Understanding the meaning of "no action is performed" in memory management routines

[naveen-rn]

We have the following statement in the memory management subsection:

When no action is performed, these routines return without performing a barrier.

And, the following statement in the changes to document sections:

Clarified that when the size argument is zero, symmetric heap allocation routines perform no action and return a null pointer; that symmetric heap management routines that perform no action do not perform a barrier; and that the alignment argument to shmem_align must be power of two multiple of sizeof(void*).

Just to be clear on the intended semantics - please clarify whether the following options can be considered as "no action" for the memory management operations:

1. On shmem_malloc, shmem_realloc, shmem_align, and shmem_calloc, if the size is zero
2. If the returned pointer from shmem_malloc and shmem_calloc is NULL
3. If the user passed ptr in shmem_free is NULL
4. If the count in shmem_calloc is zero

AFAIU, (1), (3), and (4) seems correct. Not sure with (2). Please clarify.

[jdinan]

Item 2 may be true as a consequence of item 1, but I don't recall it being specified in this way. It might simplify coding for OpenSHMEM 1.5 to use this fact, but it could become cause a bug if a future specification invalidates this rule. Then again, it might also simplify the specification to adopt this as a rule. 🤷

[naveen-rn]

I'm fine with (2), for now this is not an issue with our implementation. But, in future, I'm not sure whether there would be bugs when one PE gets a NULL and others get a valid ptr.

[jdinan]

It would break symmetry if all PEs don't either successfully allocate memory or return NULL, right?

This may actually be an oversight in the shmem_malloc_with_hints call. It can return NULL, but I'm not seeing a stipulation that the returned value must be NULL at all PEs in this case.