Develop Reference

How to enable Memory monitors in Eclipse (Java project)?

I am trying to inspect the memory contents (bytes) of an object in a Java project.
The program is paused in the Eclipse IDE.
How ever: the Memory view is disabled - as in: the Add Memory monitor + button is greyed out.
Why?

This question seems to be unanswered for quite a while and the one above sure doesn't help. This is the only post about it I could find.
In the Eclipse Help platform information about Memory view can be found in the C/C++ Development User Guide > Reference > Debug Views > Memory View but that isn't useful when were on Java. In the Java Development Guide it isn't as easy to find. Adding just Java Development Guide to the scope and searching for memory returns information about the Memory View in Running and Debugging but doesn't help very much. It is a view but isn't found in the same > Reference > Debug Views > as the C/C++ Guide.
When running a program in Debug mode in Eclipse C\C++ the + in the Memory view lights up and you can add addresses. However, running your program in Debug view doesn't seem to do the same in Eclipse Java. I'm assuming it can't be used in Java Eclipse or has a special case use that isn't mentioned.

Using JConsole
The JConsole graphical user interface is a monitoring tool that complies to the Java Management Extensions (JMX) specification. JConsole uses the extensive instrumentation of the Java Virtual Machine (Java VM) to provide information about the performance and resource consumption of applications running on the Java platform.
In the Java Platform, Standard Edition (Java SE platform) 6, JConsole has been updated to present the look and feel of the Windows and GNOME desktops (other platforms will present the standard Java graphical look and feel). The screen captures presented in this document were taken from an instance of the interface running on Windows XP.
Starting JConsole
The jconsole executable can be found in JDK_HOME/bin, where JDK_HOME is the directory in which the Java Development Kit (JDK) is installed. If this directory is in your system path, you can start JConsole by simply typing jconsole in a command (shell) prompt. Otherwise, you have to type the full path to the executable file.
Command Syntax
You can use JConsole to monitor both local applications, namely those running on the same system as JConsole, as well as remote applications, namely those running on other systems.
source : http://docs.oracle.com/javase/6/docs/technotes/guides/management/jconsole.html

Java application performance changing based on how it is executed

hopefully this is an easy and quick question. I recently developed a CPU intensive java application in Netbeans. It uses A* pathfinding tens of thousands of times per second to solve a tiles matching game. The application is finished, and it runs pretty fast (I've been testing in netbeans the whole time). I've clocked it at 700 attempts per second (each attempt is probably 20 or so pathfinds). When I build the project it creates a jar, and I can run this outside of netbeans. If I use the command line (Windows 7), and use java -jar theFile.jar, I clock it at 1000 attempts per second. This is understandable since the IDE was probably using a bit of cpu power and holding it back (My application is multicored, you can set the number. I usually use 3/4 so it doesnt slow my system too much). Now, the confusing part. Obviously I don't want the user to have to use the command line every time they want to run this application on windows. They should just be able to click the jar. The problem is that when I double click the jar file, the program runs at a sickly 300 attempts per second!!
Why on earth would these three ways of running the exact same program, all else being constant, have such a massive impact on performance? Is my fix to create a script to run the .jar by command line, or do you guys recognize what's going on here? Thanks very much!
Edit: New Information
I made a batch file with the command: java -jar theFile.jar
When this is executed, it runs at the same speed as it would if I ran it in the console (so, 1000 att/sec)
However, I also made an executable with a simple c++ program. The program had just a couple lines, and was System("java -jar theFile.jar"); and return 0;. Unbeleivably, this runs at the speed of double clicking the jar file, about 300att/sec. How bizarre! It could very well be different IDE parameters, but i'm not sure how to check the default system parameters, or how to modify them for this particular jar.

You may be running into the differences between the client and server versions of the HotSpot VM. From this article:
On platforms typically used for client applications, the JDK comes with a VM implementation called the Java HotSpot™ Client VM (client
VM). The client VM is tuned for reducing start-up time and memory
footprint. It can be invoked by using the -client command-line option
when launching an application.
On all platforms, the JDK comes with an implementation of the Java virtual machine called the Java HotSpot Server VM (server VM). The
server VM is designed for maximum program execution speed. It can be
invoked by using the -server command-line option when launching an
application.
I'm guessing that clicking the jar file may be invoking the client VM, unless you set the -server flag. This article provides some more details:
What's the difference between the -client and -server systems?
These two systems are different binaries. They are essentially two
different compilers (JITs)interfacing to the same runtime system. The
client system is optimal for applications which need fast startup
times or small footprints, the server system is optimal for
applications where the overall performance is most important. In
general the client system is better suited for interactive
applications such as GUIs. Some of the other differences include the
compilation policy,heap defaults, and inlining policy.
Where do I get the server and client systems?
Client and server systems are both downloaded with the 32-bit Solaris
and Linux downloads. For 32-bit Windows, if you download the JRE, you
get only the client, you'll need to download the SDK to get both
systems.
For 64-bit, only the server system is included. On Solaris, the 64-bit
JRE is an overlay on top of the 32-bit distribution. However, on Linux
and Windows, it's a completely separate distribution.
I would like java to default to -server. I have a lot of scripts which
I cannot change (or do not want to change). Is there any way to do
this?
Since Java SE 5.0, with the exception of 32-bit Windows, the server VM
will automatically be selected on server-class machines. The
definition of a server-class machine may change from release to
release, so please check the appropriate ergonomics document for the
definition for your release. For 5.0, it's Ergonomics in the 5.0
Java[tm] Virtual Machine.
Should I warm up my loops first so that Hotspot will compile them?
Warming up loops for HotSpot is not necessary. HotSpot contains On
Stack Replacement technology which will compile a running
(interpreted) method and replace it while it is still running in a
loop. No need to waste your applications time warming up seemingly
infinite (or very long running) loops in order to get better
application performance.

