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



NAME
       pthread_getattr_np - get attributes of created thread

SYNOPSIS
       #define _GNU_SOURCE	       /* See feature_test_macros(7) */
       #include <pthread.h>

       int pthread_getattr_np(pthread_t thread, pthread_attr_t *attr);

       Compile and link with -pthread.

DESCRIPTION
       The  pthread_getattr_np()  function  initializes	 the thread attributes
       object referred to by attr so that it contains actual attribute	values
       describing the running thread thread.

       The  returned  attribute	 values	 may  differ  from  the	 corresponding
       attribute values passed in the attr object that was used to create  the
       thread	using	pthread_create(3).    In   particular,	the  following
       attributes may differ:

       * the detach state, since a joinable thread may	have  detached	itself
	 after creation;

       * the  stack  size,  which  the	implementation may align to a suitable
	 boundary.

       * and the guard size, which the implementation may round	 upward	 to  a
	 multiple  of  the  page  size,	 or  ignore (i.e., treat as 0), if the
	 application is allocating its own stack.

       Furthermore, if the stack address attribute was not set in  the	thread
       attributes  object  used to create the thread, then the returned thread
       attributes object will report the actual stack address that the	imple-
       mentation selected for the thread.

       When  the  thread attributes object returned by pthread_getattr_np() is
       no    longer    required,    it	  should    be	   destroyed	 using
       pthread_attr_destroy(3).

RETURN VALUE
       On  success,  this  function  returns 0; on error, it returns a nonzero
       error number.

ERRORS
       ENOMEM Insufficient memory.

       In  addition,   if   thread   refers   to   the	 main	thread,	  then
       pthread_getattr_np() can fail because of errors from various underlying
       calls: fopen(3), if /proc/self/maps can't be opened; and	 getrlimit(2),
       if the RLIMIT_STACK resource limit is not supported.

VERSIONS
       This function is available in glibc since version 2.2.3.

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

       +---------------------+---------------+---------+
       |Interface	     | Attribute     | Value   |
       +---------------------+---------------+---------+
       |pthread_getattr_np() | Thread safety | MT-Safe |
       +---------------------+---------------+---------+
CONFORMING TO
       This function is a nonstandard GNU extension; hence  the	 suffix	 "_np"
       (nonportable) in the name.

EXAMPLE
       The  program  below  demonstrates the use of pthread_getattr_np().  The
       program	creates	 a  thread  that  then	uses  pthread_getattr_np()  to
       retrieve	 and  display  its  guard  size, stack address, and stack size
       attributes.  Command-line arguments can be used to set these attributes
       to  values  other than the default when creating the thread.  The shell
       sessions below demonstrate the use of the program.

       In the first run, on an	x86-32	system,	 a  thread  is	created	 using
       default attributes:

	   $ ulimit -s	    # No stack limit ==> default stack size is 2MB
	   unlimited
	   $ ./a.out
	   Attributes of created thread:
		   Guard size	       = 4096 bytes
		   Stack address       = 0x40196000 (EOS = 0x40397000)
		   Stack size	       = 0x201000 (2101248) bytes

       In  the	following run, we see that if a guard size is specified, it is
       rounded up to the next multiple of the system page size (4096 bytes  on
       x86-32):

	   $ ./a.out -g 4097
	   Thread attributes object after initializations:
		   Guard size	       = 4097 bytes
		   Stack address       = (nil)
		   Stack size	       = 0x0 (0) bytes

	   Attributes of created thread:
		   Guard size	       = 8192 bytes
		   Stack address       = 0x40196000 (EOS = 0x40397000)
		   Stack size	       = 0x201000 (2101248) bytes

       In the last run, the program manually allocates a stack for the thread.
       In this case, the guard size attribute is ignored.

	   $ ./a.out -g 4096 -s 0x8000 -a
	   Allocated thread stack at 0x804d000

	   Thread attributes object after initializations:
		   Guard size	       = 4096 bytes
		   Stack address       = 0x804d000 (EOS = 0x8055000)
		   Stack size	       = 0x8000 (32768) bytes

	   Attributes of created thread:
		   Guard size	       = 0 bytes
		   Stack address       = 0x804d000 (EOS = 0x8055000)
		   Stack size	       = 0x8000 (32768) 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_stack_related_attributes(pthread_attr_t *attr, char *prefix)
       {
	   int s;
	   size_t stack_size, guard_size;
	   void *stack_addr;

