1 /*
   2  * Copyright (c) 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 package sun.hotspot.gc;
  25 
  26 import java.util.ArrayList;
  27 import java.util.List;
  28 import sun.hotspot.WhiteBox;
  29 
  30 /**
  31  * API to obtain information about selected and supported Garbage Collectors
  32  * retrieved from the VM with the WhiteBox API.
  33  */
  34 public enum GC {
  35     Serial(1),
  36     Parallel(2),
  37     ConcMarkSweep(4),
  38     G1(8);
  39 
  40     private static final GC CURRENT_GC;
  41     private static final int ALL_GC_CODES;
  42     private static final boolean IS_BY_ERGO;
  43     static {
  44         WhiteBox WB = WhiteBox.getWhiteBox();
  45         ALL_GC_CODES = WB.allSupportedGC();
  46         IS_BY_ERGO = WB.gcSelectedByErgo();
  47 
  48         int currentCode = WB.currentGC();
  49         GC tmp = null;
  50         for (GC gc: GC.values()) {
  51             if (gc.code == currentCode) {
  52                 tmp = gc;
  53                 break;
  54             }
  55         }
  56         if (tmp == null) {
  57             throw new Error("Unknown current GC code " + currentCode);
  58         }
  59         CURRENT_GC = tmp;
  60     }
  61 
  62     private final int code;
  63     private GC(int code) {
  64         this.code = code;
  65     }
  66 
  67     /**
  68      * @return true if the collector is supported by the VM, false otherwise.
  69      */
  70     public boolean isSupported() {
  71         return (ALL_GC_CODES & code) != 0;
  72     }
  73 
  74 
  75     /**
  76      * @return the current collector used by VM.
  77      */
  78     public static GC current() {
  79         return CURRENT_GC;
  80     }
  81 
  82     /**
  83      * @return true if GC was selected by ergonomic, false if specified
  84      * explicitly by the command line flag.
  85      */
  86     public static boolean currentSetByErgo() {
  87         return IS_BY_ERGO;
  88     }
  89 
  90     /**
  91      * @return List of collectors supported by the VM.
  92      */
  93     public static List<GC> allSupported() {
  94         List<GC> list = new ArrayList<>();
  95         for (GC gc: GC.values()) {
  96             if (gc.isSupported()) {
  97                 list.add(gc);
  98             }
  99         }
 100         return list;
 101     }
 102 }
 103