/* $NetBSD: rdwr.c,v 1.1.1.6.6.1 2019/08/10 06:17:15 martin Exp $ */ /* $OpenLDAP$ */ /* This work is part of OpenLDAP Software . * * Copyright 1998-2019 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 * . */ /* 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 publically 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 __RCSID("$NetBSD: rdwr.c,v 1.1.1.6.6.1 2019/08/10 06:17:15 martin Exp $"); #include "portable.h" #include #include #include #include #include "ldap-int.h" #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 sufficent 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 */