利用__sync_bool_compare_and_swap()，实现无锁编程

CAS即compare and swap,每次都会和old 值进行比较，如果没有发生更改再用new值给ptr赋值，然后返回true

#include

#include

#include

#include

#ifdef __GNUC__

//#define ATOMIC

#define CAS

#define _ATOMIC_ADD_(x, y) __sync_fetch_and_add(x, y)

#define _ATOMIC_SUB_(x, y) __sync_fetch_and_sub(x, y)

#define _CAS_(ptr, old, new) __sync_bool_compare_and_swap(ptr, old, new)

#else

#define _ATOMIC_ADD_(x, y) ;

#define _ATOMIC_SUB_(x, y) ;

#define _CAS_(ptr, old, new) ;

#endif

int val = 0;

void* worker1(void* arg)

{

#ifdef ATOMIC

for (int i = 0; i < 50000; i++)

_ATOMIC_ADD_(&val, 1);

#endif

#ifdef CAS

int old = val;

int i = 0;

for (; i < 10000; i++) {

while (!_CAS_(&val, old, old + 1)) {

old = val;

}

}

printf("%d", i);

#endif

}

void* worker2(void* arg)

{

#ifdef ATOMIC

for (int i = 0; i < 50000; i++)

_ATOMIC_SUB_(&val, 1);

#endif

#ifdef CAS

int i = 0;

int old = val;

for (; i < 10000; i++) {

while (!_CAS_(&val, old, old - 1)) {

old = val;

}

}

printf("%d", i);

#endif

}

int main()

{

pthread_t tid[2];

pthread_create(&tid[0], NULL, worker1, NULL);

pthread_create(&tid[1], NULL, worker2, NULL);

pthread_join(tid[0], NULL);

pthread_join(tid[1], NULL);

std::cout << val << std::endl;

return 0;

}