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 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 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 dest-
			set  (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_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  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 applica-
       tion 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 effi-
       cient operation of the macros that operate on dynamically allocated CPU
       sets.  These bugs are fixed in glibc 2.9.

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);
       }

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

COLOPHON
       This  page  is  part of release 4.10 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				  2015-05-07			    CPU_SET(3)