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href="https://be.wikipedia.org/wiki/%D0%91%D0%B0%D1%80%E2%80%99%D0%B5%D1%80%D0%BD%D0%B0%D1%8F_%D1%81%D1%96%D0%BD%D1%85%D1%80%D0%B0%D0%BD%D1%96%D0%B7%D0%B0%D1%86%D1%8B%D1%8F" title="Бар’ерная сінхранізацыя – Belarusian" lang="be" hreflang="be" data-title="Бар’ерная сінхранізацыя" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target">Беларуская</a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Barrera_(inform%C3%A1tica)" title="Barrera (informática) – Spanish" lang="es" hreflang="es" data-title="Barrera (informática)" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target">Español</a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%85%D8%A7%D9%86%D8%B9_%D9%87%D9%85%DA%AF%D8%A7%D9%85%E2%80%8C%D8%B3%D8%A7%D8%B2%DB%8C_(%D8%B9%D9%84%D9%88%D9%85_%D8%B1%D8%A7%DB%8C%D8%A7%D9%86%D9%87)" title="مانع همگام‌سازی (علوم رایانه) – Persian" lang="fa" hreflang="fa" data-title="مانع همگام‌سازی (علوم رایانه)" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target">فارسی</a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Barri%C3%A8re_de_synchronisation" title="Barrière de synchronisation – French" lang="fr" hreflang="fr" data-title="Barrière de synchronisation" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target">Français</a></li><li class="interlanguage-link interwiki-sw mw-list-item"><a href="https://sw.wikipedia.org/wiki/Kizingiti_(tarakilishi)" title="Kizingiti (tarakilishi) – Swahili" lang="sw" hreflang="sw" data-title="Kizingiti (tarakilishi)" data-language-autonym="Kiswahili" data-language-local-name="Swahili" class="interlanguage-link-target">Kiswahili</a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%83%90%E3%83%AA%E3%82%A2_(%E8%A8%88%E7%AE%97%E6%A9%9F%E7%A7%91%E5%AD%A6)" title="バリア (計算機科学) – Japanese" lang="ja" hreflang="ja" data-title="バリア (計算機科学)" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target">日本語</a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%91%D0%B0%D1%80%D1%8C%D0%B5%D1%80%D0%BD%D0%B0%D1%8F_%D1%81%D0%B8%D0%BD%D1%85%D1%80%D0%BE%D0%BD%D0%B8%D0%B7%D0%B0%D1%86%D0%B8%D1%8F" title="Барьерная синхронизация – Russian" lang="ru" hreflang="ru" data-title="Барьерная синхронизация" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target">Русский</a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%91%D0%B0%D1%80%27%D1%94%D1%80_(%D0%BF%D1%80%D0%BE%D0%B3%D1%80%D0%B0%D0%BC%D1%83%D0%B2%D0%B0%D0%BD%D0%BD%D1%8F)" title="Бар'єр (програмування) – 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id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Synchronization method in parallel computing</div> In <a href="/wiki/Parallel_computing" title="Parallel computing">parallel computing</a>, a barrier is a type of <a href="/wiki/Synchronization_(computer_science)" title="Synchronization (computer science)">synchronization</a> method.<a href="#cite_note-impl-1">[1]</a> A barrier for a group of threads or processes in the source code means any thread/process must stop at this point and cannot proceed until all other threads/processes reach this barrier.<a href="#cite_note-:3-2">[2]</a> Many collective routines and directive-based parallel languages impose implicit barriers. For example, a parallel do loop in <a href="/wiki/Fortran" title="Fortran">Fortran</a> with <a href="/wiki/OpenMP" title="OpenMP">OpenMP</a> will not be allowed to continue on any thread until the last iteration is completed.[<a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed">citation needed</a>] This is in case the program relies on the result of the loop immediately after its completion. In <a href="/wiki/Message_passing" title="Message passing">message passing</a>, any global communication (such as reduction or scatter) may imply a barrier. In <a href="/wiki/Concurrent_computing" title="Concurrent computing">concurrent computing</a>, a barrier may be in a raised or lowered state. The term latch is sometimes used to refer to a barrier that starts in the raised state and cannot be re-raised once it is in the lowered state. The term count-down latch is sometimes used to refer to a latch that is automatically lowered once a predetermined number of threads/processes have arrived. <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Implementation">Implementation</h2>[<a href="/w/index.php?title=Barrier_(computer_science)&action=edit&section=1" title="Edit section: Implementation">edit</a>]</div> Take an example for thread, known as the thread barrier. The thread barrier needs a variable to keep track of the total number of threads that have entered the barrier.