SherbyNet - /page/wikibook/entry.mu

Micron Document

<!DOCTYPE html>

<title>Shared memory</title>

</head>

<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Shared memory</span></span>

</h1>

</header>

/* start https://en.wikipedia.org/ */

.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}

/* end https://en.wikipedia.org/ */

</style><div role="note" class="hatnote navigation-not-searchable">Not to be confused with <a href="Overlay_(programming)" title="Overlay (programming)">Overlay (programming)</a> or <a href="Overlapping_code" class="mw-redirect" title="Overlapping code">Overlapping code</a>.</div>

<p>In <a href="Computer_science" title="Computer science">computer science</a>, <b>shared memory</b> is <a href="Random-access_memory" title="Random-access memory">memory</a> that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Shared memory is an efficient means of passing data between programs. Depending on context, programs may run on a single processor or on multiple separate processors.

</p><p>Using memory for communication inside a single program, e.g. among its multiple <a href="Thread_(computer_science)" class="mw-redirect" title="Thread (computer science)">threads</a>, is also referred to as shared memory.

</p>

<div class="mw-heading mw-heading2"><h2 id="In_hardware">In hardware</h2></div>

<p>In computer hardware, <i>shared memory</i> refers to a (typically large) block of <a href="Random_access_memory" class="mw-redirect" title="Random access memory">random access memory</a> (RAM) that can be accessed by several different <a href="Central_processing_unit" title="Central processing unit">central processing units</a> (CPUs) in a <a href="Multiprocessing" title="Multiprocessing">multiprocessor computer system</a>.

</p><p>Shared memory systems may use:<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

</p>

<ul><li><a href="Uniform_memory_access" title="Uniform memory access">uniform memory access</a> (UMA): all the processors share the physical memory uniformly;</li>

<li><a href="Non-uniform_memory_access" title="Non-uniform memory access">non-uniform memory access</a> (NUMA): memory access time depends on the memory location relative to a processor;</li>

<li><a href="Cache-only_memory_architecture" title="Cache-only memory architecture">cache-only memory architecture</a> (COMA): the local memories for the processors at each node is used as cache instead of as actual main memory.</li></ul>

<p>A shared memory system is relatively easy to program since all processors share a single view of data and the communication between processors can be as fast as memory accesses to the same location. The issue with shared memory systems is that many CPUs need fast access to memory and will likely <a href="Cache_memory" class="mw-redirect" title="Cache memory">cache memory</a>, which has two complications:

</p>

<ul><li>access time degradation: when several processors try to access the same memory location it causes <a href="Resource_contention" title="Resource contention">contention</a>. Trying to access nearby memory locations may cause <a href="False_sharing" title="False sharing">false sharing</a>. Shared memory computers cannot scale very well. Most of them have ten or fewer processors;</li>

<li>lack of data coherence: whenever one cache is updated with information that may be used by other processors, the change needs to be reflected to the other processors, otherwise the different processors will be working with incoherent data. Such <a href="Cache_coherence" title="Cache coherence">cache coherence</a> protocols can, when they work well, provide extremely high-performance access to shared information between multiple processors. On the other hand, they can sometimes become overloaded and become a bottleneck to performance.</li></ul>

<p>Technologies like <a href="Crossbar_switch" title="Crossbar switch">crossbar switches</a>, <a href="Omega_network" title="Omega network">Omega networks</a>, <a href="HyperTransport" title="HyperTransport">HyperTransport</a> or <a href="Front-side_bus" title="Front-side bus">front-side bus</a> can be used to dampen the bottleneck-effects.

</p><p>In case of a <a href="Heterogeneous_System_Architecture" title="Heterogeneous System Architecture">Heterogeneous System Architecture</a> (processor architecture that integrates different types of processors, such as <a href="CPU" class="mw-redirect" title="CPU">CPUs</a> and <a href="GPU" class="mw-redirect" title="GPU">GPUs</a>, with shared memory), the <a href="Memory_management_unit" title="Memory management unit">memory management unit</a> (MMU) of the CPU and the <a href="Input%E2%80%93output_memory_management_unit" title="Input–output memory management unit">input–output memory management unit</a> (IOMMU) of the GPU have to share certain characteristics, like a common address space.

</p><p>The alternatives to shared memory are <a href="Distributed_memory" title="Distributed memory">distributed memory</a> and <a href="Distributed_shared_memory" title="Distributed shared memory">distributed shared memory</a>, each having a similar set of issues.

