Develop Reference

Find and kill a specific Java process from another Java App

I have several java processes running on a windows machine. I have a Java process which is supposed to monitor the other processes and periodically kill or restart new ones.
If I have a java process running com.foo.Main1 and one running com.foo.Main2 - how can my monitoring process find and kill just the Main2 process?
Update: I have some code that can execute a command line tasklist.exe and parse it, but no matter what I do, I only see the java.exe process, not which class is executing
Update 2: I do not have the ability to install non-java programs.

It's probably going to be a lot simpler using OS-specific tools and using Runtime.exec() to run them, but I'll try and give a platform independent answer:
It might be possible to do this platform independently using the Attach API. This comes with the JDK, so to use it just include tools.jar from your JDK on your program's classpath.
To get a list of virtual machines on the system, use VirtualMachine.list(). You can get/parse arguments from the virtual machine descriptor objects that are returned from this.
The attach API also allows you to load agents into already-running Java processes. Since you want to kill a Java process, you can write a Java agent that simply runs System.exit() (or if you really want it dead use Runtime.halt() instead) when the agent loads.
Once you identify the one you want to kill, attach to it and load the killer agent (the agent has to be built as a JAR file, accessible to the Java process it needs to be loaded into). Shortly after the agent is attached that process should die.
These links might help also:
An Oracle blog on the attach API
Package documentation for java.lang.instrument (has detailed instructions on how to build an agent JAR)

This is specific to Windows.
I was facing the same issue where I have to kill the specific java program using taskkill. When I run the java program, tasklist was showing the same program with Image name set as java.exe. But killing it using taskkill /F java.exe will stop all other java applications other than intended one which is not required.
So I run the same java program using:
start "MyProgramName" java java-program..
Here start command will open a new window and run the java program with window's title set to MyProgramName.
Now to kil this java-program use the following taskkill command:
taskkill /fi "MyProgramName"
Your Java program will be killed only. Rest will be unaffected.

Run Java Threads On One CPU

We Have a Multi-threaded Application in JAVA which has multiple threads running in parallel. Now we want to run all these threads on a single core. Currently application is running on a system having more then one Cores.
We know there is a technique available ProcesAffinity in .Net Framework to set process affinity.
But we don't want to depend on .Net Framework, because our application is build in java.
Do we set Process affinity using Bat file and run our application executable jar file through Bat file?
Currently our application is running on Window XP. So we need a solution that should be working fine on XP platform.

EDIT:
It's possible: See Java thread affinity
Pure Java doesn't support running a thread on specific processor. Check the SO question linked above.

Personally, I don't think that the fact that this cannot be set in pure Java is a bad thing, as to me, how an app is run does very much depend on the OS, so therefore a OS-specific solution isn't a bad thing.
You can use the MS psexec utility to set the affinity:
psexec -a 1 java -jar myapplication.jar
Would instruct that all of the threads created by java would be run on the lowest CPU.
And this line would be your .BAT file...

You cannot do it in pure Java. But on some versions of Windows, you can do it via operating system utilities; see https://superuser.com/questions/309617/how-to-limit-a-process-to-a-single-cpu-core ... and you might be able to do this by calling native libraries via JNI.

Is there a way to find given process is Idle?

I am working in an java application where i want to make sure that a given process in the computer is idle
ex:- if we start a download process in our computer my application should be able to monitor it (process) and tell when it is over,

Most operating systems provide user commands to monitor activity of a process, like CPU or I/O. Or, at a higher level, you can get the status (running or not) of a process by its process identifier. You could exec these tools from Java, but there's nothing in core Java to do this, nor am I aware of any libraries for this purpose.
However, if you are thinking about killing a process because it is "idle", that generally wouldn't be safe. You have to know enough about the process in question to be sure it's okay to kill it, and if you know that much about it, you'll probably find that there's a way to get it to shut itself down cleanly.

If you start the process from another process, you can detect when it finishes with Process.waitFor() You can even use its exit code.

What is the best way to manage unix process from java?

I'm looking for some simple tasks like listing all the running process of a user, or kill a particular process by pid etc. Basic unix process management from Java. Is there a library out there that is relatively mature and documented? I could run a external command from the JVM and then parse the standard output/error but that seems like a lot of work and not robust at all. Any suggestions?

You will need to roll your own solution I think. Killing an external process created using the Process APIs can be done using Process.destroy(). (But note that destroy() as implemented on Linux / Unix does a "soft" kill, not a SIGKILL, so the external process may be able to avoid being killed.)
Anything beyond that is non-portable.
Listing processes (on a Linux machine) can be done by reading the /proc file system.
Other things can be done by calling a native command using Process. It depends on whether your management functionality requires use of syscalls that are not available to a "pure" Java program.
It is possible (in theory) to use JNI and native code to dig around in the JVM's native data structures to find the OS-level PID for the process and send it a signal.
If you go down the JNI + native library route, beware that native pointer problems and native threading issues can kill your JVM. You may also need to deal with building and distributing the native library for multiple architectures, etc. Also beware that the internal data structures are liable to be different for different JVM platforms, releases, etc, and that they are liable to change without notice.

