WL#5363: Thread Pool Service Interface

In order to allow thread schedulers to be dynamically loaded,
it is necessary to make the following changes to the server:

- Two new service interfaces

- Modifications to InnoDB to inform the thread scheduler of state changes.

- Changes to the VIO subsystem for checking if data is available on a socket.

- Elimination of remains of the old thread pool implementation.

The two new service interfaces introduces are:

my_thread_scheduler
  A service interface to register a thread
  scheduler.

thd_wait
  A service interface to inform thread scheduler
  that the thread is about to start waiting.

In addition, the patch adds code that:

- Add a call to thd_wait for table locks in mysys
  thd_lock.c by introducing a set function that
  can be used to set a callback to be used when
  waiting on a lock and resuming from waiting.

- Calling the mysys set function from the server
  to set the callbacks correctly.

sql/sql_callback.h

@@ -0,0 +1,43 @@
+/*
+  Copyright (C) 2010, 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
+  the Free Software Foundation; version 2 of the License.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+*/
+
+#ifndef SQL_CALLBACK_INCLUDED
+#define SQL_CALLBACK_INCLUDED
+
+/**
+   Macro used for an internal callback.
+
+   The macro will check that the object exists and that the function
+   is defined. If that is the case, it will call the function with the
+   given parameters.
+
+   If the object or the function is not defined, the callback will be
+   considered successful (nothing needed to be done) and will
+   therefore return no error.
+ */
+
+#define MYSQL_CALLBACK(OBJ, FUNC, PARAMS)         \
+  do {                                            \
+    if ((OBJ) && ((OBJ)->FUNC))                   \
+      (OBJ)->FUNC PARAMS;                         \
+  } while (0)
+
+#define MYSQL_CALLBACK_ELSE(OBJ, FUNC, PARAMS, ELSE)    \
+  (((OBJ) && ((OBJ)->FUNC)) ? (OBJ)->FUNC PARAMS : (ELSE))
+
+
+#endif /* SQL_CALLBACK_INCLUDED */