1 /*
2 * Copyright (c) 2014, 2015, 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 }