// 解决哲学家就餐问题
// 每个哲学家可用一个线程来模拟。
// 设有5个哲学家，5只筷子，每个哲学家吃饭时间为一个随机值，哲学家吃饭后的思考时间也是一个随机值。
#include <Windows.h>
#include <iostream>
#include <cstdio>
#include <stdlib.h>
#include <time.h>
/*
（1）奇数号的哲学家先拿起右边的筷子再拿起左边的筷子。

（2）偶数号哲学家先拿起左边的筷子，再拿起右边的筷子。

（3）如果哲学家抢到一只筷子，在抢占另一只筷子时失败，则要放弃已经抢占到的资源。

（4）左右两边都抢到筷子的哲学家，吃完放后释放资源。*/
using namespace std;

HANDLE chop[5];
HANDLE ph[5];
HANDLE mutex;
int nums = 0;

int random()
{
  return rand() % 100 + 20;
}
void eating(int id)
{
  int num = random();
  Sleep(num);
  printf("\t\t\t哲学家%d号吃了%d秒\n", id, num);
}

DWORD WINAPI phthread(LPVOID param)
{
  nums++;
  int id = nums;
  int lc = id - 1;
  int rc = id % 5;
  int times = 0;
  int ret1, ret2;
  while (true)
  {
    Sleep(100);
    if (times >= 2)
      break;
    if (id % 2 == 0)
    {
      ret1 = WaitForSingleObject(chop[lc], 0);
      if (ret1 == WAIT_OBJECT_0)
      {
        ret2 = WaitForSingleObject(chop[rc], 0);
        if (ret2 == WAIT_OBJECT_0)
        {
          WaitForSingleObject(mutex, INFINITE);
          printf("哲学家%d号拿到两只筷子开始吃第%d顿饭。\n", id, times + 1);
          ReleaseMutex(mutex);
          times++;
          WaitForSingleObject(mutex, INFINITE);
          eating(id);
          ReleaseMutex(mutex);
          WaitForSingleObject(mutex, INFINITE);
          printf("\t\t\t哲学家%d号吃完两顿饭啦，放下筷子。\n", id);
          ReleaseMutex(mutex);
          ReleaseSemaphore(chop[rc], 1, NULL);
        }
        ReleaseSemaphore(chop[lc], 1, NULL);
      }
    }
    else
    {
      ret1 = WaitForSingleObject(chop[rc], 0);
      if (ret1 == WAIT_OBJECT_0)
      {
        ret2 = WaitForSingleObject(chop[lc], 0);
        if (ret2 == WAIT_OBJECT_0)
        {
          WaitForSingleObject(mutex, INFINITE);
          printf("哲学家%d号拿到两只筷子开始吃%d顿饭。\n", id, times + 1);
          ReleaseMutex(mutex);
          times++;
          WaitForSingleObject(mutex, INFINITE);
          eating(id);
          ReleaseMutex(mutex);
          WaitForSingleObject(mutex, INFINITE);
          printf("\t\t\t哲学家%d号吃完两顿饭啦，放下筷子。\n", id);
          ReleaseMutex(mutex);
          ReleaseSemaphore(chop[lc], 1, NULL);
        }
        ReleaseSemaphore(chop[rc], 1, NULL);
      }
    }
    WaitForSingleObject(mutex, INFINITE);
    ReleaseMutex(mutex);
  }
  printf("=======哲学家%d吃饱了然后离开了。=======\n", id);
  return 0;
}

int main()
{
  srand((unsigned)time(0));
  mutex = CreateMutex(NULL, false, NULL);
  for (int i = 0; i < 5; ++i)
  {
    chop[i] = CreateSemaphore(NULL, 1, 1, NULL);
  }
  for (int i = 0; i < 5; ++i)
  {
    int j = i + 1;
    ph[i] = CreateThread(NULL, 0, phthread, NULL, 0, NULL);
  }

  Sleep(10000); //释放句柄
  for (int i = 0; i < 5; ++i)
  {
    CloseHandle(ph[i]);
    CloseHandle(chop[i]);
  }
  CloseHandle(mutex);
  Sleep(500);
  system("pause");
  return 0;
}