<a href="#cite_note-:0-3">[3]</a> Whenever there are enough threads enter the barrier, it will be lifted. A <a href="/wiki/Synchronization_primitive" class="mw-redirect" title="Synchronization primitive">synchronization primitive</a> like <a href="/wiki/Lock_(computer_science)" title="Lock (computer science)">mutex</a> is also needed when implementing the thread barrier. This thread barrier method is also known as Centralized Barrier as the threads have to wait in front of a "central barrier" until the expected number of threads have reached the barrier before it is lifted. The following C code, which implemented thread barrier by using POSIX Threads will demonstrate this procedure:<a href="#cite_note-impl-1">[1]</a> <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr mw-highlight-lines" dir="ltr"><pre>#include <stdio.h> #include <pthread.h> #define TOTAL_THREADS 2 #define THREAD_BARRIERS_NUMBER 3 #define PTHREAD_BARRIER_ATTR NULL // pthread barrier attribute typedef struct _thread_barrier { int thread_barrier_number; pthread_mutex_t lock; int total_thread; } thread_barrier; thread_barrier barrier; void thread_barrier_init(thread_barrier *barrier, pthread_mutexattr_t *mutex_attr, int thread_barrier_number){ pthread_mutex_init(&(barrier->lock), mutex_attr); barrier->thread_barrier_number = thread_barrier_number; barrier->total_thread = 0;// Init total thread to be 0 } void thread_barrier_wait(thread_barrier *barrier){ if(!pthread_mutex_lock(&(barrier->lock))){ barrier->total_thread += 1; pthread_mutex_unlock(&(barrier->lock)); } while (barrier->total_thread < barrier->thread_barrier_number); if(!pthread_mutex_lock(&(barrier->lock))){ barrier->total_thread -= 1; // Decrease one thread as it has passed the thread barrier pthread_mutex_unlock(&(barrier->lock)); } } void thread_barrier_destroy(thread_barrier *barrier){ pthread_mutex_destroy(&(barrier->lock)); } void *thread_func(void *ptr){ printf("thread id %ld is waiting at the barrier, as not enough %d threads are running ...\n", pthread_self(), THREAD_BARRIERS_NUMBER); thread_barrier_wait(&barrier); printf("The barrier is lifted, thread id %ld is running now\n", pthread_self()); } int main() { pthread_t thread_id[TOTAL_THREADS]; thread_barrier_init(&barrier, PTHREAD_BARRIER_ATTR, THREAD_BARRIERS_NUMBER); for (int i = 0; i < TOTAL_THREADS; i++){ pthread_create(&thread_id[i], NULL, thread_func, NULL); } // As pthread_join() will block the process until all the threads it specified are finished, // and there is not enough thread to wait at the barrier, so this process is blocked for (int i = 0; i < TOTAL_THREADS; i++){ pthread_join(thread_id[i], NULL); } thread_barrier_destroy(&barrier); printf("Thread barrier is lifted\n"); // This line won't be called as TOTAL_THREADS < THREAD_BARRIERS_NUMBER } </pre></div> In this program, the thread barrier is defined as a struct, struct _thread_barrier, which include: <ul><li>total_thread: Total threads in the process</li> <li>thread_barrier_number: Total number of threads expected to enter the thread barrier so that it can be lifted</li> <li>lock: A POSIX thread mutex lock</li></ul> Based on the definition of barrier, we need to implement a function like thread_barrier_wait() in this program which will "monitor" the total number of thread in the program in order to life the barrier. In this program, every thread calls thread_barrier_wait() will be blocked until THREAD_BARRIERS_NUMBER threads reach the thread barrier. The result of that program is:<div class="mw-highlight mw-highlight-lang-output mw-content-ltr" dir="ltr"><pre>thread id <thread_id, e.g 139997337872128> is waiting at the barrier, as not enough 3 threads are running ... thread id <thread_id, e.g 139997329479424> is waiting at the barrier, as not enough 3 threads are running ... // (main process is blocked as not having enough 3 threads) // Line printf("Thread barrier is lifted\n") won't be reached </pre></div>As we can see from the program, there are just only 2 threads are created. Those 2 thread both have <code class="mw-highlight mw-highlight-lang-c mw-content-ltr" style="" dir="ltr">thread_func()</code>, as the thread function handler, which call <code class="mw-highlight mw-highlight-lang-c mw-content-ltr" style="" dir="ltr">thread_barrier_wait(&barrier)</code>, while thread barrier expected 3 threads to call <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">thread_barrier_wait</code> (<code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">THREAD_BARRIERS_NUMBER = 3</code>) in order to be lifted. Change TOTAL_THREADS to 3 and the thread barrier is lifted:<div class="mw-highlight mw-highlight-lang-output mw-content-ltr" dir="ltr"><pre>thread id <thread ID, e.g 140453108946688> is waiting at the barrier, as not enough 3 threads are running ... thread id <thread ID, e.g 140453117339392> is waiting at the barrier, as not enough 3 threads are running ... thread id <thread ID, e.g 140453100553984> is waiting at the barrier, as not enough 3 threads are running ... The barrier is lifted, thread id <thread ID, e.g 140453108946688> is running now The barrier is lifted, thread id <thread ID, e.g 140453117339392> is running now The barrier is lifted, thread id <thread ID, e.g 140453100553984> is running now Thread barrier is lifted </pre></div> <div class="mw-heading mw-heading3"><h3 id="Sense-Reversal_Centralized_Barrier">Sense-Reversal Centralized Barrier</h3>[<a href="/w/index.php?title=Barrier_(computer_science)&action=edit&section=2" title="Edit section: Sense-Reversal Centralized Barrier">edit</a>]</div> Beside decreasing the total thread number by one for every thread successfully passing the thread barrier, thread barrier can use opposite values to mark for every thread state as passing or stopping.