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Diffstat (limited to 'lib/isc/include/isc/rwlock.h')
| -rw-r--r-- | lib/isc/include/isc/rwlock.h | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/lib/isc/include/isc/rwlock.h b/lib/isc/include/isc/rwlock.h new file mode 100644 index 0000000..28052cd --- /dev/null +++ b/lib/isc/include/isc/rwlock.h @@ -0,0 +1,135 @@ +/* + * 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 */ |