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avcodec/refstruct: Allow checking for exclusive ownership

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This is the analog of av_buffer_is_writable();
it will be used in the next commit.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2022-08-04 08:40:57 +02:00
parent 61bc8764d4
commit 56dd585146
2 changed files with 25 additions and 0 deletions
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16
libavcodec/refstruct.c
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@ -71,6 +71,13 @@ static RefCount *get_refcount(void *obj)
return ref;
}
static const RefCount *cget_refcount(const void *obj)
{
const RefCount *ref = (const RefCount*)((const char*)obj - REFCOUNT_OFFSET);
ff_assert(ref->cookie == REFSTRUCT_COOKIE);
return ref;
}
static void *get_userdata(void *buf)
{
return (char*)buf + REFCOUNT_OFFSET;
@ -164,3 +171,12 @@ void ff_refstruct_replace(void *dstp, const void *src)
memcpy(dstp, &dst, sizeof(dst));
}
}
int ff_refstruct_exclusive(const void *obj)
{
const RefCount *ref = cget_refcount(obj);
/* Casting const away here is safe, because it is a load.
* It is necessary because atomic_load_explicit() does not
* accept const atomics in C11 (see also N1807). */
return atomic_load_explicit((atomic_uintptr_t*)&ref->refcount, memory_order_acquire) == 1;
}

9
libavcodec/refstruct.h
View File

@ -142,4 +142,13 @@ const void *ff_refstruct_ref_c(const void *obj);
*/
void ff_refstruct_replace(void *dstp, const void *src);
/**
* Check whether the reference count of an object managed
* via this API is 1.
*
* @param obj A pointer to an object managed via this API.
* @return 1 if the reference count of obj is 1; 0 otherwise.
*/
int ff_refstruct_exclusive(const void *obj);
#endif /* AVCODEC_REFSTRUCT_H */