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Java Forum / General / September 2006find max number of open file descriptors using java
I am writing a server which can have maximum number of simultaneous connection equal to the maximum number of open file descriptors. How can it be enforced in java as well as best design strategy? Thanks > I am writing a server which can have maximum number of simultaneous > connection equal to the maximum number of open file descriptors. How > can it be enforced in java as well as best design strategy? The operating system will enforce the limit for you. Your application will fail to open additional files, sockets etc after reaching the descriptor limit. /gordon  Signature[ don't email me support questions or followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e Hi, This just seems like a bad idea to me. In practice if this single server actually holds your max number of simultaneous connections then you wont be able to do anything else on that OS. No other applications will be able to open any other resources. I'd rather impose a configurable maximum number of simultaneous connections. My 2c Chris > I am writing a server which can have maximum number of simultaneous > connection equal to the maximum number of open file descriptors. How > can it be enforced in java as well as best design strategy? > > Thanks > In practice if this single server actually holds your max number of > simultaneous connections then you wont be able to do anything else > on that OS. No other applications will be able to open any other > resources. On most platforms I know, you'll be stopped by a per-process limit long before you reach any system wide limit. /gordon Signature[ don't email me support questions or followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > On most platforms I know, you'll be stopped by a per-process limit > long before you reach any system wide limit. Not to mention that in most configurations of most systems, that limit is set higher than a sensible architecture would attempt to use. -- chris > > On most platforms I know, you'll be stopped by a per-process limit > > long before you reach any system wide limit. [quoted text clipped - 3 lines] > > -- chris Hi, Both good points. Unfortunately I worked on an existing application that did run out of file-handles and caused the environent to sieze. To manage the problem the support team wrote a script to periodically check the number of open filehandles and when a pre-defined limit was reached the application would reboot, to prevent the environment siezing. I don't think the problem was ever actually resolved. Regards, Chris > > > On most platforms I know, you'll be stopped by a per-process limit > > > long before you reach any system wide limit. [quoted text clipped - 20 lines] > Regards, > Chris OK, is it possible in Java to find when max fd when is being (or about to be ) reached? how? what is a good design for it? thanks > OK, is it possible in Java to find when max fd when is being (or > about to be ) reached? how? what is a good design for it? There is no general way to know how many file descriptors you've got open, except by keeping track of every Socket, ServerSocket, and FileInputStream you open (and I've probably missed some), and knowing when library methods open these things for you (as Runtime.exec() does). On Linux you can cheat a little by counting the files in /proc/self/fd, and you can check the limit with "ulimit -n". But this seems to like a lot of trouble, I don't see the point of knowing that they will "soon" run out, because you'll get an exception when you attempt to exceed the limit anyway (so why stop sooner). What real problem are you trying to solve? /gordon Signature[ don't email me support questions or followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > Unfortunately I worked on an existing application that did run out of > file-handles and caused the environent to sieze. [quoted text clipped - 3 lines] > reached the application would reboot, to prevent the environment > siezing. Good sound support engineering ;-) In fact, if you have a leak in code you can't get at, such as the OS or a third-party library, then there may be nothing you can do except restart at intervals. I think it's a good idea for long-running processes to restart themselves automatically from time to time -- just as a precaution. -- chris 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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