<a href="#cite_note-:2-4">[4]</a> For example, thread 1 with state value is 0 means it's stopping at the barrier, thread 2 with state value is 1 means it has passed the barrier, thread 3's state value = 0 means it's stopping at the barrier and so on.<a href="#cite_note-:22-5">[5]</a> This is known as Sense-Reversal.<a href="#cite_note-impl-1">[1]</a> The following C code demonstrates this:<a href="#cite_note-:0-3">[3]</a><a href="#cite_note-:1-6">[6]</a> <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr mw-highlight-lines" dir="ltr"><pre>#include <stdio.h> #include <stdbool.h> #include <pthread.h> #define TOTAL_THREADS 2 #define THREAD_BARRIERS_NUMBER 3 #define PTHREAD_BARRIER_ATTR NULL // pthread barrier attribute typedef struct _thread_barrier { int thread_barrier_number; int total_thread; pthread_mutex_t lock; bool flag; } thread_barrier; thread_barrier barrier; void thread_barrier_init(thread_barrier *barrier, pthread_mutexattr_t *mutex_attr, int thread_barrier_number){ pthread_mutex_init(&(barrier->lock), mutex_attr); barrier->total_thread = 0; barrier->thread_barrier_number = thread_barrier_number; barrier->flag = false; } void thread_barrier_wait(thread_barrier *barrier){ bool local_sense = barrier->flag; if(!pthread_mutex_lock(&(barrier->lock))){ barrier->total_thread += 1; local_sense = !local_sense; if (barrier->total_thread == barrier->thread_barrier_number){ barrier->total_thread = 0; barrier->flag = local_sense; pthread_mutex_unlock(&(barrier->lock)); } else { pthread_mutex_unlock(&(barrier->lock)); while (barrier->flag != local_sense); // wait for flag } } } void thread_barrier_destroy(thread_barrier *barrier){ pthread_mutex_destroy(&(barrier->lock)); } void *thread_func(void *ptr){ printf("thread id %ld is waiting at the barrier, as not enough %d threads are running ...\n", pthread_self(), THREAD_BARRIERS_NUMBER); thread_barrier_wait(&barrier); printf("The barrier is lifted, thread id %ld is running now\n", pthread_self()); } int main() { pthread_t thread_id[TOTAL_THREADS]; thread_barrier_init(&barrier, PTHREAD_BARRIER_ATTR, THREAD_BARRIERS_NUMBER); for (int i = 0; i < TOTAL_THREADS; i++){ pthread_create(&thread_id[i], NULL, thread_func, NULL); } // As pthread_join() will block the process until all the threads it specified are finished, // and there is not enough thread to wait at the barrier, so this process is blocked for (int i = 0; i < TOTAL_THREADS; i++){ pthread_join(thread_id[i], NULL); } thread_barrier_destroy(&barrier); printf("Thread barrier is lifted\n"); // This line won't be called as TOTAL_THREADS < THREAD_BARRIERS_NUMBER } </pre></div>This program has all features similar to the previous Centralized Barrier source code. It just only implements in a different way by using 2 new variables:<a href="#cite_note-impl-1">[1]</a> <ul><li>local_sense: A thread local Boolean variable to check whether THREAD_BARRIERS_NUMBER have arrived at the barrier.</li> <li>flag: A Boolean member of struct _thread_barrier to indicate whether THREAD_BARRIERS_NUMBER have arrived at the barrier</li></ul> When a thread stops at the barrier, local_sense's value is toggled.<a href="#cite_note-impl-1">[1]</a> When there are less than THREAD_BARRIERS_NUMBER threads stopping at the thread barrier, those threads will keep waiting with the condition that the flag member of struct _thread_barrier is not equal to the private <code>local_sense</code> variable. When there are exactly THREAD_BARRIERS_NUMBER threads stopping at the thread barrier, the total thread number is reset to 0, and the flag is set to <code>local_sense</code>. <div class="mw-heading mw-heading3"><h3 id="Combining_Tree_Barrier">Combining Tree Barrier</h3>[<a href="/w/index.php?title=Barrier_(computer_science)&action=edit&section=3" title="Edit section: Combining Tree Barrier">edit</a>]</div> The potential problem with the Centralized Barrier is that due to all the threads repeatedly accessing the global variable for pass/stop, the communication traffic is rather high, which decreases the <a href="/wiki/Scalability_testing" title="Scalability testing">scalability</a>. This problem can be resolved by regrouping the threads and using multi-level barrier, e.g. Combining Tree Barrier. Also hardware implementations may have the advantage of higher <a href="/wiki/Scalability_testing" title="Scalability testing">scalability</a>. A Combining Tree Barrier is a hierarchical way of implementing barrier to resolve the <a href="/wiki/Scalability_testing" title="Scalability testing">scalability</a> by avoiding the case that all threads are spinning at the same location.<a href="#cite_note-:2-4">[4]</a> In k-Tree Barrier, all threads are equally divided into subgroups of k threads and a first-round synchronizations are done within these subgroups. Once all subgroups have done their synchronizations, the first thread in each subgroup enters the second level for further synchronization. In the second level, like in the first level, the threads form new subgroups of k threads and synchronize within groups, sending out one thread in each subgroup to next level and so on. Eventually, in the final level there is only one subgroup to be synchronized. After the final-level synchronization, the releasing signal is transmitted to upper levels and all threads get past the barrier.