Fix for memory leak in applications, like QT,that calls

my_thread_global_init() + my_thrad_global_end() repeatadily.
This caused THR_KEY_mysys to be allocated multiple times.

Deletion of THR_KEY_mysys was originally in my_thread_global_end() but was
moved to my_end() as DBUG uses THR_KEY_mysys and DBUG is released after
my_thread_global_end() is called.

Releasing DBUG before my_thread_global_end() and move THR_KEY_mysys back
into my_thread_global_end() could be a solution, but as safe_mutex and other
things called by my_thread_global_end is using DBUG it may not be completely
safe.

To solve this, I used the simple solution to add a marker that THR_KEY_mysys
is created and not re-create it in my_thread_global_init if it already
exists.

include/my_sys.h

@@ -227,7 +227,7 @@ extern ulong	my_file_opened,my_stream_opened, my_tmp_file_created;
 extern ulong    my_file_total_opened;
 extern ulong    my_sync_count;
 extern uint	mysys_usage_id;
-extern my_bool	my_init_done;
+extern my_bool	my_init_done, my_thr_key_mysys_exists;
 extern my_bool  my_assert_on_error;
 extern myf      my_global_flags;        /* Set to MY_WME for more error messages */
 					/* Point to current my_message() */

mysys/my_init.c

@@ -226,7 +226,7 @@ Voluntary context switches %ld, Involuntary context switches %ld\n",
  
   /* At very last, delete mysys key, it is used everywhere including DBUG */
   pthread_key_delete(THR_KEY_mysys);
-  my_init_done=0;
+  my_init_done= my_thr_key_mysys_exists= 0;
 } /* my_end */
 
 #ifndef DBUG_OFF

mysys/my_thr_init.c

@@ -60,6 +60,8 @@ static uint get_thread_lib(void);
 
 /** True if @c my_thread_global_init() has been called. */
 static my_bool my_thread_global_init_done= 0;
+/* True if THR_KEY_mysys is created */
+my_bool my_thr_key_mysys_exists= 0;
 
 
 /*
@@ -185,11 +187,20 @@ my_bool my_thread_global_init(void)
     return 0;
   my_thread_global_init_done= 1;
 
-  if ((pth_ret= pthread_key_create(&THR_KEY_mysys, NULL)) != 0)
+  /*
+    THR_KEY_mysys is deleted in my_end() as DBUG libraries are using it even
+    after my_thread_global_end() is called.
+    my_thr_key_mysys_exist is used to protect against application like QT
+    that calls my_thread_global_init() + my_thread_global_end() multiple times
+    without calling my_init() + my_end().
+  */
+  if (!my_thr_key_mysys_exists &&
+      (pth_ret= pthread_key_create(&THR_KEY_mysys, NULL)) != 0)
   {
     fprintf(stderr, "Can't initialize threads: error %d\n", pth_ret);
     return 1;
   }
+  my_thr_key_mysys_exists= 1;
 
   /* Mutex used by my_thread_init() and after my_thread_destroy_mutex() */
   my_thread_init_internal_mutex();