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/* $OpenLDAP$ */
/* This work is part of OpenLDAP Software <http://www.openldap.org/>.
*
* Copyright 1998-2024 The OpenLDAP Foundation.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted only as authorized by the OpenLDAP
* Public License.
*
* A copy of this license is available in file LICENSE in the
* top-level directory of the distribution or, alternatively, at
* <http://www.OpenLDAP.org/license.html>.
*/
/* This work was initially developed by Kurt D. Zeilenga for inclusion
* in OpenLDAP Software. Additional significant contributors include:
* Stuart Lynne
*/
/*
* This is an improved implementation of Reader/Writer locks does
* not protect writers from starvation. That is, if a writer is
* currently waiting on a reader, any new reader will get
* the lock before the writer.
*
* Does not support cancellation nor does any status checking.
*/
/* Adapted from publicly available examples for:
* "Programming with Posix Threads"
* by David R Butenhof, Addison-Wesley
* http://cseng.aw.com/bookpage.taf?ISBN=0-201-63392-2
*/
#include "portable.h"
#include <ac/stdlib.h>
#include <ac/errno.h>
#include <ac/string.h>
#include <ac/time.h>
#include "ldap-int.h"
#ifdef LDAP_R_COMPILE
#include "ldap_pvt_thread.h" /* Get the thread interface */
#define LDAP_THREAD_RDWR_IMPLEMENTATION
#include "ldap_thr_debug.h" /* May rename the symbols defined below */
/*
* implementations that provide their own compatible
* reader/writer locks define LDAP_THREAD_HAVE_RDWR
* in ldap_pvt_thread.h
*/
#ifndef LDAP_THREAD_HAVE_RDWR
struct ldap_int_thread_rdwr_s {
ldap_pvt_thread_mutex_t ltrw_mutex;
ldap_pvt_thread_cond_t ltrw_read; /* wait for read */
ldap_pvt_thread_cond_t ltrw_write; /* wait for write */
int ltrw_valid;
#define LDAP_PVT_THREAD_RDWR_VALID 0x0bad
int ltrw_r_active;
int ltrw_w_active;
int ltrw_r_wait;
int ltrw_w_wait;
#ifdef LDAP_RDWR_DEBUG
/* keep track of who has these locks */
#define MAX_READERS 32
int ltrw_more_readers; /* Set if ltrw_readers[] is incomplete */
ldap_pvt_thread_t ltrw_readers[MAX_READERS];
ldap_pvt_thread_t ltrw_writer;
#endif
};
int
ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rwlock )
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = (struct ldap_int_thread_rdwr_s *) LDAP_CALLOC( 1,
sizeof( struct ldap_int_thread_rdwr_s ) );
if ( !rw )
return LDAP_NO_MEMORY;
/* we should check return results */
ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
ldap_pvt_thread_cond_init( &rw->ltrw_read );
ldap_pvt_thread_cond_init( &rw->ltrw_write );
rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALID;
*rwlock = rw;
return 0;
}
int
ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rwlock )
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
return LDAP_PVT_THREAD_EINVAL;
ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
/* active threads? */
if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 0) {
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return LDAP_PVT_THREAD_EBUSY;
}
/* waiting threads? */
if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return LDAP_PVT_THREAD_EBUSY;
}
rw->ltrw_valid = 0;
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
LDAP_FREE(rw);
*rwlock = NULL;
return 0;
}
int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rwlock )
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
return LDAP_PVT_THREAD_EINVAL;
ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
if( rw->ltrw_w_active > 0 ) {
/* writer is active */
rw->ltrw_r_wait++;
do {
ldap_pvt_thread_cond_wait(
&rw->ltrw_read, &rw->ltrw_mutex );
} while( rw->ltrw_w_active > 0 );
rw->ltrw_r_wait--;
assert( rw->ltrw_r_wait >= 0 );
}
#ifdef LDAP_RDWR_DEBUG
if( rw->ltrw_r_active < MAX_READERS )
rw->ltrw_readers[rw->ltrw_r_active] = ldap_pvt_thread_self();
else
rw->ltrw_more_readers = 1;
#endif
rw->ltrw_r_active++;
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return 0;
}
int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rwlock )
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
