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comparison src/org/prevayler/implementation/PrevaylerCore.java @ 17:4580bb12db30

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Separate command execution from command logging.
author Dan Creswell <dan.creswell@gmail.com>
date Sun, 05 Jul 2009 16:26:25 +0100
parents src/org/prevayler/implementation/SnapshotPrevaylerImpl.java@3dc0c5604566
children a77f0a9ed93c
comparison
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16:46ac1a45718a 17:4580bb12db30
1 /*
2 The copyright of all source code included in this Prevayler distribution is
3 held by Klaus Wuestefeld, except the files that specifically state otherwise.
4 All rights are reserved. "PREVAYLER" is a trademark of Klaus Wuestefeld.
5
6
7 BSD License:
8
9 Redistribution and use in source and binary forms, with or without
10 modification, are permitted provided that the following conditions are met:
11
12 - Redistributions of source code must retain the above copyright notice, this
13 list of conditions and the following disclaimer.
14
15 - Redistributions in binary form must reproduce the above copyright notice,
16 this list of conditions and the following disclaimer in the documentation
17 and/or other materials provided with the distribution.
18
19 - Neither the name of Prevayler nor the names of its contributors may be used
20 to endorse or promote products derived from this software without specific
21 prior written permission.
22
23
24 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
25 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
28 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
29 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
30 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
31 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
32 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
33 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
34 POSSIBILITY OF SUCH DAMAGE.
35 */
36
37 package org.prevayler.implementation;
38
39 import java.io.*;
40
41 import java.rmi.RMISecurityManager;
42
43 import org.prevayler.*;
44
45 /** Provides transparent persistence for business objects.
46 * This applies to any deterministic system implementing the PrevalentSystem interface.
47 * All commands to the system must be represented as objects implementing the Command interface and must be executed
48 * using Prevayler.executeCommand(Command).
49 * Take a look at the demo application included with the Prevayler distribution for examples.
50 */
51 public class PrevaylerCore {
52
53 private final PrevalentSystem system;
54 private final SystemClock clock;
55 private final CommandOutputStream output;
56
57 /** Returns a new Prevayler for the given PrevalentSystem.
58 * "PrevalenceBase" shall be the directory where the snapshot and log files shall be created and read.
59 * @param newSystem The newly started, "empty" PrevalentSystem that will be used as a starting point for every
60 * system startup, until the first snapshot is taken.
61 * @param shouldReset Whether to issue resets in the underlying OOS
62 */
63 public PrevaylerCore(PrevalentSystem newSystem,
64 boolean shouldReset, boolean shouldClean,
65 int aBufferSize)
66 throws IOException, ClassNotFoundException {
67
68 this(newSystem, "PrevalenceBase", shouldReset, shouldClean,
69 aBufferSize);
70 }
71
72 /** Returns a new Prevayler for the given PrevalentSystem.
73 * @param newSystem The newly started, "empty" PrevalentSystem that will be used as a starting point for every
74 * system startup, until the first snapshot is taken.
75 * @param directory The full path of the directory where the snapshot and log files shall be created and read.
76 * @param shouldReset Whether to issue resets in the underlying OOS
77 */
78 public PrevaylerCore(PrevalentSystem newSystem, String directory,
79 boolean shouldReset, boolean shouldClean,
80 int aBufferSize)
81 throws IOException, ClassNotFoundException {
82
83 newSystem.clock(new SystemClock());
84 CommandInputStream input = new CommandInputStream(directory);
85
86 PrevalentSystem savedSystem = input.readLastSnapshot();
87 system = (savedSystem == null)
88 ? newSystem
89 : savedSystem;
90
91 recoverCommands(input);
92
93 output = input.commandOutputStream(shouldReset, shouldClean,
94 aBufferSize);
95 clock = (SystemClock) system.clock();
96 clock.resume();
97 }
98
99 public PrevaylerCore(PrevalentSystem newSystem, String directory)
100 throws IOException, ClassNotFoundException {
101
102 clock = null;
103 output = null;
104
105 newSystem.clock(new SystemClock());
106 CommandInputStream input = new CommandInputStream(directory);
107
108 PrevalentSystem savedSystem = input.readLastSnapshot();
109
110 if (savedSystem != null) {
111 system = savedSystem;
112 } else {
113 system = newSystem;
114 }
115
116 System.out.println("System base clock: " + system.clock().time().getTime());
117 Serializable[] myUserData = system.getSnapshotContributions();
118
119 for (int i = 0; i < myUserData.length; i++) {
120 System.out.println(myUserData[i].toString());
121 }
122
123 debugCommands(input);
