1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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  24 
  25 #ifndef SHARE_GC_G1_G1YOUNGREMSETSAMPLINGTHREAD_HPP
  26 #define SHARE_GC_G1_G1YOUNGREMSETSAMPLINGTHREAD_HPP
  27 
  28 #include "gc/shared/concurrentGCThread.hpp"
  29 
  30 // The G1YoungRemSetSamplingThread is used to re-assess the validity of
  31 // the prediction for the remembered set lengths of the young generation.
  32 //
  33 // At the end of the GC G1 determines the length of the young gen based on
  34 // how much time the next GC can take, and when the next GC may occur
  35 // according to the MMU.
  36 //
  37 // The assumption is that a significant part of the GC is spent on scanning
  38 // the remembered sets (and many other components), so this thread constantly
  39 // reevaluates the prediction for the remembered set scanning costs, and potentially
  40 // G1Policy resizes the young gen. This may do a premature GC or even
  41 // increase the young gen size to keep pause time length goal.
  42 class G1YoungRemSetSamplingThread: public ConcurrentGCThread {
  43 private:
  44   Monitor _monitor;
  45 
  46   double _last_periodic_gc_attempt_s;
  47 
  48   double _vtime_accum;  // Accumulated virtual time.
  49 
  50   void sample_young_list_rs_length();
  51 
  52   void run_service();
  53   void check_for_periodic_gc();
  54 
  55   void stop_service();
  56 
  57   void sleep_before_next_cycle();
  58 
  59   bool should_start_periodic_gc();
  60 
  61 public:
  62   G1YoungRemSetSamplingThread();
  63   double vtime_accum() { return _vtime_accum; }
  64 };
  65 
  66 #endif // SHARE_GC_G1_G1YOUNGREMSETSAMPLINGTHREAD_HPP