Local java processes are grayed when trying to connect via JMX

I'm running a number of java processes on a windows XP professional machine. When i attempt to connect to these processes via a local JConsole the processes are grayed out.
However i can run the same processes on another machine and connect via a local JConsole on that machine.
Both machines are running java 1.6 version for the processes and jconsole.
Any ideas why these processes are grayed out?

I'm fighting with this issue right now and I found out a work around:
You can change the local user's temp dir to something that they can definitely access (e.g. D:\temp). Make sure to do this for the process you're trying to monitor and the jconsole process.
Another thing that can apparently cause issues are usernames with uppercase letters in them. The directory will always be created with all lowercase letters, but simply renaming it to exactly how it's being shown in the Task Manager made all the issues go away: http://planeofthought.com/wp/?p=75

if the processes are running as a different user (e.g. if you start them as services), then you won't be able to connect to them. also, if they are running under an older jvm, you most likely won't be able to talk to them either.
in some cases, the local jmx communication mechanism uses the local filesystem and may have issues if permissions are not defined correctly. are you possibly running any of these processes on networked filesystems (nfs, samba)?

Say your windows user name you use to start your java application seen in task manager is YOUR_USER_NAME.
Please check a folder whose name looks like hsperfdata_XXXXX (XXXXX should be your user name) in your temp folder and make sure YOUR_USER_NAME and XXXXX are exactly the same (be careful about the upper and lower case).

From http://download.oracle.com/javase/6/docs/technotes/guides/management/jconsole.html:
Applications that are not attachable, with the management agent disabled. These include applications started on a J2SE 1.4.2 platform or started on a J2SE 5.0 platform without the -Dcom.sun.management.jmxremote or com.sun.management.jmxremote.port options. These applications appear grayed-out in the table and JConsole cannot connect to them. In the example connection dialog shown in Figure 3-1, the Anagrams application was started with a J2SE 5.0 platform VM without any of the management properties to enable the JMX agent, and consequently shows up in gray and cannot be selected.
(source: oracle.com)
Despite what's being written in the documentation, most likely your process is running under a different user. You can run jconsole as an administrator and try then.

Here is what worked for me. I changed my %TEMP% and %TMP% environment variables to point to a folder I created in my %HOME% location (like C:\Users\[YOUR_NAME]\Temp). Once I did this, all problems vanished.

I had the problem as described earlier, but was advised a simpler solution: just close all programs using Java ("IntelliJ IDEA", "SoapUI", etc. - to unlock the temporary folder) and then delete %TMP%\hsperfdata_<user.name> folder. Then, after opening any Java program, this folder will be recreated but this time with correct name (most likely %TMP%\hsperfdata_<User.Name>). And after that, local Java processes can be monitored through "JConsole" or "VisualVM" (now runs without starting error with a link to VisualVM: Troubleshooting Guide) again.

instead of this steps you can just goto the CMD and then type in jconsole.exe (PID)
Remember to go to the path where jconsole is present and then run the executable file.

Change the name of the hsperfdata folder which for me was found at C:\Users\pmimgg0\AppData\Local\Temp\hsperfdata_pmimgg0 to match the User name found on task manager. Once I changed hsperfdata_pmimgg0 to hsperfdata_PMIMGG0 my local process was no longer greyed out on jconsole.

Change your TEMP paths in Environment Variables to something like D:\temp as it could be a permission issue. Fixed this issue for me

The best way is to run local process like a remote process.
Add these conditions in runtime arguments -
-Dcom.sun.management.jmxremote=true
-Dcom.sun.management.jmxremote.port=6001
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false
-Djava.rmi.server.hostname=localhost
-Dcom.sun.management.jmxremote.rmi.port=6001
Then select Remote Process and point to localhost:6001 as shown
Click Connect and Jconsole is connected successfully.
For me this fixed as I had some admin constraints.

Profiling a jar file remotely?

Is there any profiler available in the java environment which can be used on a remote machine?
I have a .jar file (plain java code,nothing fancy) running on a remote machine and I want to profile that file. However,I can't install the profiler on the remote machine since I do not have the necessary permissions. Is there any way I can profile the application from my local machine?

Aall Java profilers I know have that ability, since the Java debugging interface (JVMTI) is inherently network-capable.
VisualVM has basic (but often sufficient) profiling features and comes with the JDK.

How to request JVM garbage collection (not from code) when run from Windows command-line

how could I request Java garbage collection externally, starting the program from JAR (Windows BAT used)?
From the Java code I can do it with System.gc()
When running a JNLP distribution, I get this "Java console" turned on from Control Panel / Java / ... and this Java console provides manual garbage collection.
But... When I'm running the jar from command-line / bat the java console doesn't seem to open. Couldn't find help with a brief googling, maybe somebody here?

For a purely command-line approach, you should be able to use jcmd. I believe jcmd has been part of the standard JDK install since at least Java 1.7. The command would be something like this:
jcmd <process-id> GC.run
You can get a list of available diagnostic commands that jcmd provides for a particular process like this:
jcmd <process-id> help

You can use jconsole to connect to a JVM that is running locally - This provides a "Perform GC" button on the GUI.
You'll need to specify -Dcom.sun.management.jmxremote when you kick off your java process.

If you use the very latest java 6 you also have jvisualvm which complements and extend the jconsole functionality. They are both very useful tools.

You normally should not have any reason to force garbage collection. Doing so, messes up the garbage collector algorithms (mainly their performance). It will also slow down the program while garbage is being collected. If there is a memory issue, you should use memory tracing tools to find out where references are being held? (Are listeners unregistered?)
As in the other answers, you can use jconsole or jvisualvm. You can also use jmx to do it programmatically.