CPU_AND(3)



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

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 bit mask.  However, the
       data structure should be treated as 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 CPU on the system corresponds to a cpu value of 0,  the  next
       CPU  corresponds to a cpu value of 1, and so on.  No assumptions should
       be made about particular CPUs being available, or the set of CPUs being
       contiguous, since CPUs can be taken offline dynamically or be otherwise
       absent.  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  dest-
              set (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 stan-
       dard 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;  other-
       wise, 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 they return 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_AL-
       LOC_SIZE(), CPU_FREE(), CPU_ZERO_S(), CPU_SET_S(), CPU_CLR_S(), CPU_IS-
       SET_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 bit masks allocated in units of long words, the  ac-
       tual  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 the bits in the bit mask), 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.

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 se-
       mantics of a program, but does result in wasted memory and  less  effi-
       cient operation of the macros that operate on dynamically allocated CPU
       sets.  These bugs are fixed in glibc 2.9.

EXAMPLES
       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);
       }

SEE ALSO
       sched_setaffinity(2), pthread_attr_setaffinity_np(3), pthread_setaffin-
       ity_np(3), cpuset(7)

COLOPHON
       This page is part of release 5.07 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

Linux                             2020-04-11                        CPU_SET(3)

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