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Linux 2.6 - man page for cpu_clr (linux section 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 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 corre-
       sponds  to  a cpu value of 1, and so on.  The constant CPU_SETSIZE (currently 1024) speci-
       fies 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 nowa-
       days 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  mal-
       loc(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.

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.

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_setaffinity_np(3), cpuset(7)

COLOPHON
       This  page  is  part of release 3.55 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					    2012-03-15				       CPU_SET(3)


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