POSIX Threads

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POSIX Threads, usually referred to as Pthreads, is a POSIX standard for threads. The standard, POSIX.1c, Threads extensions (IEEE Std 1003.1c-1995), defines an API for creating and manipulating threads.

Implementations of the API are available on many Unix-like POSIX-conformant operating systems such as FreeBSD, NetBSD, OpenBSD, GNU/Linux, Mac OS X and Solaris. DR-DOS and Microsoft Windows implementations also exist: within the SFU/SUA subsystem which provides a native implementation of a number of POSIX APIs, and also within third-party packages such as pthreads-w32,[1] which implements pthreads on top of existing Windows API.

Contents[edit]

Pthreads defines a set of C programming language types, functions and constants. It is implemented with a pthread.h header and a thread library.

There are around 100 Pthreads procedures, all prefixed "pthread_" and they can be categorized into four groups:

The POSIX semaphore API works with POSIX threads but is not part of threads standard, having been defined in the POSIX.1b, Real-time extensions (IEEE Std 1003.1b-1993) standard. Consequently the semaphore procedures are prefixed by "sem_" instead of "pthread_".

Example[edit]

An example illustrating the use of Pthreads in C:

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
 
#define NUM_THREADS     5
 
void *task_code(void *argument)
{
   int tid;
 
   tid = *((int *) argument);
   printf("Hello World! It's me, thread %d!\n", tid);
 
   /* optionally: insert more useful stuff here */
 
   return NULL;
}
 
int main(void)
{
   pthread_t threads[NUM_THREADS];
   int thread_args[NUM_THREADS];
   int rc, i;
 
   // create all threads one by one
   for (i=0; i<NUM_THREADS; ++i) {
      thread_args[i] = i;
      printf("In main: creating thread %d\n", i);
      rc = pthread_create(&threads[i], NULL, task_code, (void *) &thread_args[i]);
      assert(0 == rc);
   }
 
   // wait for each thread to complete
   for (i=0; i<NUM_THREADS; ++i) {
      // block until thread i completes
      rc = pthread_join(threads[i], NULL);
      printf("In main: thread %d is complete\n", i);
      assert(0 == rc);
   }
 
   printf("In main: All threads completed successfully\n");
   exit(EXIT_SUCCESS);
}

This program creates five threads, each executing the function task_code 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 global variable.

POSIX Threads for Windows[edit]

Windows does not support the pthreads standard natively, therefore the Pthreads-w32 project seeks to provide a portable and open-source wrapper implementation. It can also be used to port Unix software (which use pthreads) with little or no modification to the Windows platform.[2] With some additional patches the last version 2.8.0 is compatible with 64-bit Windows systems.[3][4][5] 2.9.0 is said to also be 64-bit compatible.[6]

The mingw-w64 project also contains a wrapper implementation of pthreads, winpthreads,[7] which tries to use more native system calls than the Pthreads-w32 project.[8]

Interix environment subsystem available in the Windows Services for UNIX/Subsystem for UNIX-based Applications package provides a native port of the pthreads API, i.e. not mapped on Win32/Win64 API but built directly on the operating system syscall interface.[9]

See also[edit]

References[edit]

Further reading[edit]

  • David R. Butenhof. Programming with POSIX Threads. Addison-Wesley. ISBN 0-201-63392-2. 
  • Bradford Nichols, Dick Buttlar, Jacqueline Proulx Farell. Pthreads Programming. O'Reilly & Associates. ISBN 1-56592-115-1. 
  • Charles J. Northrup. Programming with UNIX Threads. John Wiley & Sons. ISBN 0-471-13751-0. 
  • Kay A. Robbins and Steven Robbins. UNIX Systems Programming. Prentice-Hall. ISBN 0-13-042411-0. 

External links[edit]