首先初始化Pipeline如下
創建channel會調用到如下方法
protected AbstractChannel(Channel parent) {
this.parent = parent;
id = newId();
unsafe = newUnsafe();
pipeline = newChannelPipeline();
}
跟蹤newChannelPipeline()源碼如下
// DefaultChannelPipeline.java
protected DefaultChannelPipeline(Channel channel) {
this.channel = ObjectUtil.checkNotNull(channel, "channel");
succeededFuture = new SucceededChannelFuture(channel, null);
voidPromise = new VoidChannelPromise(channel, true);
// 可見初始化pipeline時,分別實例化了tail和head
tail = new TailContext(this);
head = new HeadContext(this);
head.next = tail;
tail.prev = head;
}
跟蹤代碼可看見TailContext與HeadContext均繼承了AbstractChannelHandlerContext(其中HeadContext比TailContext多實現了一個ChannelOutboundHandler 接口,其包含了一些連接、讀寫的方法聲明)
final class TailContext extends AbstractChannelHandlerContext implements ChannelInboundHandler {
TailContext(DefaultChannelPipeline pipeline) {
super(pipeline, null, TAIL_NAME, true, false);
setAddComplete();
}
...................
--
final class HeadContext extends AbstractChannelHandlerContext
implements ChannelOutboundHandler, ChannelInboundHandler {
private final Unsafe unsafe;
HeadContext(DefaultChannelPipeline pipeline) {
super(pipeline, null, HEAD_NAME, false, true);
unsafe = pipeline.channel().unsafe();
setAddComplete();
}
..................
分析:AbstractChannelHandlerContext的方法結構如下:
總結:以上就是pipeline的簡單初始化過程,下面會繼續深入分析。
添加ChannelHandler
1 首先會調用addLast()方法添加
// DefaultChannelPipeLine.java
public final ChannelPipeline addLast(EventExecutorGroup group, String name, ChannelHandler handler) {
final AbstractChannelHandlerContext newCtx;
// 這裏看出添加channelHandler是同步阻塞的
synchronized (this) {
// 1.1 判斷channelHandler是否可被重複添加
checkMultiplicity(handler);
// 1.2 創建節點並添加到鏈表
newCtx = newContext(group, filterName(name, handler), handler);
addLast0(newCtx);
if (!registered) {
newCtx.setAddPending();
callHandlerCallbackLater(newCtx, true);
return this;
}
// 1.3 添加用戶回調事件 callHandlerAdded0(newCtx)
EventExecutor executor = newCtx.executor();
if (!executor.inEventLoop()) {
newCtx.setAddPending();
executor.execute(new Runnable() {
@Override
public void run() {
callHandlerAdded0(newCtx);
}
});
return this;
}
}
callHandlerAdded0(newCtx);
return this;
}
1.1 是否可被重複復添加 解析
// DefaultChannelPipeLine.java
private static void checkMultiplicity(ChannelHandler handler) {
if (handler instanceof ChannelHandlerAdapter) { // 判斷當前實例類型必須是ChannelHandlerAdapter
ChannelHandlerAdapter h = (ChannelHandlerAdapter) handler;
if (!h.isSharable() && h.added) { // 判斷是否可被添加 (非共享 && 已被添加過) 就拋出異常
throw new ChannelPipelineException(h.getClass().getName() +
" is not a @Sharable handler, so can't be added or removed multiple times.");
}
// 被添加過之後會設置標識爲已被添加過
h.added = true;
}
}
public boolean isSharable() {
// 主要邏輯:判斷當前channelHandler是否有Sharable註解,如果有就表示可共享。可被重複添加,反之不行
Class<?> clazz = getClass();
Map<Class<?>, Boolean> cache = InternalThreadLocalMap.get().handlerSharableCache();
Boolean sharable = cache.get(clazz);
if (sharable == null) {
sharable = clazz.isAnnotationPresent(Sharable.class);
cache.put(clazz, sharable);
}
return sharable;
}
1.2 創建節點並添加到鏈表
newCtx = newContext(group, filterName(name, handler), handler);
其中filterName(name, handler)會遍歷鏈表檢查當前name是否重複,如果不重複返回(否則拋異常)。
然後通過addLast0(newCtx);添加到鏈表中,其過程如下:
private void addLast0(AbstractChannelHandlerContext newCtx) {
AbstractChannelHandlerContext prev = tail.prev;
newCtx.prev = prev;
newCtx.next = tail;
prev.next = newCtx;
tail.prev = newCtx;
}
其大致流程是把newCtx插入到尾結點tail的前面,流程圖如下
1.3 回調添加用戶完成事件 callHandlerAdded0(newCtx),回調之後移除掉
// DefaultChannelPipeline.java
........................
ctx.handler().handlerAdded(ctx);
ctx.setAddComplete();
} catch (Throwable t) {
boolean removed = false;
try {
remove0(ctx);
........................
2 channelHandler的刪除
// DefaultChannelPipeline.java
public final ChannelPipeline remove(ChannelHandler handler) {
remove(getContextOrDie(handler));
return this;
}
刪除的方法解析如下
private AbstractChannelHandlerContext remove(final AbstractChannelHandlerContext ctx) {
assert ctx != head && ctx != tail;
synchronized (this) {
// 2.1 雙向鏈表的方式直接刪除,與上面添加類似
remove0(ctx);
if (!registered) {
callHandlerCallbackLater(ctx, false);
return ctx;
}
EventExecutor executor = ctx.executor();
if (!executor.inEventLoop()) {
executor.execute(new Runnable() {
@Override
public void run() {
callHandlerRemoved0(ctx);
}
});
return ctx;
}
}
// 2.2 執行刪除成功後的事件回調
callHandlerRemoved0(ctx);
return ctx;
}
其他:
pipeline還有一個異常鏈,可通過上面的In/OutBound添加對應的異常處理。