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<a class="dropdown-item" tabindex="-1" href="IntroConcSysOverview.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="Themes.html"> 1.3. Themes and Guiding Principles</a>
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<a class="dropdown-item" href="Architectures.html"> 1.4. System Architectures</a>
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<a class="dropdown-item" href="StateModels.html"> 1.5. State Models in UML</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" href="StateModelImplementation.html"> 1.7. Extended Example: State Model Implementation</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="ProcessCycle.html"> 2.5. Process Life Cycle</a>
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<a class="dropdown-item" href="UnixFile.html"> 2.6. The UNIX File Abstraction</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 disabled"><b>Chapter 3</b></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 disabled"><b>Chapter 4</b></a>
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<a class="dropdown-item" href="SocketsOverview.html"> 4.1. Networked Concurrency</a>
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<a class="dropdown-item" href="FiveLayer.html"> 4.2. The TCP/IP Internet Model</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="Sockets.html"> 4.4. The Socket Interface</a>
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<a class="dropdown-item" href="TCPSockets.html"> 4.5. TCP Socket Programming: HTTP</a>
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<a class="dropdown-item" href="UDPSockets.html"> 4.6. UDP Socket Programming: DNS</a>
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<a class="dropdown-item" href="AppBroadcast.html"> 4.7. Application-Layer Broadcasting: DHCP</a>
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<a class="dropdown-item" href="Extended4CGI.html"> 4.8. Extended Example: CGI Web Server</a>
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<a class="dropdown-item disabled"><b>Chapter 5</b></a>
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<a class="dropdown-item" href="InternetOverview.html"> 5.1. The Internet and Connectivity</a>
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<a class="dropdown-item" href="AppLayer.html"> 5.2. Application Layer: Overlay Networks</a>
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<a class="dropdown-item" href="NetSec.html"> 5.4. Network Security Fundamentals</a>
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<a class="dropdown-item" href="ThreadsOverview.html"> 6.1. Concurrency with Multithreading</a>
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<a class="dropdown-item" href="ProcVThreads.html"> 6.2. Processes vs. Threads</a>
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<a class="dropdown-item" href="RaceConditions.html"> 6.3. Race Conditions and Critical Sections</a>
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<a class="dropdown-item" href="POSIXThreads.html"> 6.4. POSIX Thread Library</a>
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<a class="dropdown-item" href="ThreadArgs.html"> 6.5. Thread Arguments and Return Values</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="Extended6Primes.html"> 6.8. Extended Example: Concurrent Prime Number Search</a>
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<a class="dropdown-item disabled"><b>Chapter 7</b></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="Semaphores.html"> 7.4. Semaphores</a>
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<a class="dropdown-item" href="Barriers.html"> 7.5. Barriers</a>
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<a class="dropdown-item" href="Condvars.html"> 7.6. Condition Variables</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="Functions.html"> A.5. Functions and Scope</a>
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<a class="dropdown-item" href="Pointers.html"> A.6. Pointers and Dynamic Allocation</a>
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<a class="dropdown-item" href="Strings.html"> A.7. Strings</a>
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<a class="dropdown-item" href="Files.html"> A.9. Files</a>
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<script>ODSA.SETTINGS.DISP_MOD_COMP = true;ODSA.SETTINGS.MODULE_NAME = "IntroConcSysOverview";ODSA.SETTINGS.MODULE_LONG_NAME = "Introduction to Concurrent Systems";ODSA.SETTINGS.MODULE_CHAPTER = "Introduction to Computer Systems"; 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="introduction-to-concurrent-systems">
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<h1>1.1. Introduction to Concurrent Systems<a class="headerlink" href="IntroConcSysOverview.html#introduction-to-concurrent-systems" title="Permalink to this headline">¶</a></h1>
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<blockquote class="blockquote text-center">
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<p>“The Analytical Engine has no pretensions whatever to originate anything.
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It can do whatever we know how to order it to perform.”
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<footer class="blockquote-footer">Ada Lovelace</footer>
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</blockquote><p><a class="reference internal" href="Glossary.html#term-concurrency"><span class="xref std std-term">Concurrency</span></a> is hard. When your program is performing dozens of tasks at the same time, a
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single crash in any of them can cause all of them to stop. Perhaps one of the tasks was supposed to
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wait for some critical calculation to complete, but it proceeded too early. Perhaps one task
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||
corrupted a pointer that another was using, leading to a mysterious segmentation fault. Perhaps two
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tasks overwrote each other’s intermediate calculations, leading to incorrect final results. Once you
|
||
begin writing software that goes beyond a single coherent algorithm, you quickly learn that you are
|
||
entering a world with a completely new set of programming errors that you never imagined. Each line
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of code can interact and interfere with other parts of the system in new, unintended, and
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unpredictable ways. In other words, concurrency is hard. This book aims to make it less so.</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>
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<ul class="simple">
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||
<li>We will summarize the major themes and guiding principles this book addresses.</li>
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||
<li>We will describe the relationship between the notions of systems and models.</li>
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<li>We will characterize the key features of common system architectures.</li>
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<li>We will introduce UML state and sequence models, which will be used throughout the book.</li>
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</ul>
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</div>
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<p>Our focus in this book is to establish a foundation of key principles and techniques that are be
|
||
used to implement concurrent systems software. This class of software ranges from operating systems
|
||
(OS) and web servers to databases and scientific modeling platforms. What these types of programs
|
||
have in common is that they subdivide complicated tasks into smaller ones that can be run at the
|
||
same time. In doing so, these approaches introduce <a class="reference internal" href="Glossary.html#term-nondeterminism"><span class="xref std std-term">nondeterminism</span></a> and complexity, as the
|
||
programmer must give up some control over what steps and calculations will be performed in which
|
||
particular order. If the programmer writes code that says tasks A, B, and C can be executed in any
|
||
order, they will quickly learn whether or not that claim is actually true.</p>
|
||
<p>At this point, some readers may object: they do not plan to write systems software, so this material
|
||
is not relevant for them. While the first part of that claim may be true (or it may not), the latter
|
||
is certainly not the case. The principles used to build systems and infrastructure can be applied to
|
||
more traditional applications; if your application uses event handlers to detect mouse clicks or key
|
||
presses, you have a concurrent program. If your code is structured to use a web-based application
|
||
programming interface (API), you have a concurrent program. If your application performs graphical
|
||
calculations or applies artificial intelligence, you have a concurrent program (or you should, as it
|
||
would run faster).</p>
|
||
<p>In short, concurrency is everywhere. Mastering the concepts and principles of concurrent programming
|
||
can help you build better software, whether the end result is a new application or a platform for
|
||
applications. In this chapter, we will introduce the major themes and guiding principles that we
|
||
will use throughout the book. We will also define some key terminology and notation that are helpful
|
||
in characterizing concurrent systems. Without further delay, let us begin our exploration.</p>
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</div>
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