bk commit into 5.1 tree (svoj:1.2188)

[Sergey Vojtovich]

Below is the list of changes that have just been committed into a local
5.1 repository of svoj. When svoj does a push these changes will
be propagated to the main repository and, within 24 hours after the
push, to the public repository.
For information on how to access the public repository
see http://dev.mysql.com/doc/mysql/en/installing-source-tree.html

ChangeSet
  1.2188 06/06/06 17:43:31 svoj@april.(none) +1 -0
  Merge svojtovich@stripped:/home/bk/mysql-5.1-engines
  into  april.(none):/home/svoj/devel/BitKeeper/mysql-5.1-engines

  sql/sql_db.cc
    1.135 06/06/06 17:43:25 svoj@april.(none) +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:	svoj
# Host:	april.(none)
# Root:	/home/svoj/devel/BitKeeper/mysql-5.1-engines/RESYNC

--- 1.134/sql/sql_db.cc	2006-05-22 23:45:58 +05:00
+++ 1.135/sql/sql_db.cc	2006-06-06 17:43:25 +05:00
@@ -538,16 +538,27 @@
     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 @@
   }
 
 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 @@
   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 @@
   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 @@
   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
@@ -872,7 +905,6 @@
 exit:
   (void)sp_drop_db_routines(thd, db); /* QQ Ignore errors for now  */
   error= Events::drop_schema_events(thd, db);
-  start_waiting_global_read_lock(thd);
   /*
     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 @@
     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);
 }