Current File : //usr/include/mysql/mysql/service_thd_wait.h
/* Copyright (c) 2010, 2023, Oracle and/or its affiliates.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is also distributed with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have included with MySQL.
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, version 2.0, 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
#ifndef MYSQL_SERVICE_THD_WAIT_INCLUDED
#define MYSQL_SERVICE_THD_WAIT_INCLUDED
/**
@file include/mysql/service_thd_wait.h
This service provides functions for plugins and storage engines to report
when they are going to sleep/stall.
SYNOPSIS
thd_wait_begin() - call just before a wait begins
thd Thread object
Use NULL if the thd is NOT known.
wait_type Type of wait
1 -- short wait (e.g. for mutex)
2 -- medium wait (e.g. for disk io)
3 -- large wait (e.g. for locked row/table)
NOTES
This is used by the threadpool to have better knowledge of which
threads that currently are actively running on CPUs. When a thread
reports that it's going to sleep/stall, the threadpool scheduler is
free to start another thread in the pool most likely. The expected wait
time is simply an indication of how long the wait is expected to
become, the real wait time could be very different.
thd_wait_end() called immediately after the wait is complete
thd_wait_end() MUST be called if thd_wait_begin() was called.
Using thd_wait_...() service is optional but recommended. Using it will
improve performance as the thread pool will be more active at managing the
thread workload.
*/
#ifdef __cplusplus
class THD;
#define MYSQL_THD THD*
#else
#define MYSQL_THD void*
#endif
#ifdef __cplusplus
extern "C" {
#endif
/*
One should only report wait events that could potentially block for a
long time. A mutex wait is too short of an event to report. The reason
is that an event which is reported leads to a new thread starts
executing a query and this has a negative impact of usage of CPU caches
and thus the expected gain of starting a new thread must be higher than
the expected cost of lost performance due to starting a new thread.
Good examples of events that should be reported are waiting for row locks
that could easily be for many milliseconds or even seconds and the same
holds true for global read locks, table locks and other meta data locks.
Another event of interest is going to sleep for an extended time.
Note that user-level locks no longer use THD_WAIT_USER_LOCK wait type.
Since their implementation relies on metadata locks manager it uses
THD_WAIT_META_DATA_LOCK instead.
*/
typedef enum _thd_wait_type_e {
THD_WAIT_SLEEP= 1,
THD_WAIT_DISKIO= 2,
THD_WAIT_ROW_LOCK= 3,
THD_WAIT_GLOBAL_LOCK= 4,
THD_WAIT_META_DATA_LOCK= 5,
THD_WAIT_TABLE_LOCK= 6,
THD_WAIT_USER_LOCK= 7,
THD_WAIT_BINLOG= 8,
THD_WAIT_GROUP_COMMIT= 9,
THD_WAIT_SYNC= 10,
THD_WAIT_LAST= 11
} thd_wait_type;
extern struct thd_wait_service_st {
void (*thd_wait_begin_func)(MYSQL_THD, int);
void (*thd_wait_end_func)(MYSQL_THD);
} *thd_wait_service;
#ifdef MYSQL_DYNAMIC_PLUGIN
#define thd_wait_begin(_THD, _WAIT_TYPE) \
thd_wait_service->thd_wait_begin_func(_THD, _WAIT_TYPE)
#define thd_wait_end(_THD) thd_wait_service->thd_wait_end_func(_THD)
#else
void thd_wait_begin(MYSQL_THD thd, int wait_type);
void thd_wait_end(MYSQL_THD thd);
#endif
#ifdef __cplusplus
}
#endif
#endif
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