I recommend JavaSysMon: You can list processes (pid, ppid, name and so on), kill processes (inclusive child processes) and monitor your computer. If you want to use it in a Maven project:
<dependency>
<groupId>javasysmon</groupId>
<artifactId>javasysmon</artifactId>
<version>0.3.3</version>
</dependency>
<repository>
<id>javasysmon-repo</id>
<url>http://openr66.free.fr/maven2/</url>
</repository>

You could try JNA Posix. If the appropriate functions aren't exported by that library, it's very easy to add support for them with JNA (I've done so for many Win32 APIs).

Here's a method to send SIGKILL to a process from Java. It use reflection to get the pid value from the Process subclass. Tested succesfully on Mac OS X 1.6 (Snow Leopard) and OpenSuse 11.4, java 1.6 64-bit HotSpot JVM but obviously no guarantees of portability.
try {
Process p = Runtime.getRuntime().exec("sleep 10000");
Field pidField = p.getClass().getDeclaredField("pid");
pidField.setAccessible(true);
final int pid = pidField.getInt(p);
Process killProcess = Runtime.getRuntime().exec("kill -9 " + pid);
killProcess.waitFor();
System.out.println(p.exitValue());
} catch (Exception e) {
e.printStackTrace();
}

The Gnome System Monitor (linux version of Windows Task Manager) uses libgtop2 package. Documnetation here: http://library.gnome.org/devel/libgtop/stable/
Also you can check the source of System Monitor to see how it uses the libgtop2 functions.

Most of the information you require is available via the /proc filesystem, although you may require the correct permissionings to read everything there. Note that the contents of /proc are Unix-specific - e.g. different on Linux/Solaris, and I have no idea re. MacOSX.
If you want to kill a process you've spawned yourself, then Process.destroy() is worth looking at. Otherwise you're going to have to execute kill. To use this nicely you should send a SIGINT, and if that doesn't work, then send a SIGKILL (to forceably terminate - I'm not sure if Process.destroy() does this)

Spawn a process in Java that survives a JVM shutdown

I need to spawn a process in Java (under Linux exclusively) that will continue to run after the JVM has exited. How can I do this?
Basically the Java app should spawn an updater which stops the Java app, updates files and then starts it again.
I'm interested in a hack & slash method to just get it working as well as a better design proposal if you have one :)

If you're spawning the process using java.lang.Process it should "just work" - I don't believe the spawned process will die when the JVM exits. You might find that the Ant libraries make it easier for you to control the spawning though.

It does actually "just work", unless you're trying to be clever.
My wrapped java.lang.Process was trying to capture the script's output, so when the JVM died, the script didn't have anywhere to send output so it just dies. If I don't try to capture the output, or the script doesn't generate any or redirects everything to a file or /dev/null, everything works as it should.

I was having trouble with this and the launched process was getting killed when the JVM shutdown.
Redirecting stdout and stderr to a file fixed the issue. I guess the process was tied to the launched java app as by default it was expecting to pass its output to it.
Here's the code that worked for me (minus exception handling):
ProcessBuilder pb = new ProcessBuilder(cmd);
pb.redirectOutput(logFile);
pb.redirectError(logFile);
Process p = pb.start();

I thought the whole point of Java was that it's fully contained within the JVM. It's kinda hard to run bytecode when there's no runtime.
If you're looking to have a totally separate process you might look into trying to start a second java.exe instance. Although for your application, it might be easier to simply make a synchronized block that stops (but doesn't kill) your app, does the updating, and then re-initializes your app's data.

It won't always "just work". When JVM spawns the child and then shuts down, the child process will also shutdown in some cases. That is expected behaviour of the process. Under WIN32 systems, it just works.
E.g. If WebLogic server was started up by a Java process, and then that process exits, it also sends the shutdown signal to the WebLogic via shutdown hook in JVM, which causes WebLogic to also shutdown.
If it "just works" for you then there is no problem, however if you find yourself in a position that child process also shutsdown with JVM it is worth having a look at the "nohup" command. The process won't respond to SIGTERM signal, but will respond to SIGKILL signal, as well as normal operations.
Update: The way described above is a bit of an overkill. Another way of doing this would be to use "&" on the end of command. This will spawn a new process that is not a child of current java process.
P.S. Sorry for so many updates, I have been learning and trying it from scratch.

>>don't believe the spawned process will die when the JVM exits.
Child process is always dying on my box(SuSE) whenever I kill java. I think, the child process will die if it's dealing with I/O of the parent process(i.e., java)

If you're looking at making an updater on Linux, you're probably barking up the wrong tree. I believe all major linux distros have a package manager built in. You should use the package manager to do your updating. Nothing frustrates me more than programs that try to self-update... (I'm looking at you, Eclipse)