HP-UX Programmer's Guide for Java 2

Enables compiler safe points. Enabling compiler safepoints guarantees a more
deterministic delay to stop all running java threads before doing a safepoint operation,
namely garbage collection and deoptimization. In HP SDK 1.3.1 and 1.4 releases,
compiler safe points is off by default, and you may also require a HP-UX patch. Refer
to the release notes for your SDK for more information.
-XX:+UseOnStackReplacement (PA-RISC 1.3.1, 1.4 and later, Itanium 1.4.2 and
later)
Enables on stack replacement. On stack replacement enables the interpreter to go into
compiled code while it is executing the same instance of the method call. For example,
if the VM is executing a method that has a loop with a large number of iterations, an
intra-method hotspot will occur. To get better performance, the method should run in
compiled mode instead of interpreted mode. If you enable on stack replacement, you
should also enable compiler safe points (see the previous option). In HP SDK 1.3.1 and
1.4 releases, on stack replacement is off by default, and you may also require a HP-UX
patch. Refer to the release notes for your SDK for more information.
-XX:+UseParallelGC (version 1.4 and later)
Use parallel garbage collection. The parallel collector has been enhanced in 5.0 to
monitor and adapt to the memory needs of the application in order to eliminate the
need to tune command-line options to achieve the best performance. For a synopsis of
garbage collection features, refer to http://download.oracle.com/javase/1.5.0/docs/guide/
vm/gc-ergonomics.html
-XX:+UseSIGUSR2 (for SDKs 1.4.0.x and 1.3.1.00 through 1.3.1.12)
Replaced by the -Xusealtsigs option.
Instructs the JVM to use SIGUSR2 for internal operations like Thread.interrupt()
calls instead of SIGUSR1, the default. This allows you to better implement third party
middleware applications that in some versions want to use SIGUSR1 for similar
purposes in their native code.
-XX:+UseGetTimeOfDay
Instructs the JVM to use the GetTimeOfDay call instead of the mechanism used in
earlier versions whereby the number of cpu ticks since the application started is used
to calculate the current time. With this new mechanism, changes to the system date or
time using date(1), adjtime(2), or time synchronization utilities such as ntp are
not reflected in the date and time that Java™ returns, until the process is restarted. If
your application requires that Java™ immediately reflects such system time changes,
you can use the -XX:+UseGetTimeOfDay option, however you may notice a drop in
performance.
28 HotSpot Technology Tools and Commands