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
       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	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
       attributes(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
       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 limit ==> 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_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		 = %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%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
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Linux				  2016-12-12		  PTHREAD_ATTR_INIT(3)