Fix long xtradb shutdown on Windows XP

The reason for the long shutdown is hanging in io threads. It appears
that just closing completion port on XP does not necessarily signal 
thread waiting in GetIOCompletionStatus() (even if this works fine
on later Windows versions)

The fix is to wakeup background threads using PostQueuedCompletionStatus()
with a special 'key' parameter indicating shutdown.

storage/xtradb/os/os0file.c

@@ -53,6 +53,10 @@ Created 10/21/1995 Heikki Tuuri
 # endif /* __WIN__ */
 #endif /* !UNIV_HOTBACKUP */
 
+#ifdef _WIN32
+#define IOCP_SHUTDOWN_KEY (ULONG_PTR)-1
+#endif
+
 /* This specifies the file permissions InnoDB uses when it creates files in
 Unix; the value of os_innodb_umask is initialized in ha_innodb.cc to
 my_umask */
@@ -3235,9 +3239,7 @@ os_aio_array_wake_win_aio_at_shutdown(
 {
 	if(completion_port)
 	{
-		ut_a(CloseHandle(completion_port));
-		completion_port = 0;
-
+		PostQueuedCompletionStatus(completion_port, 0, IOCP_SHUTDOWN_KEY, NULL);
 	}
 }
 #endif
@@ -3836,11 +3838,17 @@ os_aio_windows_handle(
 	BOOL		ret;
 	DWORD		len;
 	BOOL		retry		= FALSE;
-	ULONG_PTR dummy_key;
+	ULONG_PTR key;
 
-	ret = GetQueuedCompletionStatus(completion_port, &len, &dummy_key, 
+	ret = GetQueuedCompletionStatus(completion_port, &len, &key, 
 		(OVERLAPPED **)&slot, INFINITE);
 
+	/* If shutdown key was received, repost the shutdown message and exit */
+	if (ret && (key == IOCP_SHUTDOWN_KEY)) {
+		PostQueuedCompletionStatus(completion_port, 0, key, NULL);
+		os_thread_exit(NULL);
+	}
+
 	if (srv_shutdown_state == SRV_SHUTDOWN_EXIT_THREADS) {
 		os_thread_exit(NULL);
 	}