<a href="#cite_note-:1-6">[6]</a><a href="#cite_note-7">[7]</a> <div class="mw-heading mw-heading3"><h3 id="Hardware_Barrier_Implementation">Hardware Barrier Implementation</h3>[<a href="/w/index.php?title=Barrier_(computer_science)&action=edit&section=4" title="Edit section: Hardware Barrier Implementation">edit</a>]</div> The hardware barrier uses hardware to implement the above basic barrier model.<a href="#cite_note-:0-3">[3]</a> The simplest hardware implementation uses dedicated wires to transmit signal to implement barrier. This dedicated wire performs OR/AND operation to act as the pass/block flags and thread counter. For small systems, such a model works and communication speed is not a major concern. In large multiprocessor systems this hardware design can make barrier implementation have high latency. The network connection among processors is one implementation to lower the latency, which is analogous to Combining Tree Barrier.<a href="#cite_note-8">[8]</a> <div class="mw-heading mw-heading2"><h2 id="POSIX_Thread_barrier_functions">POSIX Thread barrier functions</h2>[<a href="/w/index.php?title=Barrier_(computer_science)&action=edit&section=5" title="Edit section: POSIX Thread barrier functions">edit</a>]</div> POSIX Threads standard directly supports thread barrier functions which can be used to block the specified threads or the whole process at the barrier until other threads to reach that barrier.<a href="#cite_note-:3-2">[2]</a> 3 main API supports by POSIX to implement thread barriers are: <dl><dt><code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_init()</code></dt> <dd>Init the thread barrier with the number of threads needed to wait at the barrier in order to lift it<a href="#cite_note-:4-9">[9]</a></dd> <dt><code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_destroy()</code></dt> <dd>Destroy the thread barrier to release back the resource<a href="#cite_note-:4-9">[9]</a></dd> <dt><code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_wait()</code></dt> <dd>Calling this function will block the current thread until the number of threads specified by <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_init()</code> call <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_wait()</code> to lift the barrier.<a href="#cite_note-10">[10]</a></dd></dl> The following example (implemented in <a href="/wiki/C_(programming_language)" title="C (programming language)">C</a> with pthread API) will use thread barrier to block all the threads of the main process and therefore block the whole process:<div class="mw-highlight mw-highlight-lang-c mw-content-ltr mw-highlight-lines" dir="ltr"><pre>#include <stdio.h> #include <pthread.h> #define TOTAL_THREADS 2 #define THREAD_BARRIERS_NUMBER 3 #define PTHREAD_BARRIER_ATTR NULL // pthread barrier attribute pthread_barrier_t barrier; void *thread_func(void *ptr){ printf("Waiting at the barrier as not enough %d threads are running ...\n", THREAD_BARRIERS_NUMBER); pthread_barrier_wait(&barrier); printf("The barrier is lifted, thread id %ld is running now\n", pthread_self()); } int main() { pthread_t thread_id[TOTAL_THREADS]; pthread_barrier_init(&barrier, PTHREAD_BARRIER_ATTR, THREAD_BARRIERS_NUMBER); for (int i = 0; i < TOTAL_THREADS; i++){ pthread_create(&thread_id[i], NULL, thread_func, NULL); } // As pthread_join() will block the process until all the threads it specifies are finished, // and there is not enough thread to wait at the barrier, so this process is blocked for (int i = 0; i < TOTAL_THREADS; i++){ pthread_join(thread_id[i], NULL); } pthread_barrier_destroy(&barrier); printf("Thread barrier is lifted\n"); // This line won't be called as TOTAL_THREADS < THREAD_BARRIERS_NUMBER } </pre></div>The result of that source code is:<div class="mw-highlight mw-highlight-lang-output mw-content-ltr" dir="ltr"><pre>Waiting at the barrier as not enough 3 threads are running ... Waiting at the barrier as not enough 3 threads are running ... // (main process is blocked as not having enough 3 threads) // Line printf("Thread barrier is lifted\n") won't be reached </pre></div>As we can see from the source code, there are just only two threads are created. Those 2 thread both have thread_func(), as the thread function handler, which call <code class="mw-highlight mw-highlight-lang-c mw-content-ltr" style="" dir="ltr">pthread_barrier_wait(&barrier)</code>, while thread barrier expected 3 threads to call <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_wait</code> (<code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">THREAD_BARRIERS_NUMBER = 3</code>) in order to be lifted. Change TOTAL_THREADS to 3 and the thread barrier is lifted:<div class="mw-highlight mw-highlight-lang-output mw-content-ltr" dir="ltr"><pre>Waiting at the barrier as not enough 3 threads are running ... Waiting at the barrier as not enough 3 threads are running ... Waiting at the barrier as not enough 3 threads are running ... The barrier is lifted, thread id 140643372406528 is running now The barrier is lifted, thread id 140643380799232 