1 /*
   2  * Copyright (c) 2016, 2019, 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 sun.hotspot.WhiteBox;
  27 
  28 /**
  29  * API to obtain information about selected and supported Garbage Collectors
  30  * retrieved from the VM with the WhiteBox API.
  31  */
  32 public enum GC {
  33     /*
  34      * Enum values must match CollectedHeap::Name
  35      */
  36     Serial(1),
  37     Parallel(2),
  38     G1(3),
  39     Epsilon(4),
  40     Z(5),
  41     Shenandoah(6);
  42 
  43     private static final WhiteBox WB = WhiteBox.getWhiteBox();
  44 
  45     private final int name;
  46 
  47     private GC(int name) {
  48         this.name = name;
  49     }
  50 
  51     private boolean supportsOSVersion() {
  52         if (this != Z) {
  53             return true;
  54         }
  55 
  56         String osName = System.getProperty("os.name");
  57 
  58         if (!osName.startsWith("Windows")) {
  59             return true;
  60         }
  61 
  62         // ZGC has specific Windows version requirements (>= 1803).
  63         // The following check should be made more precise to
  64         // also catch the corresponding Windows 10 version.
  65         return osName.equals("Windows Server 2019");
  66     }
  67 
  68     /**
  69      * @return true if this GC is supported by the VM, i.e., it is built into the VM.
  70      */
  71     public boolean isSupported() {
  72         return WB.isGCSupported(name) && supportsOSVersion();
  73     }
  74 
  75     /**
  76      * @return true if this GC is currently selected/used
  77      */
  78     public boolean isSelected() {
  79         return WB.isGCSelected(name);
  80     }
  81 
  82     /**
  83      * @return true if GC was selected ergonomically, as opposed
  84      *         to being explicitly specified on the command line
  85      */
  86     public static boolean isSelectedErgonomically() {
  87         return WB.isGCSelectedErgonomically();
  88     }
  89 
  90     /**
  91      * @return the selected GC.
  92      */
  93     public static GC selected() {
  94       for (GC gc : values()) {
  95         if (gc.isSelected()) {
  96           return gc;
  97         }
  98       }
  99       throw new IllegalStateException("No selected GC found");
 100     }
 101 }