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CICS checks the length of the runtime options before passing them to Language
Environment. If the length is greater than 255 bytes, CICS does not attempt to start
the JVM. Error messages are written to CSMT in this case. Note that the values
you specify are not checked by CICS before being passed to Language
Environment.
If you decide to modify DFHJVMRO, note the following:
v Keep the size of the list of options to a minimum for quick processing, and
because CICS adds some options to this list.
v You can use the HEAP option (abbreviation H) to specify the initial HEAP
allocation.
v The ALL31 option, the POSIX option (abbreviation POS) and the XPLINK option
are forced on by CICS. The ABTERMENC option is set to (ABEND) and the
TRAP option is set to (ON,NOSPIE) by CICS.
Note: POSIX is turned on for CICS internal processing. CICS does not support
the POSIX interface for application use. If you use POSIX directly in your
program, you do so at your own risk."
v The output produced by the RPTO and RPTS options is written to the CESE
transient data queue.
v Be aware that any options that produce output (for example, RPTO or RPTS), do
so at each JVM termination. Consider the volume of output that may be
produced and directed to CESE.
v Although you can specify any valid Language Environment run-time options, you
are recommended to specify only those used in the CICS-supplied source of
DFHJVMRO.
See the fully-commented source code for DFHJVMRO for an example of how to set
these options.
Using DFHJVMAT to modify options in a JVM profile
DFHJVMAT is a user-replaceable program that you can use to override the options
specified in a JVM profile. Normally, a JVM profile provides sufficient flexibility to
configure a JVM as required. You should consider using DFHJVMAT only if you
need to tailor the JVM in a way that cannot be achieved by specifying options in the
JVM profile.
You can also use DFHJVMAT to override the JVMCLASS attribute on the CICS
PROGRAM resource definition. This attribute specifies the main class in the Java
program that is to execute in the JVM. If you use the PROGRAM resource
definition, the limit for the JVMCLASS attribute is 255 characters, but you can use
DFHJVMAT to specify a class name longer than 255 characters.
You can call DFHJVMAT by specifying INVOKE_DFHJVMAT=YES as an option on
the JVM profile that you want to override.
Important
You can only call DFHJVMAT for a single-use JVM, that is, a JVM with a JVM
profile that specifies the option REUSE=NO (for example, the supplied sample JVM
profile DFHJVMPS). With single-use JVMs, when the task using the JVM
terminates, CICS does not attempt to make the JVM available for reuse for another
task.
Chapter 22. Writing programs to customize JVMs 671