</p>

<div class="mw-heading mw-heading2"><h2 id="In_software">In software</h2></div>

<p>In computer software, <i>shared memory</i> is either

</p>

<ul><li>a method of <a href="Inter-process_communication" title="Inter-process communication">inter-process communication</a> (IPC), i.e. a way of exchanging data between programs running at the same time. One <a href="Process_(computing)" title="Process (computing)">process</a> will create an area in <a href="Random-access_memory" title="Random-access memory">RAM</a> which other processes can access;</li>

<li>a method of conserving memory space by directing accesses to what would ordinarily be copies of a piece of data to a single instance instead, by using <a href="Virtual_memory" title="Virtual memory">virtual memory</a> mappings or with explicit support of the program in question. This is most often used for <a href="Shared_library" title="Shared library">shared libraries</a> and for <a href="Execute_in_place" title="Execute in place">Execute in place</a> (XIP).</li></ul>

<p>Since both processes can access the shared memory area like regular working memory, this is a very fast way of communication (as opposed to other mechanisms of IPC such as <a href="Named_pipe" title="Named pipe">named pipes</a>, <a href="Unix_domain_socket" title="Unix domain socket">Unix domain sockets</a> or <a href="CORBA" class="mw-redirect" title="CORBA">CORBA</a>). On the other hand, it is less scalable, as for example the communicating processes must be running on the same machine (of other IPC methods, only Internet domain sockets—not Unix domain sockets—can use a <a href="Computer_network" title="Computer network">computer network</a>), and care must be taken to avoid issues if processes sharing memory are running on separate CPUs and the underlying architecture is not <a href="Cache_coherence" title="Cache coherence">cache coherent</a>.

</p><p>IPC by shared memory is used for example to transfer images between the application and the <a href="X_Window_System" title="X Window System">X server</a> on Unix systems, or inside the IStream object returned by CoMarshalInterThreadInterfaceInStream in the COM libraries under <a href="Microsoft_Windows" title="Microsoft Windows">Windows</a>.

</p><p><a href="Library_(computing)#Dynamic_linking" title="Library (computing)">Dynamic libraries</a> are generally held in memory once and mapped to multiple processes, and only pages that had to be customized for the individual process (because a symbol resolved differently there) are duplicated, usually with a mechanism known as <a href="Copy-on-write" title="Copy-on-write">copy-on-write</a> that transparently copies the page when a write is attempted, and then lets the write succeed on the private copy.

</p><p>Compared to multiple address space operating systems,

memory sharing -- especially of sharing procedures or pointer-based structures --

is simpler in <a href="Single_address_space_operating_system" title="Single address space operating system">single address space operating systems</a>.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading3"><h3 id="Support_on_Unix-like_systems">Support on Unix-like systems</h3></div>

<p><a href="POSIX" title="POSIX">POSIX</a> provides a standardized API for using shared memory, <i>POSIX Shared Memory</i>. This uses the function <code>shm_open</code> from sys/mman.h.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> POSIX interprocess communication (part of the POSIX:XSI Extension) includes the shared-memory functions <code>shmat</code>, <code>shmctl</code>, <code>shmdt</code> and <code>shmget</code>.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> Unix System V provides an API for shared memory as well. This uses shmget from sys/shm.h. BSD systems provide "anonymous mapped memory" which can be used by several processes.

</p><p>The shared memory created by <code>shm_open</code> is persistent. It stays in the system until explicitly removed by a process. This has a drawback in that if the process crashes and fails to clean up shared memory it will stay until system shutdown; that limitation is not present in an Android-specific implementation dubbed <code>ashmem</code>.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup>

</p><p>POSIX also provides the <code><a href="Mmap" title="Mmap">mmap</a></code> API for mapping files into memory; a mapping can be shared, allowing the file's contents to be used as shared memory.

