乱序执行实验

ts.c

#include <pthread.h>
#include <stdio.h>

int x, y;
int r1, r2;

volatile int chance, complete;

typedef struct {
	int mask;
	volatile int *x, *y, *r;
} param_t;

void* thread_main(void* ar)
{
	param_t* p = (param_t*)ar;

	volatile int* x = p->x;
	volatile int* y = p->y;
	int  r, mask = p->mask;

	for(;;)
	{
		int obs;
		do {
			obs = chance;
		} while((obs & mask) == 0  || !__sync_bool_compare_and_swap(&chance, obs, obs ^ mask));

		asm volatile ("" : : : "memory");
		*x = 1;
		//__sync_synchronize();
		asm volatile ("" : : : "memory");
		r = *y;
		asm volatile ("" : : : "memory");

		*p->r = r;

		do {
			obs = complete;
		} while(!__sync_bool_compare_and_swap(&complete, obs, obs + 1));

	}

	return NULL;
}

int main()
{
	param_t p1 = {
		.x = &x,
		.y = &y,
		.r = &r1,
		.mask = 0x1
	};

	param_t p2 = {
		.x = &y,
		.y = &x,
		.r = &r2,
		.mask = 0x2
	};

	pthread_mutex_init(&m, NULL);

	pthread_t t1, t2;
	pthread_create(&t1, NULL, thread_main, &p1);
	pthread_create(&t2, NULL, thread_main, &p2);

	int count[4] = {};
	int i;
	for(i = 0; i < 10000000; i ++)
	{
		x = y = 0;
		r1 = r2 = 0;

		while(!__sync_bool_compare_and_swap(&chance, 0, 0x3));

		while(complete != 2);

		complete = 0;
		count[r1 * 2 + r2] ++;

	}

	for(i = 0; i < 4; i ++)
		printf("r1 = %d r2 = %d count = %d\n", i / 2, i % 2, count[i]);
	return 0;
}