is running now The barrier is lifted, thread id 140643389191936 is running now Thread barrier is lifted </pre></div>As main() is treated as a thread, i.e the "main" thread of the process,<a href="#cite_note-11">[11]</a> calling <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_wait()</code> inside <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">main()</code> will block the whole process until other threads reach the barrier. The following example will use thread barrier, with <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_wait()</code> inside <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">main()</code>, to block the process/main thread for 5 seconds as waiting the 2 "newly created" thread to reach the thread barrier: <div class="mw-highlight mw-highlight-lang-c mw-content-ltr mw-highlight-lines" dir="ltr"><pre>#define TOTAL_THREADS 2 #define THREAD_BARRIERS_NUMBER 3 #define PTHREAD_BARRIER_ATTR NULL // pthread barrier attribute pthread_barrier_t barrier; void *thread_func(void *ptr){ printf("Waiting at the barrier as not enough %d threads are running ...\n", THREAD_BARRIERS_NUMBER); sleep(5); pthread_barrier_wait(&barrier); printf("The barrier is lifted, thread id %ld is running now\n", pthread_self()); } int main() { pthread_t thread_id[TOTAL_THREADS]; pthread_barrier_init(&barrier, PTHREAD_BARRIER_ATTR, THREAD_BARRIERS_NUMBER); for (int i = 0; i < TOTAL_THREADS; i++){ pthread_create(&thread_id[i], NULL, thread_func, NULL); } pthread_barrier_wait(&barrier); printf("Thread barrier is lifted\n"); // This line won't be called as TOTAL_THREADS < THREAD_BARRIERS_NUMBER pthread_barrier_destroy(&barrier); } </pre></div>This example doesn't use <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_join()</code> to wait for 2 "newly created" threads to complete. It calls <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">pthread_barrier_wait()</code> inside <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">main()</code>, in order to block the main thread, so that the process will be blocked until 2 threads finish its operation after 5 seconds wait (line 9 - <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">sleep(5)</code>). <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2>[<a href="/w/index.php?title=Barrier_(computer_science)&action=edit&section=6" title="Edit section: See also">edit</a>]</div> <ul><li><a href="/wiki/Fork%E2%80%93join_model" title="Fork–join model">Fork–join model</a></li> <li><a href="/wiki/Rendezvous_(Plan_9)" title="Rendezvous (Plan 9)">Rendezvous (Plan 9)</a></li> <li><a href="/wiki/Memory_barrier" title="Memory barrier">Memory barrier</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2>[<a href="/w/index.php?title=Barrier_(computer_science)&action=edit&section=7" title="Edit section: References">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.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}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-impl-1">^ <a href="#cite_ref-impl_1-0">a</a> <a href="#cite_ref-impl_1-1">b</a> <a href="#cite_ref-impl_1-2">c</a> <a href="#cite_ref-impl_1-3">d</a> <a href="#cite_ref-impl_1-4">e</a> <style data-mw-deduplicate="TemplateStyles:r1238218222">.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("//upload.wikimedia.org/wikipedia/commons/6/65/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("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/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}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://15418.courses.cs.cmu.edu/spring2013/article/43">"Implementing Barriers"</a>. 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Springer Berlin Heidelberg. pp. <a rel="nofollow" class="external text" href="https://archive.org/details/evolvingopenmpag00mlle/page/n49">42</a>–52. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2F978-3-642-02303-3_4">10.1007/978-3-642-02303-3_4</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9783642022845" title="Special:BookSources/9783642022845"><bdi>9783642022845</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Evolving+OpenMP+in+an+Age+of+Extreme+Parallelism&rft.series=Lecture+Notes+in+Computer+Science&rft.pages=42-52&rft.pub=Springer+Berlin+Heidelberg&rft.date=2009-06-03&rft_id=info%3Adoi%2F10.1007%2F978-3-642-02303-3_4&rft.isbn=9783642022845&rft.aulast=Nanjegowda&rft.aufirst=Ramachandra&rft.au=Hernandez%2C+Oscar&rft.au=Chapman%2C+Barbara&rft.au=Jin%2C+Haoqiang+H.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fevolvingopenmpag00mlle&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABarrier+%28computer+science%29" class="Z3988"> </li> <li id="cite_note-7"><a href="#cite_ref-7">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFNikolopoulosPapatheodorou1999" class="citation book cs1">Nikolopoulos, Dimitrios S.; Papatheodorou, Theodore S. (1999-01-01). "A quantitative architectural evaluation of synchronization algorithms and disciplines on ccNUMA systems". <a rel="nofollow" class="external text" href="https://web.archive.org/web/20170725025227/http://pure.qub.ac.uk/portal/en/publications/a-quantitative-evaluation-of-synchronization-algorithms-and-disciplines-on-ccnuma-systems-the-case-of-the-sgi-origin2000(2b9278d2-85fc-4ce9-96ed-725524379f9a).html">Proceedings of the 13th international conference on Supercomputing</a>. ICS '99. New York, NY, USA: ACM. pp. 319–328. