mirror of
https://github.com/isc-projects/bind9.git
synced 2026-03-07 07:50:29 -05:00
135 lines
3.8 KiB
C
135 lines
3.8 KiB
C
/*
|
|
* Copyright (C) 2004-2007 Internet Systems Consortium, Inc. ("ISC")
|
|
* Copyright (C) 1998-2001, 2003 Internet Software Consortium.
|
|
*
|
|
* Permission to use, copy, modify, and/or distribute this software for any
|
|
* purpose with or without fee is hereby granted, provided that the above
|
|
* copyright notice and this permission notice appear in all copies.
|
|
*
|
|
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
|
|
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
|
|
* AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
|
|
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
|
|
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
|
|
* OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
|
|
* PERFORMANCE OF THIS SOFTWARE.
|
|
*/
|
|
|
|
/* $Id: rwlock.h,v 1.28 2007/06/19 23:47:18 tbox Exp $ */
|
|
|
|
#ifndef ISC_RWLOCK_H
|
|
#define ISC_RWLOCK_H 1
|
|
|
|
/*! \file isc/rwlock.h */
|
|
|
|
#include <isc/condition.h>
|
|
#include <isc/lang.h>
|
|
#include <isc/platform.h>
|
|
#include <isc/types.h>
|
|
|
|
ISC_LANG_BEGINDECLS
|
|
|
|
typedef enum {
|
|
isc_rwlocktype_none = 0,
|
|
isc_rwlocktype_read,
|
|
isc_rwlocktype_write
|
|
} isc_rwlocktype_t;
|
|
|
|
#ifdef ISC_PLATFORM_USETHREADS
|
|
#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
|
|
#define ISC_RWLOCK_USEATOMIC 1
|
|
#endif
|
|
|
|
struct isc_rwlock {
|
|
/* Unlocked. */
|
|
unsigned int magic;
|
|
isc_mutex_t lock;
|
|
|
|
#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
|
|
/*
|
|
* When some atomic instructions with hardware assistance are
|
|
* available, rwlock will use those so that concurrent readers do not
|
|
* interfere with each other through mutex as long as no writers
|
|
* appear, massively reducing the lock overhead in the typical case.
|
|
*
|
|
* The basic algorithm of this approach is the "simple
|
|
* writer-preference lock" shown in the following URL:
|
|
* http://www.cs.rochester.edu/u/scott/synchronization/pseudocode/rw.html
|
|
* but our implementation does not rely on the spin lock unlike the
|
|
* original algorithm to be more portable as a user space application.
|
|
*/
|
|
|
|
/* Read or modified atomically. */
|
|
isc_int32_t write_requests;
|
|
isc_int32_t write_completions;
|
|
isc_int32_t cnt_and_flag;
|
|
|
|
/* Locked by lock. */
|
|
isc_condition_t readable;
|
|
isc_condition_t writeable;
|
|
unsigned int readers_waiting;
|
|
|
|
/* Locked by rwlock itself. */
|
|
unsigned int write_granted;
|
|
|
|
/* Unlocked. */
|
|
unsigned int write_quota;
|
|
|
|
#else /* ISC_PLATFORM_HAVEXADD && ISC_PLATFORM_HAVECMPXCHG */
|
|
|
|
/*%< Locked by lock. */
|
|
isc_condition_t readable;
|
|
isc_condition_t writeable;
|
|
isc_rwlocktype_t type;
|
|
|
|
/*% The number of threads that have the lock. */
|
|
unsigned int active;
|
|
|
|
/*%
|
|
* The number of lock grants made since the lock was last switched
|
|
* from reading to writing or vice versa; used in determining
|
|
* when the quota is reached and it is time to switch.
|
|
*/
|
|
unsigned int granted;
|
|
|
|
unsigned int readers_waiting;
|
|
unsigned int writers_waiting;
|
|
unsigned int read_quota;
|
|
unsigned int write_quota;
|
|
isc_rwlocktype_t original;
|
|
#endif /* ISC_PLATFORM_HAVEXADD && ISC_PLATFORM_HAVECMPXCHG */
|
|
};
|
|
#else /* ISC_PLATFORM_USETHREADS */
|
|
struct isc_rwlock {
|
|
unsigned int magic;
|
|
isc_rwlocktype_t type;
|
|
unsigned int active;
|
|
};
|
|
#endif /* ISC_PLATFORM_USETHREADS */
|
|
|
|
|
|
isc_result_t
|
|
isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
|
|
unsigned int write_quota);
|
|
|
|
isc_result_t
|
|
isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
|
|
|
|
isc_result_t
|
|
isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
|
|
|
|
isc_result_t
|
|
isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
|
|
|
|
isc_result_t
|
|
isc_rwlock_tryupgrade(isc_rwlock_t *rwl);
|
|
|
|
void
|
|
isc_rwlock_downgrade(isc_rwlock_t *rwl);
|
|
|
|
void
|
|
isc_rwlock_destroy(isc_rwlock_t *rwl);
|
|
|
|
ISC_LANG_ENDDECLS
|
|
|
|
#endif /* ISC_RWLOCK_H */
|