c - Pthread编程: Segmentation Fault: 11 while using mutex

Question

我正在尝试使用互斥锁来锁定代码区域。我已尝试发布尽可能多的代码。

//Global Variables
int sum;
long long fact=1;
pthread_mutex_t lock;
pthread_t id1,id2;

void *thread_1_And_2(void *accept_1)
{
    //Accepting Input
    int *a_ptr = (int*) accept_1;
    int a= *a_ptr;

    //Locking the resource
    pthread_mutex_lock(&lock);

    //Returning the process ID that is working right now!
    pthread_t my_current_id;
    my_current_id= pthread_self();

    if((pthread_equal(id1,my_current_id))>0)
    {

        printf("\nI am Thread 1: Processing Sum\n");

        printf("\n I am in Thread 1 \n");
        for (int i=0; i<a; i++)
        {
        sum= sum+i;
        }
    }
    else if((pthread_equal(id2, my_current_id))>0)
    {
        printf("\nI am Thread 2: Processing Factorial\n");
        if (a<0)
        {
            printf("\n Error! Factorial of Negative number not possible \n");
        }
        else
        {
            for(int i=1; i<=a; i++)
            {
            fact=fact*i;
            }
        }
    }

    //Unlocking the Mutex
    pthread_mutex_unlock(&lock);

    return 0;
}

在主函数中，它的初始化和调用如下:

printf("\n Input for thread_1:\n");
int store_1; //= atoi(argv[1]);
printf("\nEnter number up to which you want a sum of natural numbers\n");
scanf("%d", &store_1);

printf("\nInput for thread_2:\n");
int store_2; //= atoi(argv[2]);
printf("\nEnter number whose factorial needs to be found\n");
scanf("%d", &store_2);
//Mutex Initialisation
if (pthread_mutex_init(&lock, NULL) != 0)
{
    printf("\nMutex Initialisation has Failed\n");
    return 1;
}

//Creating Threads
pthread_create(&id1, NULL, &thread_1_And_2, &store_1);//For Sum
pthread_create(&id2, NULL, &thread_1_And_2, &store_2);//For Factorial


//Joining All Threads
pthread_join(id1, NULL);
pthread_join(id2, NULL);

//Destroying the Mutex
pthread_mutex_destroy(&lock);


//Printing
printf("\n Output of Thread 1 is Sum = %d \n", sum);
printf("\n Output of Thread 2 is Factorial = %llu \n", fact);

输出:

Asking input for:
"Enter number upto which you want a sum of natural numbers"
Input Given: 5
Asking input for:
"Enter number whose factorial needs to be found"
Input Given: 3

现在屏幕正在打印:

"I am in Thread 1"
"I am in Thread 2"

暂停一会儿

Segmentation Fault: 11

我不知道出了什么问题或哪里出了问题。

Answer 1

下面是更新为使用 C++ std::thread 的同一程序。更简单的程序可以避免崩溃:

#include <thread>
#include <mutex>
#include <cstdio>

//Global Variables
int sum;
long long fact = 1;
//pthread_mutex_t lock;
std::mutex m;
//pthread_t id1, id2;
std::thread id1, id2;

//void *thread_1_And_2(void *accept_1)
void thread_1_And_2(int a)
{
    ////Accepting Input
    //int *a_ptr = (int*)accept_1;
    //int a = *a_ptr;

    //Locking the resource
    //pthread_mutex_lock(&lock);
    std::lock_guard<std::mutex> lock(m);

    //Returning the process ID that is working right now!
    //pthread_t my_current_id;
    //my_current_id = pthread_self();
    std::thread::id my_current_id = std::this_thread::get_id();

    //if((pthread_equal(id1, my_current_id))>0)
    if(id1.get_id() == my_current_id)
    {

        printf("\nI am Thread 1: Processing Sum\n");

        printf("\n I am in Thread 1 \n");
        for(int i = 0; i < a; i++)
        {
            sum = sum + i;
        }
    }
    //else if((pthread_equal(id2, my_current_id))>0)
    else if(id2.get_id() == my_current_id)
    {
        printf("\nI am Thread 2: Processing Factorial\n");
        if(a < 0)
        {
            printf("\n Error! Factorial of Negative number not possible \n");
        }
        else
        {
            for(int i = 1; i <= a; i++)
            {
                fact = fact*i;
            }
        }
    }

    //Unlocking the Mutex
    //pthread_mutex_unlock(&lock); // RAII will do this

    //return 0;
}

int main()
{
    ////Mutex Initialisation
    //if(pthread_mutex_init(&lock, NULL) != 0)
    //{
    //    printf("\nMutex Initialisation has Failed\n");
    //    return 1;
    //}
    {

        std::lock_guard<std::mutex> lock(m);

        //Creating Threads
        id1 = std::thread{[]() {thread_1_And_2(3); }};
        id2 = std::thread{[]() {thread_1_And_2(4); }};
        //pthread_create(&id1, NULL, &thread_1_And_2, &store_1);//For Sum
        //pthread_create(&id2, NULL, &thread_1_And_2, &store_2);//For Factorial

        //Destroying the Mutex
        //pthread_mutex_destroy(&lock); // RAII will take care of the lock
    }

    id1.join();
    id2.join();
}