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PTHREAD_ATTR_INIT(3)       Linux Programmer's Manual      PTHREAD_ATTR_INIT(3)

NAME
       pthread_attr_init, pthread_attr_destroy - initialize and destroy thread
       attributes object

SYNOPSIS
       #include <pthread.h>

       int pthread_attr_init(pthread_attr_t *attr);
       int pthread_attr_destroy(pthread_attr_t *attr);

       Compile and link with -pthread.

DESCRIPTION
       The pthread_attr_init() function initializes the thread attributes  ob-
       ject  pointed  to  by  attr  with default attribute values.  After this
       call, individual attributes of the object can be set using various  re-
       lated  functions  (listed  under  SEE ALSO), and then the object can be
       used in one or more pthread_create(3) calls that create threads.

       Calling pthread_attr_init() on a thread attributes object that has  al-
       ready been initialized results in undefined behavior.

       When a thread attributes object is no longer required, it should be de-
       stroyed using the pthread_attr_destroy() function.  Destroying a thread
       attributes object has no effect on threads that were created using that
       object.

       Once a thread attributes object has been destroyed, it  can  be  reini-
       tialized  using  pthread_attr_init().   Any  other  use  of a destroyed
       thread attributes object has undefined results.

RETURN VALUE
       On success, these functions return 0; on error, they return  a  nonzero
       error number.

ERRORS
       POSIX.1  documents  an  ENOMEM  error for pthread_attr_init(); on Linux
       these functions always succeed (but portable and future-proof  applica-
       tions should nevertheless handle a possible error return).

ATTRIBUTES
       For  an  explanation  of  the  terms  used  in  this  section,  see at-
       tributes(7).

       +-----------------------+---------------+---------+
       |Interface              | Attribute     | Value   |
       +-----------------------+---------------+---------+
       |pthread_attr_init(),   | Thread safety | MT-Safe |
       |pthread_attr_destroy() |               |         |
       +-----------------------+---------------+---------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

NOTES
       The  pthread_attr_t type should be treated as opaque: any access to the
       object other than via pthreads functions is  nonportable  and  produces
       undefined results.

EXAMPLE
       The program below optionally makes use of pthread_attr_init() and vari-
       ous related functions to initialize a thread attributes object that  is
       used  to  create  a  single  thread.  Once created, the thread uses the
       pthread_getattr_np(3) function (a nonstandard  GNU  extension)  to  re-
       trieve the thread's attributes, and then displays those attributes.

       If  the  program  is  run with no command-line argument, then it passes
       NULL as the attr argument of pthread_create(3), so that the  thread  is
       created  with  default attributes.  Running the program on Linux/x86-32
       with the NPTL threading implementation, we see the following:

           $ ulimit -s       # No stack limit ==> default stack size is 2 MB
           unlimited
           $ ./a.out
           Thread attributes:
                   Detach state        = PTHREAD_CREATE_JOINABLE
                   Scope               = PTHREAD_SCOPE_SYSTEM
                   Inherit scheduler   = PTHREAD_INHERIT_SCHED
                   Scheduling policy   = SCHED_OTHER
                   Scheduling priority = 0
                   Guard size          = 4096 bytes
                   Stack address       = 0x40196000
                   Stack size          = 0x201000 bytes

       When we supply a stack size as a  command-line  argument,  the  program
       initializes a thread attributes object, sets various attributes in that
       object, and passes a pointer to the object in the call to  pthread_cre-
       ate(3).   Running  the  program on Linux/x86-32 with the NPTL threading
       implementation, we see the following:

           $ ./a.out 0x3000000
           posix_memalign() allocated at 0x40197000
           Thread attributes:
                   Detach state        = PTHREAD_CREATE_DETACHED
                   Scope               = PTHREAD_SCOPE_SYSTEM
                   Inherit scheduler   = PTHREAD_EXPLICIT_SCHED
                   Scheduling policy   = SCHED_OTHER
                   Scheduling priority = 0
                   Guard size          = 0 bytes
                   Stack address       = 0x40197000
                   Stack size          = 0x3000000 bytes

   Program source

       #define _GNU_SOURCE     /* To get pthread_getattr_np() declaration */
       #include <pthread.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <errno.h>

