rwlock.c revision 9c3531d72aeaad6c5f01efe6a1c82023e1379e4d
/*
* Copyright (C) 1998-2000 Internet Software Consortium.
*
* Permission to use, copy, modify, and 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 INTERNET SOFTWARE CONSORTIUM DISCLAIMS
* ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
* CONSORTIUM 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.c,v 1.16 2000/06/22 21:57:11 tale Exp $ */
#include <config.h>
#include <isc/magic.h>
#include <isc/rwlock.h>
#include <isc/util.h>
#define RWLOCK_MAGIC 0x52574C6BU /* RWLk. */
#define VALID_RWLOCK(rwl) ISC_MAGIC_VALID(rwl, RWLOCK_MAGIC)
#ifdef ISC_RWLOCK_TRACE
#include <stdio.h> /* Required for fprintf/stderr. */
static void
print_lock(char *operation, isc_rwlock_t *rwl, isc_rwlocktype_t type) {
fprintf(stderr,
"%s(%s): %s, %u active, %u granted, "
"%u rwaiting, %u wwaiting\n",
operation, (type == isc_rwlocktype_read ? "read" : "write"),
(rwl->type == isc_rwlocktype_read ? "reading" : "writing"),
rwl->active, rwl->granted, rwl->readers_waiting,
rwl->writers_waiting);
}
#endif
isc_result_t
isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
unsigned int write_quota)
{
isc_result_t result;
REQUIRE(rwl != NULL);
/*
* In case there's trouble initializing, we zero magic now. If all
* goes well, we'll set it to RWLOCK_MAGIC.
*/
rwl->magic = 0;
rwl->type = isc_rwlocktype_read;
rwl->active = 0;
rwl->granted = 0;
rwl->readers_waiting = 0;
rwl->writers_waiting = 0;
if (read_quota == 0)
read_quota = 4;
rwl->read_quota = read_quota;
if (write_quota == 0)
write_quota = 4;
rwl->write_quota = write_quota;
result = isc_mutex_init(&rwl->lock);
if (result != ISC_R_SUCCESS) {
UNEXPECTED_ERROR(__FILE__, __LINE__,
"isc_mutex_init() failed: %s",
isc_result_totext(result));
return (ISC_R_UNEXPECTED);
}
result = isc_condition_init(&rwl->readable);
if (result != ISC_R_SUCCESS) {
UNEXPECTED_ERROR(__FILE__, __LINE__,
"isc_condition_init(readable) failed: %s",
isc_result_totext(result));
return (ISC_R_UNEXPECTED);
}
result = isc_condition_init(&rwl->writeable);
if (result != ISC_R_SUCCESS) {
UNEXPECTED_ERROR(__FILE__, __LINE__,
"isc_condition_init(writeable) failed: %s",
isc_result_totext(result));
return (ISC_R_UNEXPECTED);
}
rwl->magic = RWLOCK_MAGIC;
return (ISC_R_SUCCESS);
}
isc_result_t
isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
isc_boolean_t skip = ISC_FALSE;
isc_boolean_t done = ISC_FALSE;
REQUIRE(VALID_RWLOCK(rwl));
LOCK(&rwl->lock);
#ifdef ISC_RWLOCK_TRACE
print_lock("prelock", rwl, type);
#endif
if (type == isc_rwlocktype_read) {
if (rwl->readers_waiting != 0)
skip = ISC_TRUE;
while (!done) {
if (!skip &&
((rwl->active == 0 ||
(rwl->type == isc_rwlocktype_read &&
rwl->granted < rwl->read_quota)))) {
rwl->type = isc_rwlocktype_read;
rwl->active++;
rwl->granted++;
done = ISC_TRUE;
} else {
skip = ISC_FALSE;
rwl->readers_waiting++;
WAIT(&rwl->readable, &rwl->lock);
rwl->readers_waiting--;
}
}
} else {
if (rwl->writers_waiting != 0)
skip = ISC_TRUE;
while (!done) {
if (!skip && rwl->active == 0) {
rwl->type = isc_rwlocktype_write;
rwl->active = 1;
rwl->granted++;
done = ISC_TRUE;
} else {
skip = ISC_FALSE;
rwl->writers_waiting++;
WAIT(&rwl->writeable, &rwl->lock);
rwl->writers_waiting--;
}
}
}
#ifdef ISC_RWLOCK_TRACE
print_lock("postlock", rwl, type);
#endif
UNLOCK(&rwl->lock);
return (ISC_R_SUCCESS);
}
isc_result_t
isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
REQUIRE(VALID_RWLOCK(rwl));
LOCK(&rwl->lock);
REQUIRE(rwl->type == type);
UNUSED(type);
#ifdef ISC_RWLOCK_TRACE
print_lock("preunlock", rwl, type);
#endif
rwl->active--;
if (rwl->active == 0) {
if (rwl->type == isc_rwlocktype_read) {
rwl->granted = 0;
if (rwl->writers_waiting > 0) {
rwl->type = isc_rwlocktype_write;
SIGNAL(&rwl->writeable);
} else if (rwl->readers_waiting > 0) {
/* Does this case ever happen? */
BROADCAST(&rwl->readable);
}
} else {
if (rwl->readers_waiting > 0) {
if (rwl->writers_waiting > 0 &&
rwl->granted < rwl->write_quota) {
SIGNAL(&rwl->writeable);
} else {
rwl->granted = 0;
rwl->type = isc_rwlocktype_read;
BROADCAST(&rwl->readable);
}
} else if (rwl->writers_waiting > 0) {
rwl->granted = 0;
SIGNAL(&rwl->writeable);
} else {
rwl->granted = 0;
}
}
} else {
if (rwl->type == isc_rwlocktype_read &&
rwl->writers_waiting == 0) {
INSIST(rwl->granted > 0);
rwl->granted--;
if (rwl->readers_waiting > 0)
SIGNAL(&rwl->readable);
}
}
#ifdef ISC_RWLOCK_TRACE
print_lock("postunlock", rwl, type);
#endif
UNLOCK(&rwl->lock);
return (ISC_R_SUCCESS);
}
void
isc_rwlock_destroy(isc_rwlock_t *rwl) {
REQUIRE(VALID_RWLOCK(rwl));
LOCK(&rwl->lock);
REQUIRE(rwl->active == 0 &&
rwl->readers_waiting == 0 &&
rwl->writers_waiting == 0);
UNLOCK(&rwl->lock);
rwl->magic = 0;
(void)isc_condition_destroy(&rwl->readable);
(void)isc_condition_destroy(&rwl->writeable);
(void)isc_mutex_destroy(&rwl->lock);
}