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

       pthread_getattr_np - get attributes of created thread

       #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.

       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

       * 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

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

       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.

       This function is available in glibc since version 2.2.3.

       For   an   explanation   of   the  terms  used  in  this  section,  see

       |Interface            | Attribute     | Value   |
       |pthread_getattr_np() | Thread safety | MT-Safe |

       This function is a nonstandard GNU extension; hence  the  suffix  "_np"
       (nonportable) in the name.

       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
           $ ./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

           $ ./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("%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");

       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),
                   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;

       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");

           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() */

       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)

       This page is part of release 4.15 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

Linux                             2017-09-15             PTHREAD_GETATTR_NP(3)
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