Java Processing Representations

There are three representations for displaying performance data for applications written in the Java programming language: the Java representation, the Expert-Java representation, and the Machine representation. The Java representation is shown by default where the data supports it. The following section summarizes the main differences between these three representations.

The User Representation

The User representation shows compiled and interpreted Java methods by name, and shows native methods in their natural form. During execution, there might be many instances of a particular Java method executed: the interpreted version, and, perhaps, one or more compiled versions. In the Java representation all methods are shown aggregated as a single method. This representation is selected in the Analyzer by default.

A PC for a Java method in the Java representation corresponds to the method-id and a bytecode index into that method; a PC for a native function correspond to a machine PC. The call stack for a Java thread may have a mixture of Java PCs and machine PCs. It does not have any frames corresponding to Java housekeeping code, which does not have a Java representation. Under some circumstances, the JVM software cannot unwind the Java stack, and a single frame with the special function, <no Java callstack recorded>, is returned. Typically, it amounts to no more than 5-10% of the total time.

The function list in the Java representation shows metrics against the Java methods and any native methods called. The caller-callee panel shows the calling relationships in the Java representation.

Source for a Java method corresponds to the source code in the .java file from which it was compiled, with metrics on each source line. The disassembly of any Java method shows the bytecode generated for it, with metrics against each bytecode, and interleaved Java source, where available.

The Timeline in the Java representation shows only Java threads. The call stack for each thread is shown with its Java methods.

All Java programs may have explicit synchronization, usually performed by calling the monitor-enter routine.

Synchronization-delay tracing in the Java representation is based on the JVMTI synchronization events. Data from the normal synchronization tracing is not shown in the Java representation.

Data space profiling in the Java representation is not currently supported.

The Expert-User Representation

The Expert-Java representation is similar to the Java Representation, except that some details of the JVM internals that are suppressed in the Java Representation are exposed in the Expert-Java Representation. With the Expert-Java representation, the Timeline shows all threads; the call stack for housekeeping threads is a native call stack.

The Machine Representation

The Machine representation shows functions from the JVM software itself, rather than from the application being interpreted by the JVM software. It also shows all compiled and native methods. The machine representation looks the same as that of applications written in traditional languages. The call stack shows JVM frames, native frames, and compiled-method frames. Some of the JVM frames represent transition code between interpreted Java, compiled Java, and native code.

Source from compiled methods are shown against the Java source; the data represents the specific instance of the compiled-method selected. Disassembly for compiled methods show the generated machine assembler code, not the Java bytecode. Caller-callee relationships show all overhead frames, and all frames representing the transitions between interpreted, compiled, and native methods.

The Timeline in the machine representation shows bars for all threads, LWPs, or CPUs, and the call stack in each is the machine-representation call stack.

In the machine representation, thread synchronization devolves into calls to _lwp_mutex_lock. No synchronization data is shown, since these calls are not traced.