Chapter 6. Software support 139
Draft Document for Review April 7, 2004 6:15 pm 6947ch06.fm
Figure 6-3 Logical flow of Java code execution on a zAAP
Figure 6-3 shows the logical flow of Java code running on a z990 server that has a zAAPs
available. The Java Virtual Machine (JVM), when it starts execution of a Java program,
passes control to the z/OS dispatcher that will verify the availability of a zAAP:
򐂰If a zAAP is available (not busy), the dispatcher will suspend the JVM task on the CP, and
assign the Java task to the zAAP. When the task returns control to the JVM, it passes
control back to the dispatcher that will reassign the JVM code execution to a CP.
򐂰If there is no zAAP available at that time the z/OS dispatcher may allow, a Java task to run
on a standard CP (depending on the option used in the OPT statement in the IEAOPTxx
member of SYS1.PARMLIB).
zAAPs do not affect the overall MSU or capacity rating of a system or logical partition. That is,
adding zAAPs to a system or defining to a logical partition does not affect the software license
charges. There is no additional z/OS charge for zAAPs.
Subsystems that exploit zAAPs are:
򐂰WebSphere Application Server (WAS) V5.1.
򐂰CICS/TS V2.3.
򐂰DB2 V8.
򐂰IMS V8.
򐂰WebSphere WBI for z/OS.
The functioning of a zAAP is transparent to all IBM and ISV Java programming on JVM 1.4.1
and above.
Three execution options for Java code execution are available. These options are user
specified in IEAOPTxx and can be dynamically altered by the SET OPT command.
CP Logical Processor
zAAP Logical Processor
WebSphere
EXECUTE JAVA Code
z/OS Dispatcher
Suspend JVM task on z/OSCP logical
processor
WebSphere
JAVA Application Code
Executing on a zAAP
Processor
z/OS Dispatcher
Dispatch JVM task on z/OS CP logical
processor
JVM
Call to zAAP
JVM
JVM
JVM
Switch to CP Logical Processor