</p><p>Linux distributions based on the 2.6 kernel and later offer /dev/shm as shared memory in the form of a <a href="RAM_disk" class="mw-redirect" title="RAM disk">RAM disk</a>, more specifically as a world-writable directory (a directory in which every user of the system can create files) that is stored in memory. Both the <a href="Red_Hat_Linux" title="Red Hat Linux">RedHat</a> and <a href="Debian" title="Debian">Debian</a> based distributions include it by default. Support for this type of RAM disk is completely optional within the kernel <a href="Configuration_file" title="Configuration file">configuration file</a>.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading3"><h3 id="Support_on_Windows">Support on Windows</h3></div>

<p>On Windows, one can use <code>CreateFileMapping</code> and <code>MapViewOfFile</code> functions to map a region of a file into memory in multiple processes.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading3"><h3 id="Cross-platform_support">Cross-platform support</h3></div>

<p>Some C++ libraries provide a portable and object-oriented access to shared memory functionality. For example, <a href="Boost_(C%2B%2B_libraries)" title="Boost (C++ libraries)">Boost</a> contains the Boost.Interprocess C++ Library<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> and <a href="Qt_(framework)" class="mw-redirect" title="Qt (framework)">Qt</a> provides the QSharedMemory class.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading3"><h3 id="Programming_language_support">Programming language support</h3></div>

<p>For programming languages with POSIX bindings (say, C/C++), shared memory regions can be created and accessed by calling the functions provided by the operating system. Other programming languages may have their own ways of using these operating facilities for similar effect. For example, <a href="PHP" title="PHP">PHP</a> provides an <a href="API" title="API">API</a> to create shared memory, similar to <a href="POSIX" title="POSIX">POSIX</a> functions.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup>

</p>

<ul><li><a href="Distributed_memory" title="Distributed memory">Distributed memory</a></li>

<li><a href="Distributed_shared_memory" title="Distributed shared memory">Distributed shared memory</a></li>

<li><a href="Shared_graphics_memory" title="Shared graphics memory">Shared graphics memory</a></li>

<li><a href="Heterogeneous_System_Architecture" title="Heterogeneous System Architecture">Heterogeneous System Architecture</a></li>

<li><a href="Global_variable" title="Global variable">Global variable</a></li>

<li><a href="Nano-threads" title="Nano-threads">Nano-threads</a></li>

<li><a href="Execute_in_place" title="Execute in place">Execute in place</a></li>

<li><a href="Shared_register" title="Shared register">Shared register</a></li>

<li><a href="Shared_snapshot_objects" title="Shared snapshot objects">Shared snapshot objects</a></li>

<li><a href="Von_Neumann_architecture#von_Neumann_bottleneck" title="Von Neumann architecture">Von Neumann Architecture Bottleneck</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

/* start https://en.wikipedia.org/ */

.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}

/* end https://en.wikipedia.org/ */

</style><div class="reflist">

/* start https://en.wikipedia.org/ */

.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("./mw/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("./mw/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("./mw/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("./mw/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}

/* end https://en.wikipedia.org/ */

</style><cite id="CITEREFEl-RewiniAbd-El-Barr2005" class="citation book cs1">El-Rewini, Hesham; Abd-El-Barr, Mostafa (2005). <i>Advanced Computer Architecture and Parallel Processing</i>. Wiley-Interscience. pp. <span class="nowrap">77–</span>80. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-471-46740-3</bdi>.</cite></span>

</li>

Jeffrey S. Chase; Henry M. Levy; Michael J. Feeley; and Edward D. Lazowska.

<a rel="nofollow" class="external text" href="https://homes.cs.washington.edu/~levy/opal/opal-tocs.pdf">"Sharing and Protection in a Single Address Space Operating System"</a>.

1993.

p. 3</span>

</li>

<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.opengroup.org/onlinepubs/007908799/xsh/shm_open.html">Documentation of shm_open</a> from the Single Unix Specification</span>

</li>

<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><cite id="CITEREFRobbinsRobbins2003" class="citation book cs1">Robbins, Kay A.; Robbins, Steven (2003). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/unixsystemsprogr0000robb"><i>Unix systems programming: communication, concurrency, and threads</i></a></span> (2 ed.). Prentice Hall PTR. p. <a rel="nofollow" class="external text" href="https://archive.org/details/unixsystemsprogr0000robb/page/512">512</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-13-042411-2</bdi><span class="reference-accessdate">. Retrieved <span class="nowrap">2011-05-13</span></span>. <q>The POSIX interprocess communication (IPC) is part of the POSIX:XSI Extension and has its origin in Unix System V interprocess communication.</q></cite></span>

</li>

<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.opengroup.org/onlinepubs/007908799/xsh/sysshm.h.html">Shared memory facility</a> from the Single Unix Specification.</span>

