WebLogic JRockit SDK includes the JVM profiling interface (JVMPI) and JVM debugging interface (JVMDI), interfaces that enable Java applications to interact with the JVM to assist with profiling and debugging activities. While developers will need to implement these interfaces within their application code, users' exposure to JVMPI and JVMDI will usually be through the profiling and debgging tools they select for the applications they are running.
You can use any number of third-party profiling tools to profile WebLogic JRockit performance. This section describes how to use the Java Virtual Machine Profiler Interface (JVMPI) to facilitate using those tools.
JVMPI is a two-way function call interface between the Java virtual machine and an in-process profiler agent. On one hand, the VM notifies the profiler agent of various events, corresponding to, for example, heap allocation, thread start, and so on. Concurrently, the profiler agent issues controls and requests for more information through the JVMPI. For example, the profiler agent can turn on/off a specific event notification, based on the needs of the profiler front-end.
The profiler front-end may or may not run in the same process as the profiler agent. It may reside in a different process on the same machine, or on a remote machine connected via the network. The JVMPI does not specify a standard wire protocol. Tools vendors may design wire protocols suitable for the needs of different profiler front-ends.
A profiling tool based on JVMPI can obtain a variety of information such as heavy memory allocation sites, CPU usage hot-spots, unnecessary object retention, and monitor contention, for a comprehensive performance analysis.
JVMPI supports partial profiling; that is, a user can selectively profile an application for certain subsets of the time the VM is up and can also choose to obtain only certain types of profiling information.
-Xgc:gencopy), unless you set the
-Xjvmpi:allocs=offflag. In that case, you can use any garbage collector.
When WebLogic JRockit runs with a profiling agent attached, by default a number of events are enabled that can create significant overhead. Since JVMPI doesn't require all of these events to be sent, you can disable them by setting the
-Xjvmpi flag. Use the arguments listed in Table 4-1 to modify the default behavior.:
Setting this to
JVMDI is a low-level debugging interface used by debuggers and other programming tools. It allows you to inspect the state and to control the execution of applications running in the WebLogic JRockit JVM.
JVMDI describes the functionality a JVM provides to enable debugging of Java applications running within the JVM. JVMDI defines the services a JVM must provide for debugging. JVMDI services include requests for information (for example, current stack frame), actions (set a breakpoint), and notification (when a breakpoint has been hit).
JVMDI clients run in the same VM as the application being debugged and access JVMDI through a native interface. The native, in-process interface allows maximum control with minimal intrusion of a debugging tool. Typically, JVMDI clients are relatively compact. They can be controlled by a separate process that implements the bulk of a debugger's functionality without interfering with the target application's normal execution.