Question

因此，我早些时候问了一个有关特定问题的问题。我已经查看了本网站上的其他问题，但是大多数问题都与我的问题无关，尽管我认为这个问题对其他初学者很有用。所以这是代码。

（pi.h）我的结构如何布置

#ifndef __PI_TEST_H
#define __PI_TEST_H

#include <stdio.h>
#include <stdlib.h>

struct piS                  //struct for threading
{
    int threads;  //amount of threads running
    int iterations;  //amount of iterations  
    int operation;  //whether to add or subtract
    double total;   //value of pi
};

double calcPi(int numIter);
void *piPthreads(void *info);

#endif

（pi.c）我如何将值放入struct并计算pi

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <pthread.h>
#include "pi.h"

/***************************************************
 * struct for pthreads
***************************************************/

void *piPthreads(void *arg)
{
    struct piS *threader = (struct piS*) arg;
    int operation = threader->operation;    //rank
    int threads = threader->threads;    //count
    int iterations = threader->iterations / threads;
    double begin = operation * iterations;
    double end = begin + iterations;
    printf("iterations = %d\n",iterations);
    threader->total = 0;
    int plusMinus = 1;

    if((int)begin%2)
        plusMinus = -1;

    double loop = begin;

    printf("begin: %d, end: %d\n",begin, end);

    for(loop = begin;loop < end;loop++)
    {
        if(plusMinus == 1)
        {
            threader->total += (1/(2*loop+1));
            printf("threader->total = %d\n",threader->total);
        }
        else
            {
                threader->total -= (1/(2*loop+1));
                printf("threader->total = %d\n",threader->total);
            }
        } 

        return NULL;
    }

（pithreadDriver.c）我如何运行pthread及其处理方式

//driver class to run pthread
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include "pi.h"


/**********************************************
* main()
* handles command line arguments and passes
* for pThreads
**********************************************/
int main(int argc, char** argv){

    int numIter = 100;
    int pthread = 4;


    //Handle command line args
    if(argc != 3)
    {
        printf("Default:Number of threads being set to 4.\n");
        printf("Default:Number of iterations set to 100.\n");

        if(atoi(argv[2]) > 28)
        {
            printf("Default:Number of threads being set to 4\n");
            printf("Max threads possible 28\n");
            pthread = 4;

        }
            printf("Format for running:( executable   iterations    threads)\n");
    }

    if(argc == 3)
    {
        //Assign args
        numIter = atoi(argv[1]);

        //Assign threads
        pthread = atoi(argv[2]);
    }       

    //creating and handling pthreads
    pthread_t *tids = (pthread_t*) malloc(sizeof(pthread_t) * pthread);

    struct piS *threader = (struct piS*) malloc(sizeof(struct piS) * pthread);

    int loop = 0;


    //filling in values for pthreads and creating each thread
    for(loop = 0;loop < pthread;loop++)
    {
        threader[loop].operation = loop;
        threader[loop].threads = pthread;
        threader[loop].iterations = numIter;
        printf("threader[%d].iterations = %d\n",loop,threader[loop].iterations);
        pthread_create(&tids[loop],NULL,piPthreads,&threader);
    }

     double answer = 0;

    for(loop = 0;loop < pthread; loop++)
    {
        pthread_join(tids[loop],NULL);
        answer += threader[loop].total;
        printf("threader[%d] = %d\n",loop,threader[loop].total);
    }

    answer = answer * 4;

    printf("answer is %f using %d iterations\n",answer,numIter);            

    return 0;
}

（out.txt）运行时输出

Default:Number of threads being set to 4.
Default:Number of iterations set to 100.
Format for running:( executable   iterations    threads)
threader[0].iterations = 100
threader[1].iterations = 100
threader[2].iterations = 100
iterations = 0
begin: 0, end: 0
threader[3].iterations = 100
iterations = 0
begin: 0, end: 0
threader[0] = 0
threader[1] = 1
iterations = 0
begin: 0, end: 0
iterations = 0
begin: 0, end: 0
threader[2] = 2
threader[3] = 3
answer is 0.000000 using 100 iterations

我可以看到线程正在正确运行。我还可以看到为什么它不在我的for循环中处理实际的计算。这大部分是讲师向我们展示的代码，只是真正涉及到了但没有结束。我试图在pi.c内使用print语句来弄清楚。我可以看到迭代值未正确放置。从我得到的这段代码来看，它不会以我希望的方式运行。但是我在弄清楚为什么我的迭代没有通过的问题上遇到了问题。

Answer 1

您传递给pthread_create的第四个参数是&threader。该表达式的类型为struct piS **，因为threader的类型为struct piS *。但是在线程函数中，您将参数转换为类型struct piS *。这些不匹配，因此您尝试将一种类型的对象视为另一种类型的对象。这将调用undefined behavior。

您应该将&threader[loop]传递给pthread_create，以便类型匹配。

pthread_create(&tids[loop],NULL,piPthreads,&threader[loop]);

pthread_create（）的问题

1 个答案: