#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);
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:
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:
The following macros are used to allocate and deallocate CPU sets:
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_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.
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.
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.
#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);
}