Linux Manual Pages

Free Software * Books

Source Code

Free Media

Linux

PTHREAD_GETATTR_NP

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
VERSIONS
CONFORMING TO
EXAMPLE
SEE ALSO
COLOPHON

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 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.

VERSIONS

This function is available in glibc since version 2.2.3.

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 2MB
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 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),
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() */
}

COLOPHON

This page is part of release 3.69 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 http://www.kernel.org/doc/man−pages/.

Opportunity

Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.

Education

Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.