Bug#20789 Merge Subtable Rename Causes Crash

- When a MyISAM table which belongs to a merge table union and is 
  renamed the associated file descriptors are closed on windows.
  This causes a server crash next time an insert or update is 
  performed on the merge table.
- This patch prevents the system from crashing on windows by
  checking for bad file descriptors every time the MyISAM table
  is locked by associated the merge table.


myisam/mi_locking.c:
  - Added check for bad file descriptors when table is part of merge union.
  - This patch prevents the server from crash on windows.
myisam/myisamdef.h:
  Added boolean value to indicate that this myisam table is part of
  a merge union.
myisammrg/myrg_locking.c:
  Added paramter owned_by_merge=TRUE for mi_lock_database through MYRG_TABLE struct.

1 files changed, 12 insertions, 1 deletions

diff --git a/myisammrg/myrg_locking.c b/myisammrg/myrg_locking.c
index e5a8d3f3d9d..98e8305b9ce 100644
--- a/myisammrg/myrg_locking.c
+++ b/myisammrg/myrg_locking.c
@@ -26,8 +26,19 @@ int myrg_lock_database(MYRG_INFO *info, int lock_type)
   MYRG_TABLE *file;
 
   error=0;
-  for (file=info->open_tables ; file != info->end_table ; file++)
+  for (file=info->open_tables ; file != info->end_table ; file++) 
+  {
+#ifdef __WIN__
+    /*
+      Make sure this table is marked as owned by a merge table.
+      The semaphore is never released as long as table remains
+      in memory. This should be refactored into a more generic
+      approach (observer pattern)
+     */
+    (file->table)->owned_by_merge = TRUE;
+#endif
     if ((new_error=mi_lock_database(file->table,lock_type)))
       error=new_error;
+  }
   return(error);
 }