假設有 5 個哲學家，有 5 把叉子，每個哲學家有思考，飢餓，和吃飯三個狀態。我們用 5 個訊號量分別表示 5 把叉子
一. windows實現

原始碼如下：

// PhilosopherDining.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "windows.h"

#include <process.h>
#include <time.h>
#include <stdlib.h>
#include <stdio.h>

#include <iostream>

using namespace std;

const unsigned int PHILOSOPHER_NUM=5;
const char THINKING=1;
const char HUNGRY=2;
const char DINING=3;

// each fork has a semaphore
HANDLE semph[PHILOSOPHER_NUM];

// Mutex for printing
HANDLE mutex;

void philosopherProc(void* param);

int main(int argc, char* argv[])
{
 int i;
 srand(time(0));

 mutex = CreateMutex(NULL, false, NULL);
 for (i=0; i<PHILOSOPHER_NUM; i++)
 {
  semph[i] = CreateSemaphore(NULL, 1, 1, NULL);
  _beginthread(philosopherProc, 0, (void*)&i);
  Sleep(10);
 }

 Sleep(2000);
 return 0;
}

void philosopherProc(void* param)
{
 int myid;
 char idStr[128];
 char stateStr[128];
 char mystate;
 int ret;
 unsigned int leftFork;
 unsigned int rightFork;

 myid = *((int*)(param));
 itoa(myid, idStr, 10);

 //cout << "philosopher " << myid << " begin......" << endl;
 Sleep(10);

 // initial state is THINKING
 mystate = THINKING;
 leftFork = (myid) % PHILOSOPHER_NUM;
 rightFork = (myid + 1) % PHILOSOPHER_NUM;

 while (true)
 {
  switch(mystate)
  {
  case THINKING:
   // changing my state
   mystate = HUNGRY;
   strcpy(stateStr, "HUNGRY");
   break;

  case HUNGRY:
   strcpy(stateStr, "HUNGRY");
   // first test the left fork ...
   ret = WaitForSingleObject(semph[leftFork], 0);
   if (ret == WAIT_OBJECT_0)
   {
    // left fork is ok, take it up !
    // then test the right fork ...
    ret = WaitForSingleObject(semph[rightFork], 0);
    if (ret == WAIT_OBJECT_0)
    {
     // right fork is also ok !
     // changing my state
     mystate = DINING;
     strcpy(stateStr, "DINING");
    }
    else
    {
     // right fork is being used by others, so I must put down
     // the left fork.
     ReleaseSemaphore(semph[leftFork], 1, NULL);
    }
   }
   break;

  case DINING:
   // put down both the left and right fork
   ReleaseSemaphore(semph[leftFork], 1, NULL);
   ReleaseSemaphore(semph[rightFork], 1, NULL);

   // changing my state
   mystate = THINKING;
   strcpy(stateStr, "THINKING");
   break;
  }

  // print my state
  WaitForSingleObject(mutex, INFINITE);
  cout << "philosopher " << myid << " is : " << stateStr << endl;  
  ReleaseMutex(mutex);
  
  // sleep a random time : between 1 - 5 s
  int sleepTime;
  sleepTime = 1 + (int)(5.0*rand()/(RAND_MAX+1.0));
  Sleep(sleepTime*10);
 }
}

 二. linux實現

^{PhilosopherDining.cpp}

^{#include <iostream>
#include <string>
#include <pthread.h>
#include <unistd.h>
#include <semaphore.h>}

^{#include "RasUtil.h"}

^{using namespace std;}

^{const unsigned int PHILOSOPHER_NUM=5;
const char THINKING=1;
const char HUNGRY=2;
const char DINING=3;}

^{// each fork has a semaphore
sem_t semph[PHILOSOPHER_NUM];}

^{// Mutex for printing
pthread_mutex_t mutex;}

^{void* philosopherProc(void* param);}

^{int main(int argc, char* argv[])
{
 int i;
 srand(getpid());
 pthread_t philosopherThread[PHILOSOPHER_NUM];
 int phId[PHILOSOPHER_NUM];}

 ^{pthread_mutex_init(&mutex, NULL);
 for (i=0; i<PHILOSOPHER_NUM; i++)
 {
         phId[i] = i;
  sem_init(&semph[i], 0, 1);
  pthread_create(&philosopherThread[i], NULL, philosopherProc, (void*)(&phId[i]));
  usleep(50);
 }}

 ^{sleep(3);
 return 0;
}}

^{void* philosopherProc(void* param)
{
 int myid;
 char idStr[128];
 char stateStr[128];
 char mystate;
 int ret;
 unsigned int leftFork;
 unsigned int rightFork;}

 ^{myid = *((int*)(param));
 RasUtil::intToStr(myid, idStr);
 
 cout << "philosopher " << myid << " begin......" << endl;
 //usleep(10);}

 ^{// initial state is THINKING
 mystate = THINKING;
 leftFork = (myid) % PHILOSOPHER_NUM;
 rightFork = (myid + 1) % PHILOSOPHER_NUM;}

 ^{while (true)
 {
  switch(mystate)
  {
  case THINKING:
   // changing my state
   mystate = HUNGRY;
   strcpy(stateStr, "HUNGRY");
   break;}

  ^{case HUNGRY:
   strcpy(stateStr, "HUNGRY");
   // first test the left fork ...
   ret = sem_trywait(&semph[leftFork]);
   if (ret == 0)
   {
    // left fork is ok, take it up !
    // then test the right fork ...
    ret = sem_trywait(&semph[rightFork]);
    if (ret == 0)
    {
     // right fork is also ok !
     // changing my state
     mystate = DINING;
     strcpy(stateStr, "DINING");
    }
    else
    {
     // right fork is being used by others, so I must put down
     // the left fork.
     sem_post(&semph[leftFork]);
    }
   }
   break;}

  ^{case DINING:
   // put down both the left and right fork
   sem_post(&semph[leftFork]);
   sem_post(&semph[rightFork]);}

   ^{// changing my state
   mystate = THINKING;
   strcpy(stateStr, "THINKING");
   break;
  }}

  ^{// print my state
  pthread_mutex_lock(&mutex);
  cout << "philosopher " << myid << " is : " << stateStr << endl;  
  pthread_mutex_unlock(&mutex);
  
  // sleep a random time : between 1 - 5 s
  int sleepTime;
  sleepTime = 1 + (int)(5.0*rand()/(RAND_MAX+1.0));
  usleep(sleepTime*10);
 }
}}

RasUtil.h : 完成整數轉換為字串

#ifndef _RasUtil_h_
#define _RasUtil_h_

class RasUtil
{
public:
 static inline void intToStr(int i, char* str);

};

inline void RasUtil::intToStr(int i, char* str)
{
    int dec;
    int sign;
    char* p;

    p = ecvt(i, 10, &dec, &sign);
    strcpy(str, p);
    str[dec] = 0;
}

#endif