How can I make a java program such that it is always running on the system (such as a daemon or service), but only allow one instance of the program to run? I would like it to start either when I run the program or when the system starts (either is fine).
Take a look at commons-daemon
For First part of your Question you need to make a thread running continuously,
for second part of your question look here
I've used this to run a Java program as Windows service service : http://wrapper.tanukisoftware.com/ , with good results.
Related
I have a Java application that needs to run several times. Every time it runs, it checks if there's data to process and if so, it processes the data.
I'm trying to figure out what's the best approach (performance, resource consumption, etc.) to do this:
1.- Launch it once, and if there's nothing to process make it sleep (All Java).
2.- Using a bash script to launch the Java app, and when it finishes, sleep (the script) and then relaunch the java app.
I was wondering if it is best to keep the Java app alive (sleeping) or relaunching every time.
It's hard to answer your question without the specific context. On the face of it, your questions sounds like it could be a premature optimization.
Generally, I suggest you do what's easier for you to do (and to maintain), unless you have good reasons not to. Here are some possible good reasons, pick the ones appropriate to your situation:
For sleeping in Java:
The check of whether there's new data is easier in Java
Starting the Java program takes time or other resources, for example if on startup, your program needs to load a bunch of data
Starting the Java process from bash is complex for some reason - maybe it requires you to fiddle with a bunch of environment variables, files or something else.
For re-launching the Java program from bash:
The check of whether there's new data is easier in bash
Getting the Java process to sleep is complex - maybe your Java process is a complex multi-threaded beast, and stopping, and then re-starting the various threads is complicated.
You need the memory in between Java jobs - killing the Java process entirely would free all of its memory.
I would not keep it alive.
Instead of it you can use some Job which runs at defined intervals you can use jenkins or you can use Windows scheduler and configure it to run every 5 minutes (as you wish).
Run a batch file with Windows task scheduler
And from your batch file you can do following:
javac JavaFileName.java // To Compile
java JavaFileName // to execute file
See here how to execute java file from cmd :
How do I run a Java program from the command line on Windows?
I personally would determine it, by the place where the application is working.
if it would be my personal computer, I would use second option with bash script (as resources on my local machine might change a lot, due to extensive use of some other programs and it can happen that at some point I might be running out of memory for example)
if it goes to cloud (amazon, google, whatever) I know exactly what kind of processes are running there (it should not change so dynamically comparing to my local PC) and long running java with some scheduler would be fine for me
I am working on a plugin for the Serversoftware Bukkit which should restart it. So I have added the main Function which checks for the right arguments and then starts Bukkit. But before it starts Bukkit it should wait for Bukkit to shutdown before I start it again. I know I could add a timeout but I hope there is a better way. So does anybody know how to do that?
One way would be to check the os with System.getProperty("os.name"); and run the ad hoc command for that specific platform (for example: Linux and Windows).
When you start multiple java processes they all seem to have the same identifiers, which seems to be your problem. "differentiating" the processes is your problem, not killing them.
So either you could create the process yourself programatically, and thus be able to note the PID that is used for the process. Then killing it would be VERY simple:
http://blog.igorminar.com/2007/03/how-java-application-can-discover-its.html
Another idea would be to use JPS to get information on all the java processes. A simple sudo algorithm is discussed here:
http://bluepedia.blogspot.com/2008/11/jps-differentiate-between-multiple-java.html
Hope I could be of some help..
I have written a code to send mail to user and that's running nicely, but this program i want to place on server side and runs continuously without any client interaction. It should be run automatically after specific time. When server stops then only it will stop.
So can any one help me how to do this...?
Thanks in Advance...
If your server has cron, you can have the job run at scheduled times. Without knowing more about how the application works, and how it knows when it's time to send an email, there's not much more I can say.
You should look at the Quartz and how to start a java process from the command line in your deployment environment (it's slightly different in Windows and *nix, and very different in z/OS).
If I understood correctly, in your case I would just use the at command. You can find a description in its man page1.
Probably calling at with a calculated time from the moment of execution, and adding that to a rc.d script would do it.
I've a bash script that sequentially calls a java program. That's a bit tricky but mainly what i do is to have a loop and executes about 1500 times the same java program with different arguments.
My question is, when using java 1.5 (the sun VM), each time I'm calling the java program a new instance of the jvm is created ? (I'm not sure that's the right vocabulary...)
