C++ pThread程序沒有運行到完成

Question

我有一個奇怪的問題，我的C++多線程程序沒有運行完成。它應該運行NUM_THREADS - 1次。任何資源，以幫助指向我在正確的方向，將不勝感激！ 目前，這些都是重要的功能

int main(void) { 
int ret; 
//Threads + current thread tracker 
pthread_t threads[NUM_THREADS]; int j = 0; 
int num_transacts = 0; bool isBuy = true; 

srand(time(NULL)); 
Stock MSFT("MSFT"); stocks.push_back(MSFT); 
Stock AMZN("AMZN"); stocks.push_back(AMZN); 
Stock BAC("BAC"); stocks.push_back(BAC); 
Stock NKE("NKE"); stocks.push_back(NKE); 

//Buys or Sells for NUM_THREADS - 1 times 
while (num_transacts < NUM_THREADS) { 
    if (isBuy) { 
     //Percent chance to buy 
     if (((double)rand()/(double)RAND_MAX) < Z) { 
      cout << "Making buy thread.\n"; 
      pthread_mutex_lock(&mLock); 

      ret = pthread_create(&threads[j], NULL, buy, NULL); 
      if (ret != 0) { 
       cout << "Thread failed at Buy Thread Create.\n"; 
      } 

      pthread_mutex_unlock(&mLock); 
      cout << "BuyNumTrans: " << num_transacts << "\n"; 

      ++j; 
      ++num_transacts; 
      isBuy = false; 
     } 
    } 
    else { 
     if (bought.size() > 0) { 
      //Percent chance to sell if it has increased or decreased too much in price 
      int s = rand() % bought.size(); 
      if ((bought.at(s).checkPrice()) > (((1 + X)*bought.at(s).getCost())) || (bought.at(s).checkPrice()) < (((1 + Y)*bought.at(s).getCost()))) { 
       cout << "Making sell thread.\n"; 

       pthread_mutex_lock(&mLock); 
       ret = pthread_create(&threads[j], NULL, sell, (void*) &s); 
       if (ret != 0) { 
        cout << "Thread failed at Sell Thread Create.\n"; 
       } 

       pthread_mutex_unlock(&mLock); 
       cout << "SellNumTrans: " << num_transacts << "\n"; 

       ++j; 
       ++num_transacts; 
      } 
      //Gets a new price possibility 
      bought.at(s).getPrice(); 
     } 
     isBuy = true; 
    } 
} 

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

return 0; 
} 

pthread_mutex_t mLock; 
pthread_mutex_t bLock; 
pthread_mutex_t sLock; 
vector<Stock> stocks; 
vector<Stock> bought; 
int balance = 1000000, yield = 0, profit = 0, Tcost = 0; 

//In format BUY MSFT 100 35.2 
//In format SELL MSFT 80 45 
void* processTransact(void* argument) { 
    string* arg = (string*)argument; 
    istringstream iss(*arg); 
    vector<string> words{ istream_iterator<string>(iss), istream_iterator<string> {} }; 

    if (words.front() == "BUY") { 
     words.erase(words.begin()); 

     //gets the symbol name 
     string symbol = words.front(); 
     words.erase(words.begin()); 

     //gets num of stocks to buy 
     string a = words.front(); 
     int buyNum = atoi(a.c_str()); 
     words.erase(words.begin()); 

     //gets the price per share 
     a = words.front(); 
     int sharePrice = atoi(a.c_str()); 

     //update num_shares, cost, balance, and Tcost 
     Stock newBuy(symbol, buyNum, sharePrice); 

     balance -= (buyNum * sharePrice); 
     bought.push_back(newBuy); 

     cout << "Bought stock... " << balance << endl; 

     pthread_exit(NULL); 
    } 
    else { 
     words.erase(words.begin()); 

     //gets the symbol name 
     string symbol = words.front(); 
     words.erase(words.begin()); 

     //gets num of stocks to sell 
     string a = words.front(); 
     int buyNum = atoi(a.c_str()); 
     words.erase(words.begin()); 

     //gets the price per share 
     a = words.front(); 
     int sharePrice = atoi(a.c_str()); 

     a = words.front(); 
     int s = atoi(a.c_str()); 

     //update num_shares, cost, balance, and Tcost 
     balance += (buyNum * sharePrice); 
     bought.erase(bought.begin() + s); 

     cout << "Sold stock... " << balance << endl; 

     pthread_exit(NULL); 
    } 

    sleep(2); 
} 

void* buy(void*) { 
    pthread_mutex_lock(&mLock); 
    pthread_t thread; 
    srand(time(NULL)); 
    int ret; 
    int i = rand() % stocks.size(); 

    //Creates a string that processTransact can parse 
    string transactString = "BUY " + stocks.at(i).getName() + " 100 " + to_string(stocks.at(i).getPrice());//make transaction string 

    ret = pthread_create(&thread, NULL, processTransact, (void*)&transactString); 
    if (ret != 0) { 
     cout << "Error in buy thread process create.\n"; 
    } 

    pthread_join(thread, NULL); 
    pthread_mutex_unlock(&mLock); 
    pthread_exit(NULL); 
} 

void* sell(void* argument) { 
    pthread_mutex_lock(&mLock); 
    pthread_t thread; 
    int ret, s = *((int*)argument);; 

    //Creates a string that processTransact can parse 
    string transactString = "SELL " + bought.at(s).getName() + " 100 " + to_string(bought.at(s).getPrice()) + to_string(s);//make transaction string 

    ret = pthread_create(&thread, NULL, processTransact, (void*)&transactString); 
    if (ret != 0) { 
     cout << "Error in sell thread process create.\n"; 
    } 

    pthread_join(thread, NULL); 
    pthread_mutex_unlock(&mLock); 
    pthread_exit(NULL); 
} 

Answer 1

在上面的代碼我在bought變量訪問看到潛在的未定義行爲問題。這可能是你的問題的原因。

在while循環有行：

if (bought.size() > 0) { 
    //Percent chance to sell if it has increased or decreased too much in price 
    int s = rand() % bought.size(); 

在void* processTransact(void* argument)功能：

bought.push_back(newBuy); 
// Code skipped .... 
bought.erase(bought.begin() + s); 

從processTransact代碼修改的bought大小在單獨的線程中。在while循環訪問bought.size()時，與使用mLock互斥不同步。這意味着您可以在bought.size() > 0驗證後得到空的bought載體。它導致未定義的行爲在rand() % 0。

此外，C++標準不保證thread safety當相同的容器（bought）修改和從不同線程讀取。