File Management - IBM

can be used with the current open of the file; a new open data path does not have
to be created. This reduces the amount of time that is required to open the file
after the first opened to open the file after the first open, and the amount of main
storage that is required by the job. You must specify SHARE(*YES) for the first
open and other opens of the same file to share the open data path. A well-designed
(for performance) application will normally do a shared open on database files that
multiple programs will open in the same job. Specifying SHARE(*YES) for other
files depends on the application.
Shared files in the ILE model
In the ILE model, shared files are scoped either to the job level or to the activation
group level. An activation group is a substructure of a run-time job. It consists of
system resources (storage for program or procedure variables, commitment
definitions, and open files) that are allocated to one or more programs. An
activation group is like a miniature job within a job.
Any programs that run in any activation group can share shared files that are
scoped to the job level. Only programs that run in the same activation group can
share shared files that are scoped to the activation group level.
Sharing files: considerations
Sharing files allows you to have programs within a job interact in ways that would
otherwise not be possible. However, you should read the following topics to learn
more about the effects of opening, performing read and write operations, and
closing shared files:
v “Open considerations for files shared in a job”
v “I/O considerations for files shared in a job” on page 14
v “Close considerations for files shared in a job” on page 15
You should also see the appropriate documentation for all of the file types to
understand how this support works, and the rules your programs must follow to
use it correctly.
Note: Most high-level language programs process an open or a close operation
independent of whether or not the file is being shared. You do not specify
that the file is being shared in the high-level language program. You indicate
that the file is being shared in the same job through the SHARE parameter.
You specify the SHARE parameter only on the CREATE, CHANGE, and
OVERRIDE file commands. Refer to your appropriate language information
for more information.
Open considerations for files shared in a job
Consider the following points when you open a shared file in the same job by
specifying SHARE(*YES).
v You must make sure that when the shared file is opened for the first time in a
job, all the open options that are needed for subsequent opens of the file are
specified. If the open options specified for subsequent opens of a shared file do
not match those specified for the first open of a shared file, an error message is
sent to the program. (You can correct this by making changes to your program
to remove any incompatible options.)
Chapter 2. File processing 13