6711316: Open source the Garbage-First garbage collector

First mercurial integration of the code for the Garbage-First garbage collector.

Reviewed-by: apetrusenko, iveresov, jmasa, sgoldman, tonyp, ysr

hotspot/src/share/vm/gc_implementation/g1/g1MMUTracker.hpp

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+/*
+ * Copyright 2001-2007 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+// Keeps track of the GC work and decides when it is OK to do GC work
+// and for how long so that the MMU invariants are maintained.
+
+/***** ALL TIMES ARE IN SECS!!!!!!! *****/
+
+// this is the "interface"
+class G1MMUTracker {
+protected:
+  double          _time_slice;
+  double          _max_gc_time; // this is per time slice
+
+  double          _conc_overhead_time_sec;
+
+public:
+  G1MMUTracker(double time_slice, double max_gc_time);
+
+  void update_conc_overhead(double conc_overhead);
+
+  virtual void add_pause(double start, double end, bool gc_thread) = 0;
+  virtual double longest_pause(double current_time) = 0;
+  virtual double when_sec(double current_time, double pause_time) = 0;
+
+  double max_gc_time() {
+    return _max_gc_time - _conc_overhead_time_sec;
+  }
+
+  inline bool now_max_gc(double current_time) {
+    return when_sec(current_time, max_gc_time()) < 0.00001;
+  }
+
+  inline double when_max_gc_sec(double current_time) {
+    return when_sec(current_time, max_gc_time());
+  }
+
+  inline jlong when_max_gc_ms(double current_time) {
+    double when = when_max_gc_sec(current_time);
+    return (jlong) (when * 1000.0);
+  }
+
+  inline jlong when_ms(double current_time, double pause_time) {
+    double when = when_sec(current_time, pause_time);
+    return (jlong) (when * 1000.0);
+  }
+};
+
+class G1MMUTrackerQueueElem {
+private:
+  double _start_time;
+  double _end_time;
+
+public:
+  inline double start_time() { return _start_time; }
+  inline double end_time()   { return _end_time; }
+  inline double duration()   { return _end_time - _start_time; }
+
+  G1MMUTrackerQueueElem() {
+    _start_time = 0.0;
+    _end_time   = 0.0;
+  }
+
+  G1MMUTrackerQueueElem(double start_time, double end_time) {
+    _start_time = start_time;
+    _end_time   = end_time;
+  }
+};
+
+// this is an implementation of the MMUTracker using a (fixed-size) queue
+// that keeps track of all the recent pause times
+class G1MMUTrackerQueue: public G1MMUTracker {
+private:
+  enum PrivateConstants {
+    QueueLength = 64
+  };
+
+  // The array keeps track of all the pauses that fall within a time
+  // slice (the last time slice during which pauses took place).
+  // The data structure implemented is a circular queue.
+  // Head "points" to the most recent addition, tail to the oldest one.
+  // The array is of fixed size and I don't think we'll need more than
+  // two or three entries with the current behaviour of G1 pauses.
+  // If the array is full, an easy fix is to look for the pauses with
+  // the shortest gap between them and concolidate them.
+
+  G1MMUTrackerQueueElem _array[QueueLength];
+  int                   _head_index;
+  int                   _tail_index;
+  int                   _no_entries;
+
+  inline int trim_index(int index) {
+    return (index + QueueLength) % QueueLength;
+  }
+
+  void remove_expired_entries(double current_time);
+  double calculate_gc_time(double current_time);
+
+  double longest_pause_internal(double current_time);
+  double when_internal(double current_time, double pause_time);
+
+public:
+  G1MMUTrackerQueue(double time_slice, double max_gc_time);
+
+  virtual void add_pause(double start, double end, bool gc_thread);
+
+  virtual double longest_pause(double current_time);
+  virtual double when_sec(double current_time, double pause_time);
+};