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

	   s = pthread_attr_getstack(attr, &stack_addr, &stack_size);
	   if (s != 0)
	       handle_error_en(s, "pthread_attr_getstack");
	   printf("%sStack address	 = %p", prefix, stack_addr);
	   if (stack_size > 0)
	       printf(" (EOS = %p)", (char *) stack_addr + stack_size);
	   printf("\n");
	   printf("%sStack size		 = 0x%x (%d) bytes\n",
		   prefix, stack_size, stack_size);
       }

       static void
       display_thread_attributes(pthread_t thread, char *prefix)
       {
	   int s;
	   pthread_attr_t attr;

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

	   display_stack_related_attributes(&attr, prefix);

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

       static void *	       /* Start function for thread we create */
       thread_start(void *arg)
       {
	   printf("Attributes of created thread:\n");
	   display_thread_attributes(pthread_self(), "\t");

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

       static void
       usage(char *pname, char *msg)
       {
	   if (msg != NULL)
	       fputs(msg, stderr);
	   fprintf(stderr, "Usage: %s [-s stack-size [-a]]"
		   " [-g guard-size]\n", pname);
	   fprintf(stderr, "\t\t-a means program should allocate stack\n");
	   exit(EXIT_FAILURE);
       }

       static pthread_attr_t *	 /* Get thread attributes from command line */
       get_thread_attributes_from_cl(int argc, char *argv[],
				     pthread_attr_t *attrp)
       {
	   int s, opt, allocate_stack;
	   long stack_size, guard_size;
		   void *stack_addr;
	   pthread_attr_t *ret_attrp = NULL;   /* Set to attrp if we initialize
						  a thread attributes object */
	   allocate_stack = 0;
	   stack_size = -1;
	   guard_size = -1;

	   while ((opt = getopt(argc, argv, "ag:s:")) != -1) {
	       switch (opt) {
	       case 'a':   allocate_stack = 1;			   break;
	       case 'g':   guard_size = strtoul(optarg, NULL, 0);  break;
	       case 's':   stack_size = strtoul(optarg, NULL, 0);  break;
	       default:	   usage(argv[0], NULL);
	       }
	   }

	   if (allocate_stack && stack_size == -1)
	       usage(argv[0], "Specifying -a without -s makes no sense\n");

	   if (argc > optind)
	       usage(argv[0], "Extraneous command-line arguments\n");

	   if (stack_size >= 0 || guard_size > 0) {
	       ret_attrp = attrp;

	       s = pthread_attr_init(attrp);
	       if (s != 0)
		   handle_error_en(s, "pthread_attr_init");
	   }

	   if (stack_size >= 0) {
	       if (!allocate_stack) {
		   s = pthread_attr_setstacksize(attrp, stack_size);
		   if (s != 0)
		       handle_error_en(s, "pthread_attr_setstacksize");
	       } else {
		   s = posix_memalign(&stack_addr, sysconf(_SC_PAGESIZE),
				      stack_size);
		   if (s != 0)
		       handle_error_en(s, "posix_memalign");
		   printf("Allocated thread stack at %p\n\n", stack_addr);

		   s = pthread_attr_setstack(attrp, stack_addr, stack_size);
		   if (s != 0)
		       handle_error_en(s, "pthread_attr_setstacksize");
	       }
	   }

	   if (guard_size >= 0) {
	       s = pthread_attr_setguardsize(attrp, guard_size);
	       if (s != 0)
		   handle_error_en(s, "pthread_attr_setstacksize");
	   }

	   return ret_attrp;
       }

       int
       main(int argc, char *argv[])
       {
	   int s;
	   pthread_t thr;
	   pthread_attr_t attr;
	   pthread_attr_t *attrp = NULL;    /* Set to &attr if we initialize
					       a thread attributes object */

	   attrp = get_thread_attributes_from_cl(argc, argv, &attr);

	   if (attrp != NULL) {
	       printf("Thread attributes object after initializations:\n");
	       display_stack_related_attributes(attrp, "\t");
	       printf("\n");
	   }

	   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_getaffinity_np(3), pthread_attr_getdetachstate(3),
       pthread_attr_getguardsize(3), pthread_attr_getinheritsched(3),
       pthread_attr_getschedparam(3), pthread_attr_getschedpolicy(3),
       pthread_attr_getscope(3), pthread_attr_getstack(3),
       pthread_attr_getstackaddr(3), pthread_attr_getstacksize(3),
       pthread_attr_init(3), pthread_create(3), pthreads(7)

COLOPHON
       This page is part of release 4.10 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				  2015-07-23		 PTHREAD_GETATTR_NP(3)