爲什麼此代碼不一致崩潰？

Question

我正在編寫一個使用eratosthenes'上課的主要篩選程序。我有8個線程正在進行，每個線程負責一段數字範圍[1,2^32]。出於某種原因，有時我的線程數組中的線程[0]不會將其創建到線程創建時的函數。其他人總是（看起來）這樣做。請讓我知道這段代碼有什麼問題。一個警告，但我只是學習C++，所以可能會有語法錯誤等，我認爲這是導致錯誤。花了幾個小時，並縮小到線程[0]並不總是使它的功能。我改變了#define的值，所以調試起來會更容易。 Bug發生任何一種方式。請，我對如何改進該計劃的其他評論不感興趣。它很快就會到期，所以我只想讓它按原樣運行。非常感謝！傳遞給所有線程

#include <iostream> 
#include <pthread.h> 
#include <string.h> 
#include <stdio.h> 
#include <stdlib.h> 
#include <bitset> 
#include <sys/time.h> 
#include <sys/resource.h> 
#include <sched.h> 
#include <vector> 
#include <math.h> 

using namespace std; 

#define NUM_OF_THREADS 8 
#define TWO_TO_THIRTY_SECOND 1000000 //4294967296 
#define SQRT_TWO_TO_THE_THIRTY_SECOND 1000 //65536 
#define TWO_T0_THIRTY_SECOND_OVER_EIGHT 125000 //536870976 

typedef struct { 
    unsigned long composite_to_remove_index; 
    int thread_index; 
    unsigned long prime_number; 
} thread_info_t; 

bitset<TWO_T0_THIRTY_SECOND_OVER_EIGHT> bitmap[NUM_OF_THREADS]; 
static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER; 
static pthread_t thread[NUM_OF_THREADS]; 


static void * threadFunc(void *arg) 
{ 

    thread_info_t info = *(thread_info_t *)arg; 

    bitmap[info.thread_index][info.composite_to_remove_index] = 1; 
    info.composite_to_remove_index += info.prime_number; 

    int index_to_remove = (int)info.composite_to_remove_index; 

    for(; index_to_remove < TWO_T0_THIRTY_SECOND_OVER_EIGHT; index_to_remove += info.prime_number) 
    { 
     if(bitmap[info.thread_index][index_to_remove] == 0) 
     { 
      bitmap[info.thread_index][index_to_remove] = 1; 
      if(info.thread_index == 0) 
      { 
       cout << "bit " << index_to_remove << ": " << bitmap[info.thread_index][index_to_remove] << "\n"; 
      } 
     } 
    } 

    return NULL; 
} 

int main (int argc, char * argv[]) 
{ 
    int thread_ret_val; 
    vector<unsigned long long> prime_numbers; 
    thread_info_t info; 

    for(unsigned long long i = 2; i < SQRT_TWO_TO_THE_THIRTY_SECOND; i++) 
    { 
     if(bitmap[0][i] == 0) 
     { 
      prime_numbers.push_back(i); 
      info.prime_number = i; 

      for(unsigned long j = 0; j < NUM_OF_THREADS; j++) 
      { 
       if(j == 0) 
        info.composite_to_remove_index = i*2; 
       else 
        info.composite_to_remove_index = (((TWO_TO_THIRTY_SECOND/NUM_OF_THREADS)*j) % i); 
       info.thread_index = (int)j; 


       thread_ret_val = pthread_create(&thread[info.thread_index], NULL, threadFunc, (void*)&info); 
       if(thread_ret_val != 0) 
       { 
        cerr << "create thread error " << strerror(thread_ret_val) << "\n"; 
       } 
      } 

      for(int j = 0; j < NUM_OF_THREADS; j++) 
      { 
       pthread_join(thread[j], NULL); 
      } 
     } 
    } 

    return 1; 
} 

Answer 1

info結構，就是要爲每個線程唯一的，但是在這裏線程之間不經意間偶爾共享。問題是info不保證在撥打pthread_create和threadFunc開始之間不變。在調用pthread_create後，您在下一次迭代中更改info的內容，並且可能發生的情況是，只有上一個線程實際上在threadFunc的第一行中複製info。

您應該有std::vector的信息結構，並且每次調用pthread_create時不同info。