Is Parallel Programming Hard, And, If So, What Can You Do About It?

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250 APPENDIX E. FORMAL VERIFICATION(Spin Version 4.2.5 -- 2 April 2005)+ Partial Order Reduction1 #include "lock.h"23 #define N_LOCKERS 345 bit mutex = 0;6 bit havelock[N_LOCKERS];7 int sum;89 proctype locker(byte me)10 {11 do12 :: 1 ->13 spin_lock(mutex);14 havelock[me] = 1;15 havelock[me] = 0;16 spin_unlock(mutex)17 od18 }1920 init {21 int i = 0;22 int j;2324 end: do25 :: i < N_LOCKERS ->26 havelock[i] = 0;27 run locker(i);28 i++29 :: i >= N_LOCKERS ->30 sum = 0;31 j = 0;32 atomic {33 do34 :: j < N_LOCKERS ->35 sum = sum + havelock[j];36 j = j + 137 :: j >= N_LOCKERS ->38 break39 od40 }41 assert(sum
E.6. PROMELA EXAMPLE: QRCU 251critical sections complete, but, like SRCU’ssynchronize_srcu(), QRCU’s synchronize_qrcu() need wait only for those read-side criticalsections that are using the same qrcu_struct.For example, synchronize_qrcu(&your_qrcu_struct) would not need to wait on the earlierQRCU read-side critical section. In contrast,synchronize_qrcu(&my_qrcu_struct) wouldneed to wait, since it shares the same qrcu_struct.A Linux-kernel patch for QRCU has been produced[McK07b], but has not yet been included inthe Linux kernel as of April 2008.1 #include "lock.h"23 #define N_QRCU_READERS 24 #define N_QRCU_UPDATERS 256 bit idx = 0;7 byte ctr[2];8 byte readerprogress[N_QRCU_READERS];9 bit mutex = 0;Figure E.11: QRCU Global VariablesReturning to the Promela code for QRCU, theglobal variables are as shown in Figure E.11. Thisexample uses locking, hence including lock.h. Boththe number of readers and writers can be variedusing the two #define statements, giving us notone but two ways to create combinatorial explosion.The idx variable controls which of the twoelements of the ctr array will be used by readers,and the readerprogress variable allows to assertionto determine when all the readers are finished(since a QRCU update cannot be permitted to completeuntil all pre-existing readers have completedtheir QRCU read-side critical sections). The readerprogressarray elements have values as follows, indicatingthe state of the corresponding reader:1. 0: not yet started.2. 1: within QRCU read-side critical section.3. 2: finished with QRCU read-side critical section.Finally, the mutex variable is used to serialize updaters’slowpaths.QRCU readers are modeled by the qrcu_reader() process shown in Figure E.12. A doodloop spans lines 5-16, with a single guard of1 proctype qrcu_reader(byte me)2 {3 int myidx;45 do6 :: 1 ->7 myidx = idx;8 atomic {9 if10 :: ctr[myidx] > 0 ->11 ctr[myidx]++;12 break13 :: else -> skip14 fi15 }16 od;17 readerprogress[me] = 1;18 readerprogress[me] = 2;19 atomic { ctr[myidx]-- }20 }Figure E.12: QRCU Reader Process“1” on line 6 that makes it an infinite loop. Line7 captures the current value of the global index,and lines 8-15 atomically increment it (and breakfrom the infinite loop) if its value was non-zero(atomic_inc_not_zero()). Line 17 marks entryinto the RCU read-side critical section, and line 18marks exit from this critical section, both lines forthe benefit of the assert() statement that we shallencounter later. Line 19 atomically decrements thesame counter that we incremented, thereby exitingthe RCU read-side critical section.1 #define sum_unordered \2 atomic { \3 do \4 :: 1 -> \5 sum = ctr[0]; \6 i = 1; \7 break \8 :: 1 -> \9 sum = ctr[1]; \10 i = 0; \11 break \12 od; \13 } \14 sum = sum + ctr[i]Figure E.13: QRCU Unordered SummationThe C-preprocessor macro shown in Figure E.13
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Is Parallel Programming Hard, And,
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Contents1 Introduction 11.1 Histori
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CONTENTSv6 Locking 676.1 Staying Al
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CONTENTSviiB Synchronization Primit
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CONTENTSixE.7.1 Introduction to Pre
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PrefaceThe purpose of this book is
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Chapter 1IntroductionParallel progr
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1.2. PARALLEL PROGRAMMING GOALS 3CP
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1.3. ALTERNATIVES TO PARALLEL PROGR
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1.4. WHAT MAKES PARALLEL PROGRAMMIN
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1.5. GUIDE TO THIS BOOK 9other hand
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Chapter 2Hardware and its HabitsMos
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2.1. OVERVIEW 13Therefore, as shown
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16 CHAPTER 2. HARDWARE AND ITS HABI
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18 CHAPTER 2. HARDWARE AND ITS HABI
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20 CHAPTER 3. TOOLS OF THE TRADE1 p
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22 CHAPTER 3. TOOLS OF THE TRADE1 p
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24 CHAPTER 3. TOOLS OF THE TRADE1.1
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26 CHAPTER 3. TOOLS OF THE TRADEQui
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28 CHAPTER 3. TOOLS OF THE TRADE
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30 CHAPTER 4. COUNTING1 atomic_t co
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32 CHAPTER 4. COUNTING4.2.3 Eventua
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34 CHAPTER 4. COUNTINGvanish when t
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36 CHAPTER 4. COUNTINGper-thread va
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38 CHAPTER 4. COUNTING1 unsigned lo
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42 CHAPTER 4. COUNTING1 #define THE
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46 CHAPTER 4. COUNTINGReadsAlgorith
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48 CHAPTER 5. PARTITIONING AND SYNC
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68 CHAPTER 6. LOCKING1 int delete(i
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70 CHAPTER 7. DATA OWNERSHIP
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72 CHAPTER 8. DEFERRED PROCESSINGfo
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74 CHAPTER 8. DEFERRED PROCESSINGth
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76 CHAPTER 8. DEFERRED PROCESSING
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82 CHAPTER 8. DEFERRED PROCESSINGNo
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108 CHAPTER 8. DEFERRED PROCESSING
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110 CHAPTER 9. APPLYING RCU1 struct
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112 CHAPTER 9. APPLYING RCU
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114 CHAPTER 10. VALIDATION: DEBUGGI
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116 CHAPTER 11. DATA STRUCTURES
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118 CHAPTER 12. ADVANCED SYNCHRONIZ
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138 CHAPTER 13. EASE OF USEFigure 1
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140 CHAPTER 13. EASE OF USE
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142 CHAPTER 14. TIME MANAGEMENT
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144 CHAPTER 15. CONFLICTING VISIONS
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154 APPENDIX A. IMPORTANT QUESTIONS
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156 APPENDIX A. IMPORTANT QUESTIONS
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158 APPENDIX B. SYNCHRONIZATION PRI
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160 APPENDIX B. SYNCHRONIZATION PRI
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162 APPENDIX C. WHY MEMORY BARRIERS
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330 APPENDIX G. GLOSSARY(2) A physi
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332 APPENDIX G. GLOSSARYnear by. Th
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334 APPENDIX G. GLOSSARY
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336 BIBLIOGRAPHY[But97]USA, March 2
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338 BIBLIOGRAPHY[HMB06][Hol03][HP95
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340 BIBLIOGRAPHY[McK06] Paul E. McK
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342 BIBLIOGRAPHYtor. Software - Pra
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344 BIBLIOGRAPHY[UoC08][VGS08]Berke
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346 APPENDIX H. CREDITSH.4 Original
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