OpenSolaris_b135/lib/libnisdb/nisdb_rw.c
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (the "License"). You may not use this file except in compliance
* with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright (c) 2001 by Sun Microsystems, Inc.
* All rights reserved.
*/
#pragma ident "%Z%%M% %I% %E% SMI"
#include <stdio.h>
#include <rpc/types.h>
#include <rpc/xdr.h>
#include "db_dictionary_c.h"
#include "nisdb_rw.h"
#include "nisdb_ldap.h"
/*
* Nesting-safe RW locking functions. Return 0 when successful, an
* error number from the E-series when not.
*/
int
__nisdb_rwinit(__nisdb_rwlock_t *rw) {
int ret;
if (rw == 0) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
return (EFAULT);
}
if ((ret = mutex_init(&rw->mutex, USYNC_THREAD, 0)) != 0)
return (ret);
if ((ret = cond_init(&rw->cv, USYNC_THREAD, 0)) != 0)
return (ret);
rw->destroyed = 0;
/*
* If we allow read-to-write lock migration, there's a potential
* race condition if two or more threads want to upgrade at the
* same time. The simple and safe (but crude and possibly costly)
* method to fix this is to always use exclusive locks, and so
* that has to be the default.
*
* There are two conditions under which it is safe to set
* 'force_write' to zero for a certain lock structure:
*
* (1) The lock will never be subject to migration, or
*
* (2) It's OK if the data protected by the lock has changed
* (a) Every time the lock (read or write) has been
* acquired (even if the lock already was held by
* the thread), and
* (b) After every call to a function that might have
* acquired the lock.
*/
rw->force_write = NISDB_FORCE_WRITE;
rw->writer_count = rw->reader_count = rw->reader_blocked = 0;
rw->writer.id = rw->reader.id = INV_PTHREAD_ID;
rw->writer.count = rw->reader.count = 0;
rw->writer.next = rw->reader.next = 0;
return (0);
}
static __nisdb_rl_t *
find_reader(pthread_t id, __nisdb_rwlock_t *rw) {
__nisdb_rl_t *rr;
for (rr = &rw->reader; rr != 0; rr = rr->next) {
if (rr->id == INV_PTHREAD_ID) {
rr = 0;
break;
}
if (rr->id == id)
break;
}
return (rr);
}
int
__nisdb_rw_readlock_ok(__nisdb_rwlock_t *rw) {
int ret;
pthread_t myself = pthread_self();
__nisdb_rl_t *rr;
if (rw == 0)
return (EFAULT);
if (rw->destroyed != 0)
return (ESHUTDOWN);
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
/*
* Only allow changing 'force_write' when it's really safe; i.e.,
* the lock hasn't been destroyed, and there are no readers.
*/
if (rw->destroyed == 0 && rw->reader_count == 0) {
rw->force_write = 0;
ret = 0;
} else {
ret = EBUSY;
}
(void) mutex_unlock(&rw->mutex);
return (ret);
}
int
__nisdb_rw_force_writelock(__nisdb_rwlock_t *rw) {
int ret;
pthread_t myself = pthread_self();
__nisdb_rl_t *rr;
if (rw == 0 || rw->destroyed != 0)
return (ESHUTDOWN);
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
/*
* Only allow changing 'force_write' when it's really safe; i.e.,
* the lock hasn't been destroyed, and there are no readers.
*/
if (rw->destroyed == 0 && rw->reader_count == 0) {
rw->force_write = 1;
ret = 0;
} else {
ret = EBUSY;
}
(void) mutex_unlock(&rw->mutex);
return (ret);
}
int
__nisdb_wlock_trylock(__nisdb_rwlock_t *rw, int trylock) {
int ret;
pthread_t myself = pthread_self();
int all_readers_blocked = 0;
__nisdb_rl_t *rr = 0;
if (rw == 0) {
#ifdef NISDB_MT_DEBUG
/* This shouldn't happen */
abort();
#endif /* NISDB_MT_DEBUG */
return (EFAULT);
}
if (rw->destroyed != 0)
return (ESHUTDOWN);
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
if (rw->destroyed != 0) {
(void) mutex_unlock(&rw->mutex);
return (ESHUTDOWN);
}
/* Simplest (and probably most common) case: no readers or writers */
if (rw->reader_count == 0 && rw->writer_count == 0) {
rw->writer_count = 1;
rw->writer.id = myself;
rw->writer.count = 1;
return (mutex_unlock(&rw->mutex));
}
/*
* Need to know if we're holding a read lock already, and if
* all other readers are blocked waiting for the mutex.
