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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 ob-
       ject 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 attri-
       bute values passed in the attr object  that  was  used  to  create  the
       thread  using  pthread_create(3).   In  particular,  the  following at-
       tributes 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 ap-
         plication 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_de-
       stroy(3).

RETURN VALUE
       On success, this function returns 0; on error, it returns a nonzero er-
       ror 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 at-
       tributes(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  re-
       trieve  and  display  its guard size, stack address, and stack size at-
       tributes.  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  de-
       fault 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\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 5.05 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                             2019-03-06             PTHREAD_GETATTR_NP(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | EXAMPLE | SEE ALSO | COLOPHON