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add comments to help understanding pthread

This commit is contained in:
Rogerz Zhang 2013-03-28 23:26:46 +08:00
parent 8e6a534fa3
commit e9cf10daed
2 changed files with 13 additions and 5 deletions
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6
components/pthreads/pthread.h
View File

@ -104,9 +104,9 @@ struct pthread_rwlock
pthread_cond_t rw_condreaders; /* for reader threads waiting */
pthread_cond_t rw_condwriters; /* for writer threads waiting */
int rw_nwaitreaders; /* the number waiting */
int rw_nwaitwriters; /* the number waiting */
int rw_refcount;
int rw_nwaitreaders; /* the number of reader threads waiting */
int rw_nwaitwriters; /* the number of writer threads waiting */
int rw_refcount; /* 0: unlocked, -1: locked by writer, > 0 locked by n readers */
};
typedef struct pthread_rwlock pthread_rwlock_t;

12
components/pthreads/pthread_rwlock.c
View File

@ -112,9 +112,11 @@ int pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
while (rwlock->rw_refcount < 0 || rwlock->rw_nwaitwriters > 0)
{
rwlock->rw_nwaitreaders++;
/* rw_mutex will be released when waiting for rw_condreaders */
result = pthread_cond_wait(&rwlock->rw_condreaders, &rwlock->rw_mutex);
/* rw_mutex should have been taken again when returned from waiting */
rwlock->rw_nwaitreaders--;
if (result != 0)
if (result != 0) /* wait error */
break;
}
@ -160,7 +162,9 @@ int pthread_rwlock_timedrdlock (pthread_rwlock_t * rwlock, const struct timespec
while (rwlock->rw_refcount < 0 || rwlock->rw_nwaitwriters > 0)
{
rwlock->rw_nwaitreaders++;
/* rw_mutex will be released when waiting for rw_condreaders */
result = pthread_cond_timedwait(&rwlock->rw_condreaders, &rwlock->rw_mutex, abstime);
/* rw_mutex should have been taken again when returned from waiting */
rwlock->rw_nwaitreaders--;
if (result != 0)
break;
@ -187,7 +191,9 @@ int pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock, const struct timespec
while (rwlock->rw_refcount != 0)
{
rwlock->rw_nwaitwriters++;
/* rw_mutex will be released when waiting for rw_condwriters */
result = pthread_cond_timedwait(&rwlock->rw_condwriters, &rwlock->rw_mutex, abstime);
/* rw_mutex should have been taken again when returned from waiting */
rwlock->rw_nwaitwriters--;
if (result != 0) break;
@ -233,7 +239,7 @@ int pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
if (rwlock->rw_refcount > 0)
rwlock->rw_refcount--; /* releasing a reader */
else if (rwlock->rw_refcount == -1)
rwlock->rw_refcount = 0; /* releasing a reader */
rwlock->rw_refcount = 0; /* releasing a writer */
/* give preference to waiting writers over waiting readers */
if (rwlock->rw_nwaitwriters > 0)
@ -264,7 +270,9 @@ int pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
while (rwlock->rw_refcount != 0)
{
rwlock->rw_nwaitwriters++;
/* rw_mutex will be released when waiting for rw_condwriters */
result = pthread_cond_wait(&rwlock->rw_condwriters, &rwlock->rw_mutex);
/* rw_mutex should have been taken again when returned from waiting */
rwlock->rw_nwaitwriters--;
if (result != 0) break;