pthread_attr_setaffinity_np / pthread_attr_getaffinity_np / pthread_attr_setsigmask_np / pthread_attr_getsigmask_np (3) - glibc

Split from the chapter glibc: Threads into the per-function layout; see the method page and the glibc ledger for coverage status.

Declaration and gates

#define _GNU_SOURCE
#include <pthread.h>

int pthread_attr_setaffinity_np(pthread_attr_t *attr, size_t cpusetsize,
                                const cpu_set_t *cpuset);        /* :394 */
int pthread_attr_getaffinity_np(const pthread_attr_t *attr,
                                size_t cpusetsize, cpu_set_t *cpuset);
                                                                 /* :401 */
int pthread_attr_setsigmask_np(pthread_attr_t *attr,
                               const sigset_t *sigmask);         /* :411 */
int pthread_attr_getsigmask_np(const pthread_attr_t *attr,
                               sigset_t *sigmask);               /* :417 */
#define PTHREAD_ATTR_NO_SIGMASK_NP (-1)                          /* :422 */

All four sit in one #ifdef __USE_GNU block of /usr/include/pthread.h (lines 393-430). The per-thread equivalents are in pthread-getaffinity-setaffinity-np.

Semantics

pthread_attr_setaffinity_np stores a CPU affinity mask in the attribute object, restricting the CPUs of threads later created with it; pthread_attr_getaffinity_np copies it out (pthread_attr_setaffinity_np(3)). pthread_attr_setsigmask_np stores the initial signal mask of the new thread; a NULL sigmask unsets the attribute so the mask is inherited from the creating thread. pthread_attr_getsigmask_np returns 0 and the mask when set, or the special value PTHREAD_ATTR_NO_SIGMASK_NP when unset (manual, Initial Thread Signal Mask). The manual notes that pthread_getattr_np does not recover the thread’s signal mask, so the getter reports unset for such objects.

Gotchas and portability

• glibc 2.3.3 only shipped these affinity functions without the cpusetsize argument (pthread_attr_setaffinity_np(3) NOTES).
• musl 1.2.5: none of the four exists (musl src/thread/ has no *affinity* or *sigmask* attr files).

Errors

• EINVAL (setaffinity_np): cpuset names a CPU outside the kernel range. EINVAL (getaffinity_np): a CPU of the stored mask lies outside cpusetsize. ENOMEM (setaffinity_np): allocation failed (pthread_attr_setaffinity_np(3)).
• ENOMEM (setsigmask_np): memory allocation failed (pthread_attr_setsigmask_np(3)).

References

• man3: pthread_attr_setaffinity_np(3), pthread_attr_setsigmask_np(3) (source-cache/man-pages-sparse/man3/)
• glibc manual: threads.texi, nodes Thread CPU Affinity, Initial Thread Signal Mask
• header: /usr/include/pthread.h lines 393-430
• symbols: nm -D --with-symbol-versions libc.so.6