[Openshmem-list] Effects of removing implicit finalize from the specification

[Naveen Ravichandrasekaran]

At present, the specification allows the multiple usage of shmem_finalize. 
This seems to be a defined behavior and multiple subsequent calls to finalize 
are no-ops.

The following example should pass as per the current specification;

Example:1
int main(void) {
	shmem_init();
	shmem_finalize();
	shmem_finalize();
	return 0;
}

In Example:1, we have three finalize (2 explicit + 1 implicit) operations.
Even any common SHMEM usage, will have two finalize operations 
(1 explicit + 1 implicit). Even though the specification is not clear about the 
above usage, this is the side-effect of having implicit finalize at exit() or at
return from main.

Example:2
int main(void) {
	shmem_init();
	atexit(shmem_finalize);
	return 0;
}

During F2F meeting, we decided to drop implicit finalize in the specification.
The argument was that the users can explicitly call "atexit" in the application
to achieve the above behavior as shown in Example:2. 

Example:3
int main(void) {
	shmem_init();
	atexit(shmem_finalize);
	shmem_finalize();
	return 0;
}

FWIU, if we remove implicit finalize from the specification - Example:2 is
guaranteed to work but the behavior on Example:3 is undefined. 

To allow the explicit atexit usage, we either
1. Need to specify that multiple calls to finalize are no-ops or
2. We need to have a new API - "shmem_finalized()" so that the users can 
have a wrapper from atexit which checks shmem_finalized() before calling 
shmem_finalize(). 

Please let me know, if this analysis looks valid.

-Naveen N Ravi
 Cray Inc.