My Java application has started to crash regularly with a SIGSEGV and a dump of stack data and a load of information in a text file.
I have debugged C programs in gdb and I have debugged Java code from my IDE. I'm not sure how to approach C-like crashes in a running Java program.
I'm assuming I'm not looking at a JVM bug here. Other Java programs run just fine, and the JVM from Sun is probably more stable than my code. However, I have no idea how I could even cause segfaults with Java code. There definitely is enough memory available, and when I last checked in the profiler, heap usage was around 50% with occasional spikes around 80%. Are there any startup parameters I could investigate? What is a good checklist when approaching a bug like this?
Though I'm not so far able to reliably reproduce the event, it does not seem to occur entirely at random either, so testing is not completely impossible.
ETA: Some of the gory details
(I'm looking for a general approach, since the actual problem might be very specific. Still, there's some info I already collected and that may be of some value.)
A while ago, I had similar-looking trouble after upgrading my CI server (see here for more details), but that fix (setting -XX:MaxPermSize) did not help this time.
Further investigation revealed that in the crash log files the thread marked as "current thread" is never one of mine, but either one called "VMThread" or one called "GCTaskThread"- I f it's the latter, it is additionally marked with the comment "(exited)", if it's the former, the GCTaskThread is not in the list. This makes me suppose that the problem might be around the end of a GC operation.
I'm assuming I'm not looking at a JVM bug here. Other Java programs
run just fine, and the JVM from Sun is probably more stable than my
code.
I don't think you should make that assumption. Without using JNI, you should not be able to write Java code that causes a SIGSEGV (although we know it happens). My point is, when it happens, it is either a bug in the JVM (not unheard of) or a bug in some JNI code. If you don't have any JNI in your own code, that doesn't mean that you aren't using some library that is, so look for that. When I have seen this kind of problem before, it was in an image manipulation library. If the culprit isn't in your own JNI code, you probably won't be able to 'fix' the bug, but you may still be able to work around it.
First, you should get an alternate JVM on the same platform and try to reproduce it. You can try one of these alternatives.
If you cannot reproduce it, it likely is a JVM bug. From that, you can either mandate a particular JVM or search the bug database, using what you know about how to reproduce it, and maybe get suggested workarounds. (Even if you can reproduce it, many JVM implementations are just tweaks on Oracle's Hotspot implementation, so it might still be a JVM bug.)
If you can reproduce it with an alternative JVM, the fault might be that you have some JNI bug. Look at what libraries you are using and what native calls they might be making. Sometimes there are alternative "pure Java" configurations or jar files for the same library or alternative libraries that do almost the same thing.
Good luck!
The following will almost certainly be useless unless you have native code. However, here goes.
Start java program in java debugger, with breakpoint well before possible sigsegv.
Use the ps command to obtain the processid of java.
gdb /usr/lib/jvm/sun-java6/bin/java processid
make sure that the gdb 'handle' command is set to stop on SIGSEGV
continue in the java debugger from the breakpoint.
wait for explosion.
Use gdb to investigate
If you've really managed to make the JVM take a sigsegv without any native code of your own, you are very unlikely to make any sense of what you will see next, and the best you can do is push a test case onto a bug report.
I found a good list at http://www.oracle.com/technetwork/java/javase/crashes-137240.html. As I'm getting the crashes during GC, I'll try switching between garbage collectors.
I tried switching between the serial and the parallel GC (the latter being the default on a 64-bit Linux server), this only changed the error message accordingly.
Reducing the max heap size from 16G to 10G after a fresh analysis in the profiler (which gave me a heap usage flattening out at 8G) did lead to a significantly lower "Virtual Memory" footprint (16G instead of 60), but I don't even know what that means, and The Internet says, it doesn't matter.
Currently, the JVM is running in client mode (using the -client startup option thus overriding the default of -server). So far, there's no crash, but the performance impact seems rather large.
If you have a corefile you could try running jstack on it, which would give you something a little more comprehensible - see http://download.oracle.com/javase/6/docs/technotes/tools/share/jstack.html, although if it's a bug in the gc thread it may not be all that helpful.
Try to check whether c program carsh which have caused java crash.use valgrind to know invalid and also cross check stack size.
Related
Since Java update 25 the VM crashes occasionally with internal error. With previous versions <25 it was working fine. According to the release notes, the hotspot compiler was modified in update 25. Does it produce defect code that causes the crash? It does not crash if the JIT compiler is turned off with -Xint. I filed a bug here http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7054478 .
How do I interpret the log file to find out where the crash occurs. I am not able to identify the lines in my Java code where it happenes.
