I just stumbled upon the class sun.jvm.hotspot.HelloWorld. The source of this class is present since Java 6.
The latest version can be found here.
Does someone know the purpose of this class? Is this some kind of developer playground class while developing the JDK?
Thanks in advance!
This file belongs to HotSpot Serviceability Agent.
Serviceability Agent is a kind of internal tool for JVM developers. It is not a part of any public standard, so it does not necessarily need to be covered by TCKs or the separate test suites, though it still has to be consistent with the actual version of HotSpot. I believe HelloWorld was used by JVM developers as a smoke test to make sure Serviceability Agent works in basic cases. So the term "playground class" as you called it fits perfectly.
Frankly speaking, Serviceability Agent source base is not maintained very clean - you may notice other leftover things there. But there is also some interesting stuff, e.g. HSDB or CLHSDB which is a tool for analysing internal structures inside a foreign JVM process.
Related
I am simply reading information off the interwebs, currently the cmake about page, and I need the information to fill in the gaps, it helps to see the big picture.
Surely the answer is straightforward, I hope. What is a native build environment?
Context: I need to know how to build software on my machine (CodeBlocks, etc), why I need to do this, the advantages of doing this, etc. But first, I need to know every piece of jargon I come across, and I could not find any explanations about exactly what a "Native build environment" is, although I can speculate to some degree.
"Native" as in "runs directly in the host operating system" and not "runs in a virtual machine or emulator."
The particular point that CMake's about page is trying to convey is the manner in which CMake achieves cross-platform functionality: specifically not by virtualizing, but by cooperating/collaborating directly with the host system, and the "normal" ways the host system is used to doing things.
Is the build environment then just the directory holding all the garbage needed for a compiler to build the software then?
That's an oversimplification – there's nothing to say that it's a single directory – but more or less, yes. The term is not jargon, it literally means "the state of the world" (aka, environment) needed for the build.
What would you call the other thing then, Non-native?
Sure, or virtualized, or emulated, or whatever other intermediate layer has been added.
Why do we need the distinction as well?
Why not? It's useful to have a concise, clear, simple term so we can communicate precisely and with minimal confusion and ambiguity.
Why 'non-native'? If you haven't already figured this out - there is something called cross-compilation.
Simply put, if I don't have access to target hardware (or an equivalent virtual machine) on which the software needs to run, how do I develop this software on my host and package it to run on that target?
Cross-compilation addresses this by providing necessary tools that perform a translation (or other important low-level stuff) to give you the final software. Such an environment to develop software is called non-native.
Well, I believe we need the term to state the technique.
Is there any tool that connects to a jvm and shows you in real time how classes get loaded in that jvm?
I imagine it would make a great jvisualvm plugin..however not finding anything like this makes me wonder if this would be at all feasible?
I only found a few references to some seemingly "obscure" tools, strictly related to weblogic or webspere.
Assuming that such a tool is possible, would it be strictly related to a particular container?
Thanks!
I realize this doesn't work with a JVM that's already running, but how about java -verbose:class?
If you want to debug classloader issues for a specific class, you can connect with a debugger and set a class loading breakpoint for that class (that's how Eclipse calls them, in IntelliJ you just put a breakpoint on the first line of the class).
Update: Since you mentioned you want to see the classloaders, in theory I guess you could write an agent that calls java.lang.instrument.Instrumentation.getAllLoadedClasses() in agentmain and prints a tree of classes and their classloaders. The problem though is that ClassLoader doesn't have an "identity", so you may get a pretty picture but you still don't have any idea which classloader belongs to which Java EE deployment or OSGi bundle. I guess that's why there aren't that many tools that do it...
I am writing a winforms application and eventually I would like to write unit test for this application from the DAL, and Biz Objects layers etc.
Does someone know of a FREE tool that can recieve the path to an assembly and then output unit test stubs with matching signatures for the assembly.
Any configurable options like "public interfaces only", "test framework choice", "language choice" would be a plus.
I at least would need this tool to emit vb.net against nunit.
Thanks.
Seth
Last I heard, the recommended method of unit testing was to write them as you develop the functionality in a test first style. Auto-generating unit test stubs, in my mind, would just result in a whole bunch of unimplemented unit tests which add no value and will most likely have very awful generic names that don't describe the behavior being tested.
On the other hand, maybe I'm just misunderstanding your question...
Take a look at Pex from Microsoft Research.
MS Unit test build into VS2008 can create stubs (using Reflection) in your behalf.
I found it very useful in most cases.
There is a tool called Pex that not only makes the stubs, but also fills in tests for you. There's also a video online.
edit: Mark Seemann beat me to it! Hopefully the links are still useful.
I have recently come across a situation where code is dynamically loading some libraries, wiring them up, then calling what is termed the "application entry point" (one of the libraries must implement IApplication.Run()).
Is this a valid "Appliation entry point"?