       #define handle_error_en(en, msg) \
               do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

       static void
       display_pthread_attr(pthread_attr_t *attr, char *prefix)
       {
           int s, i;
           size_t v;
           void *stkaddr;
           struct sched_param sp;

           s = pthread_attr_getdetachstate(attr, &i);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getdetachstate");
           printf("%sDetach state        = %s\n", prefix,
                   (i == PTHREAD_CREATE_DETACHED) ? "PTHREAD_CREATE_DETACHED" :
                   (i == PTHREAD_CREATE_JOINABLE) ? "PTHREAD_CREATE_JOINABLE" :
                   "???");

           s = pthread_attr_getscope(attr, &i);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getscope");
           printf("%sScope               = %s\n", prefix,
                   (i == PTHREAD_SCOPE_SYSTEM)  ? "PTHREAD_SCOPE_SYSTEM" :
                   (i == PTHREAD_SCOPE_PROCESS) ? "PTHREAD_SCOPE_PROCESS" :
                   "???");

           s = pthread_attr_getinheritsched(attr, &i);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getinheritsched");
           printf("%sInherit scheduler   = %s\n", prefix,
                   (i == PTHREAD_INHERIT_SCHED)  ? "PTHREAD_INHERIT_SCHED" :
                   (i == PTHREAD_EXPLICIT_SCHED) ? "PTHREAD_EXPLICIT_SCHED" :
                   "???");

           s = pthread_attr_getschedpolicy(attr, &i);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getschedpolicy");
           printf("%sScheduling policy   = %s\n", prefix,
                   (i == SCHED_OTHER) ? "SCHED_OTHER" :
                   (i == SCHED_FIFO)  ? "SCHED_FIFO" :
                   (i == SCHED_RR)    ? "SCHED_RR" :
                   "???");

           s = pthread_attr_getschedparam(attr, &sp);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getschedparam");
           printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);

           s = pthread_attr_getguardsize(attr, &v);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getguardsize");
           printf("%sGuard size          = %zu bytes\n", prefix, v);

           s = pthread_attr_getstack(attr, &stkaddr, &v);
           if (s != 0)
               handle_error_en(s, "pthread_attr_getstack");
           printf("%sStack address       = %p\n", prefix, stkaddr);
           printf("%sStack size          = 0x%zx bytes\n", prefix, v);
       }

       static void *
       thread_start(void *arg)
       {
           int s;
           pthread_attr_t gattr;

           /* pthread_getattr_np() is a non-standard GNU extension that
              retrieves the attributes of the thread specified in its
              first argument */

           s = pthread_getattr_np(pthread_self(), &gattr);
           if (s != 0)
               handle_error_en(s, "pthread_getattr_np");

           printf("Thread attributes:\n");
           display_pthread_attr(&gattr, "\t");

           exit(EXIT_SUCCESS);         /* Terminate all threads */
       }

       int
       main(int argc, char *argv[])
       {
           pthread_t thr;
           pthread_attr_t attr;
           pthread_attr_t *attrp;      /* NULL or &attr */
           int s;

           attrp = NULL;

           /* If a command-line argument was supplied, use it to set the
              stack-size attribute and set a few other thread attributes,
              and set attrp pointing to thread attributes object */

           if (argc > 1) {
               int stack_size;
               void *sp;

               attrp = &attr;

               s = pthread_attr_init(&attr);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_init");

               s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_setdetachstate");

               s = pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_setinheritsched");

               stack_size = strtoul(argv[1], NULL, 0);

               s = posix_memalign(&sp, sysconf(_SC_PAGESIZE), stack_size);
               if (s != 0)
                   handle_error_en(s, "posix_memalign");

               printf("posix_memalign() allocated at %p\n", sp);

               s = pthread_attr_setstack(&attr, sp, stack_size);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_setstack");
           }

           s = pthread_create(&thr, attrp, &thread_start, NULL);
           if (s != 0)
               handle_error_en(s, "pthread_create");

           if (attrp != NULL) {
               s = pthread_attr_destroy(attrp);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_destroy");
           }

           pause();    /* Terminates when other thread calls exit() */
       }

SEE ALSO
       pthread_attr_setaffinity_np(3), pthread_attr_setdetachstate(3),
       pthread_attr_setguardsize(3), pthread_attr_setinheritsched(3),
       pthread_attr_setschedparam(3), pthread_attr_setschedpolicy(3),
       pthread_attr_setscope(3), pthread_attr_setstack(3),
       pthread_attr_setstackaddr(3), pthread_attr_setstacksize(3),
       pthread_create(3), pthread_getattr_np(3),
       pthread_setattr_default_np(3), pthreads(7)

COLOPHON
       This page is part of release 5.05 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                             2019-03-06              PTHREAD_ATTR_INIT(3)

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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

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