/usr/include/isc/rwlock.h is in libbind-dev 1:9.9.5.dfsg-3ubuntu0.19.
This file is owned by root:root, with mode 0o644.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 | /*
* 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 */
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