1 /*

     2  * Copyright (c) 2014, 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 package jdk.test.lib;

    24 

    25 import com.sun.management.HotSpotDiagnosticMXBean;

    26 import java.lang.management.ManagementFactory;

    27 

    28 /**

    29  * A utility class to work with VM options which could be altered during

    30  * execution.

    31  *

    32  * This class is a wrapper around {@code com.sun.management.VMOption}.

    33  * It provides more convenient interface to read/write the values.

    34  *

    35  */

    36 public class DynamicVMOption {

    37 

    38     private final HotSpotDiagnosticMXBean mxBean;

    39 

    40     /**

    41      * VM option name, like "MinHeapFreeRatio".

    42      */

    43     public final String name;

    44 

    45     /**

    46      * Creates an instance of DynamicVMOption.

    47      *

    48      * @param name the VM option name

    49      */

    50     public DynamicVMOption(String name) {

    51         this.name = name;

    52         mxBean = ManagementFactory.getPlatformMXBean(HotSpotDiagnosticMXBean.class);

    53     }

    54 

    55     /**

    56      * Sets a new value for the option.

    57      * Trying to set not applicable value will cause IllegalArgumentException.

    58      * Behavior with null is undefined, most likely NPE will be thrown.

    59      *

    60      * @param newValue the value to be set

    61      * @see #getValue()

    62      * @throws IllegalArgumentException if newValue is not applicable to the option

    63      */

    64     public final void setValue(String newValue) {

    65         mxBean.setVMOption(name, newValue);

    66     }

    67 

    68     /**

    69      * Returns the value of option.

    70      *

    71      * @return the current option value

    72      * @see #setValue(java.lang.String)

    73      */

    74     public final String getValue() {

    75         return mxBean.getVMOption(name).getValue();

    76     }

    77 

    78     /**

    79      * Returns true, if option is writable, false otherwise.

    80      *

    81      * @return true, if option is writable, false otherwise

    82      */

    83     public final boolean isWriteable() {

    84         return mxBean.getVMOption(name).isWriteable();

    85     }

    86 

    87     /**

    88      * Checks if the given value is applicable for the option.

    89      *

    90      * This method tries to set the option to the new value. If no exception

    91      * has been thrown the value is treated as valid.

    92      *

    93      * Calling this method will not change the option value. After an attempt

    94      * to set a new value, the option will be restored to its previous value.

    95      *

    96      * @param value the value to verify

    97      * @return true if option could be set to the given value

    98      */

    99     public boolean isValidValue(String value) {

   100         boolean isValid = true;

   101         String oldValue = getValue();

   102         try {

   103             setValue(value);

   104         } catch (NullPointerException e) {

   105             if (value == null) {

   106                 isValid = false;

   107             }

   108         } catch (IllegalArgumentException e) {

   109             isValid = false;

   110         } finally {

   111             setValue(oldValue);

   112         }

   113         return isValid;

   114     }

   115 

   116     /**

   117      * Returns the value of the given VM option as String.

   118      *

   119      * This is a simple shortcut for {@code new DynamicVMOption(name).getValue()}

   120      *

   121      * @param name the name of VM option

   122      * @return value as a string

   123      * @see #getValue()

   124      */

   125     public static String getString(String name) {

   126         return new DynamicVMOption(name).getValue();

   127     }

   128 

   129     /**

   130      * Returns the value of the given option as int.

   131      *

   132      * @param name the name of VM option

   133      * @return value parsed as integer

   134      * @see #getString(java.lang.String)

   135      *

   136      */

   137     public static int getInt(String name) {

   138         return Integer.parseInt(getString(name));

   139     }

   140 

   141     /**

   142      * Sets the VM option to a new value.

   143      *

   144      * This is a simple shortcut for {@code new DynamicVMOption(name).setValue(value)}

   145      *

   146      * @param name the name of VM option

   147      * @param value the value to be set

   148      * @see #setValue(java.lang.String)

   149      */

   150     public static void setString(String name, String value) {

   151         new DynamicVMOption(name).setValue(value);

   152     }

   153 

   154     /**

   155      * Sets the VM option value to a new integer value.

   156      *

   157      * @param name the name of VM option

   158      * @param value the integer value to be set

   159      * @see #setString(java.lang.String, java.lang.String)

   160      */

   161     public static void setInt(String name, int value) {

   162         new DynamicVMOption(name).setValue(Integer.toString(value));

   163     }

   164 

   165 }