When you are developing an application
you may wish to manage a specific resource that is
being shared by a set of processes in a way that guarantees that
one process at a time has exclusive access to that resource. MPE
XL provides Resource Identification Numbers (RINs) that
enable you to manage shared resources.
You can use RINs described in this chapter to manage anything you
may consider a resource to your program, be it a device, a
portion of a file, or a section of code in your program.
In addition, the operating system provides a resource management scheme
similar to RIN management through the use of the FLOCK and
FUNLOCK intrinsics to guarantee your process exclusive
access to a file being shared by a set of processes located in
different jobs/sessions. Refer to Accessing Files Programmer's Guide
(32650-90017) for details on using FLOCK and FUNLOCK.
A RIN is not assigned by MPE XL to any particular resource. The
association of a RIN and a resource is established by cooperating
programmers whose programs are sharing the resource. The RIN
value is known to the operating system, but the resource with which it is
associated is known only to you and other
programmers who have agreed to manage the resource through RIN
management.
Within the programs being executed by different processes, you
and other programmers must first agree to associate a
RIN to a particular resource. When the process executing your
program seeks exclusive access to that resource, the process must
successfully lock the associated RIN prior to accessing the
resource. Successfully locking the RIN means that your process
can access the resource exclusively, so long as the RIN remains
locked.
If the attempt to lock the RIN is unsuccessful, it means that the
RIN is locked and another process has exclusive access to the
associated resource.
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 | NOTE:
The successful management of resources using RINs is predicated
upon the assumption that all accessors of a particular resource
have agreed to access the resource through RIN-locking
intrinsics. If a process does not use this RIN management
scheme to access the resource, exclusive access to that resource
cannot be guaranteed.
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