Linux Manual Pages

Free Software * Books

Source Code

Free Media

Linux

PTHREAD_ATTR_INIT

HOME

PTHREAD_ATTR_INIT

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

NAME

pthread_attr_init, pthread_attr_destroy − initialize and destroy thread attributes object

SYNOPSIS

#include <pthread.h>

int pthread_attr_init(pthread_attr_t *attr);
int pthread_attr_destroy(pthread_attr_t *attr);

Compile and link with −pthread.

DESCRIPTION

The pthread_attr_init() function initializes the thread attributes object pointed to by attr with default attribute values. After this call, individual attributes of the object can be set using various related functions (listed under SEE ALSO), and then the object can be used in one or more pthread_create(3) calls that create threads.

Calling pthread_attr_init() on a thread attributes object that has already been initialized results in undefined behavior.

When a thread attributes object is no longer required, it should be destroyed using the pthread_attr_destroy() function. Destroying a thread attributes object has no effect on threads that were created using that object.

Once a thread attributes object has been destroyed, it can be reinitialized using pthread_attr_init(). Any other use of a destroyed thread attributes object has undefined results.

RETURN VALUE

On success, these functions return 0; on error, they return a nonzero error number.

ERRORS

POSIX.1-2001 documents an ENOMEM error for pthread_attr_init(); on Linux these functions always succeed (but portable and future-proof applications should nevertheless handle a possible error return).

CONFORMING TO

POSIX.1-2001.

NOTES

The pthread_attr_t type should be treated as opaque: any access to the object other than via pthreads functions is nonportable and produces undefined results.

EXAMPLE

The program below optionally makes use of pthread_attr_init() and various related functions to initialize a thread attributes object that is used to create a single thread. Once created, the thread uses the pthread_getattr_np(3) function (a nonstandard GNU extension) to retrieve the thread’s attributes, and then displays those attributes.

If the program is run with no command-line argument, then it passes NULL as the attr argument of pthread_create(3), so that the thread is created with default attributes. Running the program on Linux/x86-32 with the NPTL threading implementation, we see the following:

$ ulimit −s # No stack imit ==> default stack size is 2MB
unlimited
$ ./a.out
Thread attributes:
Detach state = PTHREAD_CREATE_JOINABLE
Scope = PTHREAD_SCOPE_SYSTEM
Inherit scheduler = PTHREAD_INHERIT_SCHED
Scheduling policy = SCHED_OTHER
Scheduling priority = 0
Guard size = 4096 bytes
Stack address = 0x40196000
Stack size = 0x201000 bytes

When we supply a stack size as a command-line argument, the program initializes a thread attributes object, sets various attributes in that object, and passes a pointer to the object in the call to pthread_create(3). Running the program on Linux/x86-32 with the NPTL threading implementation, we see the following:

$ ./a.out 0x3000000
posix_memalign() allocated at 0x40197000
Thread attributes:
Detach state = PTHREAD_CREATE_DETACHED
Scope = PTHREAD_SCOPE_SYSTEM
Inherit scheduler = PTHREAD_EXPLICIT_SCHED
Scheduling policy = SCHED_OTHER
Scheduling priority = 0
Guard size = 0 bytes
Stack address = 0x40197000
Stack size = 0x3000000 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_pthread_attr(pthread_attr_t *attr, char *prefix)
{
int s, i;
size_t v;
void *stkaddr;
struct sched_param sp;

s = pthread_attr_getdetachstate(attr, &i);
if (s != 0)
handle_error_en(s, "pthread_attr_getdetachstate");
printf("%sDetach state = %s\n", prefix,
(i == PTHREAD_CREATE_DETACHED) ? "PTHREAD_CREATE_DETACHED" :
(i == PTHREAD_CREATE_JOINABLE) ? "PTHREAD_CREATE_JOINABLE" :
"???");

s = pthread_attr_getscope(attr, &i);
if (s != 0)
handle_error_en(s, "pthread_attr_getscope");
printf("%sScope = %s\n", prefix,
(i == PTHREAD_SCOPE_SYSTEM) ? "PTHREAD_SCOPE_SYSTEM" :
(i == PTHREAD_SCOPE_PROCESS) ? "PTHREAD_SCOPE_PROCESS" :
"???");

s = pthread_attr_getinheritsched(attr, &i);
if (s != 0)
handle_error_en(s, "pthread_attr_getinheritsched");
printf("%sInherit scheduler = %s\n", prefix,
(i == PTHREAD_INHERIT_SCHED) ? "PTHREAD_INHERIT_SCHED" :
(i == PTHREAD_EXPLICIT_SCHED) ? "PTHREAD_EXPLICIT_SCHED" :
"???");

s = pthread_attr_getschedpolicy(attr, &i);
if (s != 0)
handle_error_en(s, "pthread_attr_getschedpolicy");
printf("%sScheduling policy = %s\n", prefix,
(i == SCHED_OTHER) ? "SCHED_OTHER" :
(i == SCHED_FIFO) ? "SCHED_FIFO" :
(i == SCHED_RR) ? "SCHED_RR" :
"???");

s = pthread_attr_getschedparam(attr, &sp);
if (s != 0)
handle_error_en(s, "pthread_attr_getschedparam");
printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);

s = pthread_attr_getguardsize(attr, &v);
if (s != 0)
handle_error_en(s, "pthread_attr_getguardsize");
printf("%sGuard size = %d bytes\n", prefix, v);

s = pthread_attr_getstack(attr, &stkaddr, &v);
if (s != 0)
handle_error_en(s, "pthread_attr_getstack");
printf("%sStack address = %p\n", prefix, stkaddr);
printf("%sStack size = 0x%x bytes\n", prefix, v);
}

static void *
thread_start(void *arg)
{
int s;
pthread_attr_t gattr;

/* pthread_getattr_np() is a non−standard GNU extension that
retrieves the attributes of the thread specified in its
first argument */

s = pthread_getattr_np(pthread_self(), &gattr);
if (s != 0)
handle_error_en(s, "pthread_getattr_np");

printf("Thread attributes:\n");
display_pthread_attr(&gattr, "\t");

exit(EXIT_SUCCESS); /* Terminate all threads */
}

int
main(int argc, char *argv[])
{
pthread_t thr;
pthread_attr_t attr;
pthread_attr_t *attrp; /* NULL or &attr */
int s;

attrp = NULL;

/* If a command−line argument was supplied, use it to set the
stack−size attribute and set a few other thread attributes,
and set attrp pointing to thread attributes object */

if (argc > 1) {
int stack_size;
void *sp;

attrp = &attr;

s = pthread_attr_init(&attr);
if (s != 0)
handle_error_en(s, "pthread_attr_init");

s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
if (s != 0)
handle_error_en(s, "pthread_attr_setdetachstate");

s = pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);
if (s != 0)
handle_error_en(s, "pthread_attr_setinheritsched");

stack_size = strtoul(argv[1], NULL, 0);

s = posix_memalign(&sp, sysconf(_SC_PAGESIZE), stack_size);
if (s != 0)
handle_error_en(s, "posix_memalign");

printf("posix_memalign() allocated at %p\n", sp);

s = pthread_attr_setstack(&attr, sp, stack_size);
if (s != 0)
handle_error_en(s, "pthread_attr_setstack");
}

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.