上一節(jié)學(xué)習(xí)了添加ChannelHandler的過程了解了潮改，也明白了添加handler是如何促發(fā)handlerAdded事件楣导。其中還包括了ChannelInitializer這樣特殊的handler，在完成了添加handler的任務(wù)后驶鹉，就從pipeline中刪除了焕毫。
本節(jié)研究刪除ChannelHandler的邏輯惠桃。類似ChannelInitializer這種，handler用完一次就沒什么用的場(chǎng)景惰爬，類似權(quán)限校驗(yàn)喊暖，每次新連接接入需要校驗(yàn)權(quán)限，之后的數(shù)據(jù)傳輸就不需要了撕瞧，這時(shí)候就可以動(dòng)態(tài)的刪掉權(quán)限校驗(yàn)的handler陵叽。如下
class DataServerInitializer extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(
new AuthHandler(),
new DataServerHandler()
);
}
}
class AuthHandler extends SimpleChannelInboundHandler<ByteBuf> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf password) throws Exception {
//校驗(yàn)密碼
if (pass(password)) {
//校驗(yàn)通過，后續(xù)不需要繼續(xù)校驗(yàn)丛版，刪除該handler
ctx.pipeline().remove(this);
}else {
ctx.close();
}
}
private boolean pass(ByteBuf password) {
//ignore: 校驗(yàn)邏輯
return false;
}
}
ChannelHandler是背ChannelHanderContext包裝起來的咨跌。因此，刪除ChannelHandler過程如下:
- 找到
handler對(duì)應(yīng)的ChannelHandlerContext - 從鏈表中刪除
ChannelHandlerContext - 觸發(fā)
handlerRemoved事件
@Override
public final ChannelPipeline remove(ChannelHandler handler) {
//先獲取ChannelHandlerContext再刪除
remove(getContextOrDie(handler));
return this;
}
-
getContextOrDie()找到handler對(duì)應(yīng)的ChannelHandlerContext
private AbstractChannelHandlerContext getContextOrDie(ChannelHandler handler) {
//獲取ChannelHandlerContext硼婿，沒有則拋異常
AbstractChannelHandlerContext ctx = (AbstractChannelHandlerContext) context(handler);
if (ctx == null) {
throw new NoSuchElementException(handler.getClass().getName());
} else {
return ctx;
}
}
@Override
public final ChannelHandlerContext context(ChannelHandler handler) {
//handler為空則拋異常
if (handler == null) {
throw new NullPointerException("handler");
}
//從鏈表頭開始遍歷到尾锌半，直到,直到找到對(duì)應(yīng)的handler對(duì)應(yīng)的ctx
AbstractChannelHandlerContext ctx = head.next;
for (;;) {
if (ctx == null) {
return null;
}
if (ctx.handler() == handler) {
return ctx;
}
ctx = ctx.next;
}
}
- 先刪除，再調(diào)用
callHandlerRemoved0觸發(fā)handlerRemoved事件
private AbstractChannelHandlerContext remove(final AbstractChannelHandlerContext ctx) {
//斷言，非頭也非尾
assert ctx != head && ctx != tail;
synchronized (this) {
//將ctx從pipeline鏈表中刪除
remove0(ctx);
// If the registered is false it means that the channel was not registered on an eventloop yet.
// In this case we remove the context from the pipeline and add a task that will call
// ChannelHandler.handlerRemoved(...) once the channel is registered.
if (!registered) {
callHandlerCallbackLater(ctx, false);
return ctx;
}
EventExecutor executor = ctx.executor();
if (!executor.inEventLoop()) {
executor.execute(new Runnable() {
@Override
public void run() {
//觸發(fā)HandlerRemoved事件
callHandlerRemoved0(ctx);
}
});
return ctx;
}
}
//觸發(fā)HandlerRemoved事件
callHandlerRemoved0(ctx);
return ctx;
}
- 從鏈表中刪除
private static void remove0(AbstractChannelHandlerContext ctx) {
//鏈表刪除刊殉，修改兩端的前后節(jié)點(diǎn)
AbstractChannelHandlerContext prev = ctx.prev;
AbstractChannelHandlerContext next = ctx.next;
prev.next = next;
next.prev = prev;
}
- 觸發(fā)
handlerRemoved事件殉摔。該動(dòng)作獲取了handler并調(diào)用了回調(diào)函數(shù)handlerRemoved()，最后修改了handler狀態(tài)记焊，標(biāo)記已經(jīng)完成了刪除逸月。
private void callHandlerRemoved0(final AbstractChannelHandlerContext ctx) {
// Notify the complete removal.
try {
//調(diào)用ctx的觸發(fā)事件方法
ctx.callHandlerRemoved();
} catch (Throwable t) {
fireExceptionCaught(new ChannelPipelineException(
ctx.handler().getClass().getName() + ".handlerRemoved() has thrown an exception.", t));
}
}
final void callHandlerRemoved() throws Exception {
try {
// Only call handlerRemoved(...) if we called handlerAdded(...) before.
if (handlerState == ADD_COMPLETE) {
//獲取handler并觸發(fā)事件回調(diào)函數(shù)
handler().handlerRemoved(this);
}
} finally {
// Mark the handler as removed in any case.
//標(biāo)記handler已經(jīng)刪除
setRemoved();
}
}
final void setRemoved() {
//修改handler狀態(tài)為完成刪除
handlerState = REMOVE_COMPLETE;
}
