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
24 package jdk.test.lib.management;
25
26 import com.sun.management.HotSpotDiagnosticMXBean;
27 import java.lang.management.ManagementFactory;
28
29 /**
30 * A utility class to work with VM options which could be altered during
31 * execution.
32 *
33 * This class is a wrapper around {@code com.sun.management.VMOption}.
34 * It provides more convenient interface to read/write the values.
35 *
36 */
37 public class DynamicVMOption {
38
39 private final HotSpotDiagnosticMXBean mxBean;
40
41 /**
42 * VM option name, like "MinHeapFreeRatio".
43 */
44 public final String name;
45
46 /**
47 * Creates an instance of DynamicVMOption.
48 *
49 * @param name the VM option name
50 */
51 public DynamicVMOption(String name) {
52 this.name = name;
53 mxBean = ManagementFactory.getPlatformMXBean(HotSpotDiagnosticMXBean.class);
54 }
55
56 /**
57 * Sets a new value for the option.
58 * Trying to set not applicable value will cause IllegalArgumentException.
59 * Behavior with null is undefined, most likely NPE will be thrown.
60 *
61 * @param newValue the value to be set
62 * @see #getValue()
63 * @throws IllegalArgumentException if newValue is not applicable to the option
64 */
65 public final void setValue(String newValue) {
66 mxBean.setVMOption(name, newValue);
67 }
68
69 /**
70 * Returns the value of option.
71 *
72 * @return the current option value
73 * @see #setValue(java.lang.String)
74 */
75 public final String getValue() {
76 return mxBean.getVMOption(name).getValue();
77 }
78
79 /**
80 * Returns true, if option is writable, false otherwise.
81 *
82 * @return true, if option is writable, false otherwise
83 */
84 public final boolean isWriteable() {
85 return mxBean.getVMOption(name).isWriteable();
86 }
87
88 /**
89 * Checks if the given value is applicable for the option.
90 *
91 * This method tries to set the option to the new value. If no exception
92 * has been thrown the value is treated as valid.
93 *
94 * Calling this method will not change the option value. After an attempt
95 * to set a new value, the option will be restored to its previous value.
96 *
97 * @param value the value to verify
98 * @return true if option could be set to the given value
99 */
100 public boolean isValidValue(String value) {
101 boolean isValid = true;
102 String oldValue = getValue();
103 try {
104 setValue(value);
105 } catch (NullPointerException e) {
106 if (value == null) {
107 isValid = false;
108 }
109 } catch (IllegalArgumentException e) {
110 isValid = false;
111 } finally {
112 setValue(oldValue);
113 }
114 return isValid;
115 }
116
117 /**
118 * Returns the value of the given VM option as String.
119 *
120 * This is a simple shortcut for {@code new DynamicVMOption(name).getValue()}
121 *
122 * @param name the name of VM option
123 * @return value as a string
124 * @see #getValue()
125 */
126 public static String getString(String name) {
127 return new DynamicVMOption(name).getValue();
128 }
129
130 /**
131 * Returns the value of the given option as int.
132 *
133 * @param name the name of VM option
134 * @return value parsed as integer
135 * @see #getString(java.lang.String)
136 *
137 */
138 public static int getInt(String name) {
139 return Integer.parseInt(getString(name));
140 }
141
142 /**
143 * Sets the VM option to a new value.
144 *
145 * This is a simple shortcut for {@code new DynamicVMOption(name).setValue(value)}
146 *
147 * @param name the name of VM option
148 * @param value the value to be set
149 * @see #setValue(java.lang.String)
150 */
151 public static void setString(String name, String value) {
152 new DynamicVMOption(name).setValue(value);
153 }
154
155 /**
156 * Sets the VM option value to a new integer value.
157 *
158 * @param name the name of VM option
159 * @param value the integer value to be set
160 * @see #setString(java.lang.String, java.lang.String)
161 */
162 public static void setInt(String name, int value) {
163 new DynamicVMOption(name).setValue(Integer.toString(value));
164 }
165
166 }