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Java Forum / General / December 2005JVM process in status "stop"?
We are running a quite busy multithreaded inhouse application in Java 1.4.2 on a multi-processor Solaris 8 system, which also uses some socket communication (lots of process starting and file I/O, pure batch, no graphics). Very occasionally, the entire process stops executing and responding to all signals except SIGKILL (typically after a month of problem-free execution). The JVM process is shown as being in status "stop" with the "prstat" command (the enhanced version of the "top" command for Solaris, looks like this): 7219 amtrix 77M 36M stop 29 10 0:26.44 0.0% java/47 The problem has been reprocuded under both the "client" and "server" JVM, as well as under different modifications of Java 1.4.2 (currently we're using 1.4.2_05). A deadlock/racing condition in the code would be the natural explanation, of course, but that would not cause the JVM process to stop like this. We are quite certain that no user has been sending SIGSTOP to the process either...I've tried searching forums, FAQs and websites but haven't come up with any similar problem description so far. Since the process is stopped, it does not react to signals, so not possible to take a thread dump. So far, I have not been able to try sending a SIGCONT to see if it will start running again... Anyone with experiences, hints or ideas about what it means that the JVM process is in status "stop"? To follow up my own post here, I have now found that the JVM process started an identical copy of itself at the same instant it stopped. The original process looked like this: amtrix 7219 7216 0 Dec 08 ? 2082:28 java -cp bin/scheduler.jar:bin/hpcharset.jar:bin/xercesImpl.jar:bin/xmlParserAP The new child process looked like this: amtrix 8114 7219 0 20:02:39 ? 0:00 java -cp bin/scheduler.jar:bin/hpcharset.jar:bin/xercesImpl.jar:bin/xmlParserAP Both process were in status "stop" as if they had received a SIGSTOP signal: 8114 amtrix 77M 36M stop 28 10 0:00.00 0.0% java/1 7219 amtrix 77M 36M stop 29 10 0:26.44 0.0% java/47 There is nothing in the program code that can cause it to start a clone of itself -- and even if there was, that would not explain why both the new and the old processes became stopped. Has anyone seen such "spontaneous JVM cloning" behaviour before, or has any idea what it means? > We are running a quite busy multithreaded inhouse application in Java > 1.4.2 on a multi-processor Solaris 8 system, which also uses some [quoted text clipped - 6 lines] > > 7219 amtrix 77M 36M stop 29 10 0:26.44 0.0% java/47 > Has anyone seen such "spontaneous JVM cloning" behaviour before, or has > any idea what it means? It might just be that the JVM for your architecture implements threads by forking itself, and you use multiple threads somewhere in your application.  SignatureYou can't run away forever, But there's nothing wrong with getting a good head start. --- Jim Steinman, "Rock and Roll Dreams Come Through" > It might just be that the JVM for your architecture implements threads by > forking itself, and you use multiple threads somewhere in your application. Sure -- we use lots of threads, but they are contained within the application (the java/47 field in the prstat output means that the process uses 47 threads or LWPs). But the JVM process starts lots of external processes with Runtime.exec(), for every such process start the Java process needs to fork itself. Still, any of this doesn't explain why the parent process (and the child process) stop. That is what causes problems, since it also causes the data flow into our production systems to stop. I have built some workarounds that checks every 5 minutes that the JVM is active and restarts it if it isn't, but the situation is still a bit frustrating. I will try to take a stack trace and core dump of the newly started child process, to see if it brings anything. But the problem is completely non-reproducible and only occurs about once a month, so there are not many opportunities for testing... 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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