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.

1 files changed, 126 insertions, 36 deletions

diff --git a/sql/scheduler.cc b/sql/scheduler.cc
index 10009246428..19f8ddc7355 100644
--- a/sql/scheduler.cc
+++ b/sql/scheduler.cc
@@ -25,55 +25,98 @@
 #include "unireg.h"                    // REQUIRED: for other includes
 #include "scheduler.h"
 #include "sql_connect.h"         // init_new_connection_handler_thread
+#include "scheduler.h"
+#include "sql_callback.h"
 
 /*
-  'Dummy' functions to be used when we don't need any handling for a scheduler
-  event
- */
+  End connection, in case when we are using 'no-threads'
+*/
 
-static bool init_dummy(void) {return 0;}
-static void post_kill_dummy(THD* thd) {}  
-static void end_dummy(void) {}
-static bool end_thread_dummy(THD *thd, bool cache_thread) { return 0; }
+static bool no_threads_end(THD *thd, bool put_in_cache)
+{
+  unlink_thd(thd);
+  mysql_mutex_unlock(&LOCK_thread_count);
+  return 1;                                     // Abort handle_one_connection
+}
 
-/*
-  Initialize default scheduler with dummy functions so that setup functions
-  only need to declare those that are relvant for their usage
+static scheduler_functions one_thread_scheduler_functions=
+{
+  1,                                     // max_threads
+  NULL,                                  // init
+  init_new_connection_handler_thread,    // init_new_connection_thread
+  handle_connection_in_main_thread,      // add_connection
+  NULL,                                  // thd_wait_begin
+  NULL,                                  // thd_wait_end
+  NULL,                                  // post_kill_notification
+  no_threads_end,                        // end_thread
+  NULL,                                  // end
+};
+
+static scheduler_functions one_thread_per_connection_scheduler_functions=
+{
+  0,                                     // max_threads
+  NULL,                                  // init
+  init_new_connection_handler_thread,    // init_new_connection_thread
+  create_thread_to_handle_connection,    // add_connection
+  NULL,                                  // thd_wait_begin
+  NULL,                                  // thd_wait_end
+  NULL,                                  // post_kill_notification
+  one_thread_per_connection_end,         // end_thread
+  NULL,                                  // end
+};
+
+
+scheduler_functions *thread_scheduler=
+  &one_thread_per_connection_scheduler_functions;
+
+/** @internal
+  Helper functions to allow mysys to call the thread scheduler when
+  waiting for locks.
 */
 
-scheduler_functions::scheduler_functions()
-  :init(init_dummy),
-   init_new_connection_thread(init_new_connection_handler_thread),
-   add_connection(0),                           // Must be defined
-   post_kill_notification(post_kill_dummy),
-   end_thread(end_thread_dummy), end(end_dummy)
-{}
+/**@{*/
+static void scheduler_wait_begin(void) {
+  MYSQL_CALLBACK(thread_scheduler,
+                 thd_wait_begin, (current_thd, THD_WAIT_ROW_TABLE_LOCK));
+}
 
+static void scheduler_wait_end(void) {
+  MYSQL_CALLBACK(thread_scheduler, thd_wait_end, (current_thd));
+}
+/**@}*/
+
+/**
+  Common scheduler init function.
+
+  The scheduler is either initialized by calling
+  one_thread_scheduler() or one_thread_per_connection_scheduler() in
+  mysqld.cc, so this init function will always be called.
+ */
+static void scheduler_init() {
+  thr_set_lock_wait_callback(scheduler_wait_begin, scheduler_wait_end);
+}
 
 /*
-  End connection, in case when we are using 'no-threads'
+  Initialize scheduler for --thread-handling=one-thread-per-connection
 */
 
-static bool no_threads_end(THD *thd, bool put_in_cache)
+#ifndef EMBEDDED_LIBRARY
+void one_thread_per_connection_scheduler()
 {
-  unlink_thd(thd);
-  mysql_mutex_unlock(&LOCK_thread_count);
-  return 1;                                     // Abort handle_one_connection
+  scheduler_init();
+  one_thread_per_connection_scheduler_functions.max_threads= max_connections;
+  thread_scheduler= &one_thread_per_connection_scheduler_functions;
 }
-
+#endif
 
 /*
   Initailize scheduler for --thread-handling=no-threads
 */
 
-void one_thread_scheduler(scheduler_functions* func)
+void one_thread_scheduler()
 {
-  func->max_threads= 1;
-#ifndef EMBEDDED_LIBRARY
-  func->add_connection= handle_connection_in_main_thread;
-#endif
-  func->init_new_connection_thread= init_dummy;
-  func->end_thread= no_threads_end;
+  scheduler_init();
+  thread_scheduler= &one_thread_scheduler_functions;
 }
 
 
@@ -81,11 +124,58 @@ void one_thread_scheduler(scheduler_functions* func)
   Initialize scheduler for --thread-handling=one-thread-per-connection
 */
 
-#ifndef EMBEDDED_LIBRARY
-void one_thread_per_connection_scheduler(scheduler_functions* func)
+/*
+  thd_scheduler keeps the link between THD and events.
+  It's embedded in the THD class.
+*/
+
+thd_scheduler::thd_scheduler()
+  : m_psi(NULL), data(NULL)
 {
-  func->max_threads= max_connections;
-  func->add_connection= create_thread_to_handle_connection;
-  func->end_thread= one_thread_per_connection_end;
+#ifndef DBUG_OFF
+  dbug_explain[0]= '\0';
+  set_explain= FALSE;
+#endif
 }
-#endif /* EMBEDDED_LIBRARY */
+
+
+thd_scheduler::~thd_scheduler()
+{
+}
+
+static scheduler_functions *saved_thread_scheduler;
+static uint saved_thread_handling;
+
+extern "C"
+int my_thread_scheduler_set(scheduler_functions *scheduler)
+{
+  DBUG_ASSERT(scheduler != 0);
+
+  if (scheduler == NULL)
+    return 1;
+
+  saved_thread_scheduler= thread_scheduler;
+  saved_thread_handling= thread_handling;
+  thread_scheduler= scheduler;
+  // Scheduler loaded dynamically
+  thread_handling= SCHEDULER_TYPES_COUNT;
+  return 0;
+}
+
+
+extern "C"
+int my_thread_scheduler_reset()
+{
+  DBUG_ASSERT(saved_thread_scheduler != NULL);
+
+  if (saved_thread_scheduler == NULL)
+    return 1;
+
+  thread_scheduler= saved_thread_scheduler;
+  thread_handling= saved_thread_handling;
+  saved_thread_scheduler= 0;
+  return 0;
+}
+
+
+