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NAME

       CPU_SET,  CPU_CLR,  CPU_ISSET,  CPU_ZERO,  CPU_COUNT, CPU_AND, CPU_OR, CPU_XOR, CPU_EQUAL,
       CPU_ALLOC,  CPU_ALLOC_SIZE,  CPU_FREE,  CPU_SET_S,  CPU_CLR_S,  CPU_ISSET_S,   CPU_ZERO_S,
       CPU_COUNT_S,  CPU_AND_S,  CPU_OR_S,  CPU_XOR_S,  CPU_EQUAL_S - macros for manipulating CPU
       sets

SYNOPSIS

       #define _GNU_SOURCE             /* See feature_test_macros(7) */
       #include <sched.h>

       void CPU_ZERO(cpu_set_t *set);

       void CPU_SET(int cpu, cpu_set_t *set);
       void CPU_CLR(int cpu, cpu_set_t *set);
       int  CPU_ISSET(int cpu, cpu_set_t *set);

       int  CPU_COUNT(cpu_set_t *set);

       void CPU_AND(cpu_set_t *destset,
                    cpu_set_t *srcset1, cpu_set_t *srcset2);
       void CPU_OR(cpu_set_t *destset,
                    cpu_set_t *srcset1, cpu_set_t *srcset2);
       void CPU_XOR(cpu_set_t *destset,
                    cpu_set_t *srcset1, cpu_set_t *srcset2);

       int  CPU_EQUAL(cpu_set_t *set1, cpu_set_t *set2);

       cpu_set_t *CPU_ALLOC(int num_cpus);
       void CPU_FREE(cpu_set_t *set);
       size_t CPU_ALLOC_SIZE(int num_cpus);

       void CPU_ZERO_S(size_t setsize, cpu_set_t *set);

       void CPU_SET_S(int cpu, size_t setsize, cpu_set_t *set);
       void CPU_CLR_S(int cpu, size_t setsize, cpu_set_t *set);
       int  CPU_ISSET_S(int cpu, size_t setsize, cpu_set_t *set);

       int  CPU_COUNT_S(size_t setsize, cpu_set_t *set);

       void CPU_AND_S(size_t setsize, cpu_set_t *destset,
                    cpu_set_t *srcset1, cpu_set_t *srcset2);
       void CPU_OR_S(size_t setsize, cpu_set_t *destset,
                    cpu_set_t *srcset1, cpu_set_t *srcset2);
       void CPU_XOR_S(size_t setsize, cpu_set_t *destset,
                    cpu_set_t *srcset1, cpu_set_t *srcset2);

       int  CPU_EQUAL_S(size_t setsize, cpu_set_t *set1, cpu_set_t *set2);

DESCRIPTION

       The  cpu_set_t  data  structure  represents  a  set  of  CPUs.   CPU  sets  are  used   by
       sched_setaffinity(2) and similar interfaces.

       The  cpu_set_t  data type is implemented as a bitset.  However, the data structure treated
       as considered opaque: all manipulation of CPU sets should be done via the macros described
       in this page.

       The following macros are provided to operate on the CPU set set:

       CPU_ZERO()       Clears set, so that it contains no CPUs.

       CPU_SET()        Add CPU cpu to set.

       CPU_CLR()        Remove CPU cpu from set.

       CPU_ISSET()      Test to see if CPU cpu is a member of set.

       CPU_COUNT()      Return the number of CPUs in set.

       Where  a  cpu  argument  is specified, it should not produce side effects, since the above
       macros may evaluate the argument more than once.

       The first available CPU on the system corresponds to a  cpu  value  of  0,  the  next  CPU
       corresponds  to  a  cpu  value of 1, and so on.  The constant CPU_SETSIZE (currently 1024)
       specifies a value one greater than the maximum CPU number that can be stored in cpu_set_t.

       The following macros perform logical operations on CPU sets:

       CPU_AND()        Store the intersection of the sets srcset1 and srcset2 in destset  (which
                        may be one of the source sets).

       CPU_OR()         Store  the union of the sets srcset1 and srcset2 in destset (which may be
                        one of the source sets).

       CPU_XOR()        Store the XOR of the sets srcset1 and srcset2 in destset  (which  may  be
                        one  of  the  source  sets).   The  XOR means the set of CPUs that are in
                        either srcset1 or srcset2, but not both.

       CPU_EQUAL()      Test whether two CPU set contain exactly the same CPUs.

   Dynamically sized CPU sets
       Because some applications may require the ability to dynamically size CPU sets  (e.g.,  to
       allocate  sets  larger  than  that  defined  by  the  standard cpu_set_t data type), glibc
       nowadays provides a set of macros to support this.

