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117 lines
2.8 KiB
C
117 lines
2.8 KiB
C
/*
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** This basic implementation of Reader/Writer locks does not
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** protect writers from starvation. That is, if a writer is
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** currently waiting on a reader, any new reader will get
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** the lock before the writer.
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*/
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/********************************************************
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* An example source module to accompany...
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*
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* "Using POSIX Threads: Programming with Pthreads"
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* by Brad nichols, Dick Buttlar, Jackie Farrell
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* O'Reilly & Associates, Inc.
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*
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********************************************************
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* rdwr.c --
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*
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* Library of functions implementing reader/writer locks
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*/
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#include <portable.h>
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#include <stdlib.h>
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#include <lthread.h>
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#include <lthread_rdwr.h>
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int pthread_rdwr_init_np(pthread_rdwr_t *rdwrp, pthread_rdwrattr_t *attrp)
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{
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rdwrp->readers_reading = 0;
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rdwrp->writer_writing = 0;
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pthread_mutex_init(&(rdwrp->mutex), pthread_mutexattr_default);
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pthread_cond_init(&(rdwrp->lock_free), pthread_condattr_default);
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return 0;
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}
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int pthread_rdwr_rlock_np(pthread_rdwr_t *rdwrp){
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pthread_mutex_lock(&(rdwrp->mutex));
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while(rdwrp->writer_writing) {
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pthread_cond_wait(&(rdwrp->lock_free), &(rdwrp->mutex));
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}
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rdwrp->readers_reading++;
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pthread_mutex_unlock(&(rdwrp->mutex));
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return 0;
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}
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int pthread_rdwr_runlock_np(pthread_rdwr_t *rdwrp)
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{
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pthread_mutex_lock(&(rdwrp->mutex));
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if (rdwrp->readers_reading == 0) {
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pthread_mutex_unlock(&(rdwrp->mutex));
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return -1;
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}
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else {
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rdwrp->readers_reading--;
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if (rdwrp->readers_reading == 0) {
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pthread_cond_signal(&(rdwrp->lock_free));
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}
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pthread_mutex_unlock(&(rdwrp->mutex));
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return 0;
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}
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}
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int pthread_rdwr_wlock_np(pthread_rdwr_t *rdwrp)
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{
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pthread_mutex_lock(&(rdwrp->mutex));
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while(rdwrp->writer_writing || rdwrp->readers_reading) {
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pthread_cond_wait(&(rdwrp->lock_free), &(rdwrp->mutex));
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}
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rdwrp->writer_writing++;
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pthread_mutex_unlock(&(rdwrp->mutex));
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return 0;
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}
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int pthread_rdwr_wunlock_np(pthread_rdwr_t *rdwrp)
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{
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pthread_mutex_lock(&(rdwrp->mutex));
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if (rdwrp->writer_writing == 0) {
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pthread_mutex_unlock(&(rdwrp->mutex));
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return -1;
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}
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else {
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rdwrp->writer_writing = 0;
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pthread_cond_broadcast(&(rdwrp->lock_free));
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pthread_mutex_unlock(&(rdwrp->mutex));
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return 0;
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}
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}
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#ifdef LDAP_DEBUG
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/* just for testing,
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* return 0 if false, suitable for assert(pthread_rdwr_Xchk(rdwr))
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*
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* Currently they don't check if the calling thread is the one
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* that has the lock, just that there is a reader or writer.
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*
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* Basically sufficent for testing that places that should have
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* a lock are caught.
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*/
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int pthread_rdwr_rchk_np(pthread_rdwr_t *rdwrp)
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{
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return(rdwrp->readers_reading!=0);
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}
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int pthread_rdwr_wchk_np(pthread_rdwr_t *rdwrp)
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{
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return(rdwrp->writer_writing!=0);
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}
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int pthread_rdwr_rwchk_np(pthread_rdwr_t *rdwrp)
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{
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return(pthread_rdwr_rchk_np(rdwrp) || pthread_rdwr_wchk_np(rdwrp));
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}
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#endif /* LDAP_DEBUG */
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