*/
if (rw->reader_count > 0) {
if ((rr = find_reader(myself, rw)) != 0) {
if (rr->count)
/*
* We're already holding a read lock, so
* if the number of readers equals the number
* of blocked readers plus one, all other
* readers are blocked.
*/
if (rw->reader_count ==
(rw->reader_blocked + 1))
all_readers_blocked = 1;
else
/*
* We're not holding a read lock, so the
* number of readers should equal the number
* of blocked readers if all readers are
* blocked.
*/
if (rw->reader_count == rw->reader_blocked)
all_readers_blocked = 1;
}
}
/* Wait for reader(s) or writer to finish */
while (1) {
/*
* We can stop looping if one of the following holds:
* - No readers, no writers
* - No writers (or writer is myself), and one of:
* - No readers
* - One reader, and it's us
* - N readers, but all blocked on the mutex
*/
if (
(rw->writer_count == 0 && rw->reader_count == 0) ||
((rw->writer_count == 0 || rw->writer.id == myself) &&
(rw->reader_count == 0) ||
(rw->reader_count == 1 &&
rw->reader.id == myself))) {
break;
}
/*
* Provided that all readers are blocked on the mutex
* we break a potential dead-lock by acquiring the
* write lock.
*/
if (all_readers_blocked) {
if (rw->writer_count == 0 || rw->writer.id == myself) {
break;
}
}
/*
* If 'trylock' is set, tell the caller that we'd have to
* block to obtain the lock.
*/
if (trylock) {
(void) mutex_unlock(&rw->mutex);
return (EBUSY);
}
/* If we're also a reader, indicate that we're blocking */
if (rr != 0) {
rr->wait = 1;
rw->reader_blocked++;
}
if ((ret = cond_wait(&rw->cv, &rw->mutex)) != 0) {
if (rr != 0) {
rr->wait = 0;
if (rw->reader_blocked > 0)
rw->reader_blocked--;
#ifdef NISDB_MT_DEBUG
else
abort();
#endif /* NISDB_MT_DEBUG */
}
(void) mutex_unlock(&rw->mutex);
return (ret);
}
if (rr != 0) {
rr->wait = 0;
if (rw->reader_blocked > 0)
rw->reader_blocked--;
#ifdef NISDB_MT_DEBUG
else
abort();
#endif /* NISDB_MT_DEBUG */
}
}
/* OK to grab the write lock */
rw->writer.id = myself;
/* Increment lock depth */
rw->writer.count++;
/* Set number of writers (doesn't increase with lock depth) */
if (rw->writer_count == 0)
rw->writer_count = 1;
return (mutex_unlock(&rw->mutex));
}
int
__nisdb_wlock(__nisdb_rwlock_t *rw) {
return (__nisdb_wlock_trylock(rw, 0));
}
static __nisdb_rl_t *
increment_reader(pthread_t id, __nisdb_rwlock_t *rw) {
__nisdb_rl_t *rr;
for (rr = &rw->reader; rr != 0; rr = rr->next) {
if (rr->id == id || rr->id == INV_PTHREAD_ID)
break;
}
if (rw->reader_count == 0 && rr == &rw->reader) {
/* No previous reader */
rr->id = id;
rw->reader_count = 1;
} else if (rr == 0) {
if ((rr = malloc(sizeof (__nisdb_rl_t))) == 0)
return (0);
rr->id = id;
rr->count = 0;
/*
* For insertion simplicity, make it the second item
* on the list.
