-1
代码失败:
[peterson_lock.h]我peterson_lock在这种情况下
#include <pthread.h>
typedef struct {
volatile bool flag[2];
volatile int victim;
} peterson_lock_t;
void peterson_lock_init(peterson_lock_t &lock) {
lock.flag[0] = lock.flag[1] = false;
lock.victim = 0;
}
void peterson_lock(peterson_lock_t &lock, int id) {
lock.victim = id; // Mark as A
lock.flag[id] = true; // Mark as B
asm volatile ("mfence" : : : "memory");
while (lock.flag[1 - id] && lock.victim == id);
}
void peterson_unlock(peterson_lock_t &lock, int id) {
lock.flag[id] = false;
lock.victim = id;
}
[main.cpp中]
#include <stdio.h>
#include "peterson_lock.h"
peterson_lock_t lock;
int count = 0;
void *routine0(void *arg) {
int *cnt = (int *)arg;
for (int i = 0; i < *cnt; ++i) {
peterson_lock(lock, 0);
++count;
peterson_unlock(lock, 0);
}
return NULL;
}
void *routine1(void *arg) {
int *cnt = (int *)arg;
for (int i = 0; i < *cnt; ++i) {
peterson_lock(lock, 1);
++count;
peterson_unlock(lock, 1);
}
}
int main(int argc, char **argv) {
peterson_lock_init(lock);
pthread_t thread0, thread1;
int count0 = 10000;
int count1 = 20000;
pthread_create(&thread0, NULL, routine0, (void *)&count0);
pthread_create(&thread1, NULL, routine1, (void *)&count1);
pthread_join(thread0, NULL);
pthread_join(thread1, NULL);
printf("Expected: %d\n", (count0 + count1));
printf("Reality : %d\n", count);
return 0;
}
运行这个程序1000次,有时效果并非30000
。但是,我切换A
和B
,结果总是30000
。但是这怎么会发生?
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谢谢,没错。 – Charles