</li>

<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://elinux.org/Android_Kernel_Features#ashmem">"Android Kernel Features"</a>. <i>elinux.org</i><span class="reference-accessdate">. Retrieved <span class="nowrap">12 Dec</span> 2022</span>.</cite></span>

</li>

<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><cite id="CITEREFChristoph_RohlandHugh_DickinsKOSAKI_Motohiro" class="citation web cs1">Christoph Rohland; Hugh Dickins; KOSAKI Motohiro. <a rel="nofollow" class="external text" href="https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt">"tmpfs.txt"</a>. <a href="Kernel.org" title="Kernel.org">kernel.org</a><span class="reference-accessdate">. Retrieved <span class="nowrap">2010-03-16</span></span>.</cite></span>

</li>

<li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa366551%28v=vs.85%29.aspx">Creating Named Shared Memory</a> from MSDN.</span>

</li>

<li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.boost.org/doc/libs/1_48_0/doc/html/interprocess.html">Boost.Interprocess C++ Library</a></span>

</li>

<li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://doc.qt.io/archives/qt-4.8/qsharedmemory.html">"QSharedMemory Class Reference"</a>.</cite></span>

</li>

<li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.php.net/manual/en/ref.shmop.php">Shared Memory Functions in PHP-API</a></span>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://www.cs.cf.ac.uk/Dave/C/node27.html">IPC:Shared Memory</a> by Dave Marshall</li>

<li><a rel="nofollow" class="external text" href="http://www.kohala.com/start/unpv22e/unpv22e.chap12.pdf">Shared Memory Introduction</a>, Ch. 12 from book by Richard Stevens "UNIX Network Programming, Volume 2, Second Edition: Interprocess Communications".</li>

<li><a rel="nofollow" class="external text" href="https://github.com/simonhf/sharedhashfile">SharedHashFile</a>, An open source, shared memory hash table.</li></ul>

/* start https://en.wikipedia.org/ */

.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}

/* end https://en.wikipedia.org/ */

</style><style data-mw-deduplicate="TemplateStyles:r1236075235">

/* start https://en.wikipedia.org/ */

.mw-parser-output .navbox{box-sizing:border-box;border:1px solid #a2a9b1;width:100%;clear:both;font-size:88%;text-align:center;padding:1px;margin:1em auto 0}.mw-parser-output .navbox .navbox{margin-top:0}.mw-parser-output .navbox+.navbox,.mw-parser-output .navbox+.navbox-styles+.navbox{margin-top:-1px}.mw-parser-output .navbox-inner,.mw-parser-output .navbox-subgroup{width:100%}.mw-parser-output .navbox-group,.mw-parser-output .navbox-title,.mw-parser-output .navbox-abovebelow{padding:0.25em 1em;line-height:1.5em;text-align:center}.mw-parser-output .navbox-group{white-space:nowrap;text-align:right}.mw-parser-output .navbox,.mw-parser-output .navbox-subgroup{background-color:#fdfdfd}.mw-parser-output .navbox-list{line-height:1.5em;border-color:#fdfdfd}.mw-parser-output .navbox-list-with-group{text-align:left;border-left-width:2px;border-left-style:solid}.mw-parser-output tr+tr>.navbox-abovebelow,.mw-parser-output tr+tr>.navbox-group,.mw-parser-output tr+tr>.navbox-image,.mw-parser-output tr+tr>.navbox-list{border-top:2px solid #fdfdfd}.mw-parser-output .navbox-title{background-color:#ccf}.mw-parser-output .navbox-abovebelow,.mw-parser-output .navbox-group,.mw-parser-output .navbox-subgroup .navbox-title{background-color:#ddf}.mw-parser-output .navbox-subgroup .navbox-group,.mw-parser-output .navbox-subgroup .navbox-abovebelow{background-color:#e6e6ff}.mw-parser-output .navbox-even{background-color:#f7f7f7}.mw-parser-output .navbox-odd{background-color:transparent}.mw-parser-output .navbox .hlist td dl,.mw-parser-output .navbox .hlist td ol,.mw-parser-output .navbox .hlist td ul,.mw-parser-output .navbox td.hlist dl,.mw-parser-output .navbox td.hlist ol,.mw-parser-output .navbox td.hlist ul{padding:0.125em 0}.mw-parser-output .navbox .navbar{display:block;font-size:100%}.mw-parser-output .navbox-title .navbar{float:left;text-align:left;margin-right:0.5em}body.skin--responsive .mw-parser-output .navbox-image img{max-width:none!important}@media print{body.ns-0 .mw-parser-output .navbox{display:none!important}}

