c + + pthread連接有時不起作用

Question

我想在C++中使用pthread。
我用pthread寫了一個mergesort，但有時在pthread_join中，我的代碼有分段錯誤。 （見代碼調試信息）
例如，用於輸入：

4 
5 1 2 3 

輸出是：

** size is more than 2 ** 
I'm alive! 
create 1: 0 
create 2: 0 
After creating! 
i want to exit ... 2 1 
i want to exit ... 2 2 
join 1: 0 
Segmentation fault 

，當它要加入pthead號2，分割故障發生。
在此先感謝！

#include<iostream> 
#include<fstream> 
#include<cstdlib> 
#include<pthread.h> 
using namespace std; 

struct toSort 
{ 
    int size; 
    int * arr; 
    toSort(int _size = 0, int * _arr = NULL) 
    { 
     size = _size; 
     arr = _arr; 
    } 
}; 

void * mergeSort(void *args) 
{ 
    toSort * m = static_cast<toSort*>(args); 
    if(m -> size == 1) 
    { 
     pthread_exit(NULL); 
    } 
    else if(m -> size == 2) 
    { 
     if(*(m -> arr) > *((m -> arr) + 1)) 
     { 
      int temp = *(m -> arr); 
      * (m -> arr) = *((m -> arr) + 1); 
      * ((m -> arr) + 1) = temp; 
     } 
    } 
    else 
    { 
     cerr << "** size is more than 2 **" << endl; 
     int ind = (m -> size)/2; 
     pthread_t t1, t2; 
     toSort *m1, *m2; 
     m1 = new toSort(ind, (m -> arr)); 
     m2 = new toSort((m -> size) - ind, ((m -> arr) + ind)); 
     cerr << "I'm alive!" << endl; 
     cerr << "create 1: " << pthread_create(&t1, NULL, &mergeSort, static_cast<void*>(m1)) << endl; 
     cerr << "create 2: " << pthread_create(&t1, NULL, &mergeSort, static_cast<void*>(m2)) << endl; 
     cerr << "After creating!" << endl; 
     cerr << "join 1: " << pthread_join(t1, NULL) << endl; 
     cerr << "join 2: " << pthread_join(t2, NULL) << endl; 
     cerr << "After join!" << endl; 
     // merge(m -> arr, ind, m -> size); 
    } 
    cout << "i want to exit ... " << (m -> size) << " " << (*(m -> arr)) << endl; 
    pthread_exit(NULL); 
    return 0; 
} 

int main() 
{ 
    int n, arr[100]; 
    // Read 
    cin >> n; 
    for(int i = 0; i < n; i++) 
     cin >> arr[i]; 

    // Solve 
    toSort * ans = new toSort(n, arr); 
    pthread_t getAns; 
    pthread_create(&getAns, NULL, &mergeSort, static_cast<void*>(ans)); 
    pthread_join(getAns, NULL); 
    // Write 
    for(int i = 0; i < n; i++) 
     cout << arr[i] << " "; 
    cout << endl; 
    return 0; 
} 

Answer 1

你有一個錯字

cerr << "create 2: " << pthread_create(&t1, NULL, &mergeSort, static_cast<void*>(m2)) << endl;

您應該使用t2代替t1第二個線程。