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Java Forum / General / April 2007Compare java instances
Hi all, I am quite new to Java. I have an issue to be solved. I want to compare two JVM instances. Let me go in detail I am instantiating two or more java instances of particular application and I wanted to know which java instance started first. For that I am generating random numbers in the constructor of the class and trying to store it in a static variable and comparing this with newly generated randon number. But then it didnt work. Is there any other easy solution to do that? Can anyone give some hint? Thanks in advance regards, robina > Hi all, > [quoted text clipped - 16 lines] > regards, > robina How about storing System.currentTimeMillis()? http://java.sun.com/j2se/1.5.0/docs/api/java/lang/System.html#currentTimeMillis() I have no idea how you are comparing these numbers, though. Over the network? Also keep in mind that if you are in different time zones, you need to account for that. Rogan .. >I have an issue to be solved. What is the issue to be solved? What ability are you attempting to offer to the end user? (I trimmed the rest, because you seemed to be describing a strategy you thought might achieve the goal, without actually stating what the goal was)  SignatureAndrew Thompson http://www.athompson.info/andrew/ Dear Andrew, I have an aplication which will be run by different clients at a time. Each instance will first find if an update is needed through a method in the application. The instance which finds that first will be the coordinator who sends message(multicast) to all other instances. So in this scenario if two instances finds that an update is needed in exactly the same time they have to compete using some strategy and agree upon that either one of them who wins the strategy will be the coordinator who will send update message to all the others in the group. Its the issue of what strategy can I use to choose coordinator and how to share that state among other instances? Hope I have explained bit clear now. Do you have any idea? > Dear Andrew, > [quoted text clipped - 10 lines] > and how to share that state among other instances? Hope I have > explained bit clear now. Do you have any idea? Will the instances be running on the same computer, the same LAN, or over the internet? - Oliver > > Dear Andrew, > [quoted text clipped - 15 lines] > > - Oliver instances run in same computer... >> > I have an aplication which will be run by different clients at a >> > time. >> > Each instance will first find if an update is needed through a method >> > in the application. The instance which finds that first will be the >> > coordinator who sends message(multicast) to all other instances. [...] >> Will the instances be running on the same computer, the same LAN, >> or >> over the internet? > > instances run in same computer... Simplest solution is to try to acquire an exclusive resource in an atomic fashion, and the first process to have successfully required this resource is the "first" instance, and can act as the server or coordinator or whatever. Example include listening on a specific port or trying to gain exclusive write-access to a specific file. - Oliver ... >I have an aplication which will be run by different clients at a time. You mention later that this will all be happening on one single PC. * >Each instance will first find if an update is needed through a method >in the application. The instance which finds that first will be the >coordinator who sends message(multicast) to all other instances. * If that is the case, you might use the JNLP based SingleInstanceService ** to open a 'controller' application that launches a single screen of the 'user visible area' (AKA 'the application'). Later invocations will 'report to' that first controller instance, so it is possible to open other UVA's as needed, while the controller is overseeing updates for all. ** Here is an example <http://www.physci.org/jws/#sis> SignatureAndrew Thompson http://www.athompson.info/andrew/ Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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