/* end https://en.wikipedia.org/ */

</style></div><div role="navigation" class="navbox" aria-labelledby="Inter-process_communication278" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><style data-mw-deduplicate="TemplateStyles:r1239400231">

/* start https://en.wikipedia.org/ */

.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}

/* end https://en.wikipedia.org/ */

</style><div id="Inter-process_communication278" style="font-size:114%;margin:0 4em"><a href="Inter-process_communication" title="Inter-process communication">Inter-process communication</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div><a href="Data" title="Data">Data</a> exchange among <a href="Thread_(computing)" title="Thread (computing)">threads</a> in <a href="Computer_program" title="Computer program">computer programs</a></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Methods</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="Mmap" title="Mmap">Memory-mapped file</a></li>

<li><a href="Message_passing" title="Message passing">Message passing</a></li>

<li><a href="Message_queue" title="Message queue">Message queue and mailbox</a></li>

<li><a href="Named_pipe" title="Named pipe">Named pipe</a></li>

<li><a href="Anonymous_pipe" title="Anonymous pipe">Anonymous pipe</a></li>

<li><a href="Semaphore_(programming)" title="Semaphore (programming)">Semaphore</a></li>

<li><a href="Signal_(IPC)" title="Signal (IPC)">Signal</a></li>

<li>Sockets

<ul><li><a href="Network_socket" title="Network socket">Network</a></li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Communication_protocol" title="Communication protocol">Protocols</a><br>and <a href="Technical_standard" title="Technical standard">standards</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Apple_event" title="Apple event">Apple events</a></li>

<li><a href="Common_Object_Request_Broker_Architecture" title="Common Object Request Broker Architecture">CORBA</a></li>

<li><a href="OpenBinder" title="OpenBinder">OpenBinder</a></li>

<li><a href="POSIX" title="POSIX">POSIX</a> (various methods)</li>

<li><a href="Apache_Thrift" title="Apache Thrift">Thrift</a></li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Library_(computing)" title="Library (computing)">Software libraries</a><br>and <a href="Software_framework" title="Software framework">frameworks</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="Libevent" title="Libevent">libevent</a></li>

<li><a href="SIMPL" title="SIMPL">SIMPL</a></li>

</div></td></tr></tbody></table></div>

<div class="navbox-styles"></div><div role="navigation" class="navbox" aria-labelledby="Parallel_computing346" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Parallel_computing346" style="font-size:114%;margin:0 4em"><a href="Parallel_computing" title="Parallel computing">Parallel computing</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">General</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Distributed_computing" title="Distributed computing">Distributed computing</a></li>

<li><a href="Parallel_computing" title="Parallel computing">Parallel computing</a></li>

<li><a href="Parallel_algorithm" title="Parallel algorithm">Parallel algorithm</a></li>

<li><a href="Massively_parallel" title="Massively parallel">Massively parallel</a></li>

<li><a href="Cloud_computing" title="Cloud computing">Cloud computing</a></li>

<li><a href="High-performance_computing" title="High-performance computing">High-performance computing</a></li>

<li><a href="Multiprocessing" title="Multiprocessing">Multiprocessing</a></li>

<li><a href="Manycore_processor" title="Manycore processor">Manycore processor</a></li>

<li><a href="General-purpose_computing_on_graphics_processing_units" title="General-purpose computing on graphics processing units">GPGPU</a></li>

<li><a href="Computer_network" title="Computer network">Computer network</a></li>

<li><a href="Systolic_array" title="Systolic array">Systolic array</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Levels</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="Instruction-level_parallelism" title="Instruction-level parallelism">Instruction</a></li>

<li><a href="Task_parallelism" title="Task parallelism">Thread</a></li>

<li><a href="Memory-level_parallelism" title="Memory-level parallelism">Memory</a></li>

<li><a href="Pipeline_(computing)" title="Pipeline (computing)">Pipeline</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Multithreading_(computer_architecture)" title="Multithreading (computer architecture)">Multithreading</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Temporal_multithreading" title="Temporal multithreading">Temporal</a></li>