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1145%2F305138.305209">10.1145/305138.305209</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1581131642" title="Special:BookSources/978-1581131642"><bdi>978-1581131642</bdi></a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:6097544">6097544</a>. Archived from <a rel="nofollow" class="external text" href="https://pure.qub.ac.uk/portal/en/publications/a-quantitative-evaluation-of-synchronization-algorithms-and-disciplines-on-ccnuma-systems-the-case-of-the-sgi-origin2000(2b9278d2-85fc-4ce9-96ed-725524379f9a).html">the original</a> on 2017-07-25. Retrieved 2019-01-18.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=A+quantitative+architectural+evaluation+of+synchronization+algorithms+and+disciplines+on+ccNUMA+systems&rft.btitle=Proceedings+of+the+13th+international+conference+on+Supercomputing&rft.place=New+York%2C+NY%2C+USA&rft.series=ICS+%2799&rft.pages=319-328&rft.pub=ACM&rft.date=1999-01-01&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A6097544%23id-name%3DS2CID&rft_id=info%3Adoi%2F10.1145%2F305138.305209&rft.isbn=978-1581131642&rft.aulast=Nikolopoulos&rft.aufirst=Dimitrios+S.&rft.au=Papatheodorou%2C+Theodore+S.&rft_id=https%3A%2F%2Fpure.qub.ac.uk%2Fportal%2Fen%2Fpublications%2Fa-quantitative-evaluation-of-synchronization-algorithms-and-disciplines-on-ccnuma-systems-the-case-of-the-sgi-origin2000%282b9278d2-85fc-4ce9-96ed-725524379f9a%29.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABarrier+%28computer+science%29" class="Z3988"> </li> <li id="cite_note-8"><a href="#cite_ref-8">^</a> N.R. Adiga, et al. An Overview of the BlueGene/L Supercomputer. Proceedings of the Conference on High Performance Networking and Computing, 2002. </li> <li id="cite_note-:4-9">^ <a href="#cite_ref-:4_9-0">a</a> <a href="#cite_ref-:4_9-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://linux.die.net/man/3/pthread_barrier_init">"pthread_barrier_init(), pthread_barrier_destroy()"</a>. Linux man page. Retrieved 2024-03-16.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Linux+man+page&rft.atitle=pthread_barrier_init%28%29%2C+pthread_barrier_destroy%28%29&rft_id=https%3A%2F%2Flinux.die.net%2Fman%2F3%2Fpthread_barrier_init&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABarrier+%28computer+science%29" class="Z3988"> </li> <li id="cite_note-10"><a href="#cite_ref-10">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://linux.die.net/man/3/pthread_barrier_wait">"pthread_barrier_wait()"</a>. Linux man page. Retrieved 2024-03-16.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Linux+man+page&rft.atitle=pthread_barrier_wait%28%29&rft_id=https%3A%2F%2Flinux.die.net%2Fman%2F3%2Fpthread_barrier_wait&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABarrier+%28computer+science%29" class="Z3988"> </li> <li id="cite_note-11"><a href="#cite_ref-11">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://stackoverflow.com/questions/52758132/how-to-get-number-of-processes-and-threads-in-a-c-program">"How to get number of processes and threads in a C program?"</a>. <a href="/wiki/Stackoverflow" class="mw-redirect" title="Stackoverflow">stackoverflow</a>. Retrieved 2024-03-16.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=stackoverflow&rft.atitle=How+to+get+number+of+processes+and+threads+in+a+C+program%3F&rft_id=https%3A%2F%2Fstackoverflow.com%2Fquestions%2F52758132%2Fhow-to-get-number-of-processes-and-threads-in-a-c-program&rfr_id=info%3Asid%2Fen.wikipedia.org%3ABarrier+%28computer+science%29" class="Z3988"> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2>[<a href="/w/index.php?title=Barrier_(computer_science)&action=edit&section=8" title="Edit section: External links">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://blogs.sourceallies.com/2012/03/parallel-programming-with-barrier-synchronization/">"Parallel Programming with Barrier Synchronization"</a>. sourceallies.com. 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class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Parallel_computing" title="Template:Parallel computing"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Parallel_computing" title="Template talk:Parallel computing"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Parallel_computing" title="Special:EditPage/Template:Parallel computing"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Parallel_computing" style="font-size:114%;margin:0 4em"><a href="/wiki/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="/wiki/Distributed_computing" title="Distributed computing">Distributed computing</a></li> <li><a href="/wiki/Parallel_computing" title="Parallel computing">Parallel computing</a></li> <li><a href="/wiki/Massively_parallel" title="Massively parallel">Massively parallel</a></li> <li><a href="/wiki/Cloud_computing" title="Cloud computing">Cloud computing</a></li> <li><a href="/wiki/High-performance_computing" title="High-performance computing">High-performance