I searched the Bug Database for the string "Unexpected result from topLevelExceptionFilter", and there were three other hits. They all seem to be about unexpected exceptions in native code propagating back across the JNI boundary.
Is that clue relevant to your application?
The reason is that an internal assertion failed - the JVM was not in the state it expected to be. This is a good thing because it avoids propagating errors, but a bad thing because it doesn't tell you how to get around it.
If simple tricks like -client or -server doesn't help, then consider a different JVM.
IBM has a Windows JVM, but it is a bit tricky to get. The easiest for now would be a development package http://www.ibm.com/developerworks/java/jdk/eclipse/index.html
Oracle also have JRockit. http://www.oracle.com/technetwork/middleware/jrockit/index.html
This will allow you to work while Oracle has a look at your bug. It is low priority though, so it make take a while.
An application that we have recently started sporadically crashing with a message about "java.lang.OutOfMemoryError: requested 8589934608 bytes for Chunk::new. Out of swap space?".
I've looked around on the net, and everywhere suggestions are limited to
revert to a previous version of Java
fiddle with the memory settings
use client instead of server mode
Reverting to a previous version implies that the new Java has a bug, but I haven't seen any indication of that. The memory isn't an issue at all; the server has 32GB available, and Xmx is set to 20 while Xms is 10. I can't see the the JVM running out of the remaining 12GB (less the amount given to the handful of other processes on the machine). And we're stuck with server mode due to the nature of the application and environment.
When I look at the memory and CPU usage for the application, I see constant memory usage for the whole day, but then suddenly right before it dies CPU usage goes up to 100% and the memory usage goes from X, to X + 2GB, to X + 4GB, to (sometimes) X + 8GB, to JVM death. It would appear that there is maybe cycle of repeated array resizing going on in the JIT compilation.
I've now seen the error occur with the above 8GB request and also 16GB requests. All times, the method being compiled when this happens is the same. It is a simple method that has non-nested loops, no recursion, and uses methods on objects that return static member fields or instance member fields directly with little computation.
So I have 2 questions:
Does anybody have any suggestions?
Can I test out whether there is a problem compiling this specific method on a test environment, without running the whole application, invoking the JIT compiler directly? Or should I start up the application and tell it to compile methods after a much smaller call count (like 2) to force it to compile the method almost instantly instead of at a random point in the day?
#StephenC
The JVM is 1.6.0_20 (previously 1.6.0_0), running on Solaris. I know it's the compilation that is causing a problem for a couple reasons.
ps in the seconds leading up to it shows that a java thread with id corresponding to the compiler thread (from jstack) is taking up 100% of the CPU time
jstack shows the issue is in JavaThread "CompilerThread1" daemon [_thread_in_native, id=34, ...]
The method mentioned in jstack is always the same one, and is one we wrote. If you look at sample jstack output you will know what I mean, but for obvious reasons I can't provide code samples or filenames. I will say that it is a very simple method. Essentiall a handful of null checks, 2 for loops that do equality checks and possibly assign values, and some simple method calls after. All in all maybe 40 lines of code.
This issue has happened 2 times in 2 weeks, though the application runs every day and is restarted daily. In addition, the application wasn't under heavy load any of these times.
You can exclude a particular method from being JIT'ed by creating a file called .hotspot_compiler and putting it in your applications 'working directory'. Simply add an entry in the file in the following format:
exclude com/amir/SomeClass someMethod
And the console output from the compiler will look like:
### Excluding compile: com.amir.SomeClasst::someMethod
For more information, read this. If you're not sure what you're applications 'working directory' is, use the
-XX:CompileCommandFile=/my/excludefile/location/.hotspot_compiler
in your Java start script or command line.
Alternatively, if you're not sure its the JIT compilers fault, and want to see if you can reproduce the problem without any JIT'ing, run your Java process with -Xint.
Okay, I did a quick search and found a thread on sun java forums that discusses this. Hope it helps.
Here another entry on Oracles forum. Similiar sporadic crash. There is one answer where one solved the problem by reconfiguring the gc's survivor ratio.
We have recently been migrating a number of applications from running under RedHat linux JDK1.6.0_03 to Solaris 10u8 JDK1.6.0_16 (much higher spec machines) and we have noticed what seems to be a rather pressing problem: under certain loads our JVMs get themselves into a "Death Spiral" and eventually go out of memory. Things to note:
this is not a case of a memory leak. These are applications which have been running just fine (in one case for over 3 years) and the out-of-memory errors are not certain in any case. Sometimes the applications work, sometimes they don't
this is not us moving to a 64-bit VM - we are still running 32 bit
In one case, using the latest G1 garbage collector on 1.6.0_18 seems to have solved the problem. In another, moving back to 1.6.0_03 has worked
Sometimes our apps are falling over with HotSpot SIGSEGV errors
This is affecting applications written in Java as well as Scala
The most important point is this: the behaviour manifests itself in those applications which suddenly get a deluge of data (usually via TCP). It's as if the VM decides to keep adding more data (possibly progressing it to the TG) rather than running a GC on "newspace" until it realises that it has to do a full GC and then, despite practically everything in the VM being garbage, it somehow decides not to collect it!