<li><a href="Simultaneous_multithreading" title="Simultaneous multithreading">Simultaneous</a> (SMT)</li>

<li><a href="Simultaneous_and_heterogeneous_multithreading" title="Simultaneous and heterogeneous multithreading">Simultaneous and heterogenous</a></li>

<li><a href="Speculative_multithreading" title="Speculative multithreading">Speculative</a> (SpMT)</li>

<li><a href="Preemption_(computing)" title="Preemption (computing)">Preemptive</a></li>

<li><a href="Computer_multitasking#Cooperative_multitasking" title="Computer multitasking">Cooperative</a></li>

<li><a href="Bulldozer_(microarchitecture)#Bulldozer_core" title="Bulldozer (microarchitecture)">Clustered multi-thread</a> (CMT)</li>

<li><a href="Hardware_scout" title="Hardware scout">Hardware scout</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Theory</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Parallel_RAM" title="Parallel RAM">PRAM model</a></li>

<li><a href="Parallel_external_memory" title="Parallel external memory">PEM model</a></li>

<li><a href="Analysis_of_parallel_algorithms" title="Analysis of parallel algorithms">Analysis of parallel algorithms</a></li>

<li><a href="Amdahl's_law" title="Amdahl's law">Amdahl's law</a></li>

<li><a href="Gustafson's_law" title="Gustafson's law">Gustafson's law</a></li>

<li><a href="Cost_efficiency" title="Cost efficiency">Cost efficiency</a></li>

<li><a href="Karp%E2%80%93Flatt_metric" title="Karp–Flatt metric">Karp–Flatt metric</a></li>

<li><a href="Parallel_slowdown" title="Parallel slowdown">Slowdown</a></li>

<li><a href="Speedup" title="Speedup">Speedup</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Elements</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Process_(computing)" title="Process (computing)">Process</a></li>

<li><a href="Thread_(computing)" title="Thread (computing)">Thread</a></li>

<li><a href="Fiber_(computer_science)" title="Fiber (computer science)">Fiber</a></li>

<li><a href="Instruction_window" title="Instruction window">Instruction window</a></li>

<li><a href="Array_(data_structure)" title="Array (data structure)">Array</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Coordination</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Multiprocessing" title="Multiprocessing">Multiprocessing</a></li>

<li><a href="Memory_coherence" title="Memory coherence">Memory coherence</a></li>

<li><a href="Cache_coherence" title="Cache coherence">Cache coherence</a></li>

<li><a href="Cache_invalidation" title="Cache invalidation">Cache invalidation</a></li>

<li><a href="Barrier_(computer_science)" title="Barrier (computer science)">Barrier</a></li>

<li><a href="Synchronization_(computer_science)" title="Synchronization (computer science)">Synchronization</a></li>

<li><a href="Application_checkpointing" title="Application checkpointing">Application checkpointing</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Computer_programming" title="Computer programming">Programming</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Stream_processing" title="Stream processing">Stream processing</a></li>

<li><a href="Dataflow_programming" title="Dataflow programming">Dataflow programming</a></li>

<li><a href="Parallel_programming_model" title="Parallel programming model">Models</a>

<ul><li><a href="Implicit_parallelism" title="Implicit parallelism">Implicit parallelism</a></li>

<li><a href="Explicit_parallelism" title="Explicit parallelism">Explicit parallelism</a></li>

<li><a href="Concurrency_(computer_science)" title="Concurrency (computer science)">Concurrency</a></li></ul></li>

<li><a href="Non-blocking_algorithm" title="Non-blocking algorithm">Non-blocking algorithm</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Computer_hardware" title="Computer hardware">Hardware</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Flynn's_taxonomy" title="Flynn's taxonomy">Flynn's taxonomy</a>

<ul><li><a href="Single_instruction%2C_multiple_threads" title="Single instruction, multiple threads">Array processing</a> (SIMT)</li>

<li><a href="Flynn's_taxonomy#Pipelined_processor" title="Flynn's taxonomy">Pipelined processing</a></li>

<li><a href="Flynn's_taxonomy#Associative_processor" title="Flynn's taxonomy">Associative processing</a></li></ul></li>

<li><a href="Dataflow_architecture" title="Dataflow architecture">Dataflow architecture</a></li>

<li><a href="Instruction_pipelining" title="Instruction pipelining">Pipelined processor</a></li>

