1 /*

     2  * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     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.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    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

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    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

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 #ifndef SHARE_VM_GC_G1_G1YOUNGREMSETSAMPLINGTHREAD_HPP

    26 #define SHARE_VM_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   void sample_young_list_rs_lengths();

    47 

    48   void run_service();

    49   void stop_service();

    50 

    51   void sleep_before_next_cycle();

    52 

    53   double _vtime_accum;  // Accumulated virtual time.

    54 

    55 public:

    56   G1YoungRemSetSamplingThread();

    57   double vtime_accum() { return _vtime_accum; }

    58 };

    59 

    60 #endif // SHARE_VM_GC_G1_G1YOUNGREMSETSAMPLINGTHREAD_HPP