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  1. JDK
  2. JDK-6440250

On Windows System.nanoTime() may be 25x slower than System.currentTimeMillis()

    Details

    • Type: Enhancement
    • Status: Closed
    • Priority: P3
    • Resolution: Not an Issue
    • Affects Version/s: 6
    • Fix Version/s: None
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
    • CPU:
      x86
    • OS:
      windows_xp

      Description

      FULL PRODUCT VERSION :
      applies to all there:

      java version "1.6.0-beta2-fastdebug"
      Java(TM) SE Runtime Environment (build 1.6.0-beta2-fastdebug-b84)
      Java HotSpot(TM) Server VM (build 1.6.0-beta2-fastdebug-b84-debug, mixed mode)

      java version "1.6.0-beta2-fastdebug"
      Java(TM) SE Runtime Environment (build 1.6.0-beta2-fastdebug-b84)
      Java HotSpot(TM) Client VM (build 1.6.0-beta2-fastdebug-b84-debug, mixed mode)

      java version "1.5.0_06"
      Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_06-b05)
      Java HotSpot(TM) Client VM (build 1.5.0_06-b05, mixed mode)


      ADDITIONAL OS VERSION INFORMATION :
      Microsoft Windows XP [Version 5.1.2600]

      EXTRA RELEVANT SYSTEM CONFIGURATION :
      Athlon64 X2 4400+ with /usepmtimer in boot.ini

      A DESCRIPTION OF THE PROBLEM :
      System.nanoTime() is more then 25x times slower then System.currentTimeMillis().

      If I use nanoTime() for benchmarking it slows down my application by a huge factor.
      If I use currentTimeMillis() then I don't have enough time precision.


      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      Run the test case

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      nanoTime: 169 ns
      currentTimeMillis: 57 ns

      ACTUAL -
      nanoTime: 1659 ns
      currentTimeMillis: 57 ns


      REPRODUCIBILITY :
      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      class PerfTest {
          private static final int COUNT = 1000000;
          public static void main(String[] args) {
              long start = System.nanoTime();
              long end = start;
              for(int i=0 ; i<COUNT ; i++) {
                  end = System.nanoTime();
              }
              System.out.println("nanoTime: " + (end-start) / COUNT + " ns");
              
              long dummy = 0;
              start = System.nanoTime();
              for(int i=0 ; i<COUNT ; i++) {
                  dummy = System.currentTimeMillis();
              }
              end = System.nanoTime();
              System.out.println("currentTimeMillis: " + (end-start) / COUNT + " ns");
          }
      }
      ---------- END SOURCE ----------

      CUSTOMER SUBMITTED WORKAROUND :
      Use a JNI DLL which uses the processor counter (RDTSC) and normalize the counter after the measurement - but this has then JNI overhead which is not the case for currentTimeMillis() because it is inlined by the JVM.

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              • Assignee:
                dholmes David Holmes
                Reporter:
                ndcosta Nelson Dcosta (Inactive)
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                Dates

                • Created:
                  Updated:
                  Resolved:
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