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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
     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  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_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.

VERSIONS

     This function is available in glibc since version 2.2.3.

ATTRIBUTES

     For   an   explanation   of   the  terms  used  in  this  section,  see
     attributes(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
     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  <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  initial-
     ize
                                                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() */ }