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Diffstat (limited to 'lib/isc/include/isc/rwlock.h')
| -rw-r--r-- | lib/isc/include/isc/rwlock.h | 148 |
1 files changed, 148 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..b957509 --- /dev/null +++ b/lib/isc/include/isc/rwlock.h @@ -0,0 +1,148 @@ +/* + * Copyright (C) Internet Systems Consortium, Inc. ("ISC") + * + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. + * + * See the COPYRIGHT file distributed with this work for additional + * information regarding copyright ownership. + */ + + +#ifndef ISC_RWLOCK_H +#define ISC_RWLOCK_H 1 + +#include <inttypes.h> + +/*! \file isc/rwlock.h */ + +#include <isc/condition.h> +#include <isc/lang.h> +#include <isc/platform.h> +#include <isc/types.h> + +#if defined(ISC_PLATFORM_HAVESTDATOMIC) +#if defined(__cplusplus) +#include <isc/stdatomic.h> +#else +#include <stdatomic.h> +#endif +#endif + +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_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) || (defined(ISC_PLATFORM_HAVEXADD) && defined(ISC_PLATFORM_HAVECMPXCHG)) +#define ISC_RWLOCK_USEATOMIC 1 +#if (defined(ISC_PLATFORM_HAVESTDATOMIC) && defined(ATOMIC_INT_LOCK_FREE)) +#define ISC_RWLOCK_USESTDATOMIC 1 +#endif +#endif + +struct isc_rwlock { + /* Unlocked. */ + unsigned int magic; + isc_mutex_t lock; + int32_t spins; + +#if defined(ISC_RWLOCK_USEATOMIC) + /* + * 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. */ +#if defined(ISC_RWLOCK_USESTDATOMIC) + atomic_int_fast32_t write_requests; + atomic_int_fast32_t write_completions; + atomic_int_fast32_t cnt_and_flag; +#else + int32_t write_requests; + int32_t write_completions; + int32_t cnt_and_flag; +#endif + + /* 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_RWLOCK_USEATOMIC */ + + /*%< 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_RWLOCK_USEATOMIC */ +}; +#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 */ |