BUG#39053 - UNISTALL PLUGIN does not allow the storage engine

            to cleanup open connections

It was possible to UNINSTALL storage engine plugin when binding
between THD object and storage engine is still active (e.g. in
the middle of transaction).

To avoid unclean deactivation (uninstall) of storage engine plugin
in the middle of transaction, additional storage engine plugin
lock is acquired by thd_set_ha_data().

If ha_data is not null and storage engine plugin was not locked
by thd_set_ha_data() in this connection before, storage engine
plugin gets locked.

If ha_data is null and storage engine plugin was locked by
thd_set_ha_data() in this connection before, storage engine
plugin lock gets released.

If handlerton::close_connection() didn't reset ha_data, server does
it immediately after calling handlerton::close_connection().

Note that this is just a framework fix, storage engines must switch
to thd_set_ha_data() from thd_ha_data() if they want to see fit.

include/mysql/plugin.h:
  As thd_{get|set}_ha_data() have some extra logic now, they
  must be implemented on server side.
include/mysql/plugin.h.pp:
  As thd_{get|set}_ha_data() have some extra logic now, they
  must be implemented on server side.
sql/handler.cc:
  Make sure ha_data is reset and ha_data lock is released.
sql/handler.h:
  hton is not supposed to be updated by ha_lock_engine(),
  make it const.
sql/sql_class.cc:
  As thd_{get|set}_ha_data() have some extra logic now, they
  must be implemented on server side.
sql/sql_class.h:
  Added ha_data lock.

1 files changed, 31 insertions, 0 deletions

diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index 266064f9f08..bf5af7141c0 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -284,6 +284,37 @@ void **thd_ha_data(const THD *thd, const struct handlerton *hton)
   return (void **) &thd->ha_data[hton->slot].ha_ptr;
 }
 
+
+/**
+  Provide a handler data getter to simplify coding
+*/
+extern "C"
+void *thd_get_ha_data(const THD *thd, const struct handlerton *hton)
+{
+  return *thd_ha_data(thd, hton);
+}
+
+
+/**
+  Provide a handler data setter to simplify coding
+  @see thd_set_ha_data() definition in plugin.h
+*/
+extern "C"
+void thd_set_ha_data(THD *thd, const struct handlerton *hton,
+                     const void *ha_data)
+{
+  plugin_ref *lock= &thd->ha_data[hton->slot].lock;
+  if (ha_data && !*lock)
+    *lock= ha_lock_engine(NULL, (handlerton*) hton);
+  else if (!ha_data && *lock)
+  {
+    plugin_unlock(NULL, *lock);
+    *lock= NULL;
+  }
+  *thd_ha_data(thd, hton)= (void*) ha_data;
+}
+
+
 extern "C"
 long long thd_test_options(const THD *thd, long long test_options)
 {