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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 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  initial-
       ized 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  func-
       tions  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 exten-
       sion) 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 argu-
       ment 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
       This page is part of release 3.55 of the Linux man-pages project.  A description of the
       project, and information about reporting bugs, can be found at
       http://www.kernel.org/doc/man-pages/.

Linux					    2008-11-11			     PTHREAD_ATTR_INIT(3)
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