/* * 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 */