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

       CPU_XOR_S, CPU_EQUAL_S - macros for manipulating CPU sets

       #define _GNU_SOURCE
       #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);

       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 logical AND of the sets srcset1 and srcset2
                        in destset (which may be one of the source sets).

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

       CPU_XOR()        Store  the logical XOR of the sets srcset1 and srcset2
                        in destset (which may be one of the source sets).

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

   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

       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.

       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 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.

       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_ISSET_S(),  CPU_AND_S(), CPU_OR_S(), CPU_XOR_S(), and CPU_EQUAL_S()
       first appeared in glibc 2.7.

       These interfaces are Linux-specific.

       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 con-
       sider 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 set-
       size 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.

       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>

       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]);

           num_cpus = atoi(argv[1]);

           cpusetp = CPU_ALLOC(num_cpus);
           if (cpusetp == NULL) {

           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));


       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 effi-
       cient operation of the macros that operate on dynamically allocated CPU
       sets.  These bugs are fixed in glibc 2.9.

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

       This page is part of release 3.25 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                             2010-02-21                        CPU_SET(3)

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