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comparison src/org/prevayler/implementation/SnapshotPrevaylerImpl.java @ 0:3dc0c5604566

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Initial checkin of blitz 2.0 fcs - no installer yet.
author Dan Creswell <dan.creswell@gmail.com>
date Sat, 21 Mar 2009 11:00:06 +0000
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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.util.Date;
40 import java.io.*;
41
42 import java.rmi.RMISecurityManager;
43
44 import org.prevayler.*;
45
46 /** Provides transparent persistence for business objects.
47 * This applies to any deterministic system implementing the PrevalentSystem interface.
48 * All commands to the system must be represented as objects implementing the Command interface and must be executed using Prevayler.executeCommand(Command).
49 * Take a look at the demo application included with the Prevayler distribution for examples.
50 */
51 public class SnapshotPrevaylerImpl implements SnapshotPrevayler {
52
53 private final PrevalentSystem system;
54 private final SystemClock clock;
55 private final CommandOutputStream output;
56
57
58 /** Returns a new Prevayler for the given PrevalentSystem.
59 * "PrevalenceBase" shall be the directory where the snapshot and log files shall be created and read.
60 * @param newSystem The newly started, "empty" PrevalentSystem that will be used as a starting point for every system startup, until the first snapshot is taken.
61 * @param shouldReset Whether to issue resets in the underlying OOS
62 */
63 public SnapshotPrevaylerImpl(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
73 /** Returns a new Prevayler for the given PrevalentSystem.
74 * @param newSystem The newly started, "empty" PrevalentSystem that will be used as a starting point for every 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 SnapshotPrevaylerImpl(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 SnapshotPrevaylerImpl(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 System.out.println("System base clock: " + system.clock().time().getTime());
116 Serializable[] myUserData = system.getSnapshotContributions();
117
118 for (int i = 0; i < myUserData.length; i++) {
119 System.out.println(myUserData[i].toString());
120 }
121
122 debugCommands(input);
123 }
124
125 /**
126 Returns the underlying PrevalentSystem.
127 */
128 public PrevalentSystem system() {
129 return system;
130 }
131
132 /** Logs the received command for crash or shutdown recovery and executes it on the underlying PrevalentSystem.
133 * @see system()
134 * @return The serializable object that was returned by the execution of command.
135 * @throws IOException if there is trouble writing the command to the log.
136 * @throws Exception if command.execute() throws an exception.
137 */
138 public Serializable executeCommand(Command command) throws Exception {
139
140 synchronized(this) {
141 try {
142 clock.pause(); //To be deterministic, the system must know exactly at what time the command is being executed.
143 output.writeCommand(new ClockRecoveryCommand(command, clock.time()));
144 } finally {
145 clock.resume();
146 }
147 }
148
149 return command.execute(system);
150 }
151
152 public Serializable executeCommand(Command command,
153 boolean doSync)
154 throws Exception {
155
156 synchronized(this) {
157 try {
158 clock.pause();
159 output.writeCommand(new ClockRecoveryCommand(command,
160 clock.time()),
161 doSync);
162 } finally {
163 clock.resume();
164 }
165 }
166
167 return command.execute(system);
168 }
169
170 /**
171 * This method prepares a snapshot of the system and returns it in a
172 * Snapshotter instance which can be used to save the snapshot to disk
173 * once dirty state has been sync'd to disk. If your application has no
174 * additional state, you can simply invoke on the Snapshotter immediately.
175 * @return Snapshotter to be used to save an appropriate snapshot post
176 * sync'ing of dirty state to disk.
177 * @see system()
178 * @throws IOException if there is trouble preparing the snapshot file.
179 */
180 public synchronized Snapshotter takeSnapshot() throws IOException {
181 clock.pause();
182 try {
183 return output.writeSnapshot(system);
184 } finally {
185 clock.resume();
186 }
187 }
188
189 private void debugCommands(CommandInputStream input) throws IOException, ClassNotFoundException {
190 Command command;
191 while(true) {
192 try {
193 command = input.readCommand();
194 } catch (EOFException eof) {
195 break;
196 }
197
198 try {
199 System.out.println(command);
200 System.out.println();
201 // command.execute(system);
202 } catch (Exception e) {
203 //Don't do anything at all. Commands may throw exceptions normally.
204 System.err.println("Command threw exception");
205 e.printStackTrace(System.err);
206 }
207 }
208 }
209
210 private void recoverCommands(CommandInputStream input) throws IOException, ClassNotFoundException {
211 Command command;
212 while(true) {
213 try {
214 command = input.readCommand();
215 } catch (EOFException eof) {
216 break;
217 }
218
219 try {
220 command.execute(system);
221 } catch (Exception e) {
222 //Don't do anything at all. Commands may throw exceptions normally.
223 System.err.println("Command threw exception");
224 e.printStackTrace(System.err);
225 }
226 }
227 }
228
229 public static void main(String anArgs[]) {
230 try {
231 System.setSecurityManager(new RMISecurityManager());
232
233 new SnapshotPrevaylerImpl(new DebugSystem(), anArgs[0]);
234 } catch (Exception anE) {
235 System.err.println("Whoops");
236 anE.printStackTrace(System.err);
237 }
238 }
239
240 static class DebugSystem implements org.prevayler.PrevalentSystem {
241 private org.prevayler.AlarmClock theClock;
242
243 public void clock(org.prevayler.AlarmClock clock) {
244 theClock = clock;
245 }
246
247 public org.prevayler.AlarmClock clock() {
248 return theClock;
249 }
250
251 public void add(SnapshotContributor aContributor) {
252 }
253
254 public void remove(SnapshotContributor aContributor) {
255 }
256
257 public Serializable[] getSnapshotContributions() {
258 return new Serializable[0];
259 }
260 }
261 }