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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 particu-
       lar, 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 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.

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 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					    2010-09-10			    PTHREAD_GETATTR_NP(3)
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