0 Replies Latest reply: Feb 22, 2010 6:25 AM by 843829 RSS

    Thread CPU time measurement.

    843829
      Hello,



      I have a simple scenario where I want to measure the CPU time a Java Thread has already spent in kernel and user space.
      I would like to do this within a native Library - I know already about the java.lang.management.ThreadMXBean interface.

      Therefore, I wrote a simple native Lib (a Windows DLL) which makes a call to the WIN API GetThreadTimes() function.
      In order to do this in Windows a Thread HANDLE is requierd.
      That HANDLE is constructed via the WIN API function OpenThread().
      In order to return a valid handle OpenThread() needs a valid Thread ID.
      In my example that Thread ID is acquired within the "Java world" via Thread.getId() and passed through JNI to the library call.

      Here is a small code example:
      JNIEXPORT jlong JNICALL Java_GetCPUTime_cpuTime (JNIEnv * env, jclass clazz, jlong id) {
           HANDLE hThread;
           FILETIME creation, exit, kernel, user;
           long long tuser, tkernel;
           
           hThread = OpenThread(THREAD_ALL_ACCESS, TRUE, (DWORD)id);
      
           if (hThread == NULL) {
                fprintf(stderr, "ERROR: OpenThread failed! \n");
                fprintf(stderr, "REASON: %d", (long)GetLastError());
                return (jlong)-1;
           }
      
           if (!GetThreadTimes(hThread, &creation, &exit, &kernel, &user)) { ... }
      
           tuser = 0;
           tuser = tuser & user.dwHighDateTime;
           tuser = tuser & user.dwLowDateTime;
      
           tkernel = 0;
           tkernel = tkernel & kernel.dwHighDateTime;
           tkernel = tkernel & kernel.dwLowDateTime;
           
           return (jlong)(tkernel + tuser);
      }
      Running the example leads to failure of the OpenThread() call with an Error Code 87 that means: ERROR_INVALID_PARAMETER !
      Due to my investigations the problem occurs because OpenThread() cannot find a Thread with the specified ID.
      Regarding this situation I assumed that the JVM internal Thread IDs are not mapped 1:1 to the OS Thread IDs.
      Is that right?

      Question: How is that mapping accomplished within the Sun HotSpot?
      How is CPU Time measurement done via java.lang.management.ThreadMXBean?
      How can I identify grab a certain Java Thread at native level ?
      I've spent some time browsing the JDK6 sources, but I could not find the appropriate place at code that could give me more clarity about this.

      I'm glad if anyone could give me a hint ?

      Thank you in advance.

      Vladimir

      Edited by: Vladimir.Nikolov on Feb 22, 2010 4:23 AM

      Edited by: Vladimir.Nikolov on Feb 22, 2010 4:24 AM