116 lines
3.4 KiB
C
116 lines
3.4 KiB
C
#pragma once
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/*
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* Copyright (c) 2016 MariaDB Corporation Ab
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*
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* Use of this software is governed by the Business Source License included
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* in the LICENSE.TXT file and at www.mariadb.com/bsl11.
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*
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* Change Date: 2020-01-01
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*
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* On the date above, in accordance with the Business Source License, use
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* of this software will be governed by version 2 or later of the General
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* Public License.
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*/
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/**
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* @file spinlock.h
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*
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* Spinlock implementation for MaxScale.
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*
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* Spinlocks are cheap locks that can be used to protect short code blocks, they are
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* generally wasteful as any blocked threads will spin, consuming CPU cycles, waiting
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* for the lock to be released. However they are useful in that they do not involve
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* system calls and are light weight when the expected wait time for a lock is low.
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*/
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#include <maxscale/cdefs.h>
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#include <stdbool.h>
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#include <maxscale/debug.h>
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MXS_BEGIN_DECLS
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#define SPINLOCK_PROFILE 0
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/**
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* The spinlock structure.
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*
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* In normal builds the structure merely contains a lock value which
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* is 0 if the spinlock is not taken and greater than zero if it is held.
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*
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* In builds with the SPINLOCK_PROFILE option set this structure also holds
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* a number of profile related fields that count the number of spins, number
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* of waiting threads and the number of times the lock has been acquired.
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*/
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typedef struct spinlock
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{
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int lock; /*< Is the lock held? */
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#if SPINLOCK_PROFILE
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uint64_t spins; /*< Number of spins on this lock */
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uint64_t maxspins; /*< Max no of spins to acquire lock */
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uint64_t acquired; /*< No. of times lock was acquired */
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uint64_t waiting; /*< No. of threads acquiring this lock */
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uint64_t max_waiting; /*< Max no of threads waiting for lock */
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uint64_t contended; /*< No. of times acquire was contended */
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THREAD owner; /*< Last owner of this lock */
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#endif
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} SPINLOCK;
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#if SPINLOCK_PROFILE
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#define SPINLOCK_INIT { 0, 0, 0, 0, 0, 0, 0, 0 }
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#else
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#define SPINLOCK_INIT { 0 }
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#endif
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/**
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* Debugging macro for testing the state of a spinlock.
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*
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* @attention ONLY to be used in debugging context.
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*/
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#define SPINLOCK_IS_LOCKED(l) ((l)->lock != 0 ? true : false)
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/**
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* Initialise a spinlock.
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*
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* @param lock The spinlock to initialise.
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*/
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extern void spinlock_init(SPINLOCK *lock);
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/**
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* Acquire a spinlock.
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*
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* @param lock The spinlock to acquire
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*/
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extern void spinlock_acquire(const SPINLOCK *lock);
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/**
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* Acquire a spinlock if it is not already locked.
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*
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* @param lock The spinlock to acquire
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* @return True if the spinlock was acquired, otherwise false
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*/
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extern bool spinlock_acquire_nowait(const SPINLOCK *lock);
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/*
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* Release a spinlock.
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*
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* @param lock The spinlock to release
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*/
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extern void spinlock_release(const SPINLOCK *lock);
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/**
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* Report statistics on a spinlock. This only has an effect if the
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* spinlock code has been compiled with the SPINLOCK_PROFILE option set.
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*
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* NB A callback function is used to return the data rather than
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* merely printing to a DCB in order to avoid a dependency on the DCB
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* form the spinlock code and also to facilitate other uses of the
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* statistics reporting.
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*
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* @param lock The spinlock to report on
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* @param reporter The callback function to pass the statistics to
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* @param hdl A handle that is passed to the reporter function
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*/
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extern void spinlock_stats(const SPINLOCK *lock, void (*reporter)(void *, char *, int), void *hdl);
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MXS_END_DECLS
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