Should I avoid this situation by introducing a level of indirection, i.e building a list of all the parameters and then executing one java program which takes these parameters and executes what was previously my entry point ?
Or can I deal with the problem by configuring the JVM as resident or something like that and dynamically invokes my program....
hope this is clear....
thx...
You could save the parameters into a file and use the Java program to process it without constant restart. You could also pipe in the parameters into the running Java app through the console, similarly as for example ls | grep java
Edit: And for the first question. I doubt the java runtime would stay deliberately in memory. Probably most JRE files would remain in the disk cache anyway. On Windows there is a Java Quick Start service which keeps the JRE files around to reduce the startup time for a java program. Don't know whether there is a similar thing for *nix.
Obviously having all the parameters beforehand and running the program once after that would be the best solution. If you cannot do that for any reason i have a very dirty solution to this. Have your program register a port and listen to it for input. Then simply pass the arguments to that port and have your program handle them as a new instance.
JVM startup is notoriously slow, and it certainly not intended to be done in a loop like that. Unfortunately the only way to avoid this if you are passing command line parameters to the java program is to modify the java program itself in some way to have alternative forms of interaction (either from the console, or a port, or a read a file). Java Quick Start is the only (closest thing to a) solution if the java program cannot be changed.
The real solution is to change the Java program. The most obvious change would be to have your loop write to a file, and then start the java program that would read the file one line at a time. That works if the loop doesn't care about the results from the java program for the next set of parameters.
If it does, then it would really be necessary to understand that relationship to advise on an appropriate solution. The socket solution suggested by Savvas is certain a general purpose solution, but there may be better options, depending on what you need to accomplish.
You can use a launcher like in the answer to
Simultaneously run java programs run on same JVM? to read input line by line and start your program's main() method.
I have a program 'foo' running different threads, fooT1, fooT2, .. fooTn.
Now if I want write another program 'bar', which could kill the thread fooTr, is that possible?
Reason: One of the thread fooTr tracks product license. If this thread is killed; one may run this product indefinitely. And killing 'foo' itself is tolerable as 'foo' as that is exactly what is being done on license expiry.
System: Fedora Distribution of Linux
Note: The commands which start JVM and program foo are placed in /etc/init.d and anyone who has a decent knowledge of rc.1/rc.2/rc.3 structure can change/add the starting parameters to these.
I hope my question is clear. If not, I can always edit it.
Actually the java debugger will allow you to kill a thread by injecting an exception into it. I was just trying to work out how to use this feature to kill a thread without wiping out the whole jvm, when I came across this question. If you run the jvm with command line options like:
java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8888 your.app.Main
and connect the debugger with something like:
jdb -attach 127.0.0.1:8888
you can type:
threads
to get a list of the running threads, and use the kill command to kill a running thread. The bit I'm currently not sure about is the syntax of this kill command, I have tried the obvious:
kill 0xe2e new java.lang.IllegalArgumentException("er");
and I get the messages:
killing thread: Swank REPL Thread
Thread not suspended
Expression must evaluate to an object
("Swank REPL Thread" is the thread I want to kill, and yes, I've tried suspending it first ;)
Still my inability to use the java debugger aside, it looks to me like a thread can be killed at random. Maybe you can just make sure you ignore all exceptions and keep running and that will be enough, but I'm not sure about that.
To my knowledge it is not possible to do this directly. What you could consider however is to create some kind of service on your 'foo' that can be called from 'bar' to kill the thread. There are, of course, hundreds of ways to implement this. My first thought would be to do this using RMI.
You could do this even without a separate application. Write your own startup class, which performs a pass-through of parameters to the original startup class of the application. Your class's main method though would create a thread that periodically checks the list of all threads (e.g., Thread.getAllStackTraces or Thread.enumerate), finds the offending thread, and invokes stop() on it. Although Thread.stop is deprecated, it still works.
Another option is to run the application under a Java debugger, say, jdb and then suspend/kill the required thread. You could also add parameters to the application's startup so that the JVM can be attached to, then attach jdb to the running JVM and suspect/kill the thread.
Until now isn´t possible to run to diferent programs in the same JVM, but some people is investigating it, in order to reduce the startup time and the memory and cpu usage of diferent java programs runing in the same machine