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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 object pointed to by
       attr with default attribute values.  After this call, individual attributes of the  object
       can  be  set  using various related 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  already   been
       initialized results in undefined behavior.

       When  a  thread  attributes object is no longer required, it should be destroyed 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 reinitialized 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.1-2001  documents  an ENOMEM error for pthread_attr_init(); on Linux these functions
       always succeed (but portable and future-proof applications should  nevertheless  handle  a
       possible error return).

CONFORMING TO

       POSIX.1-2001.

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  various  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 retrieve 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 imit ==> default stack size is 2MB
           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_create(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          = %d 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%x 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), pthreads(7)

COLOPHON

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       project, and information about reporting bugs, can be found at  http://man7.org/linux/man-
       pages/.