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 appli-
	 cation 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 implementation 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 2 MB
	   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
", 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("
");
	   printf("%sStack size 	 = 0x%x (%d) bytes
",
		   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:
");
	   display_thread_attributes(pthread_self(), "	");

	   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]
", pname);
	   fprintf(stderr, "		-a means program should allocate stack
");
	   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
");

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

	   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

", 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:
");
	       display_stack_related_attributes(attrp, "	");
	       printf("
");
	   }

	   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

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       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2017-09-15						     PTHREAD_GETATTR_NP(3)