return LDAP_PVT_THREAD_EINVAL;
ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
if( rw->ltrw_w_active > 0) {
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return LDAP_PVT_THREAD_EBUSY;
}
#ifdef LDAP_RDWR_DEBUG
if( rw->ltrw_r_active < MAX_READERS )
rw->ltrw_readers[rw->ltrw_r_active] = ldap_pvt_thread_self();
else
rw->ltrw_more_readers = 1;
#endif
rw->ltrw_r_active++;
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return 0;
}
int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rwlock )
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
return LDAP_PVT_THREAD_EINVAL;
ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
rw->ltrw_r_active--;
#ifdef LDAP_RDWR_DEBUG
/* Remove us from the list of readers */
{
ldap_pvt_thread_t self = ldap_pvt_thread_self();
int i, j;
for( i = j = rw->ltrw_r_active; i >= 0; i--) {
if (rw->ltrw_readers[i] == self) {
rw->ltrw_readers[i] = rw->ltrw_readers[j];
rw->ltrw_readers[j] = 0;
break;
}
}
if( !rw->ltrw_more_readers )
assert( i >= 0 );
else if( j == 0 )
rw->ltrw_more_readers = 0;
}
#endif
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
ldap_pvt_thread_cond_signal( &rw->ltrw_write );
}
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return 0;
}
int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rwlock )
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
return LDAP_PVT_THREAD_EINVAL;
ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
rw->ltrw_w_wait++;
do {
ldap_pvt_thread_cond_wait(
&rw->ltrw_write, &rw->ltrw_mutex );
} while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
rw->ltrw_w_wait--;
assert( rw->ltrw_w_wait >= 0 );
}
#ifdef LDAP_RDWR_DEBUG
rw->ltrw_writer = ldap_pvt_thread_self();
#endif
rw->ltrw_w_active++;
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return 0;
}
int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rwlock )
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
return LDAP_PVT_THREAD_EINVAL;
ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return LDAP_PVT_THREAD_EBUSY;
}
#ifdef LDAP_RDWR_DEBUG
rw->ltrw_writer = ldap_pvt_thread_self();
#endif
rw->ltrw_w_active++;
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return 0;
}
int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rwlock )
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
return LDAP_PVT_THREAD_EINVAL;
ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
rw->ltrw_w_active--;
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
if (rw->ltrw_r_wait > 0) {
ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
} else if (rw->ltrw_w_wait > 0) {
ldap_pvt_thread_cond_signal( &rw->ltrw_write );
}
#ifdef LDAP_RDWR_DEBUG
assert( rw->ltrw_writer == ldap_pvt_thread_self() );
rw->ltrw_writer = 0;
#endif
ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
return 0;
}
#ifdef LDAP_RDWR_DEBUG
/* just for testing,
* return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
*
* Currently they don't check if the calling thread is the one
* that has the lock, just that there is a reader or writer.
*
* Basically sufficient for testing that places that should have
* a lock are caught.
*/
int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rwlock)
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
return( rw->ltrw_r_active );
}
int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rwlock)
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
return( rw->ltrw_w_active );
}
int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rwlock)
{
struct ldap_int_thread_rdwr_s *rw;
assert( rwlock != NULL );
rw = *rwlock;
assert( rw != NULL );
assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
assert( rw->ltrw_w_active >= 0 );
assert( rw->ltrw_w_wait >= 0 );
assert( rw->ltrw_r_active >= 0 );
assert( rw->ltrw_r_wait >= 0 );
return(ldap_pvt_thread_rdwr_readers(rwlock) +
ldap_pvt_thread_rdwr_writers(rwlock));
}
#endif /* LDAP_RDWR_DEBUG */
#endif /* LDAP_THREAD_HAVE_RDWR */
#endif /* LDAP_R_COMPILE */
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