<li><a href="Superscalar_processor" title="Superscalar processor">Superscalar processor</a></li>

<li><a href="Vector_processor" title="Vector processor">Vector processor</a></li>

<li><a href="Multiprocessing" title="Multiprocessing">Multiprocessor</a>

<ul><li><a href="Symmetric_multiprocessing" title="Symmetric multiprocessing">symmetric</a></li>

<li><a href="Asymmetric_multiprocessing" title="Asymmetric multiprocessing">asymmetric</a></li></ul></li>

<li><a href="Semiconductor_memory" title="Semiconductor memory">Memory</a>

<ul>

<li><a href="Distributed_memory" title="Distributed memory">distributed</a></li>

<li><a href="Distributed_shared_memory" title="Distributed shared memory">distributed shared</a></li>

<li><a href="Massively_parallel" title="Massively parallel">Massively parallel</a> computer</li>

<li><a href="Computer_cluster" title="Computer cluster">Computer cluster</a>

<ul><li><a href="Beowulf_cluster" title="Beowulf cluster">Beowulf cluster</a></li></ul></li>

<li><a href="Grid_computing" title="Grid computing">Grid computer</a></li>

<li><a href="Hardware_acceleration" title="Hardware acceleration">Hardware acceleration</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="API" title="API">APIs</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Ateji_PX" title="Ateji PX">Ateji PX</a></li>

<li><a href="Boost_(C%2B%2B_libraries)" title="Boost (C++ libraries)">Boost</a></li>

<li><a href="Chapel_(programming_language)" title="Chapel (programming language)">Chapel</a></li>

<li><a href="Charm%2B%2B" title="Charm++">Charm++</a></li>

<li><a href="Coarray_Fortran" title="Coarray Fortran">Coarray Fortran</a></li>

<li><a href="Dryad_(programming)" title="Dryad (programming)">Dryad</a></li>

<li><a href="Global_Arrays" title="Global Arrays">Global Arrays</a></li>

<li><a href="GPUOpen" title="GPUOpen">GPUOpen</a></li>

<li><a href="OpenMP" title="OpenMP">OpenMP</a></li>

<li><a href="OpenCL" title="OpenCL">OpenCL</a></li>

<li><a href="OpenHMPP" title="OpenHMPP">OpenHMPP</a></li>

<li><a href="OpenACC" title="OpenACC">OpenACC</a></li>

<li><a href="Parallel_Extensions" title="Parallel Extensions">Parallel Extensions</a></li>

<li><a href="Pthreads" title="Pthreads">pthreads</a></li>

<li><a href="RaftLib" title="RaftLib">RaftLib</a></li>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Problems</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Automatic_parallelization" title="Automatic parallelization">Automatic parallelization</a></li>

<li><a href="Deadlock_(computer_science)" title="Deadlock (computer science)">Deadlock</a></li>

<li><a href="Deterministic_algorithm" title="Deterministic algorithm">Deterministic algorithm</a></li>

<li><a href="Embarrassingly_parallel" title="Embarrassingly parallel">Embarrassingly parallel</a></li>

<li><a href="Parallel_slowdown" title="Parallel slowdown">Parallel slowdown</a></li>

<li><a href="Race_condition" title="Race condition">Race condition</a></li>

<li><a href="Software_lockout" title="Software lockout">Software lockout</a></li>

<li><a href="Scalability" title="Scalability">Scalability</a></li>

<li><a href="Starvation_(computer_science)" title="Starvation (computer science)">Starvation</a></li></ul>

</div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div>

<ul><li><span class="noviewer" typeof="mw:File"><span title="Category"></span></span> Category: Parallel computing</li></ul>

</div></td></tr></tbody></table></div>

<div class="navbox-styles"></div><div role="navigation" class="navbox authority-control" aria-label="Navbox390" style="padding:3px"><table class="nowraplinks hlist navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="row" class="navbox-group" style="width:1%">Authority control databases: National </th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"><ul><li><span class="uid"><a rel="nofollow" class="external text" href="https://d-nb.info/gnd/4294156-8">Germany</a></span></li></ul></div></td></tr></tbody></table></div></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-03-02" href="https://en.wikipedia.org/wiki/?title=Shared_memory&oldid=1278494947">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

</div>

</div></div>

</div>

</main>

</div>

</body></html>