computing</a></li> <li><a href="/wiki/Multiprocessing" title="Multiprocessing">Multiprocessing</a></li> <li><a href="/wiki/Manycore_processor" title="Manycore processor">Manycore processor</a></li> <li><a href="/wiki/General-purpose_computing_on_graphics_processing_units" title="General-purpose computing on graphics processing units">GPGPU</a></li> <li><a href="/wiki/Computer_network" title="Computer network">Computer network</a></li> <li><a href="/wiki/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"> <ul><li><a href="/wiki/Bit-level_parallelism" title="Bit-level parallelism">Bit</a></li> <li><a href="/wiki/Instruction-level_parallelism" title="Instruction-level parallelism">Instruction</a></li> <li><a href="/wiki/Task_parallelism" title="Task parallelism">Thread</a></li> <li><a href="/wiki/Task_parallelism" title="Task parallelism">Task</a></li> <li><a href="/wiki/Data_parallelism" title="Data parallelism">Data</a></li> <li><a href="/wiki/Memory-level_parallelism" title="Memory-level parallelism">Memory</a></li> <li><a href="/wiki/Loop-level_parallelism" title="Loop-level parallelism">Loop</a></li> <li><a href="/wiki/Pipeline_(computing)" title="Pipeline (computing)">Pipeline</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/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="/wiki/Temporal_multithreading" title="Temporal multithreading">Temporal</a></li> <li><a href="/wiki/Simultaneous_multithreading" title="Simultaneous multithreading">Simultaneous</a> (SMT)</li> <li><a href="/wiki/Simultaneous_and_heterogeneous_multithreading" title="Simultaneous and heterogeneous multithreading">Simultaneous and heterogenous</a></li> <li><a href="/wiki/Speculative_multithreading" title="Speculative multithreading">Speculative</a> (SpMT)</li> <li><a href="/wiki/Preemption_(computing)" title="Preemption (computing)">Preemptive</a></li> <li><a href="/wiki/Computer_multitasking#Cooperative_multitasking" title="Computer multitasking">Cooperative</a></li> <li><a href="/wiki/Bulldozer_(microarchitecture)#Bulldozer_core" title="Bulldozer (microarchitecture)">Clustered multi-thread</a> (CMT)</li> <li><a href="/wiki/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="/wiki/Parallel_RAM" title="Parallel RAM">PRAM model</a></li> <li><a href="/wiki/Parallel_external_memory" title="Parallel external memory">PEM model</a></li> <li><a href="/wiki/Analysis_of_parallel_algorithms" title="Analysis of parallel algorithms">Analysis of parallel algorithms</a></li> <li><a href="/wiki/Amdahl%27s_law" title="Amdahl's law">Amdahl's law</a></li> <li><a href="/wiki/Gustafson%27s_law" title="Gustafson's law">Gustafson's law</a></li> <li><a href="/wiki/Cost_efficiency" title="Cost efficiency">Cost efficiency</a></li> <li><a href="/wiki/Karp%E2%80%93Flatt_metric" title="Karp–Flatt metric">Karp–Flatt metric</a></li> <li><a href="/wiki/Parallel_slowdown" title="Parallel slowdown">Slowdown</a></li> <li><a href="/wiki/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="/wiki/Process_(computing)" title="Process (computing)">Process</a></li> <li><a href="/wiki/Thread_(computing)" title="Thread (computing)">Thread</a></li> <li><a href="/wiki/Fiber_(computer_science)" title="Fiber (computer science)">Fiber</a></li> <li><a href="/wiki/Instruction_window" title="Instruction window">Instruction window</a></li> <li><a href="/wiki/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="/wiki/Multiprocessing" title="Multiprocessing">Multiprocessing</a></li> <li><a href="/wiki/Memory_coherence" title="Memory coherence">Memory coherence</a></li> <li><a href="/wiki/Cache_coherence" title="Cache coherence">Cache coherence</a></li> <li><a href="/wiki/Cache_invalidation" title="Cache invalidation">Cache invalidation</a></li> <li><a class="mw-selflink selflink">Barrier</a></li> <li><a href="/wiki/Synchronization_(computer_science)" title="Synchronization (computer science)">Synchronization</a></li> <li><a href="/wiki/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="/wiki/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="/wiki/Stream_processing" title="Stream processing">Stream processing</a></li> <li><a href="/wiki/Dataflow_programming" title="Dataflow programming">Dataflow programming</a></li> <li><a href="/wiki/Parallel_programming_model" title="Parallel programming model">Models</a> <ul><li><a href="/wiki/Implicit_parallelism" title="Implicit parallelism">Implicit parallelism</a></li> <li><a href="/wiki/Explicit_parallelism" title="Explicit parallelism">Explicit parallelism</a></li> <li><a href="/wiki/Concurrency_(computer_science)" title="Concurrency (computer science)">Concurrency</a></li></ul></li> <li><a href="/wiki/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="/wiki/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="/wiki/Flynn%27s_taxonomy" title="Flynn's taxonomy">Flynn's taxonomy</a> <ul><li><a href="/wiki/Single_instruction,_single_data" title="Single instruction, single data">SISD</a></li> <li><a href="/wiki/Single_instruction,_multiple_data" title="Single instruction, multiple data">SIMD</a> <ul><li><a href="/wiki/Single_instruction,_multiple_threads" title="Single instruction, multiple threads">Array