Question

我尝试使用pthreads进行相当简单的搜索，我将文本文件分成5列，每个5个线程执行搜索。发生这种情况后，将发生合并以确定输入是否与文本文件中的任何单个条目匹配。但是，当我运行它时，它似乎挂了。我认为我的竞争条件有些变化，但使用DDD进行调试还没有产生任何影响。

我认为我正在创建pthread并正确加入，但我并不确定我是否正确使用互斥锁。

搜索功能在给定列中创建唯一值的链接列表，然后创建一个位掩码，用于保存找到该值的位置。无论如何，如果我运行一个标准的线性搜索，我的测试数据会比我的线程搜索获得多7个结果，我认为这意味着在搜索或合并线程中出现了问题。将批量大小从我的数据集的10％块减少到1或2个值一次增加了匹配的数量，但我仍然错过了几个正确的总数。

如果有人在完成之前有关于程序为什么会挂起（可能是由于搜索或合并线程）的想法，我会很感激帮助。

为了简洁起见，我省略了大约一半的代码，但如果它有用，我可以发布更多代码。

void * search(void* pthread_arg){
  search_thread_param * myParams = (search_thread_param*) pthread_arg;
  int k=0; // how many searches have been done so far
  int m;
  while (k<NUM_PACKETS){
    pthread_mutex_lock(&mutex);
    if(n !=0){
      pthread_cond_wait(&search_cv, &mutex);  // mege is in progress, go to sleep
    }
    pthread_mutex_unlock(&mutex);     // release th lock so the other search threads can acquire it

    for (m =0; m < BATCH; m++)
      myParams->buffer[m] = mySearchFunction(myParams->packet_field[k+m], myParams->rule_field, unique_no[myParams->thread_id]);  // given a value, return its BV

    k=k+m;
    pthread_mutex_lock(&mutex);
    if (n==NUM_FIELDS-1) // this search thread is the only active one
      {
    n++;

    pthread_mutex_unlock(&mutex);   
    pthread_cond_signal(&merge_cv); // wake up merge thread
      } 
    else{  // not the last one goes to sleep
      n++;
      pthread_mutex_unlock(&mutex); 
    }   
  } 
  return NULL;
}

void merge_function(unsigned long b0,unsigned long b1,unsigned long b2,unsigned long b3,unsigned long b4){
  unsigned long final_BV;

  final_BV = b0 & b1 & b2 & b3 & b4;

  if( final_BV )
  int counter = 0;
    while(final_BV){
      counter++;
      final_BV = final_BV >> 1; //bit shift 
    }
    if( counter)
      printf("matched rule %i\n", counter);

}
void * merge (void* pthread_arg){
  merge_thread_param * myParams = (merge_thread_param*) pthread_arg;
  int k=0; // how many merges have been done so far
  int m;

  pthread_mutex_lock(&mutex);
  if (n<NUM_FIELDS) // the first batch is not ready
    pthread_cond_wait(&merge_cv, &mutex);    // go to sleep

  while (k<NUM_PACKETS){
    for (m =0; m < BATCH; m++){
      merge_function(myParams->buffer[0][m],myParams->buffer[1][m],myParams->buffer[2][m],myParams->buffer[3][m],myParams->buffer[4][m]);
    }
      printf("Merge thread: finish merging one batch\n");   
      k=k+m;
      n = 0; //ready to wake up all search threads
      if(k ==NUM_PACKETS){  // the program is over
    pthread_mutex_unlock(&mutex);   
    printf("Merge thread:  I am done, found %i results, compared to %i linear search  n = %i\n",res,lin,n);
    return NULL;
      }
      else  {
    pthread_cond_broadcast(&search_cv);
    pthread_mutex_unlock(&mutex);
    pthread_cond_wait(&merge_cv, &mutex);    // go to sleep
      }  
  }     
  return NULL;
}

int main () {
///////setup info omitted for brevity
  // create search threads
  for (i=0; i< NUM_FIELDS; i++)
    if(pthread_create(&s_thread[i], &attr, search, (void*) &stp[i])!=0){printf("Creating Thread failed!\n");}

  // create merge thread        
  if(pthread_create(&m_thread, &attr, merge, (void*) &mtp)!=0){printf("Creating Thread failed!\n");}

  // join the threads
    for (i=0; i<NUM_FIELDS; i++)
    if (pthread_join(s_thread[i], NULL)==0){printf("joined thread %i\n",i);}
    else{printf("Joining thread %i failed!\n",i);}

  if (pthread_join(m_thread, NULL)!=0){printf("joined merge thread");}
  else{printf("Joining thread failed!\n");}     

  pthread_attr_destroy(&attr);
  pthread_mutex_destroy(&mutex);
  pthread_cond_destroy(&search_cv);
  pthread_cond_destroy(&merge_cv);      
  //free dat memory
  printf("finished joining all the threads");
  fflush(stdout);
  return 0;
}

Answer 1

事实证明，问题是检查是否在合并线程中设置pthread_cond_wait是错误的，导致合并线程在搜索线程之前执行。这意味着合并线程在搜索线程完成生成结果之前完成。搜索线程然后发信号通知一个不存在的线程并进入休眠状态。它从未加入，因为它从未完成。所以，你有它。

Pthread程序在执行pthread_join之前挂起，无法弄清楚原因

1 个答案: