在C中的for循環中創建多個pthread

Question

我正在研究銀行家算法，並且正在使用循環創建我的線程。 問題在於，僅當應創建5個線程時才創建4個線程的循環。 我已經檢查了我的循環，除非缺少任何東西，否則一切似乎都是正確的。

/* these may be any values >= 0 */

#define NUMBER_OF_CUSTOMERS 5
#define NUMBER_OF_RESOURCES 3

/* the available amount of each resource */
int available[NUMBER_OF_RESOURCES];

/*the maximum demand of each customer */
int maximum[NUMBER_OF_CUSTOMERS][NUMBER_OF_RESOURCES];

/* the amount currently allocated to each customer */
int allocation[NUMBER_OF_CUSTOMERS][NUMBER_OF_RESOURCES];

/* the remaining need of each customer */
int need[NUMBER_OF_CUSTOMERS][NUMBER_OF_RESOURCES];

int release_resources(int customer_num, int release[]){
   allocation[customer_num][NUMBER_OF_RESOURCES];
   return 1;
}

pthread_mutex_t mutex;

int main(int argc, char *argv[]){

  pthread_mutex_init(&mutex, NULL);

  pthread_t threads [3];
  int result;
  unsigned index;

  for(index = 0; index < NUMBER_OF_RESOURCES; index++){
    available[index] = strtol(argv[index+1], NULL,10);
  } 

  for(index = 0; index < NUMBER_OF_CUSTOMERS; ++index){
    printf("\nCreating thead %d", index);
    result = pthread_create(&threads[index],NULL,release_resources,1);  
  }

  //printf("Done");
  return 0;
}

Answer 1

如我所見，您的主程序中存在一個錯誤：

int main(int argc, char *argv[]){

  //...

  pthread_t threads [3];
  int result;
  unsigned index;

  //... 

  for(index = 0; index < NUMBER_OF_CUSTOMERS; ++index){
    printf("\nCreating thead %d", index);
    result = pthread_create(&threads[index],NULL,release_resources,1);  
  }

  //...
  return 0;
}

在這種情況下，數組threads 的大小為3個項目 ，而索引（對於for循環） 的范圍為0到4（大小為5個項目） ，請記住常量#define NUMBER_OF_CUSTOMERS 5 。 我很驚訝您獲得4個線程，而該線程應該在發生內存訪問沖突之前創建了3個線程。

您應該使用正確的大小重新定義數組線程，並使用常量NUMBER_OF_CUSTOMERS，如下所示： pthread_t threads [NUMBER_OF_CUSTOMERS];