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<a class="dropdown-item" tabindex="-1" href="SynchProblemsOverview.html#"><b>Chapter 1</b></a>
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<a class="dropdown-item" href="IntroConcSysOverview.html"> 1.1. Introduction to Concurrent Systems</a>
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<a class="dropdown-item" href="SysAndModels.html"> 1.2. Systems and Models</a>
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<a class="dropdown-item" href="SequenceModels.html"> 1.6. Sequence Models in UML</a>
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<a class="dropdown-item disabled"><b>Chapter 2</b></a>
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<a class="dropdown-item" href="ProcessesOverview.html"> 2.1. Processes and OS Basics</a>
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<a class="dropdown-item" href="Multiprogramming.html"> 2.2. Processes and Multiprogramming</a>
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<a class="dropdown-item" href="KernelMechanics.html"> 2.3. Kernel Mechanics</a>
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<a class="dropdown-item" href="Syscall.html"> 2.4. System Call Interface</a>
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<a class="dropdown-item" href="EventsSignals.html"> 2.7. Events and Signals</a>
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<a class="dropdown-item" href="Extended2Processes.html"> 2.8. Extended Example: Listing Files with Processes</a>
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<a class="dropdown-item" href="IPCOverview.html"> 3.1. Concurrency with IPC</a>
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<a class="dropdown-item" href="IPCModels.html"> 3.2. IPC Models</a>
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<a class="dropdown-item" href="Pipes.html"> 3.3. Pipes and FIFOs</a>
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<a class="dropdown-item" href="MMap.html"> 3.4. Shared Memory With Memory-mapped Files</a>
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<a class="dropdown-item" href="POSIXvSysV.html"> 3.5. POSIX vs. System V IPC</a>
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<a class="dropdown-item" href="MQueues.html"> 3.6. Message Passing With Message Queues</a>
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<a class="dropdown-item" href="ShMem.html"> 3.7. Shared Memory</a>
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<a class="dropdown-item" href="IPCSems.html"> 3.8. Semaphores</a>
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<a class="dropdown-item" href="Extended3Bash.html"> 3.9. Extended Example: Bash-lite: A Simple Command-line Shell</a>
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<a class="dropdown-item" href="NetApps.html"> 4.3. Network Applications and Protocols</a>
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<a class="dropdown-item" href="ImplicitThreads.html"> 6.6. Implicit Threading and Language-based Threads</a>
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<a class="dropdown-item" href="Extended6Input.html"> 6.7. Extended Example: Keyboard Input Listener</a>
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<a class="dropdown-item" href="SynchOverview.html"> 7.1. Synchronization Primitives</a>
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<a class="dropdown-item" href="CritSect.html"> 7.2. Critical Sections and Peterson's Solution</a>
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<a class="dropdown-item" href="Locks.html"> 7.3. Locks</a>
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<a class="dropdown-item" href="Deadlock.html"> 7.7. Deadlock</a>
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<a class="dropdown-item disabled"><b>Chapter 8</b></a>
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<a class="dropdown-item" href="SynchProblemsOverview.html"> 8.1. Synchronization Patterns and Problems</a>
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<a class="dropdown-item" href="SynchDesign.html"> 8.2. Basic Synchronization Design Patterns</a>
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<a class="dropdown-item" href="ProdCons.html"> 8.3. Producer-Consumer Problem</a>
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<a class="dropdown-item" href="ReadWrite.html"> 8.4. Readers-Writers Problem</a>
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<a class="dropdown-item" href="DiningPhil.html"> 8.5. Dining Philosophers Problem and Deadlock</a>
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<a class="dropdown-item" href="CigSmokers.html"> 8.6. Cigarette Smokers Problem and the Limits of Semaphores and Locks</a>
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<a class="dropdown-item" href="Extended8ModExp.html"> 8.7. Extended Example: Parallel Modular Exponentiation</a>
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<a class="dropdown-item disabled"><b>Chapter 9</b></a>
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<a class="dropdown-item" href="ParallelDistributedOverview.html"> 9.1. Parallel and Distributed Systems</a>
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<a class="dropdown-item" href="ParVConc.html"> 9.2. Parallelism vs. Concurrency</a>
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<a class="dropdown-item" href="ParallelDesign.html"> 9.3. Parallel Design Patterns</a>
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<a class="dropdown-item" href="Scaling.html"> 9.4. Limits of Parallelism and Scaling</a>
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<a class="dropdown-item" href="DistTiming.html"> 9.5. Timing in Distributed Environments</a>
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<a class="dropdown-item" href="DistDataStorage.html"> 9.6. Reliable Data Storage and Location</a>
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<a class="dropdown-item" href="DistConsensus.html"> 9.7. Consensus in Distributed Systems</a>
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<a class="dropdown-item" href="Extended9Blockchain.html"> 9.8. Extended Example: Blockchain Proof-of-Work</a>
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<a class="dropdown-item disabled"><b>Appendix A</b></a>
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<a class="dropdown-item" href="CLangOverview.html"> A.1. C Language Reintroduction</a>
