Mercurial > hg > blitz_condensed
annotate src/org/prevayler/implementation/BufferingPrevaylerImpl.java @ 34:6f68e94c1fb8 default tip
Add CondensedStats monitoring utility, equivalent to vmstat
author | Dominic Cleal <dominic-cleal@cdo2.com> |
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date | Thu, 05 Aug 2010 11:07:25 +0100 |
parents | 3dc0c5604566 |
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1 package org.prevayler.implementation; |
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2 |
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3 import java.util.LinkedList; |
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4 import java.util.Date; |
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5 import java.io.*; |
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6 |
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7 import org.prevayler.*; |
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8 |
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9 import org.dancres.blitz.ActiveObject; |
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10 import org.dancres.blitz.ActiveObjectRegistry; |
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11 |
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12 /** |
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13 <p>Prevayler which guarentees that all logged changes will be made |
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14 persistent within a certain fixed amount of time - e.g. after 5 seconds. |
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15 When a snapshot is requested, any logged changes will be flushed to disk and |
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16 then a snapshot will be prepared. This provides correct recovery should |
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17 we crash before we save the snapshot (which could be a while) but after |
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18 we've flushed the log.</p> |
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19 |
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20 <p>This Prevayler is designed to work in co-operation with Blitz's |
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21 OpCountingCheckpointTrigger and the ActiveObjectRegistry.</p> |
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22 |
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23 @see org.dancres.blitz.txn.OpCountingCheckpointTrigger |
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24 @see org.dancres.blitz.ActiveObjectRegistry |
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25 */ |
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26 public class BufferingPrevaylerImpl implements SnapshotPrevayler { |
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27 |
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28 private final PrevalentSystem system; |
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29 private final SystemClock clock; |
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30 private final CommandOutputStream output; |
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31 |
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32 private LinkedList theBuffer = new LinkedList(); |
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33 |
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34 /** Returns a new Prevayler for the given PrevalentSystem. |
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35 * "PrevalenceBase" shall be the directory where the snapshot and log files shall be created and read. |
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36 * @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. |
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37 * @param shouldReset Whether to issue resets in the underlying OOS |
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38 */ |
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39 public BufferingPrevaylerImpl(PrevalentSystem newSystem, |
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40 boolean shouldReset, boolean shouldClean, |
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41 int aBufferSize) |
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42 throws IOException, ClassNotFoundException { |
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43 |
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44 this(newSystem, "PrevalenceBase", shouldReset, shouldClean, |
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45 aBufferSize); |
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46 } |
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47 |
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48 |
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49 /** Returns a new Prevayler for the given PrevalentSystem. |
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50 * @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. |
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51 * @param directory The full path of the directory where the snapshot and log files shall be created and read. |
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52 * @param shouldReset Whether to issue resets in the underlying OOS |
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53 */ |
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54 public BufferingPrevaylerImpl(PrevalentSystem newSystem, String directory, |
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55 boolean shouldReset, boolean shouldClean, |
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56 int aBufferSize) |
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57 throws IOException, ClassNotFoundException { |
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58 |
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59 newSystem.clock(new SystemClock()); |
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60 CommandInputStream input = new CommandInputStream(directory); |
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61 |
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62 PrevalentSystem savedSystem = input.readLastSnapshot(); |
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63 system = (savedSystem == null) |
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64 ? newSystem |
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65 : savedSystem; |
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66 |
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67 recoverCommands(input); |
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68 |
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69 output = input.commandOutputStream(shouldReset, shouldClean, |
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70 aBufferSize); |
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71 clock = (SystemClock)system.clock(); |
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72 clock.resume(); |
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73 } |
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74 |
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75 |
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76 /** Returns the underlying PrevalentSystem. |
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77 */ |
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78 public PrevalentSystem system() { |
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79 return system; |
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80 } |
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81 |
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82 /** Logs the received command for crash or shutdown recovery and executes it on the underlying PrevalentSystem. |
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83 * @see system() |
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84 * @return The serializable object that was returned by the execution of command. |
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85 * @throws IOException if there is trouble writing the command to the log. |
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86 * @throws Exception if command.execute() throws an exception. |
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87 */ |
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88 public synchronized Serializable executeCommand(Command command) throws Exception { |
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89 clock.pause(); //To be deterministic, the system must know exactly at what time the command is being executed. |
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90 try { |
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91 theBuffer.add(new ClockRecoveryCommand(command, clock.time())); |
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92 |
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93 return command.execute(system); |
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94 |
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95 } finally { |
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96 clock.resume(); |
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97 } |
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98 } |
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99 |
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100 public synchronized Serializable executeCommand(Command command, |
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101 boolean doSync) |
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102 throws Exception { |
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103 |
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104 clock.pause(); |
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105 try { |
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106 theBuffer.add(new ClockRecoveryCommand(command, clock.time())); |
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107 |
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108 return command.execute(system); |
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109 |
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110 } finally { |
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111 clock.resume(); |
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112 } |
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113 } |
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114 |
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115 /** |
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116 * This method prepares a snapshot of the system and returns it in a |
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117 * Snapshotter instance which can be used to save the snapshot to disk |
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118 * once dirty state has been sync'd to disk. If your application has no |
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119 * additional state, you can simply invoke on the Snapshotter immediately. |
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120 * @return Snapshotter to be used to save an appropriate snapshot post |
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121 * sync'ing of dirty state to disk. |
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122 * @see system() |
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123 * @throws IOException if there is trouble preparing the snapshot file. |
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124 */ |
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125 public synchronized Snapshotter takeSnapshot() throws IOException { |
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126 clock.pause(); |
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127 try { |
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128 flush(); |
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129 |
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130 return output.writeSnapshot(system); |
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131 } finally { |
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132 clock.resume(); |
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133 } |
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134 } |
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135 |
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136 |
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137 private synchronized void flush() throws IOException { |
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138 while (! theBuffer.isEmpty()) { |
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139 Command myCommand = (Command) theBuffer.remove(0); |
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140 |
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141 output.writeCommand(myCommand, theBuffer.isEmpty()); |
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142 } |
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143 } |
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144 |
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145 private void recoverCommands(CommandInputStream input) throws IOException, ClassNotFoundException { |
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146 Command command; |
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147 while(true) { |
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148 try { |
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149 command = input.readCommand(); |
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150 } catch (EOFException eof) { |
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151 break; |
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152 } |
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153 |
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154 try { |
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155 command.execute(system); |
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156 } catch (Exception e) { |
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157 //Don't do anything at all. Commands may throw exceptions normally. |
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158 System.err.println("Command threw exception"); |
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159 e.printStackTrace(System.err); |
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160 } |
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161 } |
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162 } |
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163 } |
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164 |