双核 临界区问题

Question

#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;
}
/********************************
虽然弹出错误提示；
但是命令段显示的是
thread2 sell ticket :100
thread2 sell ticket ：99
thread2 sell ticket ：98
thread2 sell ticket ：97
thread2 sell ticket ：96
thread2 sell ticket ：95
按道理应该是互锁的啊…………

Answer 1

InitializeCriticalSection(&g_csA);
InitializeCriticalSection(&g_csB);
应该放在创建线程之前，不然Enter的时候还没有初始化肯定是会出错的

Answer 2

创建线程后，你又CloseHandle干啥？线程调用时机是不确定的，跟操作系统任务调度算法有关，不要想这种跟线程时机有关的问题。Sleep(1)是达不到睡1ms的精度，至少是10ms以上了。

Answer 3

#3说的是个问题，还有两个线程enter leave的顺序要一样#include <windows.h>
#include <iostream.h>
#include<conio.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 wmain()
{
HANDLE hThreads[2];
InitializeCriticalSection(&g_csA);
InitializeCriticalSection(&g_csB);
hThreads[0]=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL);
hThreads[1]=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL);
//CloseHandle(hThread1);
//CloseHandle(hThread2);
WaitForMultipleObjects(2,hThreads,1,INFINITE);
//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_csA);
Sleep(1);
EnterCriticalSection(&g_csB);
if(tickets>0)
{
Sleep(1);
cout<<"thread2 sell ticket : "<<tickets--<<endl;
}
else
break;
LeaveCriticalSection(&g_csB);
LeaveCriticalSection(&g_csA);
}
cout<<"thread2 is running!"<<endl;
return 0;
}