pthreads

<h2 id="contents">Contents</h2>
<p>pthreads defines a set of <a href="/facts/C_(programming_language)/Ky2No763">C</a> programming language <a href="/facts/Data_type/fcx5hgVL">types</a>, <a href="/facts/Function_(computer_science)/9vFJrg0A">functions</a> and constants. It is implemented with a pthread.h header and a thread <a href="/facts/Library_(computing)/xRzL3P7q">library</a>.
</p><p>There are around 100 threads procedures, all prefixed pthread_ and they can be categorized into five groups:
</p>
<ul><li>Thread management – creating, joining threads etc.</li>
<li><a href="/facts/Mutex/e3a9gnJT">Mutexes</a></li>
<li><a href="/facts/Condition_variable/g2zfRatV">Condition variables</a></li>
<li><a href="/facts/Synchronization_(computer_science)/n7ID76uM">Synchronization</a> between threads using <a href="/facts/Readers%25E2%2580%2593writer_lock/1zXdg5a7">read write locks</a> and <a href="/facts/Barrier_(computer_science)/DUdsRXEP">barriers</a></li>
<li><a href="/facts/Spinlock/KHsCgjk5">Spinlocks</a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></li></ul>
<p>The POSIX <a href="/facts/Semaphore_(programming)/BrE1W4Je">semaphore</a> API works with POSIX threads but is not part of the threads standard, having been defined in the <i>POSIX.1b, Real-time extensions (IEEE Std 1003.1b-1993)</i> standard. Consequently, the semaphore procedures are prefixed by sem_ instead of pthread_.
</p>
<h2 id="example">Example</h2>
<p>An example illustrating the use of pthreads in C:
</p>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <pthread.h>
#include <unistd.h>

#define NUM_THREADS 5

void *perform_work(void *arguments){
  int index = *((int *)arguments);
  int sleep_time = 1 + rand() % NUM_THREADS;
  printf("Thread %d: Started.\n", index);
  printf("Thread %d: Will be sleeping for %d seconds.\n", index, sleep_time);
  sleep(sleep_time);
  printf("Thread %d: Ended.\n", index);
  return NULL;
}

int main(void) {
  pthread_t threads[NUM_THREADS];
  int thread_args[NUM_THREADS];
  int i;
  int result_code;
  
  //create all threads one by one
  for (i = 0; i < NUM_THREADS; i++) {
    printf("In main: Creating thread %d.\n", i);
    thread_args[i] = i;
    result_code = pthread_create(&threads[i], NULL, perform_work, &thread_args[i]);
    assert(!result_code);
  }

printf("In main: All threads are created.\n");

//wait for each thread to complete
  for (i = 0; i < NUM_THREADS; i++) {
    result_code = pthread_join(threads[i], NULL);
    assert(!result_code);
    printf("In main: Thread %d has ended.\n", i);
  }

printf("Main program has ended.\n");
  return 0;
}

<p>This program creates five threads, each executing the function <i>perform_work</i> that prints the unique number of this thread to standard output.  If a programmer wanted the threads to communicate with each other, this would require defining a variable outside of the scope of any of the functions, making it a <a href="/facts/Global_variable/XWF9zC08">global variable</a>. This program can be compiled using the <a href="/facts/GNU_Compiler_Collection/t07jh01k">gcc</a> compiler with the following command:
</p>
gcc pthreads_demo.c -pthread -o pthreads_demo

<p>Here is one of the many possible outputs from running this program.
</p>
In main: Creating thread 0.
In main: Creating thread 1.
In main: Creating thread 2.
In main: Creating thread 3.
Thread 0: Started.
In main: Creating thread 4.
Thread 3: Started.
Thread 2: Started.
Thread 0: Will be sleeping for 3 seconds.
Thread 1: Started.
Thread 1: Will be sleeping for 5 seconds.
Thread 2: Will be sleeping for 4 seconds.
Thread 4: Started.
Thread 4: Will be sleeping for 1 seconds.
In main: All threads are created.
Thread 3: Will be sleeping for 4 seconds.
Thread 4: Ended.
Thread 0: Ended.
In main: Thread 0 has ended.
Thread 2: Ended.
Thread 3: Ended.
Thread 1: Ended.
In main: Thread 1 has ended.
In main: Thread 2 has ended.
In main: Thread 3 has ended.
In main: Thread 4 has ended.
Main program has ended.