       The following macros are used to allocate and deallocate CPU sets:

       CPU_ALLOC()      Allocate a CPU  set  large  enough  to  hold  CPUs  in  the  range  0  to
                        num_cpus-1.

       CPU_ALLOC_SIZE() Return the size in bytes of the CPU set that would be needed to hold CPUs
                        in the range 0 to num_cpus-1.  This macro provides the value that can  be
                        used for the setsize argument in the CPU_*_S() macros described below.

       CPU_FREE()       Free a CPU set previously allocated by CPU_ALLOC().

       The macros whose names end with "_S" are the analogs of the similarly named macros without
       the suffix.  These macros perform the same tasks as their  analogs,  but  operate  on  the
       dynamically allocated CPU set(s) whose size is setsize bytes.

RETURN VALUE

       CPU_ISSET() and CPU_ISSET_S() return nonzero if cpu is in set; otherwise, it returns 0.

       CPU_COUNT() and CPU_COUNT_S() return the number of CPUs in set.

       CPU_EQUAL()  and  CPU_EQUAL_S() return nonzero if the two CPU sets are equal; otherwise it
       returns 0.

       CPU_ALLOC() returns a pointer on  success,  or  NULL  on  failure.   (Errors  are  as  for
       malloc(3).)

       CPU_ALLOC_SIZE()  returns the number of bytes required to store a CPU set of the specified
       cardinality.

       The other functions do not return a value.

VERSIONS

       The CPU_ZERO(), CPU_SET(), CPU_CLR(), and CPU_ISSET() macros were added in glibc 2.3.3.

       CPU_COUNT() first appeared in glibc 2.6.

       CPU_AND(), CPU_OR(), CPU_XOR(), CPU_EQUAL(),  CPU_ALLOC(),  CPU_ALLOC_SIZE(),  CPU_FREE(),
       CPU_ZERO_S(),    CPU_SET_S(),   CPU_CLR_S(),   CPU_ISSET_S(),   CPU_AND_S(),   CPU_OR_S(),
       CPU_XOR_S(), and CPU_EQUAL_S() first appeared in glibc 2.7.

CONFORMING TO

       These interfaces are Linux-specific.

NOTES

       To duplicate a CPU set, use memcpy(3).

       Since CPU sets are bitsets allocated in units of long words, the actual number of CPUs  in
       a dynamically allocated CPU set will be rounded up to the next multiple of sizeof(unsigned
       long).  An application should consider the contents of these extra bits to be undefined.

       Notwithstanding the similarity in the names, note that the constant CPU_SETSIZE  indicates
       the  number of CPUs in the cpu_set_t data type (thus, it is effectively a count of bits in
       the bitset), while the setsize argument of the CPU_*_S() macros is a size in bytes.

       The data types for arguments and return values shown in the SYNOPSIS are hints what  about
       is  expected in each case.  However, since these interfaces are implemented as macros, the
       compiler won't necessarily catch all type errors if you violate the suggestions.

EXAMPLE

       The following program demonstrates the use of some of  the  macros  used  for  dynamically
       allocated CPU sets.

       #define _GNU_SOURCE
       #include <sched.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <stdio.h>
       #include <assert.h>

       int
       main(int argc, char *argv[])
       {
           cpu_set_t *cpusetp;
           size_t size;
           int num_cpus, cpu;

           if (argc < 2) {
               fprintf(stderr, "Usage: %s <num-cpus>\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           num_cpus = atoi(argv[1]);

           cpusetp = CPU_ALLOC(num_cpus);
           if (cpusetp == NULL) {
               perror("CPU_ALLOC");
               exit(EXIT_FAILURE);
           }

           size = CPU_ALLOC_SIZE(num_cpus);

           CPU_ZERO_S(size, cpusetp);
           for (cpu = 0; cpu < num_cpus; cpu += 2)
               CPU_SET_S(cpu, size, cpusetp);

           printf("CPU_COUNT() of set:    %d\n", CPU_COUNT_S(size, cpusetp));

           CPU_FREE(cpusetp);
           exit(EXIT_SUCCESS);
       }

BUGS

       On  32-bit platforms with glibc 2.8 and earlier, CPU_ALLOC() allocates twice as much space
       as is required, and CPU_ALLOC_SIZE() returns a value twice as large as  it  should.   This
       bug  should  not  affect  the semantics of a program, but does result in wasted memory and
       less efficient operation of the macros that operate on  dynamically  allocated  CPU  sets.
       These bugs are fixed in glibc 2.9.

SEE ALSO

       sched_setaffinity(2), pthread_attr_setaffinity_np(3), pthread_setaffinity_np(3), cpuset(7)

COLOPHON

       This  page  is  part of release 3.35 of the Linux man-pages project.  A description of the
       project, and information about reporting bugs, can be found at  http://man7.org/linux/man-
       pages/.