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
       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).

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

       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 attributes(7).

       │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

           $ 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          = %zu 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          = %#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)
               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;
           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 >= 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 5.11 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                              2021-03-22              PTHREAD_GETATTR_NP(3)