It sounds crazy but I just don't see what else it is. How else can you explain an app which one minute falls over with a max heap of 1Gb and the next works just fine (never going about 256M when the app is doing exactly the same thing)
So my questions are:
Has anyone else observed this kind of behaviour?
has anyone any suggestions as to how I might debug the JVM itself (as opposed to my app)? How do I prove this is a VM issue?
Are there any VM-specialist forums out there where I can ask the VM's authors (assuming they aren't on SO)? (We have no support contract)
If this is a bug in the latest versions of the VM, how come no-one else has noticed it?
Interesting problem. Sounds like one of the garbage collectors works poorly on your particular situation.
Have you tried changing the garbage collector being used? There are a LOT of GC options, and figuring out which ones are optimal seems to be a bit of a black art, but I wonder if a basic change would work for you.
I know there is a "Server" GC that tends to work a lot better than the default ones. Are you using that?
Threaded GC (which I believe is the default) is probably the worst for your particular situation, I've noticed that it tends to be much less aggressive when the machine is busy.
One thing I've noticed, it often takes two GCs to convince Java to actually take out the trash. I think the first one tends to unlink a bunch of objects and the second actually deletes them. What you might want to do is occasionally force two garbage collections. This WILL cause a significant GC pause, but I've never seen a case where it took more than two to clean out the entire heap.
I have had the same issue on Solaris machines, and I solved it by decreasing the maximum size of the JVM. The 32 bit Solaris implementation apparently needs some overhead room beyond what you allocate for the JVM when doing garbage collections. So, for example, with -Xmx3580M I'd get the errors you describe, but with -Xmx3072M it would be fine.
Yes, I've observed this behavior before, and usually after countless hours of tweaking JVM parameters it starts working.
Garbage Collection, especially in multithreaded situations is nondeterministic. Defining a bug in nondeterministic code can be a challenge. But you could try DTrace if you are using Solaris, and there are a lot of JVM options for peering into HotSpot.
Go on Scala IRC and see if Ismael Juma is hanging around (ijuma). He's helped me before, but I think real in-depth help requires paying for it.
I think most people doing this kind of stuff accept that they either need to be JVM tuning experts, have one on staff, or hire a consultant. There are people who specialize in JVM tuning.
In order to solve these problems I think you need to be able to replicate them in a controlled environment where you can precisely duplicate runs with different tuning parameters and/or code changes. If you can't do that hiring an expert probably isn't going to do you any good, and the cheapest way out of the problem is probably buying more RAM.
What kind of OutOfMemoryError are you getting? Is the heap space exhausted or is the problem related to any of the other memory pools (the Error usually have a message giving more details on its cause).
If the heap is exhausted and the problem can be reproduced (it sounds as if it can), I would first of all configure the VM to produce a heap dump on OutOfMemoryErrors. You can then analyze the heap and make sure that it's not filled with objects, which are still reachable through some unexpected references.
It's of course not impossible that you are running into a VM bug, but if your application is relying on implementation specific behaviour in 1.6.0_03, it may for some reason or another end up as a memory hog when running on 1.6.0_16. Such problems may also be found if you are using some kind of server container for your application. Some developers are obviously unable to read documentation, but tend to observe the API behaviour and make their own conclusions about how something is supposed to work. This is of course not always correct and I've ran into similar problems both with Tomcat and with JBoss (both products at least used to work only with specific VMs).
Also make sure it's not a hardware fault (try running MemTest86 or similar on the server.)
Which kind of SIGSEV errors exactly do you encounter?
If you run a 32bit VM, it could be what I described here: http://janvanbesien.blogspot.com/2009/08/mysterious-jvm-crashes-explained.html
What should I (as a Java programmer who doesn't know anything about JVM internals) do when I come across a JVM crash?
In particular, how would you produce a reproducible test case? What should I be searching for in Sun's (or IBM's) bug database? What information can I get from the log files produced (e.g. hs_err_pidXYZ.log)?
If the crashes occur only one one specific machine, run memtest. I've seen recurring JVM crashes only two times, and in both cases the culprit turned out to be a hardware problem, namely faulty RAM.
In my experience they are nearly always caused by native code using JNI, either mine or someone else's. If you can, try re-running without the native code to see if you can reproduce it.
Sometimes it is worth trying with the JIT compiler turned off, if your bug is easily reproducible.
As others have pointed out, faulty hardware can also cause this, I've seen it for both Memory and video cards (when the crash was in swing code). Try running whatever hardware diagnostics are most appropriate for your system.
As JVM crashes are rare I'd report them to Sun. This can be done at their bug database. Use category Java SE, Subcategory jvm_exact or jit.
Under Unix/Linux you might get a Core dump. Under windows the JVM will usually tell you where it has stored a log of what has happened. These files often given some hint, but will vary from JVM to JVM. Sun gives full details of these files on their website. or IBM the files can be analysed using the Java Core Analyzer and Java heapdump Analyzer from IBM's alphaworks.
Unfortunately Java debuggers in my experience tend to hurt more than help. However, attaching an OS specific debugger (eg Visual Studio) can help if you are familiar with reading C stack traces.
Trying to get a reproducible test case is hard. If you have a large amount of code that always (or nearly always) crashes it is easier, just slowly remove parts while it keeps crashing, getting the result as small as possible. If you have no reproducible test code at all then it is very difficult. I'd suggest getting hints from my numbered selection above.
Sun documents the details of the crash log here. There is also a nice tutorial written up here, if you want to get into the dirty details (it sounds like you don't, though)
However, as a commenter mentioned, a JVM crash is a pretty rare and serious event, and it might be worthwhile to call Sun or IBM professional support in this situation.
When an iBM JVM crashes, it might have written to the file /tmp/dump_locations in there it lists any heapdump or javacore files it has written.
These files can be analysed using the Java Core Analyzer and Java heapdump Analyzer from IBM's alphaworks.
There's a great page on the Oracle website to troubleshoot these types of problems.
Check out the relevant sections for:
Hung Processes (eg. jstack utility)
Post Mortem diagnostics
When a Java VM crashes with an EXCEPTION_ACCESS_VIOLATION and produces an hs_err_pidXXX.log file, what does that indicate? The error itself is basically a null pointer exception. Is it always caused by a bug in the JVM, or are there other causes like malfunctioning hardware or software conflicts?
Edit: there is a native component, this is an SWT application on win32.
Most of the times this is a bug in the VM.
But it can be caused by any native code (e.g. JNI calls).
The hs_err_pidXXX.log file should contain some information about where the problem happened.
You can also check the "Heap" section inside the file. Many of the VM bugs are caused by the garbage collection (expecially in older VMs). This section should show you if the garbage was running at the time of the crash. Also this section shows, if some sections of the heap are filled (the percentage numbers).
The VM is also much more likely to crash in a low memory situation than otherwise.
Answer found!
I had the same error and noticed that others who provided the contents of the pid log file were running 64 bit Windows. Just like me. At the end log file, it included the PATH statement. There I could see C:\Windows\SysWOW64 was incorrectly listed ahead of: %SystemRoot%\system32. Once I corrected it, the exception disappeared.
First thing you should do is upgrade your JVM to the latest you can.
Can you repeat the issue? Or does it seem to happen randomly? We recently had a problem where our JVM was crashing all over the place, at random times. Turns out it was a hardware problem. We put the drives in a new server and it completely went away.
Bottom line, the JVM should never crash, as the poster above mentioned if your not doing any JNI then my gut is that you have a hardware problem.
The cause of the problem will be documented in the hs_err* file, if you know what to look for. Take a look, and if it still isn't clear, consider posting the first 5 or 10 lines of the stack trace and other pertinent info (don't post the whole thing, there's tons of info in there that won't help - but you have to figure out which 1% is important :-) )
Are you using a Browser widget and executing javascript in the Browser widget? If so, then there are bugs in some versions of SWT that causes the JVM to crash in native code, in various Windows libraries.
Two examples (that I opened) are bug 217306 and bug 127960. These two bug reports are not the only bug reports of the JVM crashing in SWT, however.
If you aren't using the Browser widget then these suggestions won't help you. In that case, you can search for a list of SWT bugs causing a JVM crash. If none of those are your issue, then I highly recommend that you open a bug report with SWT.
I have the same problem with a JNLP application that I have been using for a long time and is pretty reliable. The problem started immediately after I upgraded from Windows 7 to Windows 10. According to my investigation, it is most likely a bug in Win 10.
The following is not a solution, but an ugly workaround. In jre/bin directory, there is javaws.exe. If I right-clicked /Properties/Compatibility and ticked Run this program as an administrator, the JNLP app started to work.
Please, be aware that this approach could cause security issues and use it only if you have no other option and 100% know what you are doing.