Memory Analyzer provides several queries to inspect the threads at the moment the snapshot was taken.
Threads Overview
To get an overview of all the threads in the heap dump use the "Thread Overview" button in the toolbar, as shown on the image below. Alternatively one could use the
query:The query provide some properties like Name, Object, Context Classloader, etc... for each of the threads.
Some heap dump formats (e.g. HPROF dumps from recent Java 6 VMs and IBM system dumps) contain information about the call stacks of threads, and the Java local objects per stack frame.
Exploring the call-stacks and the local Java objects is a powerful feature, giving a debugger like capabilities over a snapshot. It allows analyzing in details the reason for a memory intensive operations. And it also enables that heap dumps and Memory Analyzer are used not only for memory-related problems, but also for a wide range of other problems e.g. unresponsive applications.
Threads Details
You can proceed with the analysis of a single thread by using
context menu. Memory Analyzer provides an extension point, such that extensions can provide semantic information about the threads activity. The result of the Thread Details query will contain such information (if available), some overview information, and possibly the stacktrace of the thread.For DTFJ based dumps (IBM system dumps and IBM PHD files with associated java dump) the thread details view gives more information, including the thread state, priority and native stack trace.
Threads Stacks in Dumps from IBM VMs
Normal operation with stack frames not considered as objects.
Stack frames as pseudo-objects.
Note that the type of the stack frame is <stack frame>.
Stack frames as pseudo-objects and running methods as pseudo-classes.
Note the different types for the stack frame such as java.io.FileStream.getBytes([BIII)I;.
The class histogram shows that only running methods are pseudo-classes, and the size of the class object is 0.
Stack frames as pseudo-objects and all methods as pseudo-classes.
The outbound references tree looks the same,
but the class histogram has a lot more pseudo-classes with 0 instances (i.e. with no running methods), and the
pseudo-class objects have a non-zero size.