读写锁的一个简单实现

#include  < stdio.h >
#include  < assert.h >
#include  < windows.h >

#define  LOCK_READ 0
#define  LOCK_WRITE 1

class  rwlock{
     public :
        rwlock();
         ~ rwlock();

     public :
         void   lock ( int  direct);
         void  unlock( int  direct);

         void  lock_exclusive( void );
         void  unlock_exclusive( void );

         void  wrlock() {  lock (LOCK_WRITE); }
         void  wrunlock() { unlock(LOCK_WRITE); }

         void  rdlock() {  lock (LOCK_READ); }
         void  rdunlock() { unlock(LOCK_READ); }

     private :
         volatile  LONG count;
         volatile  LONG direct;
        HANDLE finish_event;
        CRITICAL_SECTION start_lock;
};

rwlock::rwlock()
{
    count  =   0 ;
    direct  =   0 ;
    finish_event  =  CreateEvent(NULL, FALSE, FALSE, NULL);
    InitializeCriticalSection( & start_lock);
}

rwlock:: ~ rwlock()
{
    assert(count  ==   0 );
    CloseHandle(finish_event);
    DeleteCriticalSection( & start_lock);
}

void  rwlock:: lock ( int  _direct)
{
    EnterCriticalSection( & start_lock);
     while  (count  >   0   &&
            direct  !=  _direct) {
        WaitForSingleObject(finish_event, INFINITE);
    }
    direct  =  _direct;
    InterlockedIncrement( & count);
    LeaveCriticalSection( & start_lock);
}

void  rwlock::unlock( int  _direct)
{
    assert(count  >   0 );
    assert(direct  ==  _direct);
    InterlockedDecrement( & count);
    SetEvent(finish_event);
}

void  rwlock::lock_exclusive( void )
{
    EnterCriticalSection( & start_lock);
     while  (count  >   0   &&
            direct  !=  _direct) {
        WaitForSingleObject(finish_event, INFINITE);
    }
    InterlockedIncrement( & count);
}

void  unlock_exclusive( void )
{
    InterlockedDecrement( & count);
    LeaveCriticalSection( & start_lock);
}

static  DWORD CALLBACK ReadFunc(LPVOID lpVoid)
{
    rwlock  *  plock  =  (rwlock  * )lpVoid;
     while  (  1  ) {
        plock -> rdlock();
        printf( " Start Read: threaid %x\n " , GetCurrentThreadId());
        printf( " Call Read: threaid %x\n " , GetCurrentThreadId());
        printf( " End Read: threaid %x\n " , GetCurrentThreadId());
        plock -> rdunlock();
    }
     return   0 ;
}

int  main( int  argc,  char   *  argv[])
{
    DWORD id;
    rwlock  lock ;

     for  ( int  i  =   0 ; i  <   10 ; i  ++ ) {
        HANDLE handle  =  CreateThread(NULL,  0 , ReadFunc,  & lock ,  0 ,  & id);
        CloseHandle(handle);
    }

     while  (  1  ) {
         lock .wrlock();
        printf( " Start Write: threaid %x\n " , GetCurrentThreadId());
         for  ( int  j  =   0 ; j  <   10 ; j ++ ) {
            printf( " Call Write: threaid %x\n " , GetCurrentThreadId());
        }
        printf( " End Write: threaid %x\n " , GetCurrentThreadId());
         lock .wrunlock();
    }

     return   0 ;
}