pthread_getattr_np(3) — Linux manual page


pthread_getattr_np(3)   Library Functions Manual   pthread_getattr_np(3)

NAME         top

       pthread_getattr_np - get attributes of created thread

LIBRARY         top

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS         top

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

       int pthread_getattr_np(pthread_t thread, pthread_attr_t *attr);

DESCRIPTION         top

       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 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         top

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

ERRORS         top

       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

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ pthread_getattr_np()                │ Thread safety │ MT-Safe │

STANDARDS         top

       GNU; hence the suffix "_np" (nonportable) in the name.

HISTORY         top

       glibc 2.2.3.

EXAMPLES         top

       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

       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 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 <err.h>
       #include <errno.h>
       #include <pthread.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       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)
               errc(EXIT_FAILURE, s, "pthread_attr_getguardsize");
           printf("%sGuard size          = %zu bytes\n", prefix, guard_size);

           s = pthread_attr_getstack(attr, &stack_addr, &stack_size);
           if (s != 0)
               errc(EXIT_FAILURE, 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          = %#zx (%zu) 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)
               errc(EXIT_FAILURE, s, "pthread_getattr_np");

           display_stack_related_attributes(&attr, prefix);

           s = pthread_attr_destroy(&attr);
           if (s != 0)
               errc(EXIT_FAILURE, 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;
           size_t 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 != -1 || guard_size > 0) {
               ret_attrp = attrp;

               s = pthread_attr_init(attrp);
               if (s != 0)
                   errc(EXIT_FAILURE, s, "pthread_attr_init");

           if (stack_size != -1) {
               if (!allocate_stack) {
                   s = pthread_attr_setstacksize(attrp, stack_size);
                   if (s != 0)
                       errc(EXIT_FAILURE, s, "pthread_attr_setstacksize");
               } else {
                   s = posix_memalign(&stack_addr, sysconf(_SC_PAGESIZE),
                   if (s != 0)
                       errc(EXIT_FAILURE, 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)
                       errc(EXIT_FAILURE, s, "pthread_attr_setstacksize");

           if (guard_size != -1) {
               s = pthread_attr_setguardsize(attrp, guard_size);
               if (s != 0)
                   errc(EXIT_FAILURE, 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)
               errc(EXIT_FAILURE, s, "pthread_create");

           if (attrp != NULL) {
               s = pthread_attr_destroy(attrp);
               if (s != 0)
                   errc(EXIT_FAILURE, s, "pthread_attr_destroy");

           pause();    /* Terminates when other thread calls exit() */

SEE ALSO         top

       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)

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Linux man-pages 6.9.1          2024-06-15          pthread_getattr_np(3)

Pages that refer to this page: pthread_attr_init(3)pthread_attr_setguardsize(3)pthread_create(3)