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1. Re: Ensure single instance of Java application
You could take a look at the source code. This forum thread seems to indicate where to find it:
[http://forums.sun.com/thread.jspa?threadID=788974|http://forums.sun.com/thread.jspa?threadID=788974] -
2. Re: Ensure single instance of Java application
SwordDevil wrote:
Not especially. How it finds local Java processes is primarily platform-specific, and messy. Or it uses JMX, if it can. That's a possibility, but I'm not seeing a clear advantage over the simple server socket approach.
Hi,
I'd like to make sure that only one instance of my Java application can be run and I've done some search around. The recommended approach seems to be using ServerSocket that occupies a certain port.
On the other hand I've seen that JConsole could display the names of all Java processes that are running. This is perhaps another approach to the issue? JConsole is said to be a pure Java tool. -
3. Re: Ensure single instance of Java application
Use some kind of locking mechanism. This method uses a simple lock on a file and cleans up behind itself reliably and works across all platforms...
Or if you can think of another locking mechanism through DB interaction, that would be equally effective as well.private static boolean lockInstance(final String lockFile) { try { final File file = new File(lockFile); final RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw"); final FileLock fileLock = randomAccessFile.getChannel().tryLock(); if (fileLock != null) { Runtime.getRuntime().addShutdownHook(new Thread() { public void run() { try { fileLock.release(); randomAccessFile.close(); file.delete(); } catch (Exception e) { log.error("Unable to remove lock file: " + lockFile, e); } } }); return true; } } catch (Exception e) { log.error("Unable to create and/or lock file: " + lockFile, e); } return false; } -
4. Re: Ensure single instance of Java application
kilyas wrote:
Not in the case of a power cut.
Use some kind of locking mechanism. This method uses a simple lock on a file and cleans up behind itself reliably -
5. Re: Ensure single instance of Java application
Using a ServerSocket is basically a one liner. It is the simplest approach IMHO. -
6. Re: Ensure single instance of Java application
Does this lock mechanism work when e.g. the user kills the app using Task Manager? I've never tested this myself although some discussions say it may fail. -
7. Re: Ensure single instance of Java application
SwordDevil wrote:
So what, in your mind, is wrong with the ServerSocket approach? Why do all "newbies" immediately discard this approach and then go out and try all these other complex, unreliable, obscure, and/or otherwise questionable practices?
Does this lock mechanism work when e.g. the user kills the app using Task Manager? I've never tested this myself although some discussions say it may fail. -
8. Re: Ensure single instance of Java application
ServerSocket seems to be a reliable approach, and it's simple, and I like it. I'm just curious how JConsole detects all running Java processes. -
9. Re: Ensure single instance of Java application
SwordDevil wrote:
I think one has to be careful in that "pure Java" != "platform independence" even though at first glance you might think otherwise. Some code could be "pure Java" in that it doesn't actually call any native code (directly) but it could still be platform dependent in doing things like for example examining process lists on an OS. Of course that code could also detect which OS and do the "right thing" for such activity based on that information but it's not completely platform independent in the "run anywhere" philosophy.
ServerSocket seems to be a reliable approach, and it's simple, and I like it. I'm just curious how JConsole detects all running Java processes. -
10. Re: Ensure single instance of Java application
SwordDevil wrote:
It varies from platform to platform.
ServerSocket seems to be a reliable approach, and it's simple, and I like it. I'm just curious how JConsole detects all running Java processes. -
11. Re: Ensure single instance of Java application
SwordDevil wrote:
Does the app. have a GUI? Can you distribute it from a server or the web?
..I'd like to make sure that only one instance of my Java application can be run ..
If yes to both, launch it using JWS and use the SingleInstanceService to ensure the goal. Here is a small [demo. of the SingleInstanceService|http://pscode.org/jws/api.html#sis]. -
12. Re: Ensure single instance of Java application
masijade wrote:
Found this thread via Google on the original Sun forums. Searching here on the exact title didn't find it!
So what, in your mind, is wrong with the ServerSocket approach? Why do all "newbies" immediately discard this approach and then go out and try all these other complex, unreliable, obscure, and/or otherwise questionable practices?
Anyway, I'm using the ServerSocket approach:
Unfortunately, this is not working reliably. It works some of the time; I can see in the logs the "Program already running" message. But then from time to time I'll see 4 instances running at the same time, and they are each trying to do actual work, not just hung in some exit state.try { InetAddress localAddress = InetAddress.getLocalHost(); log.info("InetAddress.getLocalHost(): " + localAddress); socket = new ServerSocket(12345, 1, localAddress); } // end try catch (Exception e) { throw new Exception("Program already running, exiting"); } // end catch
The runtime platform is Linux 2.6.9-34.ELsmp x86_64, via cron; I think it is running some version of Redhat, old obviously. Java version is 1.6.0_16, 64-bit.
The job runs every 15 minutes. Any ideas why this is not working all the time?
Thanks.
Edited by: ow003765 on Nov 3, 2010 4:01 PM -
13. Re: Ensure single instance of Java application
Either getLocalHost() is returning different InetAddresses, or each previous instance has closed its socket by the time the next one starts. -
14. Re: Ensure single instance of Java application
Get rid of the local address and use null instead. And make sure that 'socket' is a class member that is going to persist for the life of the application: if it gets GCs it will be closed.