124 }
125
126 /**
127 Returns the underlying PrevalentSystem.
128 */
129 public PrevalentSystem system() {
130 return system;
131 }
132
133 /** Logs the received command for crash or shutdown recovery and executes it on the underlying PrevalentSystem.
134 * @see system()
135 * @return The serializable object that was returned by the execution of command.
136 * @throws IOException if there is trouble writing the command to the log.
137 * @throws Exception if command.execute() throws an exception.
138 */
139 public void logCommand(Command command) throws Exception {
140 synchronized (this) {
141 output.writeCommand(command);
142 }
143 }
144
145 public void logCommand(Command command, boolean doSync) throws Exception {
146 synchronized (this) {
147 output.writeCommand(command, doSync);
148 }
149 }
150
151 /**
152 * This method prepares a snapshot of the system and returns it in a
153 * Snapshotter instance which can be used to save the snapshot to disk
154 * once dirty state has been sync'd to disk. If your application has no
155 * additional state, you can simply invoke on the Snapshotter immediately.
156 * @return Snapshotter to be used to save an appropriate snapshot post
157 * sync'ing of dirty state to disk.
158 * @see system()
159 * @throws IOException if there is trouble preparing the snapshot file.
160 */
161 public synchronized Snapshotter takeSnapshot() throws IOException {
162 clock.pause();
163 try {
164 return output.writeSnapshot(system);
165 } finally {
166 clock.resume();
167 }
168 }
169
170 private void debugCommands(CommandInputStream input) throws IOException, ClassNotFoundException {
171 Command command;
172
173 while (true) {
174 try {
175 command = input.readCommand();
176 } catch (EOFException eof) {
177 break;
178 }
179
180 try {
181 System.out.println(command);
182 System.out.println();
183 // command.execute(system);
184 } catch (Exception e) {
185 //Don't do anything at all. Commands may throw exceptions normally.
186 System.err.println("Command threw exception");
187 e.printStackTrace(System.err);
188 }
189 }
190 }
191
192 private void recoverCommands(CommandInputStream input) throws IOException, ClassNotFoundException {
193 Command command;
194 while (true) {
195 try {
196 command = input.readCommand();
197 } catch (EOFException eof) {
198 break;
199 }
200
201 try {
202 command.execute(system);
203 } catch (Exception e) {
204 //Don't do anything at all. Commands may throw exceptions normally.
205 System.err.println("Command threw exception");
206 e.printStackTrace(System.err);
207 }
208 }
209 }
210
211 public static void main(String anArgs[]) {
212 try {
213 System.setSecurityManager(new RMISecurityManager());
214
215 new PrevaylerCore(new DebugSystem(), anArgs[0]);
216 } catch (Exception anE) {
217 System.err.println("Whoops");
218 anE.printStackTrace(System.err);
219 }
220 }
221
222 static class DebugSystem implements org.prevayler.PrevalentSystem {
223
224 private org.prevayler.AlarmClock theClock;
225
226 public void clock(org.prevayler.AlarmClock clock) {
227 theClock = clock;
228 }
229
230 public org.prevayler.AlarmClock clock() {
231 return theClock;
232 }
233
234 public void add(SnapshotContributor aContributor) {
235 }
236
237 public void remove(SnapshotContributor aContributor) {
238 }
239
240 public Serializable[] getSnapshotContributions() {
241 return new Serializable[0];
242 }
243 }
244 }