<h2 id="posix-threads-for-windows">POSIX Threads for Windows</h2>
<p>Windows does not support the pthreads standard natively, therefore the Pthreads4w project seeks to provide a portable and open-source <a href="/facts/Wrapper_library/b61otW6r">wrapper</a> implementation. It can also be used to port <a href="/facts/Unix/0pNL2seI">Unix</a> software (which uses pthreads) with little or no modification to the Windows platform.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> Pthreads4w version 3.0.0<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> or later, released under the Apache Public License v2.0, is compatible with 64-bit or 32-bit Windows systems. Version 2.11.0,<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> released under the LGPLv3 license, is also 64-bit or 32-bit compatible.
</p><p>The <a href="/facts/Mingw-w64/MAMPHY9g">Mingw-w64</a> project also contains a wrapper implementation of 'pthreads, winpthreads, which tries to use more native system calls than the Pthreads4w project.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a>
</p><p><a href="/facts/Interix/aHJ5LEu8">Interix</a> environment subsystem available in the <a href="/facts/Windows_Services_for_UNIX/GnDjKTeh">Windows Services for UNIX/Subsystem for UNIX-based Applications</a> package provides a native port of the pthreads API, i.e. not mapped on Win32 API but built directly on the operating system <a href="/facts/Syscall/NW44AFJr">syscall</a> interface.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a>
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Runtime_system/YmCuC4xP">Runtime system</a></li>
<li><a href="/facts/OpenMP/69IpI80o">OpenMP</a></li>
<li><a href="/facts/Cilk/nIftzSWW">Cilk</a>/<a href="/facts/Cilk_Plus/nIftzSWW">Cilk Plus</a></li>
<li><a href="/facts/Threading_Building_Blocks/6DChhaHg">Threading Building Blocks</a> (TBB)</li>
<li><a href="/facts/Native_POSIX_Thread_Library/Lzy6AGgo">Native POSIX Thread Library</a> (NPTL)</li>
<li><a href="/facts/DCEThreads/l9Dh5JXK">DCEThreads</a></li>
<li><a href="/facts/Clone_(Linux_system_call)/M1jtvaT4">clone (Linux system call)</a></li>
<li><a href="/facts/Spurious_wakeup/8nLjMp7h">Spurious wakeup</a></li>
<li><a href="/facts/Thread-local_storage/BPDI8VDU">Thread-local storage</a></li>
<li><a href="/facts/GNU_Portable_Threads/A3fd81Is">GNU Portable Threads</a></li>
<li><a href="/facts/Grand_Central_Dispatch/sAImWKG0">Grand Central Dispatch</a> (Apple's thread library)</li>
<li><a href="/facts/Beginthread/4BfNF9T0">Beginthread</a> (a subroutine within Windows for creating a new thread and Unix thread)</li>
<li><a href="/facts/State_Threads/PmBdEpyN">State Threads</a>, an event driven approach to threading</li></ul>

<h2 id="further-reading">Further reading</h2>
<ul><li>David R. Butenhof (1997). <i>Programming with POSIX Threads</i>. Addison-Wesley. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-201-63392-4.</li>
<li>Bradford Nichols; Dick Buttlar; Jacqueline Proulx Farell (September 1996). <a href="https://archive.org/details/pthreadsprogramm00nich"><i>Pthreads Programming</i></a>. O'Reilly & Associates. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-56592-115-3.</li>
<li>Charles J. Northrup (1996-01-25). <a href="https://archive.org/details/programmingwithu0000nort"><i>Programming with UNIX Threads</i></a>. John Wiley & Sons. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-471-13751-1.</li>
<li>Kay A. Robbins & Steven Robbins (2003). <a href="https://archive.org/details/unixsystemsprogr0000robb"><i>UNIX Systems Programming</i></a>. Prentice-Hall. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-13-042411-2.</li></ul>
<h2 id="external-links">External links</h2>
<ul><li><a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/pthread.h.html">The Open Group Base Specifications Issue 7, IEEE Std 1003.1</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"libc/bionic/pthread.c - platform/bionic - Git at Google". android.googlesource.com. <a href="https://android.googlesource.com/platform/bionic/+/10ce969/libc/bionic/pthread.c" target="_blank">https://android.googlesource.com/platform/bionic/+/10ce969/libc/bionic/pthread.c</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Pthread Win-32: Level of standards conformance". 2006-12-22. Archived from the original on 2010-06-11. Retrieved 2010-08-29. <a href="https://web.archive.org/web/20100611172430/http://sources.redhat.com/pthreads-win32/conformance.html" target="_blank">https://web.archive.org/web/20100611172430/http://sources.redhat.com/pthreads-win32/conformance.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"pthread.h(0p) — Linux manual page". Retrieved 18 December 2022. <a href="https://www.man7.org/linux/man-pages/man0/pthread.h.0p.html" target="_blank">https://www.man7.org/linux/man-pages/man0/pthread.h.0p.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Hart, Johnson M. (2004-11-21). "Experiments with the Open Source Pthreads Library and Some Comments". Archived from the original on 2010-08-30. Retrieved 2010-08-29. <a href="https://web.archive.org/web/20100830235615/http://world.std.com/~jmhart/opensource.htm" target="_blank">https://web.archive.org/web/20100830235615/http://world.std.com/~jmhart/opensource.htm</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>File: pthreads4w-code-v3.0.0.zip – Source for pthreads4w v3.0.0 <a href="https://sourceforge.net/projects/pthreads4w/files/" target="_blank">https://sourceforge.net/projects/pthreads4w/files/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>File: pthreads4w-code-v2.11.0.zip – Source for pthreads4w v2.11.0 <a href="https://sourceforge.net/projects/pthreads4w/files/" target="_blank">https://sourceforge.net/projects/pthreads4w/files/</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>see http://locklessinc.com/articles/pthreads_on_windows which is where it was originally derived from <a href="http://locklessinc.com/articles/pthreads_on_windows" target="_blank">http://locklessinc.com/articles/pthreads_on_windows</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>"Chapter 1: Introduction to Windows Services for UNIX 3.5". 5 December 2007. <a href="https://technet.microsoft.com/en-us/library/bb496994.aspx" target="_blank">https://technet.microsoft.com/en-us/library/bb496994.aspx</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
</ol>

pthreads open-in-new

pthreads