Bug #21467458 - UNINSTALL PLUGIN DAEMON_EXAMPLE CRASHES

                MYSQLD.

DESCRIPTION
===========
Crash occurs when daemon_example plugin is uninstalled
immediately after its installed. This can be reproduced
by installing and uninstalling the plugin repeatedly.

ANALYSIS
========
The daemon_example_plugin_deinit() function of the daemon
example plugin calls pthread_cancel() but doesn't wait for
the worker thread to actually complete before deallocating
the data buffer and closing the file that it writes to.
This is causing SEGFAULT!

FIX
===
Added a pthread_join() to wait for the thread to complete
before doing the cleanup work.

Removed a stray 'x' variable from the example code.

NOTE
====
Have made an entry in .opt file as given below:
--plugin-dir=$DAEMONEXAMPLE_DIR

This is done so that the program takes plugin directory as
../<dbg>/plugin/daemon_example/ instead of
../lib/plugin/

plugin/daemon_example/daemon_example.cc

-/* Copyright (c) 2006, 2011, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2006, 2015, Oracle and/or its affiliates. All rights
+   reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -46,7 +47,6 @@ pthread_handler_t mysql_heartbeat(void *p)
   DBUG_ENTER("mysql_heartbeat");
   struct mysql_heartbeat_context *con= (struct mysql_heartbeat_context *)p;
   char buffer[HEART_STRING_BUFFER];
-  unsigned int x= 0;
   time_t result;
   struct tm tm_tmp;
 
@@ -65,7 +65,6 @@ pthread_handler_t mysql_heartbeat(void *p)
                 tm_tmp.tm_min,
                 tm_tmp.tm_sec);
     my_write(con->heartbeat_file, (uchar*) buffer, strlen(buffer), MYF(0));
-    x++;
   }
 
   DBUG_RETURN(0);
@@ -173,6 +172,13 @@ static int daemon_example_plugin_deinit(void *p)
               tm_tmp.tm_min,
               tm_tmp.tm_sec);
   my_write(con->heartbeat_file, (uchar*) buffer, strlen(buffer), MYF(0));
+
+  /*
+    Need to wait for the hearbeat thread to terminate before closing
+    the file it writes to and freeing the memory it uses.
+  */
+  pthread_join(con->heartbeat_thread, NULL);
+
   my_close(con->heartbeat_file, MYF(0));
 
   my_free(con);