPDATE_WITH_READLOCK if applicable.
+  */
   if (wait_if_global_read_lock(thd, 0, 1))
   {
     error= -1;
     goto exit2;
   }
 
+  VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
+
   length= build_table_filename(path, sizeof(path), db, "", "");
   strmov(path+length, MY_DB_OPT_FILE);		// Append db option file name
   del_dbopt(path);				// Remove dboption hash entry
@@ -871,8 +904,7 @@ bool mysql_rm_db(THD *thd,char *db,bool 
 
 exit:
   (void)sp_drop_db_routines(thd, db); /* QQ Ignore errors for now  */
-  (void)evex_drop_db_events(thd, db); /* QQ Ignore errors for now  */
-  start_waiting_global_read_lock(thd);
+  error= Events::drop_schema_events(thd, db);
   /*
     If this database was the client's selected database, we silently change the
     client's selected database to nothing (to have an empty SELECT DATABASE()
@@ -901,9 +933,9 @@ exit:
     thd->db= 0;
     thd->db_length= 0;
   }
-exit2:
   VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
-
+  start_waiting_global_read_lock(thd);
+exit2:
   DBUG_RETURN(error);
 }