1 /*
   2  * Copyright (c) 2014, 2015, Dynatrace and/or its affiliates. All rights reserved.
   3  * 
   4  * This file is part of the Lock Contention Tracing Subsystem for the HotSpot
   5  * Virtual Machine, which is developed at Christian Doppler Laboratory on
   6  * Monitoring and Evolution of Very-Large-Scale Software Systems. Please
   7  * contact us at <http://mevss.jku.at/> if you need additional information
   8  * or have any questions.
   9  *
  10  * This code is free software; you can redistribute it and/or modify it
  11  * under the terms of the GNU General Public License version 2 only, as
  12  * published by the Free Software Foundation.
  13  *
  14  * This code is distributed in the hope that it will be useful, but WITHOUT
  15  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  16  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  17  * version 2 for more details (a copy is included in the LICENSE file that
  18  * accompanied this code).
  19  *
  20  * You should have received a copy of the GNU General Public License version
  21  * 2 along with this work. If not, see <http://www.gnu.org/licenses/>.
  22  *
  23  */ 
  24 package sun.evtracing.processing.statistics.aggregator;
  25 
  26 import sun.evtracing.processing.Sanity;
  27 import sun.evtracing.processing.statistics.metadata.Contention;
  28 
  29 public class NegativeDurationContentionFilter implements ContentionProcessor {
  30 
  31     private final ContentionProcessor delegate;
  32 
  33     public NegativeDurationContentionFilter(ContentionProcessor delegate) {
  34         this.delegate = delegate;
  35     }
  36 
  37     @Override
  38     public void submit(Contention c) {
  39         if (c.duration >= 0) {
  40             delegate.submit(c);
  41         } else {
  42             // The participating threads typically execute on different CPUs. The
  43             // clocks of different CPUs are always slightly out of sync, which
  44             // results in some error. In some cases, this causes small durations to
  45             // become negative.
  46 
  47             // TODO: filtering negative durations is ok for computing sums, but for
  48             // correct counts and averages, we need to find a way to deal with them.
  49 
  50             if (c.duration < -1000000) {
  51                 Sanity.warn("dropped contention with negative duration above 1ms: %.3f ms", c.duration / (1000.f * 1000));
  52             } else {
  53                 Sanity.warn("dropped contention with negative duration in sub-millisecond range: %.3f us", c.duration);
  54             }
  55         }
  56     }
  57 
  58     @Override
  59     public void merge() {
  60         delegate.merge();
  61     }
  62 
  63 }