A secondary use of REUS is serialization. I wouldf argue that it's better to 
use ENQ for the purposes, but it is documented, and if an application depends 
on it then even if the code is reentrant, rebinding the module as RENT may 
break the caller.


--
Shmuel (Seymour J.) Metz
http://mason.gmu.edu/~smetz3

________________________________________
From: IBM Mainframe Discussion List [[email protected]] on behalf of 
Peter Relson [[email protected]]
Sent: Friday, November 12, 2021 8:44 AM
To: [email protected]
Subject: Re: specific purpose for the REUS parameter in a binder operation

The specific purpose of the REUS binder option is to tell the system (that
being program fetch) that this module is to be considered serially
reusable. Serially reusable is different than reentrant. Serially reusable
is considerably "weaker" than reentrant. But it is "stronger" than not
reusable and not reentrant.

I would think it very unusual these days to have any interest in creating
a serially reusable module.

Given that the system definition of serially reusable is that the module
may be used only once at a time, you land with a "wait queue" if there are
additional requests to use the module while it is currently in use. So to
the question of whether a (serially) reusable module will be fetched each
time, the answer is "no". If the module is already in storage and there is
a waiter, that copy will be used once it is not being used by something
else.

But your case really sounds like it has nothing to do with any of this.
You don't use a routine to "designate the program as reusable"; you use
the binder to set the directory entry to indicate that the program is
reusable. And reusable is an attribute of the whole load module / program
object, not of a piece within it. So maybe this interface tells LE to
treat the program as reusable whether it is or is not?

Peter Relson
z/OS Core Technology Design


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