I would always have considered the application entry point to be before the loading of the libraries and found the IApplication.Run() being called after a considerable amount of work slightly misleading.
The terms application and system are terms that are so widely and diversely used that you need to agree what they mean upfront with your conversation partner. E.g. sometimes an application is something with a UI, and a system is 'UI-less'. In general it's just a case of you say potato, I say potato.
As for the example you use: that's just what a runtime (e.g. .NET or java) does: loading a set of libraries and calling the application entry point, i.e. the "main" method.
So in your case, the code loading the libraries is doing just the same, and probably calling a method on an interface, you could then consider the loading code to be the runtime for that application. It's just a matter of perspective.
The term "application" can mean whatever you want it to mean. "Application" merely means a collection of resources (libraries, code, images, etc) that work together to help you solve a problem.
So to answer your question, yes, it's a valid use of the term 'application'.
Application on its own means actually nothing. It is often used by people to talk about computer programs that provide some value to the user. A more correct term is application software and this has the following definition:
Application software is a subclass of
computer software that employs the
capabilities of a computer directly
and thoroughly to a task that the user
wishes to perform. This should be
contrasted with system software which
is involved in integrating a
computer's various capabilities, but
typically does not directly apply them
in the performance of tasks that
benefit the user. In this context the
term application refers to both the
application software and its
implementation.
And since application really means application software, and software is any piece of code that performs any kind of task on a computer, I'd say also a library can be an application.
Most terms are of artificial nature anyway. Is a plugin no application? Is the flash plugin of your browser no application? People say no, it's just a plugin. Why? Because it can't run on it's own, it needs to be loaded into a real process. But there is no definition saying only things that "can run on their own" are applications. Same holds true for a library. The core application could just be an empty container and all logic and functionality, even the interaction with the user, could be performed by plugins or libraries, in which case that would be more an application than the empty container that just provides some context for the application to run. Compare this to Java. A Java application can't run on it's own, it must run within a Java Virtual Machine (JVM), does that mean the JVM is the application and the Java Code is just... well what? Isn't the Java code the real application and the JVM just an empty runtime environment that provides nothing to the end user without the loaded Java code?
I think in this context "application entry point" means "the point at which the application (your code) enters the library".
I think probably what you're referring to is the main() function in C/C++ code or WinMain in a Windows app. That is, it's the point where execution is normally started in an app. Your question is pretty broad and vague--for example, which OS are you running this on--but this may be what you're looking for. This might also address the question.
Bear in mind when you're asking questions, details are your friend. People can give you a much better, more informed answer when you provide them with details.
EDIT:
In a broader context consider what has to happen from the standpoint of the OS. When the user specifies that they want to run an app, the OS has to load the app from the hard drive and then when the app is loaded into memory, it has to pass control to some point in the memory blocked occupied by the newly loaded app to continue execution. That would be the "Application Entry Point". When an app is constructed with dynamically linked code the OS has to load all that dynamically linked code in order to get the correct app image into memory. Loading up those shared bits of code does not change the fact that the OS must have a point to which to pass control when the app is loaded into memory.
Am looking for a regression test framework where I can add tests to.. Tests could be any sort of binaries that poke an application..
This really depends on what you're trying to do, but one of the features of the new Test::Harness (disclaimer: I'm the original author and still a core developer) is that if your tests output TAP (the Test Anything Protocol), you can use Test::Harness to run test suites written in multiple languages. As a result, you don't have to worry about getting "locked in" to a particular language because that's all your testing software supports. In one of my talks on the subject, I even give an example of a test suite written in Perl, C, Ruby, and HTML (yes, HTML -- you'd have to see it).
Just thought I would tell you guys what I ended up using..
QMtest ::=> http://mentorembedded.github.io/qmtest/
I found QMTest to full fill my needs. Its extensible framework, allows you to write very flexible test classes. Then, these test classes could be instantiated to large test suites to do regression testing.
QMTest is also very forward thinking, it allows for weak test dependencies and the creation of test resources. After a while of using QMTest, I started writing better quality tests. However, like any other piece of complex software, it requires some time to learn and understand the concepts, the API is documented and the User Manual give a good introduction. With sometime in your hand, I think QMTest is well worth it.
You did not indicate what language you are working in, but the xUnit family is available for a lot of different languages.
/Allan
It also depends heavily what kind of application you're working on. For a commandline app, for example, its probably easy enough to just create a shell script that calls it with a whole bunch of different options and compares its result to a previously known stable version, warning you if any of the output differs so that you can check whether the change is intentional or not.
If you want something more fancy, of course, you'll probably want some sort of dedicated testing framework.
I assume you are regression-testing a web application?
There are some tools in this kb article from Microsoft
And if I remember correctly, certain editions of Visual Studio also offer its own flavor of regression testing tools as well.
But if you just want a unit testing framework, the xUnit family does it pretty well.
Here's JUnit and NUnit.