pthread_getattr_default_np, pthread_setattr_default_np, - get or set default thread-creation attributes

#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <pthread.h>
int pthread_getattr_default_np(pthread_attr_t *attr);
int pthread_setattr_default_np(pthread_attr_t *attr);
Compile and link with  -pthread.

The pthread_setattr_default_np() function sets the default attributes used for creation of a new thread—that is, the attributes that are used when pthread_create(3) is called with a second argument that is NULL. The default attributes are set using the attributes supplied in *attr, a previously initialized thread attributes object. Note the following details about the supplied attributes object:
The attribute settings in the object must be valid.
The stack address attribute must not be set in the object.
Setting the stack size attribute to zero means leave the default stack size unchanged.
The pthread_getattr_default_np() function initializes the thread attributes object referred to by attr so that it contains the default attributes used for thread creation.

(pthread_setattr_default_np()) One of the attribute settings in attr is invalid, or the stack address attribute is set in attr.
(pthread_setattr_default_np()) Insufficient memory.

These functions are available in glibc since version 2.18.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
pthread_getattr_default_np (), pthread_setattr_default_np () Thread safety MT-Safe

These functions are nonstandard GNU extensions; hence the suffix "_np" (nonportable) in their names.

The program below uses pthread_getattr_default_np() to fetch the default thread-creation attributes and then displays various settings from the returned thread attributes object. When running the program, we see the following output:

$  ./a.out
Stack size:          8388608
Guard size:          4096
Scheduling policy:   SCHED_OTHER
Scheduling priority: 0
Detach state:        JOINABLE
Inherit scheduler:   INHERIT

#define _GNU_SOURCE
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#define errExitEN(en, msg) \ do { errno = en; perror(msg); \ exit(EXIT_FAILURE); } while (0)
static void display_pthread_attr(pthread_attr_t *attr) { int s; size_t stacksize; size_t guardsize; int policy; struct sched_param schedparam; int detachstate; int inheritsched;
s = pthread_attr_getstacksize(attr, &stacksize); if (s != 0) errExitEN(s, "pthread_attr_getstacksize"); printf("Stack size: %zd\n", stacksize);
s = pthread_attr_getguardsize(attr, &guardsize); if (s != 0) errExitEN(s, "pthread_attr_getguardsize"); printf("Guard size: %zd\n", guardsize);
s = pthread_attr_getschedpolicy(attr, &policy); if (s != 0) errExitEN(s, "pthread_attr_getschedpolicy"); printf("Scheduling policy: %s\n", (policy == SCHED_FIFO) ? "SCHED_FIFO" : (policy == SCHED_RR) ? "SCHED_RR" : (policy == SCHED_OTHER) ? "SCHED_OTHER" : "[unknown]");
s = pthread_attr_getschedparam(attr, &schedparam); if (s != 0) errExitEN(s, "pthread_attr_getschedparam"); printf("Scheduling priority: %d\n", schedparam.sched_priority);
s = pthread_attr_getdetachstate(attr, &detachstate); if (s != 0) errExitEN(s, "pthread_attr_getdetachstate"); printf("Detach state: %s\n", (detachstate == PTHREAD_CREATE_DETACHED) ? "DETACHED" : (detachstate == PTHREAD_CREATE_JOINABLE) ? "JOINABLE" : "???");
s = pthread_attr_getinheritsched(attr, &inheritsched); if (s != 0) errExitEN(s, "pthread_attr_getinheritsched"); printf("Inherit scheduler: %s\n", (inheritsched == PTHREAD_INHERIT_SCHED) ? "INHERIT" : (inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" : "???"); }
int main(int argc, char *argv[]) { int s; pthread_attr_t attr;
s = pthread_getattr_default_np(&attr); if (s != 0) errExitEN(s, "pthread_getattr_default_np");

pthread_attr_getaffinity_np(3), pthread_attr_getdetachstate(3), pthread_attr_getguardsize(3), pthread_attr_getinheritsched(3), pthread_attr_getschedparam(3), pthread_attr_getschedpolicy(3), pthread_attr_getscope(3), pthread_attr_getstack(3), pthread_attr_getstackaddr(3), pthread_attr_getstacksize(3), pthread_attr_init(3), pthread_create(3), pthreads(7)
2019-03-06 Linux