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Sundararajan's Weblog

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Running Java observability tools on "events"

Java serviceability, observability tools such as jstack, jmap, jstatare run asynchronously. i.e., these tools can be "attached" to running Java program at any...

Java serviceability, observability tools such as jstack, jmap, jstatare run asynchronously. i.e., these tools can be "attached" to running Java program at any time (without requiring any VM event). But sometimes, you may want to run these tools on specific "event(s)". For example,you can use -XX:OnError flag to run any of these tools at the time of fatal error exit. Forexample, you can create heapdump on exit using jmap -F -dump command. What aboutother events such as gc...

Observability highlights of Mustang

The following is list of observability highlights of Mustang (Java SE 6). This may not be exhaustive. I may have missed few things! jhat - Java Heap Analysis...

The following is list of observability highlights of Mustang (Java SE 6). This may not be exhaustive. I may have missed few things! jhat - Java Heap Analysis ToolThis is a new command line tool [HAT +fixes+improvements + OQL (Object Query Language)]. Helps in analyzing OOM situations. More info is here:Heap dumps are back with a vengeance!Heap Dump SnapshotsWhat's in my Java heap?Querying Java heap with OQLjmap -dump optionWith this option, jmap dumps snapshot of heap in...

Using Mustang's Attach API

You may have read that Mustang JDK now includes attach-on-demand.i.e., With the Mustang JDK you can now attach jconsole to any application, even if it wasn't...

You may have read that Mustang JDK now includes attach-on-demand.i.e., With the Mustang JDK you can now attach jconsole to any application, even if it wasn't launched with the magic -Dcom.sun.management.jmxremote. In fact, this is not specific to jconsole agent.You can load any suitably coded native or Java agent into running JVM using the attach API. Let us see how to write a simple "hello world"agent. A typical JVM agent would bytecode instrument classes on class load...

Continuations in JavaScript

Rhino JavaScript engine (which is included in Mustang) supports Continuations.Rhino optimizer needs to be switched off to enable continuations -- i.e., scripts...

Rhino JavaScript engine (which is included in Mustang) supports Continuations.Rhino optimizer needs to be switched off to enable continuations -- i.e., scripts are run in interpreted mode and Rhino does not generate bytecodes for scripts. In Mustang, Rhino optimizer has been removed -- so Rhino in Mustang runs in interpreter mode always. So, continuations are enabled always.

finals in JavaScript

Java has final fields, parameters and local variables. And JavaScript 2.0 has const modifier. But, there is no support for finals or consts in JavaScript 1.x...

Java has final fields, parameters and local variables. And JavaScript 2.0 has const modifier. But, there is no support for finals or consts in JavaScript 1.x (although const and final are reserved words). We will see how we can implement equivalent of finals in JavaScript (in Mustang's JavaScript engine).function finals() { var map = new Object(); return new JSAdapter() { __put__ : sync(function (name, value) { // already exists, do not allow assignment again if (name in map)...

Using jhat to analyze finalizer queue

Java objects of classes that override Object.finalize()method put lot of pressure on garbage collector. There was a nice talk on finalization in JavaOne 2005...

Java objects of classes that override Object.finalize()method put lot of pressure on garbage collector. There was a nice talk on finalization in JavaOne 2005 (TS-3281).Important advice in this talk was avoid finalize() if you can!But, you may have an application (or use a library) that uses finalize() methods.So, you may want to analyze your heap and see which objects, if any, are queued forfinalization. Using jhat in Mustang build 61+, you can analyze finalizer queue. When...

SCRIPT tag for Swing HTML?

With Mustang, Rhino JavaScript engine is included in JRE. Now, do you want <SCRIPT> support (and DOM) for Swing's JEditorPane? If so, please take the survey...

With Mustang, Rhino JavaScript engine is included in JRE. Now, do you want <SCRIPT> support (and DOM) for Swing's JEditorPane? If so, please take the survey at http://java.sun.com/webapps/survey/display?survey_id=5370. And how about using javax.script framework, so that we can have support for language="<your-favorite-language>" and not just JavaScript (assuming ofcourse there will JSR 223 compliant script engine for your favorite language!).

using namespace in JavaScript

This is continuation of my earlier post on namespaces. We saw how to implement namespace forJavaScript. How about a feature equivalent to Java's import (or C++...

This is continuation of my earlier post on namespaces. We saw how to implement namespace forJavaScript. How about a feature equivalent to Java's import (or C++ using)? We can implement something like:/\*\* \* imports all or subset of names from given namespace. \* \* @param ns namespace \* @param patten names matching this pattern will be imported \* pattern is optional. If not specified, all names are \* imported (like Java's import package_name.\*). \*/function using(ns,...

Namespaces in JavaScript

It is difficult to work with independently developed JavaScripts. There is no built-in Java "package" (or C++ "namespace")-like feature in JavaScript. You have...

It is difficult to work with independently developed JavaScripts. There is no built-in Java "package" (or C++ "namespace")-like feature in JavaScript. You have to use script objects for everything. Yes, there is a namespaceproposal in JavaScript 2.0. But, what do we do now?Well designed JavaScript APIs (like TrimPath API) avoid polluting global namespace by exposing API as methods in few (may be just one!) objects. But, most of the useful JavaScript code out there may not...