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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 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 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 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.

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 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.

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 3.54 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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