PTHREADSETAFFINITYNP(3) Linux Programmer's Manual PTHREADSETAFFINITYNP(3)

NAME
       pthreadsetaffinitynp,  pthreadgetaffinitynp  - set/get CPU affinity
       of a thread

SYNOPSIS
       #define GNUSOURCE             /* See featuretestmacros(7) */
       #include 

       int pthreadsetaffinitynp(pthreadt thread, sizet cpusetsize,
                                  const cpusett *cpuset);
       int pthreadgetaffinitynp(pthreadt thread, sizet cpusetsize,
                                  cpusett *cpuset);

       Compile and link with -pthread.

DESCRIPTION
       The pthreadsetaffinitynp() function sets the CPU affinity mask of the
       thread thread to the CPU set pointed to by cpuset.  If the call is suc‐
       cessful, and the thread is not currently running on one of the CPUs  in
       cpuset, then it is migrated to one of those CPUs.

       The  pthreadgetaffinitynp() function returns the CPU affinity mask of
       the thread thread in the buffer pointed to by cpuset.

       For more details on CPU affinity masks, see schedsetaffinity(2).   For
       a  description  of  a  set of macros that can be used to manipulate and
       inspect CPU sets, see CPUSET(3).

       The argument cpusetsize is the length (in bytes) of the buffer  pointed
       to   by  cpuset.   Typically,  this  argument  would  be  specified  as
       sizeof(cpusett).  (It may be some other value, if  using  the  macros
       described in CPUSET(3) for dynamically allocating a CPU set.)

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

ERRORS
       EFAULT A supplied memory address was invalid.

       EINVAL (pthreadsetaffinitynp()) The affinity bit mask  mask  contains
              no  processors  that  are currently physically on the system and
              permitted to the thread according to any restrictions  that  may
              be imposed by the "cpuset" mechanism described in cpuset(7).

       EINVAL (pthreadsetaffinitynp())  cpuset specified a CPU that was out‐
              side the set supported by the kernel.  (The kernel configuration
              option  CONFIGNRCPUS defines the range of the set supported by
              the kernel data type used to represent CPU sets.)

       EINVAL (pthreadgetaffinitynp()) cpusetsize is smaller than  the  size
              of the affinity mask used by the kernel.

       ESRCH  No thread with the ID thread could be found.

VERSIONS
       These functions are provided by glibc since version 2.3.4.

ATTRIBUTES
       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       ┌──────────────────────────┬───────────────┬─────────┐
       │Interface                 │ Attribute     │ Value   │
       ├──────────────────────────┼───────────────┼─────────┤
       │pthreadsetaffinitynp(), │ Thread safety │ MT-Safe │
       │pthreadgetaffinitynp()  │               │         │
       └──────────────────────────┴───────────────┴─────────┘
CONFORMING TO
       These  functions are nonstandard GNU extensions; hence the suffix "np"
       (nonportable) in the names.

NOTES
       After a call to pthreadsetaffinitynp(), the set of CPUs on which  the
       thread  will  actually  run is the intersection of the set specified in
       the cpuset argument and the set of CPUs actually present on the system.
       The  system  may  further  restrict the set of CPUs on which the thread
       runs if the "cpuset" mechanism described in cpuset(7)  is  being  used.
       These  restrictions  on the actual set of CPUs on which the thread will
       run are silently imposed by the kernel.

       These functions are implemented on top of the schedsetaffinity(2)  and
       schedgetaffinity(2) system calls.

       In glibc 2.3.3 only, versions of these functions were provided that did
       not have a cpusetsize argument.  Instead the CPU set size given to  the
       underlying system calls was always sizeof(cpusett).

       A  new  thread created by pthreadcreate(3) inherits a copy of its cre‐
       ator's CPU affinity mask.

EXAMPLE
       In the following program, the main thread uses pthreadsetaffinitynp()
       to  set its CPU affinity mask to include CPUs 0 to 7 (which may not all
       be available on the system), and then calls pthreadgetaffinitynp() to
       check the resulting CPU affinity mask of the thread.

       #define GNUSOURCE
       #include 
       #include 
       #include 
       #include 

       #define handleerroren(en, msg) \
               do { errno = en; perror(msg); exit(EXITFAILURE); } while (0)

       int
       main(int argc, char *argv[])
       {
           int s, j;
           cpusett cpuset;
           pthreadt thread;

           thread = pthreadself();

           /* Set affinity mask to include CPUs 0 to 7 */

           CPUZERO(&cpuset);
           for (j = 0; j < 8; j++)
               CPUSET(j, &cpuset);

           s = pthreadsetaffinitynp(thread, sizeof(cpusett), &cpuset);
           if (s != 0)
               handleerroren(s, "pthreadsetaffinitynp");

           /* Check the actual affinity mask assigned to the thread */

           s = pthreadgetaffinitynp(thread, sizeof(cpusett), &cpuset);
           if (s != 0)
               handleerroren(s, "pthreadgetaffinitynp");

           printf("Set returned by pthreadgetaffinitynp() contained:\n");
           for (j = 0; j < CPUSETSIZE; j++)
               if (CPUISSET(j, &cpuset))
                   printf("    CPU %d\n", j);

           exit(EXITSUCCESS);
       }

SEE ALSO
       schedsetaffinity(2),   schedsetscheduler(2),   pthreadattrsetaffin‐
       itynp(3), pthreadself(3), schedgetcpu(3), cpuset(7), pthreads(7)

COLOPHON
       This page is part of release 3.53 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2010-09-10         PTHREADSETAFFINITYNP(3)