00b67f09dd
Also known as ISC bind. This import adds utilities such as host(1), dig(1), and nslookup(1), as well as many other tools and libraries. Change-Id: I035ca46e64f1965d57019e773f4ff0ef035e4aa3
140 lines
3.9 KiB
C
140 lines
3.9 KiB
C
/* $NetBSD: rwlock.h,v 1.5 2014/12/10 04:38:00 christos Exp $ */
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/*
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* Copyright (C) 2004-2007 Internet Systems Consortium, Inc. ("ISC")
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* Copyright (C) 1998-2001, 2003 Internet Software Consortium.
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
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* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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* AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
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* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
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* OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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* PERFORMANCE OF THIS SOFTWARE.
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*/
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/* Id: rwlock.h,v 1.28 2007/06/19 23:47:18 tbox Exp */
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#ifndef ISC_RWLOCK_H
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#define ISC_RWLOCK_H 1
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/*! \file isc/rwlock.h */
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#include <isc/condition.h>
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#include <isc/lang.h>
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#include <isc/platform.h>
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#include <isc/types.h>
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ISC_LANG_BEGINDECLS
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typedef enum {
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isc_rwlocktype_none = 0,
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isc_rwlocktype_read,
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isc_rwlocktype_write
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} isc_rwlocktype_t;
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#ifdef ISC_PLATFORM_USETHREADS
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#ifndef ISC_PLATFORM_USE_NATIVE_RWLOCKS
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#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
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#define ISC_RWLOCK_USEATOMIC 1
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#endif
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struct isc_rwlock {
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/* Unlocked. */
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unsigned int magic;
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isc_mutex_t lock;
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#if defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)
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/*
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* When some atomic instructions with hardware assistance are
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* available, rwlock will use those so that concurrent readers do not
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* interfere with each other through mutex as long as no writers
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* appear, massively reducing the lock overhead in the typical case.
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*
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* The basic algorithm of this approach is the "simple
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* writer-preference lock" shown in the following URL:
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* http://www.cs.rochester.edu/u/scott/synchronization/pseudocode/rw.html
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* but our implementation does not rely on the spin lock unlike the
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* original algorithm to be more portable as a user space application.
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*/
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/* Read or modified atomically. */
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isc_int32_t write_requests;
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isc_int32_t write_completions;
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isc_int32_t cnt_and_flag;
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/* Locked by lock. */
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isc_condition_t readable;
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isc_condition_t writeable;
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unsigned int readers_waiting;
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/* Locked by rwlock itself. */
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unsigned int write_granted;
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/* Unlocked. */
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unsigned int write_quota;
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#else /* ISC_PLATFORM_HAVEXADD && ISC_PLATFORM_HAVECMPXCHG */
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/*%< Locked by lock. */
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isc_condition_t readable;
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isc_condition_t writeable;
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isc_rwlocktype_t type;
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/*% The number of threads that have the lock. */
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unsigned int active;
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/*%
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* The number of lock grants made since the lock was last switched
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* from reading to writing or vice versa; used in determining
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* when the quota is reached and it is time to switch.
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*/
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unsigned int granted;
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unsigned int readers_waiting;
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unsigned int writers_waiting;
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unsigned int read_quota;
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unsigned int write_quota;
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isc_rwlocktype_t original;
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#endif /* ISC_PLATFORM_HAVEXADD && ISC_PLATFORM_HAVECMPXCHG */
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};
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#endif /* !ISC_PLATFORM_USE_NATIVE_RWLOCKS */
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#else /* ISC_PLATFORM_USETHREADS */
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struct isc_rwlock {
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unsigned int magic;
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isc_rwlocktype_t type;
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unsigned int active;
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};
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#endif /* ISC_PLATFORM_USETHREADS */
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isc_result_t
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isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
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unsigned int write_quota);
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isc_result_t
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isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
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isc_result_t
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isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
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isc_result_t
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isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type);
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isc_result_t
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isc_rwlock_tryupgrade(isc_rwlock_t *rwl);
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void
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isc_rwlock_downgrade(isc_rwlock_t *rwl);
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void
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isc_rwlock_destroy(isc_rwlock_t *rwl);
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ISC_LANG_ENDDECLS
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#endif /* ISC_RWLOCK_H */
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