/*
 * Copyright (c) 2000-2008
 * Author: Weiming Zhou
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  
 */

#include <windows.h>
#include <stdio.h>
#include "CapiGlobal.h"


typedef struct RWLOCK_st {
    LOCK    ReadLock;     /* 讀操作鎖，主要用來保護計數器變量的讀寫 */
    LOCK    WriteLock;    /* 寫操作鎖 */
    UINT    uReadCount;   /* 正在進行的讀操作的數量 */
} RWLOCK;

/**	讀寫鎖的創建函數，負責創建一個讀寫鎖對象	
	@return	RWLOCK * - RWLOCK指針，失敗返回NULL	
*/
RWLOCK *RWLock_Create(void)
{
    RWLOCK  *pRWLock;
    pRWLock = (RWLOCK *)malloc(sizeof(RWLOCK));
    if ( pRWLock != NULL )
    {
        pRWLock->ReadLock = LockCreate();
        if ( pRWLock->ReadLock != NULL )
        {
            pRWLock->WriteLock = LockCreate();
            pRWLock->uReadCount = 0;
        }
        else
        {
            free(pRWLock);
            pRWLock = NULL;
        }
    }
    return pRWLock;
}

/**	釋放一個RWLOCK對象

	@param	RWLOCK *pRWLock - 讀寫鎖對象指針	
	@return	void - 無	
*/
void RWLock_Destroy(RWLOCK *pRWLock)
{
    if ( pRWLock != NULL )
    {
        LockClose(pRWLock->ReadLock);
        LockClose(pRWLock->WriteLock);
        free(pRWLock);
    }
}

/**	讀寫鎖的讀操作鎖函數，有讀操作時需要調用這個函數進行讀操作保護

	@param	RWLOCK *pRWLock - 讀寫鎖對象指針	
	@return	void - 無	
*/
void RWLock_LockRead(RWLOCK *pRWLock)
{
    Lock(pRWLock->ReadLock);
    
    pRWLock->uReadCount += 1;

    if ( pRWLock->uReadCount == 1 )
    {
        /* 當是第1個讀者的時候，需要將寫鎖鎖上防止寫操作 */
        Lock(pRWLock->WriteLock);
    }

    Unlock(pRWLock->ReadLock);
}

/**	讀寫鎖的讀操作解鎖函數，需要和RWLock_LockRead()函數配對使用

	@param	RWLOCK *pRWLock - 讀寫鎖對象指針	
	@return	void - 無	
*/
void RWLock_UnlockRead(RWLOCK *pRWLock)
{
    Lock(pRWLock->ReadLock);
    
    pRWLock->uReadCount -= 1;
    
    if ( pRWLock->uReadCount == 0 )
    {
        /* 當沒有讀者的時候，需要將些鎖釋放以便于其他任務可以進行寫操作 */
        Unlock(pRWLock->WriteLock);
    }
    
    Unlock(pRWLock->ReadLock);
}

/**	讀寫鎖的寫操作鎖函數，寫操作發生前需要先調用這個函數進行寫操作保護 

	@param	RWLOCK *pRWLock - 讀寫鎖對象指針	
	@return	void - 無	
*/
void RWLock_LockWrite(RWLOCK *pRWLock)
{
    Lock(pRWLock->WriteLock);
}

/**	讀寫鎖的寫操作解鎖函數，需要和RWLock_LockWrite()函數配對使用 

	@param	RWLOCK *pRWLock - 讀寫鎖對象指針	
	@return	void - 無	
*/
void RWLock_UnlockWrite(RWLOCK *pRWLock)
{
    Unlock(pRWLock->WriteLock);
}