#include <pthread.h> int pthread_attr_init(pthread_attr_t *attr); int pthread_attr_destroy(pthread_attr_t *attr); Compile and link with -pthread.
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.
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
#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() */
}