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<a class="dropdown-item" tabindex="-1" href="IPCOverview.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" href="StateModelImplementation.html"> 1.7. Extended Example: State Model Implementation</a>
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<div class="dropdown-divider"></div>
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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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<div class="dropdown-divider"></div>
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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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<div class="dropdown-divider"></div>
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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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<div class="dropdown-divider"></div>
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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="TransLayer.html"> 5.3. Transport Layer</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="NetLayer.html"> 5.5. Network Layer: IP</a>
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<a class="dropdown-item" href="LinkLayer.html"> 5.6. Link Layer</a>
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<a class="dropdown-item" href="Wireless.html"> 5.7. Wireless Connectivity: Wi-Fi, Bluetooth, and Zigbee</a>
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<a class="dropdown-item" href="Extended5DNS.html"> 5.8. Extended Example: DNS client</a>
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<div class="dropdown-divider"></div>
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<a class="dropdown-item disabled"><b>Chapter 6</b></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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<div class="dropdown-divider"></div>
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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" href="Extended7Events.html"> 7.8. Extended Example: Event Log File</a>
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<div class="dropdown-divider"></div>
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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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<div class="dropdown-divider"></div>
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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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<div class="dropdown-divider"></div>
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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="FunctionPointers.html"> A.8. Function Pointers</a>
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<a class="dropdown-item" href="Files.html"> A.9. Files</a>
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«  <a id="prevmod" href="Extended2Processes.html">2.8. Extended Example: Listing Files with Processes</a>
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  ::  
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<a class="uplink" href="index.html">Contents</a>
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  ::  
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<a id="nextmod" href="IPCModels.html">3.2. IPC Models</a>  »
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<div class="container">
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<script>ODSA.SETTINGS.DISP_MOD_COMP = true;ODSA.SETTINGS.MODULE_NAME = "IPCOverview";ODSA.SETTINGS.MODULE_LONG_NAME = "Concurrency with IPC";ODSA.SETTINGS.MODULE_CHAPTER = "Concurrency with IPC"; 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="concurrency-with-ipc">
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<h1>3.1. Concurrency with IPC<a class="headerlink" href="IPCOverview.html#concurrency-with-ipc" 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.3.png"><img class="p-3 mb-2 align-center border border-dark rounded-lg" alt="Timeline of major CSF topics with Processes and IPC highlighted" src="_images/CSF-Timeline.3.png" style="width: 90%;" /></a>
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</div>
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<blockquote class="blockquote text-center">
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<p>“The fundamental problem of communication is that of reproducing at one point either
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exactly or approximately a message selected at another point.”
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<footer class="blockquote-footer">Claude Shannon</footer>
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</blockquote><p>As soon as computers were able to run multiple processes concurrently, the natural next step was to
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make the processes communicate with each other. This chapter focuses on interprocess communication
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technologies, which emerged in the 1960s and 1970s. For instance, Douglas McIlroy, who had
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previously contributed to the Multics OS in the late 1960s, introduced the concept of pipes in UNIX
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(1973).</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 distinguish the properties of the two basic models for performing IPC.</li>
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<li>We will compare and contrast the mechanics and uses of message passing IPC.</li>
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<li>We will explore how shared memory techniques blur the lines of what constitutes a process.</li>
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<li>We will examine code illustrating practical applications of IPC.</li>
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</ul>
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</div>
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<p>Processes are a robust mechanism for isolating programs from one another. In a multiprogramming
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environment with hundreds of processes running concurrently, the kernel ensures that a segmentation
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fault in one process (say, a web browser media plugin) cannot affect another (your email client).
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Similarly, once a process uses <code class="docutils literal notranslate"><span class="pre">fork()</span></code> to create a child process, the parent and child have
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distinct copies of every variable; changing the value of the variable in the child will not affect
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the parent, and vice versa.</p>
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<p>In some circumstances, however, the isolation imposed by separate processes can be undesirable. For
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instance, all of the tabs in a modern web browser run in different processes but share the same
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overall browser configuration settings. If you add a new bookmark in one tab, it would be tedious to
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have to add that bookmark manually to all other open tabs. Similarly, it would be a waste of system
|
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resources for all of those processes to have duplicate copies of the browser source code.</p>
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<p>As another example of why you might need to break the isolation guarantees of processes, consider a
|
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printer queue. While the kernel itself is responsible for controlling and accessing the printer,
|
||
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there are certain devoted system processes that provide the user with an interface to work with.
|
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With this process, you can find out if the printer is low on toner, what documents are queued up to
|
||
|
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be printed, and what printer errors might be occurring. This queue is running in a separate process.
|
||
|
|
When you want to print the document in your word processor, the data must be transferred from one
|
||
|
|
process to another.</p>
|
||
|
|
<p>This chapter focuses on the mechanics and uses of <a class="reference internal" href="Glossary.html#term-interprocess-communication"><span class="xref std std-term">interprocess communication</span></a> (IPC). IPC
|
||
|
|
allows two or more processes to exchange data while maintaining most of the guarantees of isolation.
|
||
|
|
Some IPC exchanges are transient and are established only at the time the data is needed; once the
|
||
|
|
transfer is complete, the IPC connection is terminated and the processes return to complete
|
||
|
|
isolation from one another. Other IPC exchanges involve a persistent connection that can last for
|
||
|
|
long durations, even when the two processes are not explicitly communicating. In this case, since
|
||
|
|
these are distinct processes, they retain some isolation guarantees; if one of the processes
|
||
|
|
crashes, the other is unlikely to be affected, unless the crash actually affects the shared IPC
|
||
|
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connection. Our goal is to examine the different techniques that can be used and when each technique
|
||
|
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is most appropriate.</p>
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</div>
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<div class="container">
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<div class="mt-4 container center">
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«  <a id="prevmod1" href="Extended2Processes.html">2.8. Extended Example: Listing Files with Processes</a>
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  ::  
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||
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<a class="uplink" href="index.html">Contents</a>
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  ::  
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<a id="nextmod1" href="IPCModels.html">3.2. IPC Models</a>  »
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