processing</a> (SIMT)</li> <li><a href="/wiki/Flynn%27s_taxonomy#Pipelined_processor" title="Flynn's taxonomy">Pipelined processing</a></li> <li><a href="/wiki/Flynn%27s_taxonomy#Associative_processor" title="Flynn's taxonomy">Associative processing</a></li></ul></li> <li><a href="/wiki/Multiple_instruction,_single_data" title="Multiple instruction, single data">MISD</a></li> <li><a href="/wiki/Multiple_instruction,_multiple_data" title="Multiple instruction, multiple data">MIMD</a></li></ul></li> <li><a href="/wiki/Dataflow_architecture" title="Dataflow architecture">Dataflow architecture</a></li> <li><a href="/wiki/Instruction_pipelining" title="Instruction pipelining">Pipelined processor</a></li> <li><a href="/wiki/Superscalar_processor" title="Superscalar processor">Superscalar processor</a></li> <li><a href="/wiki/Vector_processor" title="Vector processor">Vector processor</a></li> <li><a href="/wiki/Multiprocessing" title="Multiprocessing">Multiprocessor</a> <ul><li><a href="/wiki/Symmetric_multiprocessing" title="Symmetric multiprocessing">symmetric</a></li> <li><a href="/wiki/Asymmetric_multiprocessing" title="Asymmetric multiprocessing">asymmetric</a></li></ul></li> <li><a href="/wiki/Semiconductor_memory" title="Semiconductor memory">Memory</a> <ul><li><a href="/wiki/Shared_memory" title="Shared memory">shared</a></li> <li><a href="/wiki/Distributed_memory" title="Distributed memory">distributed</a></li> <li><a href="/wiki/Distributed_shared_memory" title="Distributed shared memory">distributed shared</a></li> <li><a href="/wiki/Uniform_memory_access" title="Uniform memory access">UMA</a></li> <li><a href="/wiki/Non-uniform_memory_access" title="Non-uniform memory access">NUMA</a></li> <li><a href="/wiki/Cache-only_memory_architecture" title="Cache-only memory architecture">COMA</a></li></ul></li> <li><a href="/wiki/Massively_parallel" title="Massively parallel">Massively parallel</a> computer</li> <li><a href="/wiki/Computer_cluster" title="Computer cluster">Computer cluster</a> <ul><li><a href="/wiki/Beowulf_cluster" title="Beowulf cluster">Beowulf cluster</a></li></ul></li> <li><a href="/wiki/Grid_computing" title="Grid computing">Grid computer</a></li> <li><a href="/wiki/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="/wiki/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="/wiki/Ateji_PX" title="Ateji PX">Ateji PX</a></li> <li><a href="/wiki/Boost_(C%2B%2B_libraries)" title="Boost (C++ libraries)">Boost</a></li> <li><a href="/wiki/Chapel_(programming_language)" title="Chapel (programming language)">Chapel</a></li> <li><a href="/wiki/HPX" title="HPX">HPX</a></li> <li><a href="/wiki/Charm%2B%2B" title="Charm++">Charm++</a></li> <li><a href="/wiki/Cilk" title="Cilk">Cilk</a></li> <li><a href="/wiki/Coarray_Fortran" title="Coarray Fortran">Coarray Fortran</a></li> <li><a href="/wiki/CUDA" title="CUDA">CUDA</a></li> <li><a href="/wiki/Dryad_(programming)" title="Dryad (programming)">Dryad</a></li> <li><a href="/wiki/C%2B%2B_AMP" title="C++ AMP">C++ AMP</a></li> <li><a href="/wiki/Global_Arrays" title="Global Arrays">Global Arrays</a></li> <li><a href="/wiki/GPUOpen" title="GPUOpen">GPUOpen</a></li> <li><a href="/wiki/Message_Passing_Interface" title="Message Passing Interface">MPI</a></li> <li><a href="/wiki/OpenMP" title="OpenMP">OpenMP</a></li> <li><a href="/wiki/OpenCL" title="OpenCL">OpenCL</a></li> <li><a href="/wiki/OpenHMPP" title="OpenHMPP">OpenHMPP</a></li> <li><a href="/wiki/OpenACC" title="OpenACC">OpenACC</a></li> <li><a href="/wiki/Parallel_Extensions" title="Parallel Extensions">Parallel Extensions</a></li> <li><a href="/wiki/Parallel_Virtual_Machine" title="Parallel Virtual Machine">PVM</a></li> <li><a href="/wiki/Pthreads" title="Pthreads">pthreads</a></li> <li><a href="/wiki/RaftLib" title="RaftLib">RaftLib</a></li> <li><a href="/wiki/ROCm" title="ROCm">ROCm</a></li> <li><a href="/wiki/Unified_Parallel_C" title="Unified Parallel C">UPC</a></li> <li><a href="/wiki/Threading_Building_Blocks" title="Threading Building Blocks">TBB</a></li> <li><a href="/wiki/ZPL_(programming_language)" class="mw-redirect" title="ZPL (programming language)">ZPL</a></li></ul> </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="/wiki/Automatic_parallelization" title="Automatic parallelization">Automatic parallelization</a></li> <li><a href="/wiki/Deadlock_(computer_science)" title="Deadlock (computer science)">Deadlock</a></li> <li><a href="/wiki/Deterministic_algorithm" title="Deterministic algorithm">Deterministic algorithm</a></li> <li><a href="/wiki/Embarrassingly_parallel" title="Embarrassingly parallel">Embarrassingly parallel</a></li> <li><a href="/wiki/Parallel_slowdown" title="Parallel slowdown">Parallel slowdown</a></li> <li><a href="/wiki/Race_condition" title="Race condition">Race condition</a></li> <li><a href="/wiki/Software_lockout" title="Software lockout">Software lockout</a></li> <li><a href="/wiki/Scalability" title="Scalability">Scalability</a></li> <li><a href="/wiki/Starvation_(computer_science)" title="Starvation (computer science)">Starvation</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><img alt="" 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