*/
rr->next = rw->reader.next;
rw->reader.next = rr;
rw->reader_count++;
}
rr->count++;
return (rr);
}
int
__nisdb_rlock(__nisdb_rwlock_t *rw) {
int ret;
pthread_t myself = pthread_self();
__nisdb_rl_t *rr;
if (rw == 0) {
#ifdef NISDB_MT_DEBUG
/* This shouldn't happen */
abort();
#endif /* NISDB_MT_DEBUG */
return (EFAULT);
}
if (rw->destroyed != 0)
return (ESHUTDOWN);
if (rw->force_write)
return (__nisdb_wlock(rw));
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
if (rw->destroyed != 0) {
(void) mutex_unlock(&rw->mutex);
return (ESHUTDOWN);
}
rr = find_reader(myself, rw);
/* Wait for writer to complete; writer == myself also OK */
while (rw->writer_count > 0 && rw->writer.id != myself) {
if (rr != 0) {
rr->wait = 1;
rw->reader_blocked++;
}
if ((ret = cond_wait(&rw->cv, &rw->mutex)) != 0) {
if (rr != 0) {
rr->wait = 0;
if (rw->reader_blocked > 0)
rw->reader_blocked--;
#ifdef NISDB_MT_DEBUG
else
abort();
#endif /* NISDB_MT_DEBUG */
}
(void) mutex_unlock(&rw->mutex);
return (ret);
}
if (rr != 0) {
rr->wait = 0;
if (rw->reader_blocked > 0)
rw->reader_blocked--;
#ifdef NISDB_MT_DEBUG
else
abort();
#endif /* NISDB_MT_DEBUG */
}
}
rr = increment_reader(myself, rw);
ret = mutex_unlock(&rw->mutex);
return ((rr == 0) ? ENOMEM : ret);
}
int
__nisdb_wulock(__nisdb_rwlock_t *rw) {
int ret;
pthread_t myself = pthread_self();
if (rw == 0) {
#ifdef NISDB_MT_DEBUG
/* This shouldn't happen */
abort();
#endif /* NISDB_MT_DEBUG */
return (EFAULT);
}
if (rw->destroyed != 0)
return (ESHUTDOWN);
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
if (rw->destroyed != 0) {
(void) mutex_unlock(&rw->mutex);
return (ESHUTDOWN);
}
/* Sanity check */
if (rw->writer_count == 0 ||
rw->writer.id != myself || rw->writer.count == 0) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
(void) mutex_unlock(&rw->mutex);
return (ENOLCK);
}
rw->writer.count--;
if (rw->writer.count == 0) {
rw->writer.id = INV_PTHREAD_ID;
rw->writer_count = 0;
if ((ret = cond_broadcast(&rw->cv)) != 0) {
(void) mutex_unlock(&rw->mutex);
return (ret);
}
}
return (mutex_unlock(&rw->mutex));
}
int
__nisdb_rulock(__nisdb_rwlock_t *rw) {
int ret;
pthread_t myself = pthread_self();
__nisdb_rl_t *rr, *prev;
if (rw == 0) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
return (EFAULT);
}
if (rw->destroyed != 0)
return (ESHUTDOWN);
if (rw->force_write)
return (__nisdb_wulock(rw));
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
if (rw->destroyed != 0) {
(void) mutex_unlock(&rw->mutex);
return (ESHUTDOWN);
}
/* Sanity check */
if (rw->reader_count == 0 ||
(rw->writer_count > 0 && rw->writer.id != myself)) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
(void) mutex_unlock(&rw->mutex);
return (ENOLCK);
}
/* Find the reader record */
for (rr = &rw->reader, prev = 0; rr != 0; prev = rr, rr = rr->next) {
if (rr->id == myself)
break;
}
if (rr == 0 || rr->count == 0) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
(void) mutex_unlock(&rw->mutex);
return (ENOLCK);
}
rr->count--;
if (rr->count == 0) {
if (rr != &rw->reader) {
/* Remove item from list and free it */
prev->next = rr->next;
free(rr);
} else {
/*
* First record: copy second to first, and free second
* record.
*/
if (rr->next != 0) {
rr = rr->next;
rw->reader.id = rr->id;
rw->reader.count = rr->count;
rw->reader.next = rr->next;
free(rr);
} else {
/* Decomission the first record */
rr->id = INV_PTHREAD_ID;
}
}
rw->reader_count--;
}
/* If there are no readers, wake up any waiting writer */
if (rw->reader_count == 0) {
if ((ret = cond_broadcast(&rw->cv)) != 0) {
(void) mutex_unlock(&rw->mutex);
return (ret);
}
}
return (mutex_unlock(&rw->mutex));
}
/* Return zero if write lock held by this thread, non-zero otherwise */
int
__nisdb_assert_wheld(__nisdb_rwlock_t *rw) {
int ret;
if (rw == 0) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
return (EFAULT);
}
if (rw->destroyed != 0)
return (ESHUTDOWN);
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
if (rw->destroyed != 0) {
(void) mutex_unlock(&rw->mutex);
return (ESHUTDOWN);
}
if (rw->writer_count == 0 || rw->writer.id != pthread_self()) {
ret = mutex_unlock(&rw->mutex);
return ((ret == 0) ? -1 : ret);
}
/*
* We're holding the lock, so we should return zero. Since
* that's what mutex_unlock() does if it succeeds, we just
* return the value of mutex_unlock().
