首先,資源讀取線(xiàn)程可以簡(jiǎn)單設(shè)計(jì)為一個(gè)循環(huán)等待的線(xiàn)程結(jié)構(gòu),每隔一段時(shí)間檢查加載隊(duì)列中是否有內(nèi)容,如果有則進(jìn)行加載工作,如果沒(méi)有則繼續(xù)等待一段時(shí)間。這種方式雖然簡(jiǎn)單清晰,但卻存在問(wèn)題,如果等待時(shí)間設(shè)得過(guò)長(zhǎng),則加載會(huì)產(chǎn)生延遲,如果設(shè)得過(guò)短,則該線(xiàn)程被喚醒的次數(shù)過(guò)于頻繁,會(huì)耗費(fèi)很多不必要的CPU時(shí)間。
然后,主線(xiàn)程是邏輯線(xiàn)程還是渲染線(xiàn)程?因?yàn)檫壿嬀€(xiàn)程需要處理鍵盤(pán)鼠標(biāo)等輸入設(shè)備的消息,所以我起初將邏輯線(xiàn)程設(shè)為主線(xiàn)程,而渲染線(xiàn)程另外創(chuàng)建,但實(shí)際發(fā)現(xiàn),幀數(shù)很不正常,估計(jì)與WM_PAINT消息有關(guān),有待進(jìn)一步驗(yàn)證。于是掉轉(zhuǎn)過(guò)來(lái),幀數(shù)正常了,但帶來(lái)了一個(gè)新的問(wèn)題,邏輯線(xiàn)程如何處理鍵盤(pán)鼠標(biāo)消息?
對(duì)于第一個(gè)問(wèn)題,有兩種解決方案:
第一,我們可以創(chuàng)建一個(gè)Event,資源讀取線(xiàn)程使用WaitForSingleObject等待著個(gè)Event,當(dāng)渲染線(xiàn)程向加載隊(duì)列添加新的需加載的資源后,將這個(gè)Event設(shè)為Signal,將資源讀取線(xiàn)程喚醒,為了安全,我們?nèi)孕枰阡秩揪€(xiàn)程向加載隊(duì)列添加元素,以及資源加載線(xiàn)程從加載隊(duì)列讀取元素時(shí)對(duì)操作過(guò)程加鎖。
第二,使用在渲染線(xiàn)程調(diào)用PostThreadMessage,將資源加載的請(qǐng)求以消息的形式發(fā)送到資源價(jià)值線(xiàn)程,并在wParam中傳遞該資源對(duì)象的指針,資源加載線(xiàn)程調(diào)用WaitMessage進(jìn)行等待,收到消息后即被喚醒,這種解決方案完全不需要加鎖。
對(duì)于第二個(gè)問(wèn)題,我們同樣可以用PostThreadMessage來(lái)解決,在主線(xiàn)程的WndProc中,將邏輯線(xiàn)程需要處理的消息發(fā)送出去,邏輯線(xiàn)程收到后進(jìn)行相關(guān)處理。
需要注意的是,我們必須搞清楚線(xiàn)程是在何時(shí)創(chuàng)建消息隊(duì)列的,微軟如是說(shuō):
The thread to which the message is posted must have created a message queue, or else the call to PostThreadMessage fails. Use one of the following methods to handle this situation.
- Call PostThreadMessage. If it fails, call the Sleep function and call PostThreadMessage again. Repeat until PostThreadMessage succeeds.
- Create an event object, then create the thread. Use the WaitForSingleObject function to wait for the event to be set to the signaled state before calling PostThreadMessage. In the thread to which the message will be posted, call PeekMessage as shown here to force the system to create the message queue.
PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_NOREMOVE)
Set the event, to indicate that the thread is ready to receive posted messages.
看來(lái),我們只需要在線(xiàn)程初始化時(shí)調(diào)一句PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_NOREMOVE)就可以了,然后在主線(xiàn)程中如此這般:
switch ( uMsg )

{
case WM_PAINT:

{
hdc = BeginPaint(hWnd, &ps);
EndPaint(hWnd, &ps);
}
break;
case WM_DESTROY:

{
m_pLogic->StopThread();
WaitForSingleObject( m_pLogic->GetThreadHandle(), INFINITE );
PostQuitMessage(0);
}
break;
default:

{
if ( IsLogicMsg( uMsg ) )

{
PostThreadMessage( m_pLogic->GetThreadID(), uMsg, wParam, lParam );
}
else

{
return DefWindowProc( hWnd, uMsg, wParam, lParam );
}
}
break;
}
在邏輯線(xiàn)程中這般如此:
MSG msg;
while ( m_bRunning )

{
if ( PeekMessage( &msg, NULL, 0, 0, PM_NOREMOVE ) )

{
if ( ! GetMessageW( &msg, NULL, 0, 0 ) )

{
return (int) msg.wParam;
}

MessageProc( msg.message, msg.wParam, msg.lParam );
}

LogicTick();
}
完成!

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