# pthread_getattr_np

## 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).
           ┌──────────────────────────────────────┬───────────────┬─────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├──────────────────────────────────────┼───────────────┼─────────┤
           │ **pthread_getattr_np**()                 │ Thread safety │ MT-Safe │
           └──────────────────────────────────────┴───────────────┴─────────┘
    


## STANDARDS



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


## 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() */
           }
    


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