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 
  25 package sun.hotspot.gc;
  26 
  27 import java.util.ArrayList;
  28 import java.util.List;
  29 import sun.hotspot.WhiteBox;
  30 
  31 /**
  32  * API to obtain information about selected and supported Garbage Collectors
  33  * retrieved from the VM with the WhiteBox API.
  34  */
  35 public enum GC {
  36     Serial(1),
  37     Parallel(2),
  38     ConcMarkSweep(4),
  39     G1(8);
  40 
  41     private static final GC CURRENT_GC;
  42     private static final int ALL_GC_CODES;
  43     private static final boolean IS_BY_ERGO;
  44     static {
  45         WhiteBox WB = WhiteBox.getWhiteBox();
  46         ALL_GC_CODES = WB.allSupportedGC();
  47         IS_BY_ERGO = WB.gcSelectedByErgo();
  48 
  49         int currentCode = WB.currentGC();
  50         GC tmp = null;
  51         for (GC gc: GC.values()) {
  52             if (gc.code == currentCode) {
  53                 tmp = gc;
  54                 break;
  55             }
  56         }
  57         if (tmp == null) {
  58             throw new Error("Unknown current GC code " + currentCode);
  59         }
  60         CURRENT_GC = tmp;
  61     }
  62 
  63     private final int code;
  64     private GC(int code) {
  65         this.code = code;
  66     }
  67 
  68     /**
  69      * @return true if the collector is supported by the VM, false otherwise.
  70      */
  71     public boolean isSupported() {
  72         return (ALL_GC_CODES & code) != 0;
  73     }
  74 
  75 
  76     /**
  77      * @return the current collector used by VM.
  78      */
  79     public static GC current() {
  80         return CURRENT_GC;
  81     }
  82 
  83     /**
  84      * @return true if GC was selected by ergonomic, false if specified
  85      * explicitly by the command line flag.
  86      */
  87     public static boolean currentSetByErgo() {
  88         return IS_BY_ERGO;
  89     }
  90 
  91     /**
  92      * @return List of collectors supported by the VM.
  93      */
  94     public static List<GC> allSupported() {
  95         List<GC> list = new ArrayList<>();
  96         for (GC gc: GC.values()) {
  97             if (gc.isSupported()) {
  98                 list.add(gc);
  99             }
 100         }
 101         return list;
 102     }
 103 }
 104