c - 带互斥同步的 Pi 计算器

Question

在这里完成作业。使代码可以工作并计算饼图，但随机值除外，我收到以下错误:

1. ./piesync 10 3在 3 个线程中使用 10 个项计算的 pi 为 3.14183961892940200045* `./piesync' 中的错误:free():下一个尺寸无效(快速):0x0000000001ca3010 *

2. ./piesync 100 5* `./piesync' 中的错误:双重释放或损坏(输出):0x0000000000ee5040 *

我知道这可能与数组或互斥体有关，但无法弄清楚是什么。

代码:

//Pini Vaknine
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

//global variables
int N, T;
double gpie = 3.0;
pthread_mutex_t mutex;

//pie function
void* pie_runner(void* arg)
{
    long j = (long)arg;    
    long lower = (N/T)*(j-1)+1;
    long upper = ((N/T)*(j));
    double myPartialSum = 0;
    //printf("lower=%lu upper=%lu\n",lower , upper);

    for(long i = lower; i <= upper; i++)
    {        
        if(i % 2 == 0){
            myPartialSum -= 4.0/((2*i)*(2*i+1)*(2*i+2)); 
            //printf("vsum %lu = %f\n", j, vsum[j]);
                  }
        else{
            myPartialSum += 4.0/((2*i)*(2*i+1)*(2*i+2));
            //printf("vsum %lu = %f\n", j, vsum[j]);
                  }


    }
    pthread_mutex_lock (&mutex);
    gpie = gpie + myPartialSum;
    pthread_mutex_unlock (&mutex);    

    pthread_exit(0);
    //return NULL;
}

int main(int argc, char **argv)
{

    if(argc != 3) {
        printf("Error: Must send it 2 parameters, you sent %d\n", argc-1);
        exit(1);
    }
    N = atoi(argv[1]);
    T = atoi(argv[2]); 


    if(N <= T) {
        printf("Error: Number of terms must be greater then number of threads.\n");
        exit(1);    
    }



    //launch threads
    pthread_attr_t attr;
    pthread_t *tids = (pthread_t *) calloc(T, sizeof(pthread_t));
    if(tids == NULL) {
        fprintf(stderr, "Memory allocation problem\n");
        exit(1);
    }


        pthread_mutex_init(&mutex, NULL);
        pthread_attr_init(&attr);
        pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

    for(long i = 1; i<=T; i++)
    {

        int r = pthread_create(&tids[i], &attr, pie_runner, (void*)i);
        if(r<0) {
            printf("ERROR: pthread_create() returned %d\n", r);
            exit(2);
        }
    }

    //wait for threads...
    for(int k = 1; k<=T; k++)
    {
        pthread_join(tids[k], NULL);
    }


    printf("pi computed with %d terms in %d threads is %.20f\n", N, T, gpie);

    pthread_mutex_destroy(&mutex);    
    pthread_attr_destroy(&attr);

    free(tids);

    return 0;
}

Answer 1

您的索引超出了数组的范围。您已在此处为 T 元素分配了一个数组

pthread_t *tids = (pthread_t *) calloc(T, sizeof(pthread_t));

但你在这里索引错误

for(int k = 1; k<=T; k++)
    {
        pthread_join(tids[k], NULL);
    }

还有其他实例。在 C 中，您从 0 索引一个数组，因此循环应该是

for(int k=0; k<T; k++)