学步园

例1 使用关键代码段(临界区)实现线程同步

#include <windows.h>
#include <iostream.h>

DWORD WINAPI Fun1Proc(
  LPVOID lpParameter   // thread data
);

DWORD WINAPI Fun2Proc(
  LPVOID lpParameter   // thread data
);

int tickets=100;

CRITICAL_SECTION g_cs;
void main()
{
 HANDLE hThread1;
 HANDLE hThread2;
 hThread1=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL);
 hThread2=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL);
 CloseHandle(hThread1);
 CloseHandle(hThread2);

 InitializeCriticalSection(&g_cs);
 Sleep(4000);

 DeleteCriticalSection(&g_cs);
}

DWORD WINAPI Fun1Proc(
  LPVOID lpParameter   // thread data
)
{
 while(TRUE)
 {
  EnterCriticalSection(&g_cs);
  if(tickets>0)
  {
   Sleep(1);
   cout<<"thread1 sell ticket : "<<tickets--<<endl;
  }
  else
   break;
  LeaveCriticalSection(&g_cs);
 }
 
 return 0;
}

DWORD WINAPI Fun2Proc(
  LPVOID lpParameter   // thread data
)
{
 
 while(TRUE)
 {
  EnterCriticalSection(&g_cs);
  if(tickets>0)
  {
   Sleep(1);
   cout<<"thread2 sell ticket : "<<tickets--<<endl;
  }
  else
   break;
  LeaveCriticalSection(&g_cs);
 }
 cout<<"thread2 is running!"<<endl;
 return 0;
}

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例2 使用关键代码段(临界区)（创建多个临界区对象时）容易产生死锁，比如下面代码：

#include <windows.h>
#include <iostream.h>

DWORD WINAPI Fun1Proc(
  LPVOID lpParameter   // thread data
);

DWORD WINAPI Fun2Proc(
  LPVOID lpParameter   // thread data
);

int tickets=100;

CRITICAL_SECTION g_csA;
CRITICAL_SECTION g_csB;

void main()
{
 HANDLE hThread1;
 HANDLE hThread2;
 hThread1=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL);
 hThread2=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL);
 CloseHandle(hThread1);
 CloseHandle(hThread2);

 InitializeCriticalSection(&g_csA);
 InitializeCriticalSection(&g_csB);
 Sleep(4000);

 DeleteCriticalSection(&g_csA);
 DeleteCriticalSection(&g_csB);
}

DWORD WINAPI Fun1Proc(
  LPVOID lpParameter   // thread data
)
{
 while(TRUE)
 {
  EnterCriticalSection(&g_csA);
  Sleep(1);
  EnterCriticalSection(&g_csB);
  if(tickets>0)
  {
   Sleep(1);
   cout<<"thread1 sell ticket : "<<tickets--<<endl;
  }
  else
   break;
  LeaveCriticalSection(&g_csB);
  LeaveCriticalSection(&g_csA);
 }
 
 return 0;
}

DWORD WINAPI Fun2Proc(
  LPVOID lpParameter   // thread data
)
{
 
 while(TRUE)
 {
  EnterCriticalSection(&g_csB);
  Sleep(1);
  EnterCriticalSection(&g_csA);
  if(tickets>0)
  {
   Sleep(1);
   cout<<"thread2 sell ticket : "<<tickets--<<endl;
  }
  else
   break;
  LeaveCriticalSection(&g_csA);
  LeaveCriticalSection(&g_csB);
 }
 cout<<"thread2 is running!"<<endl;
 return 0;
}