*/
return (mutex_unlock(&rw->mutex));
}
/* Return zero if read lock held by this thread, non-zero otherwise */
int
__nisdb_assert_rheld(__nisdb_rwlock_t *rw) {
int ret;
pthread_t myself = pthread_self();
__nisdb_rl_t *rr;
if (rw == 0) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
return (EFAULT);
}
if (rw->destroyed != 0)
return (ESHUTDOWN);
if (rw->force_write)
return (__nisdb_assert_wheld(rw));
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
if (rw->destroyed != 0) {
(void) mutex_unlock(&rw->mutex);
return (ESHUTDOWN);
}
/* Write lock also OK */
if (rw->writer_count > 0 && rw->writer.id == myself) {
(void) mutex_unlock(&rw->mutex);
return (0);
}
if (rw->reader_count == 0) {
(void) mutex_unlock(&rw->mutex);
return (EBUSY);
}
rr = &rw->reader;
do {
if (rr->id == myself) {
(void) mutex_unlock(&rw->mutex);
return (0);
}
rr = rr->next;
} while (rr != 0);
ret = mutex_unlock(&rw->mutex);
return ((ret == 0) ? EBUSY : ret);
}
int
__nisdb_destroy_lock(__nisdb_rwlock_t *rw) {
int ret;
pthread_t myself = pthread_self();
__nisdb_rl_t *rr;
if (rw == 0) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
return (EFAULT);
}
if (rw->destroyed != 0)
return (ESHUTDOWN);
if ((ret = mutex_lock(&rw->mutex)) != 0)
return (ret);
if (rw->destroyed != 0) {
(void) mutex_unlock(&rw->mutex);
return (ESHUTDOWN);
}
/*
* Only proceed if if there are neither readers nor writers
* other than this thread. Also, no nested locks may be in
* effect.
*/
if ((rw->writer_count > 0 &&
(rw->writer.id != myself || rw->writer.count != 1) ||
(rw->reader_count > 0 &&
!(rw->reader_count == 1 && rw->reader.id == myself &&
rw->reader.count == 1))) ||
(rw->writer_count > 0 && rw->reader_count > 0)) {
#ifdef NISDB_MT_DEBUG
abort();
#endif /* NISDB_MT_DEBUG */
(void) mutex_unlock(&rw->mutex);
return (ENOLCK);
}
/*
* Mark lock destroyed, so that any thread waiting on the mutex
* will know what's what. Of course, this is a bit iffy, since
* we're probably being called from a destructor, and the structure
* where we live will soon cease to exist (i.e., be freed and
* perhaps re-used). Still, we can only do our best, and give
* those other threads the best chance possible.
*/
rw->destroyed++;
return (mutex_unlock(&rw->mutex));
}
void
__nisdb_lock_report(__nisdb_rwlock_t *rw) {
char *myself = "__nisdb_lock_report";
if (rw == 0) {
printf("%s: NULL argument\n", myself);
return;
}
if (rw->destroyed)
printf("0x%x: DESTROYED\n", rw);
printf("0x%x: Read locking %s\n",
rw, rw->force_write ? "disallowed" : "allowed");
if (rw->writer_count == 0)
printf("0x%x: No writer\n", rw);
else if (rw->writer_count == 1) {
printf("0x%x: Write locked by %d, depth = %d\n",
rw, rw->writer.id, rw->writer.count);
if (rw->writer.wait)
printf("0x%x:\tWriter blocked\n", rw);
} else
printf("0x%x: Invalid writer count = %d\n",
rw, rw->writer_count);
if (rw->reader_count == 0)
printf("0x%x: No readers\n", rw);
else {
__nisdb_rl_t *r;
printf("0x%x: %d readers, %d blocked\n",
rw, rw->reader_count, rw->reader_blocked);
for (r = &rw->reader; r != 0; r = r->next) {
printf("0x%x:\tthread %d, depth = %d%s\n",
rw, r->id, r->count,
(r->wait ? " (blocked)" : ""));
}
}
}