Difference between revisions of "MemoryAnalyzer/Extending Memory Analyzer"

Revision as of 03:02, 16 October 2010

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Introduction

The Memory Analyzer tool offers several possibilities to extend it. This page contains an overview of the different extension points and what can be achieved with them.

Within the extensions one will usually extract certain pieces of information from the objects in the heap dump. See TODO for more details on how to read data from a heap dump.

IClassSpecificNameResolver

The name resolver extension point provides a mechanism to give a readable description of an object, similar to what a toString() method will do. Some extensions which MAT provides are for example for to show the content of objects representing String, to show the bundle symbolic name for Equinox classloaders, to show the name for Thread objects, etc…

The extension should implement the IClassSpecificNameResolver interface which defines a single method.

public String resolve(IObject object) throws SnapshotException;

The method takes an IObject as an argument and should return a string representation.

To specify the class for which the resolver should be used one can use the @Subject( annotation.

The method getClassSpecificName of IObject will look for extensions which match the class of the object and execute the resolve() method to return the proper String. Thus it is relatively easy to return a description based on one or more String fields, as strings are already resolved.

Here is a sample implementation that will return the name of an Eclipse Job:

@Subject("org.eclipse.core.runtime.jobs.Job")
public class JobNameResolver implements IClassSpecificNameResolver
{

	@Override
	public String resolve(IObject object) throws SnapshotException
	{
		IObject name = (IObject) object.resolveValue("name");
		if (name != null) return name.getClassSpecificName();
		return null;
	}

}

Queries in Memory Analyzer

Introduction to Queries

Most of the functionality in Memory Analyzer which is exposed to the user of the tool is provided via queries (implementing the IQuery interface, for example "Histogram", "Retained Set", etc... Queries extract and process data from the heap dump using the MAT's API, and provide the result to the user in the form of a table, a tree, free text, etc... Queries shpw up in the "Queries" meni of the tool, and often in the context menus on objects. An important feature of the queries is that they can "collaborate", i.e. the user can use (part of) the result of one query and pass it as input parameters to another query. Here is an example of such "cooperation" - you select "Histogram" to show a class histogram of all objects, then choose say java.util.HashMap and from the context menu call "Retained Set". You can then select a line in this retained set and pass the corresponding objects to yet another (possibly created by you) query.

The IQuery Interface

The IQuery interface defines just one method: TODO describe the interface

As a parameter only one gets only a progress listener (IProgressListener) to report progress. All other input that a query needs is deaclared with annotations on the fields of the query and injected from Memory Analyzer at runtime. See [inout paramerers link]. The return type of the execute method is IResult, which is just a marker interface. The different result types are described [ TODO here].