在 C/Linux 中使用多线程的 Eratosthenes 筛选

Question

我目前正在使用 C 多线程计算 Eratosthenes Sieve。

目标是首先创建一个主线程，使用split函数来划分多个线程上的数字探索。

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

void *creat_thread(int *nbThreads);

void *SieveEratosthenes(int *tailleTab);

int* tab;
int sizeTab;
int nbTachesParThread=0;

int main(void)
{
  int nbThreads;
  int n;
  do{
    printf("Enter an integer > 1 :  ");
    scanf("%d", &n);
  } while(n<2);


  sizeTab = n+1;
  tab = (int*)malloc(tailleTab*sizeof(int));
  for (unsigned int i=0; i<tailleTab; i++)
  {
    tab[i] = 1;
  }

  do{
    printf("Enter a number positive number of threads : ");
    scanf("%d", &nbThreads);
  } while(nbThreads<1);

  pthread_t threadPrincipal;

  if (pthread_create(&threadPrincipal, NULL, creat_thread, NULL)) {
    perror("pthread_create");
    return EXIT_FAILURE;
  }

  if (pthread_join(threadPrincipal, NULL)) {
    perror("pthread_join");
    return EXIT_FAILURE;
  }

  printf("The Prime numbers are : \n");
  for(unsigned int i=0; i<sizeTab; i++)
  {
    if(tab[i]==1)
    {
      printf("%d\n", (i));
    }
  }


}

void *creat_thread(int *nbThreads)
{

  int nbTachesParThread = (int) sqrt(sizeTab) / nbThreads;
  pthread_t* threads = (pthread_t*)malloc(nbThreads*sizeof(pthread_t));

  int plageThreadi = nbTachesParThread;

  for(int i = 0; i < nbThreads; ++i)
    pthread_create (&threads[i], NULL, SieveEratosthenes, plageThreadi);
    plageThreadi += nbTachesParThread;
}

void *SieveEratosthenes(int *plageThread)
{


  for( int i=(plageThread - nbTachesParThread); i<=plageThread; i++)
  {
    if (tab[i] == 1)
    {
      for (int j = i*i; j<sizeTab; j += i)
      {
        tab[j]=0;
      }
    }
  }

}

我试图实现一个代码，但在运行时出现错误：

segmentation error (core dumped)  

Answer 1

除了my comment here 中提到的问题之外，还有更多需要解决的问题：

首先，PThread 函数必须是void *(*)(void*) 类型。代码使用的类型是void *(*)(int*)。不好。

第二，代码错过了加入工作线程，因此分配线程在创建所有工作线程后结束，然后它加入main()，然后访问工作人员最有可能仍在工作的变量导致未定义行为这样做然后结束，结束过程。结束进程会取消所有工作线程。

Answer 2

我听从了您的建议，并创建了一个结构来包含所有线程将使用的变量。

但是我注意到有时它可以工作（它很好地显示素数）但有时它不起作用并且它只显示 0 或从 0 到 i 的所有数字。

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


void *creat_thread(void* arg);

void *SieveEratosthenes(void* arg);

struct param
{
  int* tab;
  int sizeTab;
  int nbTachesParThread;
  int nbThreads;
  int plageThreadi;
  int plageThreadPrecedent;
};

int main(void)
{
  struct param p;

  int n;
  do{
    printf("Enter an integer > 1 :  ");
    scanf("%d", &n);
  } while(n<2);


  p.sizeTab = n+1;

  p.tab = (int*)malloc(p.sizeTab*sizeof(int));
  for (unsigned int i=0; i<p.sizeTab; i++)
  {
    p.tab[i] = 1;
  }

  do{
    printf("Enter a number positive number of threads : ");
    scanf("%d", &p.nbThreads);
  } while(p.nbThreads<1);

  pthread_t threadPrincipal;

  if (pthread_create(&threadPrincipal, NULL, (void*)creat_thread, &p)) {
    perror("pthread_create");
    return EXIT_FAILURE;
  }
  if (pthread_join(threadPrincipal, NULL)) {
    perror("pthread_join");
    return EXIT_FAILURE;
  }

