Question

我正在尝试使用信号量来解决哲学家的餐饮问题。哲学家首先拿起左叉然后右叉，吃完后将它们放下。我使用5个线程为每个哲学家实现这个，每个筷子使用5个信号量。需要由父级执行死锁检查并在发现时解除死锁。当我只是运行哲学家THINKING和EATING的循环时，程序会因错误而崩溃 The futex facility returned an unexpected error code.Aborted。我没有收到有关如何调试此错误的任何信息。

Philosoper的主题如下：

void *Philospoher_behaviour(void *param){
int id  = *(int *)param; // assigns a ID to the Phil
int state; // hungry , thinking, eating
// first the philopher thinks
while(1) {
    state = THINKING;
    float time = (float)rand()/RAND_MAX;
    printf("Philosopher %d starts THINKING for %f\n",id,time);
    sleep(time);
    // the phil goes hungrg
    state = HUNGRY;
    printf("Philosopher %d is now HUNGRY\n",id);
    // first wait for left
    sem_wait(&chopsticks[id]);
    printf("Philosopher %d grabs chopstick %d to this LEFT\n",id,id);

    // got left chopstick
    sem_wait(&chopsticks[(id+1)%5]);
    printf("Philosopher %d grabs chopstick %d to this RIGHT\n",id,(id+1)%5);

    // got the right chopstick
    state = EATING;
    time = (float)rand()/RAND_MAX;
    printf("Philosopher %d starts EATING for time  %f\n",id,time);

    sleep(time);

    sem_post(&chopsticks[(id + 1)%5]);
    printf("Philosopher %d releases chopstick %d to this RIGHT\n",id,(id+1)%5);
    sem_post(&chopsticks[id]);
    printf("Philosopher %d releases chopstick %d to this LEFT\n",id,(id));
    state = THINKING;

    time = (float)rand()/RAND_MAX;
    sleep(time);

}

}

主程序如下

sem_t chopsticks[5];// five chopsticks as a resource
pthread_t philosopher[5]; //five philosoophers

int main(){
srand(time(NULL));
for ( int i=0 ;i <5;i++){
    sem_init(&chopsticks[i], 0, 1); // local to the threads with initial value of 1
}

// now create the indiviual threads
for(int i=0;i<5;i++){
    if( pthread_create(&philosopher[i],NULL, Philospoher_behaviour ,&i) != 0) { // create thread one
        printf("Cant create thread %d\n",i);
        return 1;
    }
    else{
        printf("Creadted Philosopher Number : %d\n",i);
    }
}

for(int i=0;i<5;i++){
    pthread_join(philosopher[i],NULL);
}

}

如何调试此错误。我也粘贴了一次运行的输出

Creadted Philosopher Number : 0
Philosopher 1 starts THINKING for 0.483853
Creadted Philosopher Number : 1
Philosopher 1 starts THINKING for 0.059081
Creadted Philosopher Number : 2
Philosopher 3 starts THINKING for 0.149168
Creadted Philosopher Number : 3
Philosopher 4 starts THINKING for 0.073436
Creadted Philosopher Number : 4
Philosopher 5 starts THINKING for 0.833351
Philosopher 5 is now HUNGRY
Philosopher 1 is now HUNGRY
Philosopher 5 grabs chopstick 5 to this LEFT
Philosopher 1 grabs chopstick 1 to this LEFT
Philosopher 1 grabs chopstick 2 to this RIGHT
Philosopher 1 starts EATING for time  0.147257
Philosopher 3 is now HUNGRY
Philosopher 3 grabs chopstick 3 to this LEFT
Philosopher 3 grabs chopstick 4 to this RIGHT
Philosopher 1 is now HUNGRY
Philosopher 3 starts EATING for time  0.572829
Philosopher 4 is now HUNGRY
Philosopher 1 releases chopstick 2 to this RIGHT
Philosopher 1 releases chopstick 1 to this LEFT
Philosopher 5 grabs chopstick 1 to this RIGHT
Philosopher 5 starts EATING for time  0.857843
Philosopher 3 releases chopstick 4 to this RIGHT
Philosopher 3 releases chopstick 3 to this LEFT
Philosopher 4 grabs chopstick 4 to this LEFT
Philosopher 4 grabs chopstick 0 to this RIGHT
Philosopher 4 starts EATING for time  0.783497
Philosopher 1 starts THINKING for 0.308573
Philosopher 5 releases chopstick 1 to this RIGHT
Philosopher 4 releases chopstick 0 to this RIGHT
Philosopher 4 releases chopstick 4 to this LEFT
Philosopher 1 grabs chopstick 1 to this LEFT
Philosopher 3 starts THINKING for 0.086635
Philosopher 1 grabs chopstick 2 to this RIGHT
Philosopher 1 starts EATING for time  0.015005
The futex facility returned an unexpected error code.Aborted

还有一个问题，你可以看到哲学家0和2没有互动，为什么会发生这种情况。

在GDB中运行我得到这个信息

Thread 6 "part22" received signal SIGABRT, Aborted.
[Switching to Thread 0x7ffff57eb700 (LWP 12247)]
0x00007ffff7825428 in __GI_raise (sig=sig@entry=6)
    at ../sysdeps/unix/sysv/linux/raise.c:54
54  ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.

Answer 1

您将main()循环变量i的地址传递给每个帖子：

pthread_create(&philosopher[i],NULL, Philospoher_behaviour ,&i)

当你的线程执行时

int id  = *(int *)param;

i中的值可能已更改。

futex工具返回了意外的错误代码并已中止

1 个答案: