5

Oct 10



Hung, Deadlocked, or Looping Process


  • Print thread stack for all Java threads:
    • Control-\
    • kill -QUIT pid
    • jstack pid (or jstack -F pid if jstack pid does not respond)
  • Detect deadlocks:
    • Request deadlock detection: JConsole tool, Threads tab
    • Print information on deadlocked threads: Control-\
    • Print list of concurrent locks owned by each thread: -XX:+PrintConcurrentLocks set, then Control-\
    • Print lock information for a process: jstack -l pid
  • Get a heap histogram for a process:
    • Start Java process with -XX:+PrintClassHistogram, then Control-\
    • jmap -histo pid (with -F option if pid does not respond)
  • Dump Java heap for a process in binary format to file:
    • jmap -dump:format=b,file=filename pid (with -F option if pid does not respond)
  • Print shared object mappings for a process:
    • jmap pid
  • Print heap summary for a process:
    • Control-\
    • jmap -heap pid
  • Print finalization information for a process:
    • jmap -finalizerinfo pid
  • Attach the command-line debugger to a process:
    • jdb -connect sun.jvm.hotspot.jdi.SAPIDAttachingConnector:pid=pid

Post-mortem Diagnostics, Memory Leaks


  • Examine the fatal error log file. Default file name is hs_err_pidpid.log in the working-directory.
  • Create a heap dump:
    • Start the application with HPROF enabled: java -agentlib:hprof=file=file,format=bapplication; then Control-\
    • Start the application with HPROF enabled: java -agentlib:hprof=heap=dump application
    • JConsole tool, MBeans tab
    • Start VM with -XX:+HeapDumpOnOutOfMemoryError; if OutOfMemoryError is thrown, VM generates a heap dump.
  • Browse Java heap dump:
    • jhat heap-dump-file
  • Dump Java heap from core file in binary format to a file:
    • jmap -dump:format=b,file=filename corefile
  • Get a heap histogram for a process:
    • Start Java process with -XX:+PrintClassHistogram, then Control-\
    • jmap -histo pid (with -F option if pid does not respond)
  • Get a heap histogram from a core file:
    • jmap -histo corefile
  • Print shared object mappings from a core file:
    • jmap corefile
  • Print heap summary from a core file:
    • jmap -heap corefile
  • Print finalization information from a core file:
    • jmap -finalizerinfo corefile
  • Print Java configuration information from a core file:
    • jinfo corefile
  • Print thread trace from a core file:
    • jstack corefile
  • Print lock information from a core file:
    • jstack -l corefile
  • Attach the command-line debugger to a core file on the same machine:
    • jdb -connect sun.jvm.hotspot.jdi.SACoreAttachingConnector:javaExecutable=path,core=corefile
  • Attach the command-line debugger to a core file on a different machine:
    • On the machine with the core file: jsadebugd path corefile
      and on the machine with the debugger: jdb -connect sun.jvm.hotspot.jdi.SADebugServerAttachingConnector:debugServerName=machine
  • libumem can be used to debug memory leaks.

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