  printf("The Prime numbers are : \n");
  for(unsigned int i=0; i<p.sizeTab; i++)
  {
    if(p.tab[i]==1)
    {
      printf("%d\n", i);
    }
  }
}

void *creat_thread(void* arg)
{
  struct param *args = (void*)arg;
  args->nbTachesParThread = (int) sqrt(args->sizeTab) / args->nbThreads;
  pthread_t* threads = (pthread_t*)malloc(args->nbThreads*sizeof(pthread_t));

  args->plageThreadi = args->nbTachesParThread;

  for(int i = 0; i < args->nbThreads; ++i)
    {
      pthread_create (&threads[i], NULL, (void*)SieveEratosthenes, &(*args));
      args->plageThreadPrecedent = args->plageThreadi;
      args->plageThreadi += args->nbTachesParThread;
    }

  for(int i = 0; i < args->nbThreads; ++i)
      {
        pthread_join(threads[i], NULL);
      }
  pthread_exit(NULL);
}

void *SieveEratosthenes(void* arg)
{
  struct param *args = (void *)arg;
  for(int i=(args->plageThreadPrecedent); i<=args->plageThreadi; i++)
  {
    if (args->tab[i] == 1)
    {
      for (int j = i*i; j<args->sizeTab; j += i)
      {
        args->tab[j]=0;
      }
    }

  }
  pthread_exit(NULL);
}

Answer 3

我已经修改了我的代码，所以实际上我没有更多的错误代码，但是一旦我输入了 2 个变量（要计算的数字 + 线程数），程序就会运行但什么也不显示。

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


void *creat_thread();

void *SieveEratosthenes();

int* tab;
int sizeTab = 0;
int nbTachesParThread=0;
int nbThreads = 0;
int plageThreadi = 0;
int plageThreadPrecedent = 0;

int main(void)
{
  int n;
  do{
    printf("Enter an integer > 1 :  ");
    scanf("%d", &n);
  } while(n<2);


  sizeTab = n+1;
  tab = (int*)malloc(sizeTab*sizeof(int));
  for (unsigned int i=0; i<sizeTab; i++)
  {
    tab[i] = 1;
  }

  do{
    printf("Enter a number positive number of threads : ");
    scanf("%d", &nbThreads);
  } while(nbThreads<1);

  pthread_t threadPrincipal;

  if (pthread_create(&threadPrincipal, NULL, creat_thread, NULL)) {
    perror("pthread_create");
    return EXIT_FAILURE;
  }

  if (pthread_join(threadPrincipal, NULL)) {
    perror("pthread_join");
    return EXIT_FAILURE;
  }

  printf("The Prime numbers are : \n");
  for(unsigned int i=0; i<sizeTab; i++)
  {
    if(tab[i]==1)
    {
      printf("%d\n", (i));
    }
  }
}

void *creat_thread()
{

  int nbTachesParThread = (int) sqrt(sizeTab) / nbThreads;
  pthread_t* threads = (pthread_t*)malloc(nbThreads*sizeof(pthread_t));

  int plageThreadi = nbTachesParThread;

  for(int i = 0; i < nbThreads; ++i)
    {
      pthread_create (&threads[i], NULL, SieveEratosthenes, NULL);
      pthread_join(threads[i], NULL);
      plageThreadPrecedent = plageThreadi;
      plageThreadi += nbTachesParThread;
    }

  for(int i = 0; i < nbThreads; ++i)
      {
        pthread_join(threads[i], NULL);
      }
  pthread_exit(NULL);
}

void *SieveEratosthenes()
{
  for(int i=(plageThreadPrecedent); i<=plageThreadi; i++)
  {
    if (tab[i] == 1)
    {
      for (int j = i*i; j<sizeTab; j += i)
      {
        tab[j]=0;
      }
    }
  }
  pthread_exit(NULL);
}