Re: Quickest, easiest way to check for existence of a program, from ILE C?

On 03-Mar-2015 11:40 -0600, James H. H. Lampert wrote:

Would anybody happen to know the quickest, easiest way to check (from
an ILE C program) whether a program exists, before attempting to call
it?

i.e., if C program FOO has:

#pragma linkage(BAR,OS,nowiden)
...
int BAR(void *);
...

and wants to call:

iretcd = BAR(baz);

but ONLY if BAR actually exists on the system, what's the quickest,
easiest, least resource-intensive way to determine whether BAR
exists, before calling it?

The quickest way to effect a call to a problem if the program exists is to *not* check first for existence; i.e. simply invoke the program. In the case the program does not exist, then handle the exception when the Activation\Invocation [LIC AI] feature determines no such program can be called due to non-existence; other work to check existence may have to perform with a similar handler active or just perform some return-code checking. Of course an exception-path is probably slower than a existence check with a return-code, but omitting the up-front check for existence [thus having coded the call in a presumed-success style] also ensures that there is no window of opportunity for the call to fail _despite_ the success of a _prior_ existence-check that no longer holds true.