Ubuntu Manpage: CPU_SET, CPU_CLR, CPU_ISSET, CPU_ZERO, CPU_COUNT, CPU_AND, CPU_OR, CPU_XOR, CPU

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

LIBRARY

       Standard C library (libc, -lc)

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 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 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.

STANDARDS

       Linux.

HISTORY

       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.

NOTES

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

       Since  CPU  sets are bit masks 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 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 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.

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 <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       #include <assert.h>

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

           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 (size_t 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);
       }