In the interest of giving back, here's what I wound up doing: import java.net.InetAddress; import java.rmi.dgc.VMID; import java.util.GregorianCalendar; int vmidHash = new VMID().hashCode(); long currentTime = new GregorianCalendar().getTimeInMillis(); int ipHash = InetAddress.getLocalHost().hashCode(); long seed = vmidHash + currentTime + ipHash; Random randomGenerator = new Random(seed); int seconds = randomGenerator.nextInt(200) + 100;
It's a combination of the VMID (which is supposed ot be unique for each VM, but in actuality even on the SAME machine I'm getting a different value each time, which is better for my use case) plus the current time plus the machine's IP address. Even on the same machine this is generating unique values for each of three threads I am spawning (I've done it about 30 times now and have never seen a duplicate value). Does the trick, I am happy. Thanks for all the insight everyone! -- Frank W. Zammetti Founder and Chief Software Architect Omnytex Technologies http://www.omnytex.com On Fri, March 18, 2005 12:14 pm, Dakota Jack said: > InetAddress might not get the answer for you, Frank. I don't know > what your setup is, but you can go to any ip address service outside > your system and get a unique return address for your machines with a > mini-browser. > > Jack > > > On Fri, 18 Mar 2005 11:36:10 -0500 (EST), Frank W. Zammetti > <[EMAIL PROTECTED]> wrote: >> Yes, I think InetAddress just might do the trick. Thank you Kris! >> >> -- >> Frank W. Zammetti >> Founder and Chief Software Architect >> Omnytex Technologies >> http://www.omnytex.com >> >> On Fri, March 18, 2005 11:24 am, Kris Schneider said: >> > Will InetAddress.getLocalHost() work for you? >> > NetworkInterface.getNetworkInterfaces() might also be of interest. Or, >> you >> > might want to create yourself an instance of java.rmi.dgc.VMID... >> > >> > Quoting "Frank W. Zammetti" <[EMAIL PROTECTED]>: >> > >> >> Oh boy, I got a good one! It's only related to Struts in that the >> >> application in question is Struts-based, so I hope no one minds a >> >> semi-OT >> >> question... >> >> >> >> Here's the situation... An app I wrote has a daemon thread that is >> >> spawned >> >> at startup (from a Struts plugin) that does periodic background >> >> processing >> >> tasks. This works great, never had a bit of trouble. >> >> >> >> Now though, the app is moving from a single server to a clusted >> >> environment. >> >> >> >> So, what's going to happen is that each server in the cluster will >> have >> >> its own instance of the thread running on it. Not a huge problem >> except >> >> that I have to be sure only one instance of the thread (i.e., one >> server >> >> in the cluster) is executing concurrently. >> >> >> >> The easy solution is just a database table that is checked when the >> >> thread >> >> wakes up. If there is no entry in it, then there is no other >> instance >> >> running, so it can write an entry to the table and go off and do its >> >> thing. >> >> >> >> I want to be extremely certain that no issues arise in terms of one >> >> instance of the thread reading from the database while another >> instance >> >> is >> >> writing, etc. So, aside from transactional database calls and >> row-level >> >> locking, I want to do one more thing: I want the thread to sleep a >> >> random >> >> number of seconds (1-300) at startup. This will ensure that, all the >> >> database locking and such aside, the threads should all be offset >> from >> >> one >> >> another in terms of when they run. >> >> >> >> So, I need a random number generated when the thread starts up. As >> we >> >> all >> >> know though, random number generation on most computers that don't >> have >> >> something like a Brownian motion sensor attached stuck in a cup of >> >> boiling >> >> coffee can't generate truly random numbers. So, in theory, what >> could >> >> happen is that if all the servers in the cluster come up at the same >> >> time, >> >> the threads could wind up running at the same time regardless of the >> >> random sleep at the start! It might never happen in reality, small >> >> fluctuations would probably offset them anyway, but I want to be more >> >> certain than that. >> >> >> >> So now we're at the crux of the problem... >> >> >> >> I can't just seed the random number generator with the current time >> >> because it concievably might not be random enough. So, I thought I >> >> could >> >> just tally up the octets of the server's IP address and add that to >> the >> >> current time. Then the seed on each server should be different >> enough. >> >> >> >> But, there doesn't appear to be any way to get the server IP address >> >> independant of a request, so I can't get at it in my plugin. Anyone >> >> know >> >> differently? >> >> >> >> Assuming that is the case, can anyone think of any other way to seed >> the >> >> generator that would ensure a different value on different machines >> in >> >> the >> >> cluster? There are some options like encoding the individual server >> >> names >> >> in my app's config file with a different seed value for each, but >> that >> >> makes maintenance a pain if a new server is added or one removed or >> >> addresses simply changed. >> >> >> >> Any ideas? Thanks! >> >> >> >> -- >> >> Frank W. Zammetti >> >> Founder and Chief Software Architect >> >> Omnytex Technologies >> >> http://www.omnytex.com >> > >> > -- >> > Kris Schneider <mailto:[EMAIL PROTECTED]> >> > D.O.Tech <http://www.dotech.com/> >> > >> > --------------------------------------------------------------------- >> > To unsubscribe, e-mail: [EMAIL PROTECTED] >> > For additional commands, e-mail: [EMAIL PROTECTED] >> > >> > >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: [EMAIL PROTECTED] >> For additional commands, e-mail: [EMAIL PROTECTED] >> >> > > > -- > "You can lead a horse to water but you cannot make it float on its back." > ~Dakota Jack~ > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
