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.

include/mysql/plugin.h.pp

@@ -33,6 +33,27 @@ void *thd_memdup(void* thd, const void* str, unsigned int size);
 MYSQL_LEX_STRING *thd_make_lex_string(void* thd, MYSQL_LEX_STRING *lex_str,
                                       const char *str, unsigned int size,
                                       int allocate_lex_string);
+#include <mysql/service_thd_wait.h>
+typedef enum _thd_wait_type_e {
+  THD_WAIT_MUTEX= 1,
+  THD_WAIT_DISKIO= 2,
+  THD_WAIT_ROW_TABLE_LOCK= 3,
+  THD_WAIT_GLOBAL_LOCK= 4
+} thd_wait_type;
+extern struct thd_wait_service_st {
+  void (*thd_wait_begin_func)(void*, thd_wait_type);
+  void (*thd_wait_end_func)(void*);
+} *thd_wait_service;
+void thd_wait_begin(void* thd, thd_wait_type wait_type);
+void thd_wait_end(void* thd);
+#include <mysql/service_thread_scheduler.h>
+struct scheduler_functions;
+extern struct my_thread_scheduler_service {
+  int (*set)(struct scheduler_functions *scheduler);
+  int (*reset)();
+} *my_thread_scheduler_service;
+int my_thread_scheduler_set(struct scheduler_functions *scheduler);
+int my_thread_scheduler_reset();
 struct st_mysql_xid {
   long formatID;
   long gtrid_length;