pthread_attr_init(3) Library Functions Manual pthread_attr_init(3)
NAME
pthread_attr_init, pthread_attr_destroy - initialize and destroy thread
attributes object
LIBRARY
POSIX threads library (libpthread, -lpthread)
SYNOPSIS
#include <pthread.h>
int pthread_attr_init(pthread_attr_t *attr);
int pthread_attr_destroy(pthread_attr_t *attr);
DESCRIPTION
The pthread_attr_init() function initializes the thread attributes ob-
ject 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 al-
ready been initialized results in undefined behavior.
When a thread attributes object is no longer required, it should be de-
stroyed 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 reinitial-
ized using pthread_attr_init(). Any other use of a destroyed thread at-
tributes object has undefined results.
RETURN VALUE
On success, these functions return 0; on error, they return a nonzero
error number.
ERRORS
POSIX.1 documents an ENOMEM error for pthread_attr_init(); on Linux
these functions always succeed (but portable and future-proof applica-
tions should nevertheless handle a possible error return).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│ pthread_attr_init(), │ Thread safety │ MT-Safe │
│ pthread_attr_destroy() │ │ │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
POSIX.1-2008.
HISTORY
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 un-
defined results.
EXAMPLES
The program below optionally makes use of pthread_attr_init() and vari-
ous 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 limit ==> default stack size is 2 MB
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 ini-
tializes a thread attributes object, sets various attributes in that ob-
ject, and passes a pointer to the object in the call to pthread_cre-
ate(3). Running the program on Linux/x86-32 with the NPTL threading im-
plementation, 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 <err.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
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)
errc(EXIT_FAILURE, 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)
errc(EXIT_FAILURE, 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)
errc(EXIT_FAILURE, 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)
errc(EXIT_FAILURE, 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)
errc(EXIT_FAILURE, s, "pthread_attr_getschedparam");
printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);
s = pthread_attr_getguardsize(attr, &v);
if (s != 0)
errc(EXIT_FAILURE, s, "pthread_attr_getguardsize");
printf("%sGuard size = %zu bytes\n", prefix, v);
s = pthread_attr_getstack(attr, &stkaddr, &v);
if (s != 0)
errc(EXIT_FAILURE, s, "pthread_attr_getstack");
printf("%sStack address = %p\n", prefix, stkaddr);
printf("%sStack size = %#zx 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)
errc(EXIT_FAILURE, 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) {
size_t stack_size;
void *sp;
attrp = &attr;
s = pthread_attr_init(&attr);
if (s != 0)
errc(EXIT_FAILURE, s, "pthread_attr_init");
s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
if (s != 0)
errc(EXIT_FAILURE, s, "pthread_attr_setdetachstate");
s = pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);
if (s != 0)
errc(EXIT_FAILURE, s, "pthread_attr_setinheritsched");
stack_size = strtoul(argv[1], NULL, 0);
s = posix_memalign(&sp, sysconf(_SC_PAGESIZE), stack_size);
if (s != 0)
errc(EXIT_FAILURE, s, "posix_memalign");
printf("posix_memalign() allocated at %p\n", sp);
s = pthread_attr_setstack(&attr, sp, stack_size);
if (s != 0)
errc(EXIT_FAILURE, s, "pthread_attr_setstack");
}
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_setaffinity_np(3), pthread_attr_setdetachstate(3),
pthread_attr_setguardsize(3), pthread_attr_setinheritsched(3),
pthread_attr_setschedparam(3), pthread_attr_setschedpolicy(3),
pthread_attr_setscope(3), pthread_attr_setsigmask_np(3),
pthread_attr_setstack(3), pthread_attr_setstackaddr(3),
pthread_attr_setstacksize(3), pthread_create(3), pthread_getattr_np(3),
pthread_setattr_default_np(3), pthreads(7)
Linux man-pages 6.9.1 2024-06-15 pthread_attr_init(3)
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