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<a class="dropdown-item" href="Debugging.html"> A.2. Documentation and Debugging</a>
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<a class="dropdown-item" href="BasicTypes.html"> A.3. Basic Types and Pointers</a>
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<a class="dropdown-item" href="Arrays.html"> A.4. Arrays, Structs, Enums, and Type Definitions</a>
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<a class="dropdown-item" href="Pointers.html"> A.6. Pointers and Dynamic Allocation</a>
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<script>ODSA.SETTINGS.DISP_MOD_COMP = true;ODSA.SETTINGS.MODULE_NAME = "SynchProblemsOverview";ODSA.SETTINGS.MODULE_LONG_NAME = "Synchronization Patterns and Problems";ODSA.SETTINGS.MODULE_CHAPTER = "Synchronization Patterns and Problems"; ODSA.SETTINGS.BUILD_DATE = "2021-06-01 15:31:50"; ODSA.SETTINGS.BUILD_CMAP = false;JSAV_OPTIONS['lang']='en';JSAV_EXERCISE_OPTIONS['code']='java';</script><div class="section" id="synchronization-patterns-and-problems">
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<h1>8.1. Synchronization Patterns and Problems<a class="headerlink" href="SynchProblemsOverview.html#synchronization-patterns-and-problems" title="Permalink to this headline">¶</a></h1>
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<div class="figure mb-2 align-center" style="width: 100%">
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<a class="reference internal image-reference" href="_images/CSF-Timeline.8.png"><img class="p-3 mb-2 align-center border border-dark rounded-lg" alt="Timeline of major CSF topics with Multicore and Threads highlighted" src="_images/CSF-Timeline.8.png" style="width: 90%;" /></a>
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</div>
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<blockquote class="blockquote text-center">
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<p>“If you’re not failing 90% of the time, then you’re probably not
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working on sufficiently challenging problems.”
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<footer class="blockquote-footer">Alan Kay</footer>
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</blockquote><p>From the earliest work on synchronization, it became clear that there were common software patterns
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that could solve key timing issues and race conditions that frequently occurred. Edsger Dijkstra
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characterized one such pattern as the Dining Philosophers problem in 1965. Tony Hoare—while working
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on his Communicating Sequential Processes (CSP) language to support formal analysis of
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concurrency—revisited this problem in 1985 and defined the standard version of it. Solutions for
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these types of synchronization problems are powerful and reusable techniques for creating robust and
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safe implementations of concurrent software.</p>
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<div class="topic border border-dark rounded-lg bg-light px-2 mb-3">
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<div class="figure align-left" style="width: 5%">
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<a class="reference internal image-reference" href="_images/CSF-Images-Objectives.png"><img alt="Decorative chapter objectives image" src="_images/CSF-Images-Objectives.png" style="width: 100%;" /></a>
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</div>
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<p class="topic-title first pt-2 mb-1">Chapter Objectives</p><hr class="mt-1" />
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<p>In this chapter, we will address the following instructional objectives:</p>
|
||
<ul class="simple">
|
||
<li>We will illustrate several design patterns that can be used for simple
|
||
synchronization tasks.</li>
|
||
<li>We will examine classical synchronization problems that have been studied
|
||
extensively, with well-known solutions.</li>
|
||
<li>We will highlight classical synchronization problems that demonstrate the
|
||
limitations of basic synchronization primitives.</li>
|
||
<li>We will consider additional synchronization problems with more complex
|
||
requirements that can be mapped to simpler design patterns.</li>
|
||
</ul>
|
||
</div>
|
||
<p><a class="reference internal" href="Glossary.html#term-race-condition"><span class="xref std std-term">Race condition</span></a> bugs can be extremely difficult to diagnose and fix.
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||
Observing these bugs depends on the programmer’s ability to reconstruct the
|
||
timing that makes the bug manifest. This task becomes even more difficult when
|
||
the bug is caused by the interaction of multiple system components that may or
|
||
may not be under that programmer’s control. Fortunately, many common tasks in
|
||
concurrent software are simple in nature and can be achieved by applying basic
|
||
synchronization design patterns with semaphores, locks, or other
|
||
<a class="reference internal" href="Glossary.html#term-synchronization-primitive"><span class="xref std std-term">synchronization primitives</span></a>. Other tasks are
|
||
variations on well-known <a class="reference internal" href="Glossary.html#term-synchronization-problem"><span class="xref std std-term">synchronization problems</span></a>.
|
||
These problems tend to have an underlying structure that has a known solution
|
||
that provides safe and efficient execution.</p>
|
||
<p>This chapter will focus on known solutions to common tasks that arise in
|
||
concurrent software. We will describe the scenarios in which these design
|
||
patterns and solutions apply and provide informal explanations of why they work.
|
||
For the more complex problems, we will consider how the requirements can be
|
||
decomposed into pieces that map to the more basic design patterns.</p>
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</div>
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