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NAME

       pthread_getattr_np - get attributes of created thread

LIBRARY

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS

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

       int pthread_getattr_np(pthread_t thread, pthread_attr_t *attr);

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
       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

       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.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├───────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │pthread_getattr_np()                                           │ Thread safety │ MT-Safe │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

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

HISTORY

       glibc 2.2.3.

EXAMPLES

       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
           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 <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("\n");
           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");
           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;
           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),
                                      stack_size);
                   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;
       }

       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)
               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

       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)