1 package org.e2etrace.timer;
2
3 /*
4 * Copyright 2006 Gunther Popp
5 *
6 * Licensed under the Apache License, Version 2.0 (the "License");
7 * you may not use this file except in compliance with the License.
8 * You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18
19 import java.lang.reflect.Method;
20
21 import org.apache.commons.logging.Log;
22 import org.apache.commons.logging.LogFactory;
23
24 /**
25 * Default Factory class for Timer instances.
26 * <p>
27 *
28 * The factory returns a new Timer instance. In the default configuration, the
29 * new Timer is of the type {@link org.e2etrace.timer.DefaultTimer}. Please refer
30 * to the documentation of this class to learn about the restrictions of the
31 * underlying implementation.
32 * <p>
33 *
34 * However, if e2etrace has been compiled and is executed using JDK 5.0 (or
35 * higher), the factory will return instances of the type
36 * {@link org.e2etrace.timer.ExactTimer}. This Timer implementation uses the
37 * advanced timing features of the new JDK releases and avoids all problems
38 * described in the documentation of <code>DefaultTimer</code>.
39 * <p>
40 *
41 * Please note the different constructors of the factory. You can force the
42 * factory to create specific types of Timers by using the appropriate
43 * constructor. If you use the default constructor, the above described logic
44 * applies.
45 * <p>
46 *
47 * You can use the class {@link org.e2etrace.timer.PrintTimerAccuracy} to determine
48 * which Timer type will be used by e2etrace on your system and which accuracy
49 * the Timers are able to deliver.
50 * <p>
51 *
52 *
53 * @author Gunther Popp
54 *
55 */
56 public class DefaultTimerFactory implements ITimerFactory {
57
58 private static final Log log = LogFactory.getLog(DefaultTimerFactory.class);
59 private static final boolean supportsExactMeasuring = supportsNanoTime();
60
61 private Class timerType;
62
63 /**
64 * Default constructor.
65 * <p>
66 */
67 public DefaultTimerFactory() {
68 if (supportsExactMeasuring) {
69 setTimerType(ExactTimer.class);
70
71 } else {
72 setTimerType(DefaultTimer.class);
73
74 }
75
76 }
77
78 /**
79 * Constructor using a pre-defined Timer type.
80 * <p>
81 *
82 * @param timerType type of timers the factory will return
83 */
84 public DefaultTimerFactory(Class timerType) {
85 setTimerType(timerType);
86 }
87
88 /** {@inheritDoc} */
89 public ITimer newInstance() {
90 ITimer timer = null;
91
92 try {
93 timer = (ITimer) timerType.newInstance();
94 } catch (Exception e) {
95 log.error("Error creating a new Timer of type " + timerType.getName()
96 + ". Will create a DefaultTimer instead.", e);
97 timer = new DefaultTimer();
98 }
99
100 return timer;
101
102 }
103
104 /**
105 * Changes the type of Timer returned by the Factory.
106 *
107 * @param timerType New Timer type
108 */
109 public void setTimerType(Class timerType) {
110 // log.info("TimerFactory uses now Timers of type " +
111 // timerType.getName());
112
113 this.timerType = timerType;
114 }
115
116 /**
117 * Returns the type of Timers currently used by the Factory.
118 * <p>
119 *
120 * @return Timer type
121 */
122 public Class getTimerType() {
123 return timerType;
124 }
125
126 /**
127 * Helper-method: Checks, if the current VM supports the System.nanoTime()
128 * Method.
129 *
130 * @return true: VM supports the exact time measuring
131 */
132 private static boolean supportsNanoTime() {
133 boolean ret = false;
134 Method[] methods = System.class.getDeclaredMethods();
135
136 for (int i = 0; i < methods.length; i++) {
137 Method method = methods[i];
138
139 if (method.getName().equals("nanoTime")) {
140 ret = true;
141 break;
142 }
143 }
144
145 if (ret) {
146 log.info("This VM supports exact time measuring using System.nanoTime()");
147 } else {
148 log
149 .warn("This VM only supports only System.currentTimeMillis(). This may lead to inaccurate results.");
150 }
151
152 return ret;
153 }
154
155 }