c++ - 使用 sleep() 时生产者消费者(使用 Monitor)代码不工作？

Question

#include<bits/stdc++.h>
#include<pthread.h>
#include<unistd.h>
#define MAX 10
using namespace std;
class BoundedBuffer
{
private:
  int buffer[MAX];
  int fill, use;
  int fullEntries;
  pthread_mutex_t monitor;  // monitor lock
  pthread_cond_t empty;
  pthread_cond_t full;
public:
  BoundedBuffer ()
  {
    use = fill = fullEntries = 0;
  }
  void produce (int element)
  {
    pthread_mutex_lock (&monitor);
    while (fullEntries == MAX)
      pthread_cond_wait (&empty, &monitor);
    buffer[fill] = element;
    fill = (fill + 1) % MAX;
    fullEntries++;
    //sleep(rand()%2);
    pthread_cond_signal (&full);
    pthread_mutex_unlock (&monitor);
  }
  int consume ()
  {
    pthread_mutex_lock (&monitor);
    while (fullEntries == 0)
      pthread_cond_wait (&full, &monitor);
    int tmp = buffer[use];
    use = (use + 1) % MAX;
    fullEntries--;
    //sleep(rand()%2);
    pthread_cond_signal (&empty);
    pthread_mutex_unlock (&monitor);
    return tmp;
  }
}b;
void* producer(void *arg){
int i=1;
while(true){
b.produce(i);
i++;
}
}
void* consumer(void *arg){
while(true){
cout<<b.consume()<<" ";
}
}
int main(){
pthread_t t1,t2;
pthread_create(&t1,NULL,producer,NULL);
pthread_create(&t2,NULL,consumer,NULL);
pthread_join(t1,NULL);
pthread_join(t2,NULL);
return 0;
}

每当在 BoundedBuffer.consume() 和 BoundedBuffer.produce(int ) 中添加 sleep() 时，它不会打印任何输出。但是当这些函数中没有 sleep() 时，它可以正常工作并将输出打印为应该是。为什么会这样？
引用: http://pages.cs.wisc.edu/~remzi/OSTEP/threads-monitors.pdf

Answer 1

当我使用 fflush(stdout) 时，我看到正在打印输出

while(true){
cout<<"["<<b.consume()<<"] ";
fflush(stdout)
}

输出:

Magnum@SimpleGuy:~ [52]$ ./a.out [1] [2] [3] [4] [5] [6] [7] [8]