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Java Forum / General / January 2006Get the size of allocated objects
Hi to all ! Is it possible to get the size of RAM occupied by one or more java objects ? My problem is that I've a long-running thread that continue to allocate RAM even if it shouldn't. I've debugged the code in order to understand if some objects are cached or not correctly closed/finalized and I forced the GC too, but a lot of memory remains occupied. I cannot understand which are the objects that use so much memory so I'd like to know if there are some tricks to get the allocated memory of existing objects. Thanks in advance. Davide > Is it possible to get the size of RAM occupied by one or more java > objects ? > > My problem is that I've a long-running thread that continue to allocate > RAM even if it shouldn't. Any memory leak is the real problem here, and that is what you need to concentrate on. The actual size of objects will (most probably) be seen to be irrelevant once that is fixed. >..I've debugged the code in order to understand > if some objects are cached or not correctly closed/finalized and I > forced the GC too, No you haven't. You can suggest GC, but the VM will do it when it is good and ready. If the VM determines a call to GC is unnecessary, it will most likely ignore it entirely. >...but a lot of memory remains occupied. You must be retaining references to objects somehow in your code.. Speaking of which, do you have a short, compilable example that fails? <http://mindprod.com/jgloss/sscce.html>  SignatureAndrew Thompson physci, javasaver, 1point1c, lensescapes - athompson.info/andrew > > Is it possible to get the size of RAM occupied by one or more java > > objects ? [quoted text clipped - 20 lines] > example that fails? > <http://mindprod.com/jgloss/sscce.html> Unluckly, I use some external jars and, even if they're open source, I would like to avoid the inspection of all that code. Anyway, the "sscce approach" could be useful for me, at least to be sure if the leaks are caused by my code or by those external codes. Thank you Davide >>>Is it possible to get the size of RAM occupied by one or more java >>>objects ? [quoted text clipped - 28 lines] > Thank you > Davide one thing to keep in mind, typically when the GC does kick off (either because current available memory has been exhausted or because of a developer invoked 'suggestion' too), the GC will reclaim as much memory as it can, *plus* pre-allocate another chuck of system ram for its heap. For example.... 1) current heap size is 80mb, available heap memory 0mb 2) OutOfMemoryException raised, 3) GC reclaims 10mb worth of objects 4) current heap size 100mb, available heap memory 30mb Looking at the JVM's memory usage via the OS, will show it consuming more memory, even though technically within the JVM, the application itself is using less. Andrew McDonagh <news@andrewcdonagh.f2s.com> wrote in news:dpj609$qcg$1 @news.freedom2surf.net: > one thing to keep in mind, typically when the GC does kick off (either > because current available memory has been exhausted or because of a [quoted text clipped - 12 lines] > more memory, even though technically within the JVM, the application > itself is using less. If the application no longer needs that 100mb, does the JVM release it again before the application closes? SignatureBeware the False Authority Syndrome > Andrew McDonagh <news@andrewcdonagh.f2s.com> wrote in news:dpj609$qcg$1 > @news.freedom2surf.net: [quoted text clipped - 15 lines] >> more memory, even though technically within the JVM, the application >> itself is using less. My understanding is that it will only pre-allocate another chunk if it feels like it needs to. Using your same example for step 1 and 2, at step 3, let's pretend the GC instead reclaims 70mb worth of objects. Then step 4, current heap size will remain 80mb, and available heap memory will be 70mb. I don't know exactly what heuristic the JVM uses for deciding when to allocate an extra chunk or not, but I'm pretty sure it's not every time a garbage collection is done. > If the application no longer needs that 100mb, does the JVM release it > again before the application closes? Yes, I believe so, based on watching the memory consumption bar in Eclipse. Occasionally the heap size will shrink. - Oliver http://java.sun.com/j2se/1.5.0/docs/guide/management/jconsole.html The link above is for JConsole. JConsole will assist by providing a rich profile of your application including much information about memory consumption. Have fun, http://www.geocities.com/opalpaweb/ Wow, jconsole seems full of magic, but the box I using is a win without NTFS file system. can not learn it right now. I will explore it latter while home. <opalpa@gmail.com> ??????:1136467874.253031.149070@z14g2000cwz.googlegroups.com... > http://java.sun.com/j2se/1.5.0/docs/guide/management/jconsole.html > [quoted text clipped - 4 lines] > Have fun, > http://www.geocities.com/opalpaweb/ Hi. Well, you can consider using some of the latest and greatest tools techniques bundled within Java5, I believe. Here you can find more information about this http://java.sun.com/j2se/1.5.0/docs/guide/jvmti/jvmti.html You'd be surprized how easy yet efficient is to do low-level memory profiling and other stuff with these things. On an other hand, if you're short of time consider to use latest NetBeans5.0beta2 from http://www.netbeans.org/downloads/index.html along with latest Profiler bits. This new Profiler can do a lot of thing (including remote profiling). It's all based on JVMTI layer, so you don't need to get your hands dirty yourself :-) Take care, Cos http://weblogs.java.net/blog/cos/ >> Is it possible to get the size of RAM occupied by one or more java >> objects ? [quoted text clipped - 13 lines] > when it is good and ready. If the VM determines a call to > GC is unnecessary, it will most likely ignore it entirely. No it won't. From the javadoc on System.gc() and Runtime.gc(): "When control returns from the method call, the virtual machine has made its best effort to recycle all discarded objects." This doesn't guarantee that the garbage collector will have run (as there may be no more objects to recycle - the garbage collector could have just been run) but unless you do: public void sillyMethod() { System.gc(); System.gc(); //Safely ignored in a single-threaded environment } It almost certainly will run. Alun Harford > Hi to all ! > [quoted text clipped - 8 lines] > know if there are some tricks to get the allocated memory of existing > objects. You might look at http://www.javapractices.com/Topic83.cjp "Here is a utility which can estimate the size of an object in memory, if the object has a no-argument constructor. It follows the style used by Java Platform Performance, by Wilson and Kesselman." SignatureJim Janney 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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