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65 Implementation calculations that are triggered when the next LPCC processing is needed. An additional parameter for the method receiveGvt() of the LogicalProcess class indicates to the LP that an LPCC processing is needed after the new GVT has been received. Finally the user can also trigger a GVT calculation, which is useful for simulations in normal Time Warp mode that might not require any GVT calculation for large parts of the simulation. Forcing a GVT calculation allows the user to check what progress the simulation has made so far as the GVT is an approximation for the confirmed simulation times that has been reached by all LPs. End of simulation The detection of the simulation end is closely linked to the GVT calculation because a provisional simulation end reached by one of the LPs can only be confirmed by a GVT. The background of detecting the simulation end has already been discussed in 4.4 but the actual implementation will be explained here. When an LP reaches a provisional simulation end then the parallel simulator will attempt to confirm this simulation end as soon as possible if at all possible. First the LP reaching the provisional simulation end will request a GVT calculation from the Simulation Controller. But the resulting GVT might not confirm the provisional simulation end if the LP is ahead of other LPs in respect of the simulation time. For this case a scheme is introduced in which the LP reaching the provisional simulation end tells all other LPs to request a GVT calculation themselves if they pass the simulation time of that provisional simulation end. The method forceGvtAt() of the LogicalProcess class is used to tell other LPs about the provisional simulation end time. Because it is possible for more than one LP to reach a provisional simulation end before any of them is confirmed this method will keep a list of the times at which the LPs need to request GVT calculations. Whether or not a provisional simulation end reached by one of the LPs is confirmed, is detected by the private method performGvtCalculation() of the SimulationController class that also performs the calculation of the GVT. In order to make this possible the method requestGvtCalculation() of the LogicProcess class returns additional information about a possible simulation end reached by that LP. This way the GVT calculation process described above is also used to confirm a provisional simulation end. Such a simulation end is confirmed during the GVT calculation when it is found that all other LPs have reached a later simulation time than the one that reported the
66 Implementation provisional simulation end. In this case no future rollback could occur that can undo the provisional simulation end, which is therefore guaranteed. If the GVT calculation confirms a simulation end then no GVT is send back to the LPs but instead the Simulation Controller calls the method endOfSimulationByTransaction() of all LPs as shown in Figure 15 of section 5.2.3. 5.3.3 State Saving and Rollbacks Optimistic synchronisation algorithms execute all local events without guarantee that additional events received later will not violate the causal order of events already execute. In order to correct such causal violations they have to provide means to restore a past state before the causal violation occurred so that the new event can be inserted into the event chain and the events be executed again in the correct order. A common technique to allow the restoration of past states is called State Saving or State Checkpointing where an LP saves the state of the simulation into a list of simulation states each time the state changes or in defined intervals. The parallel simulator implemented employs a relatively simple state saving scheme. Each time the simulation time is incremented the LP serialises the state of the Simulation Engine and saves it together with the corresponding simulation time into a state list. Each state record therefore describes the simulation state at the beginning of that time, i.e. before any Transactions were moved. To keep the complexity of this solution low the standard object serialisation functionality provided by Java is used to serialise and deserialise the state to and from a Stream object that is then stored in the state list. The state list keeps all states sorted by their time. The saving of the state is implemented in the method saveCurrentState() of the LogicalProcess class. The purpose of saving the simulation state is to allow LPs to rollback to past simulation states if required. The functionality to rollback to a past simulation state is implemented in the method rollbackState(). Using the example shown in Figure 22 the principle of rolling back to a past simulation state is briefly explained.
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TRANSACTION-ORIENTED SIMULATION IN
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Table of Content II Table of Conten
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IV Table of Content 6 VALIDATION OF
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Figures VI Figures Figure 1: Ad Hoc
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Tables VIII Tables Table 1: Change
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2 Introduction synchronisation algo
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2 Fundamental Concepts Fundamental
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Figure 1: Ad Hoc Grid architecture
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8 Fundamental Concepts In continuou
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10 Fundamental Concepts Two other a
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12 Fundamental Concepts known as st
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Page 25 and 26: 3 Ad Hoc Grid Aspects 16 Ad Hoc Gri
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Page 51 and 52: 42 Implementation confirm a provisi
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Page 55 and 56: 46 Implementation A detailed descri
Page 57 and 58: 48 Implementation But in a parallel
Page 59 and 60: 50 Implementation GPSS test models
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Page 79 and 80: 70 Implementation log4j.logger.para
Page 81 and 82: proactive-log4j 72 Implementation T
Page 83 and 84: 74 Implementation Memory Allocation
Page 85 and 86: 76 Validation of the Parallel Simul
Page 93 and 94: 6.4 Validation 4 84 Validation of t
Page 97 and 98: … LpccEnabled=true LpccClusterNum
Page 99 and 100: Validation 5.2 Validation of the Pa
Page 105 and 106: 7 Conclusions 96 Conclusions Even s
Page 107 and 108: References 98 References [1] Amin K
Page 109 and 110: [19] Krafft G. Parallelisation of T
Page 111 and 112: Appendix A: Detailed GPSS Syntax 10
Page 113 and 114: Reserved word: DEPART Syntax: [] DE
Page 115 and 116: Reserved word: SEIZE Syntax: [] SEI
Page 117 and 118: Setting: LpccClusterNumber Default
Page 119 and 120: Appendix C: Simulator log4j loggers
Page 121 and 122: Logger: parallelJavaGpssSimulator.l
Page 123 and 124: 114 Appendix D: Structure of the at
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Appendix E: Documentation of select
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!/+/.7/8$ Appendix E: Documentation
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Returns: Appendix E: Documentation
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!"#$%&'()#%*+,"-*.# Appendix E: Doc
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Constructor Detail !"#$%&'$(#$)*$%+
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Validation 1.1, output of simulate:
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Validation 2, output of LP: Appendi
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Appendix F: Validation output logs
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Validation 2, output of simulate: A
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Validation 3.1, output of LP1: Appe
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Validation 4, output of LP1: Append
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simulation for time 2000) (628) 20:
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Validation 4, output of simulate: A
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(135) 19:37:56,477 Total transactio
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(68) 19:37:56,619 by the transactio
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(1295) 14:25:22,740 Simulation stop
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Validation 6.2, output of LP2: (1)
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(32) (1,2) 0 765 Block: TRANSFER 0.
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