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posix: semaphore: optimize named semaphore implementation a bit

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- Regroup refcount decrement and semaphore destruction by making the
  linked state into a counted reference for it. This allows for
  simplifying the code and cleanly adding a few assertions in a common
  location.

- Remove redundant initialization to NULL on memory about to be freed
  and local pointer in nsem_cleanup().

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2024-01-09 12:42:19 -05:00 • committed by Chris Friedt
commit cf74f22524
2 changed files with 16 additions and 22 deletions
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36
lib/posix/semaphore.c
View file

@ -15,7 +15,7 @@
struct nsem_obj { struct nsem_obj {
sys_snode_t snode; sys_snode_t snode;
sem_t sem; sem_t sem;
unsigned int ref_count; int ref_count;
char *name; char *name;
}; };
@ -53,17 +53,20 @@ static void nsem_cleanup(struct nsem_obj *nsem)
if (nsem != NULL) { if (nsem != NULL) {
if (nsem->name != NULL) { if (nsem->name != NULL) {
k_free(nsem->name); k_free(nsem->name);
nsem->name = NULL;
} }
k_free(nsem); k_free(nsem);
nsem = NULL;
} }
} }
/* Remove a named semaphore if it isn't unsed */ /* Remove a named semaphore if it isn't unsed */
static void nsem_remove_if_unused(struct nsem_obj *nsem) static void nsem_unref(struct nsem_obj *nsem)
{ {
nsem->ref_count -= 1;
__ASSERT(nsem->ref_count >= 0, "ref_count may not be negative");
if (nsem->ref_count == 0) { if (nsem->ref_count == 0) {
__ASSERT(nsem->name == NULL, "ref_count is 0 but sem is not unlinked");
sys_slist_find_and_remove(&nsem_list, (sys_snode_t *) nsem); sys_slist_find_and_remove(&nsem_list, (sys_snode_t *) nsem);
/* Free nsem */ /* Free nsem */
@ -255,7 +258,7 @@ sem_t *sem_open(const char *name, int oflags, ...)
goto error_unlock; goto error_unlock;
} }
__ASSERT_NO_MSG(nsem->ref_count != UINT_MAX); __ASSERT_NO_MSG(nsem->ref_count != INT_MAX);
nsem->ref_count++; nsem->ref_count++;
goto unlock; goto unlock;
} }
@ -282,7 +285,9 @@ sem_t *sem_open(const char *name, int oflags, ...)
} }
strcpy(nsem->name, name); strcpy(nsem->name, name);
nsem->ref_count = 1;
/* 1 for this open instance, +1 for the linked name */
nsem->ref_count = 2;
(void)k_sem_init(&nsem->sem, value, CONFIG_SEM_VALUE_MAX); (void)k_sem_init(&nsem->sem, value, CONFIG_SEM_VALUE_MAX);
@ -328,8 +333,7 @@ int sem_unlink(const char *name)
k_free(nsem->name); k_free(nsem->name);
nsem->name = NULL; nsem->name = NULL;
nsem_unref(nsem);
nsem_remove_if_unused(nsem);
unlock: unlock:
nsem_list_unlock(); nsem_list_unlock();
@ -345,28 +349,18 @@ int sem_close(sem_t *sem)
return -1; return -1;
} }
__ASSERT_NO_MSG(nsem != NULL);
nsem_list_lock(); nsem_list_lock();
nsem_unref(nsem);
__ASSERT_NO_MSG(nsem->ref_count != 0);
nsem->ref_count--;
/* remove sem if marked for unlink */
if (nsem->name == NULL) {
nsem_remove_if_unused(nsem);
}
nsem_list_unlock(); nsem_list_unlock();
return 0; return 0;
} }
#ifdef CONFIG_ZTEST #ifdef CONFIG_ZTEST
/* Used by ztest to get the ref count of a named semaphore */ /* Used by ztest to get the ref count of a named semaphore */
unsigned int nsem_get_ref_count(sem_t *sem) int nsem_get_ref_count(sem_t *sem)
{ {
struct nsem_obj *nsem = CONTAINER_OF(sem, struct nsem_obj, sem); struct nsem_obj *nsem = CONTAINER_OF(sem, struct nsem_obj, sem);
unsigned int ref_count; int ref_count;
__ASSERT_NO_MSG(sem != NULL); __ASSERT_NO_MSG(sem != NULL);
__ASSERT_NO_MSG(nsem != NULL); __ASSERT_NO_MSG(nsem != NULL);

2
tests/posix/common/src/semaphore.c
View file

@ -107,7 +107,7 @@ ZTEST(posix_apis, test_semaphore)
semaphore_test(&sema); semaphore_test(&sema);
} }
unsigned int nsem_get_ref_count(sem_t *sem); int nsem_get_ref_count(sem_t *sem);
size_t nsem_get_list_len(void); size_t nsem_get_list_len(void);
#define N_LOOPS 999 #define N_LOOPS 999