Netty在啟動的時候需要配置相應的NioEventLoopGroup,才能保證當channel進行注冊的時候能夠注冊相應的eventloop,并且保證當channel接收到請求的時候有相應的eventloop交給相應的channelPipeline進行處理。
在NioEventLoopGroup的繼承鍊中,NioEventLoopGroup的構造方法實際在其超類的超類MultithreadEventExecutorGroup中進行。
protected MultithreadEventExecutorGroup(int nThreads, ThreadFactory threadFactory, Object... args) {
if (nThreads <= 0) {
throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads));
}
if (threadFactory == null) {
threadFactory = newDefaultThreadFactory();
}
children = new SingleThreadEventExecutor[nThreads];
if (isPowerOfTwo(children.length)) {
chooser = new PowerOfTwoEventExecutorChooser();
} else {
chooser = new GenericEventExecutorChooser();
}
for (int i = 0; i < nThreads; i ++) {
boolean success = false;
try {
children[i] = newChild(threadFactory, args);
success = true;
} catch (Exception e) {
// TODO: Think about if this is a good exception type
throw new IllegalStateException("failed to create a child event loop", e);
} finally {
if (!success) {
for (int j = 0; j < i; j ++) {
children[j].shutdownGracefully();
}
for (int j = 0; j < i; j ++) {
EventExecutor e = children[j];
try {
while (!e.isTerminated()) {
e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
}
} catch (InterruptedException interrupted) {
Thread.currentThread().interrupt();
break;
}
}
}
}
}
在其構造方法中,首先保證傳入的nThread參數大于0,而該參數就是該eventLoopGroup中線程的數量。在構造方法的一開始,就會建立一個SingleThreadEventExecutor數組,顧名思義,這個數組就是存放單個線程的容器,而這個數組的大小也恰恰就是傳入的nThread的值。
之後便會在這個數組中一個個通過newChild()方法獲得新的NioEventLoop,而NioEventLoop恰恰繼承自SingleThreadEventExecutor。
newChild()方法在NioEventLoopGroup中被實作。
protected EventExecutor newChild(
ThreadFactory threadFactory, Object... args) throws Exception {
return new NioEventLoop(this, threadFactory, (SelectorProvider) args[0]);
}
在這裡,會生成新的NioEventLoop,也就是需要和channel綁定的eventLoop,但在這裡隻是單純的建立,所需要的SelectorProvider參數,在一開始的NioEventLoopGroup提供。
NioEventLoop(NioEventLoopGroup parent, ThreadFactory threadFactory, SelectorProvider selectorProvider) {
super(parent, threadFactory, false);
if (selectorProvider == null) {
throw new NullPointerException("selectorProvider");
}
provider = selectorProvider;
selector = openSelector();
}
NioEventLoop的構造方法首先是執行父類的構造方法,其次就是打開selector以便接下來的channel的注冊的時候和channel綁定。在其繼承鍊上SingleThreadEventExector給出了更詳細的構造方法。
protected SingleThreadEventExecutor(
EventExecutorGroup parent, ThreadFactory threadFactory, boolean addTaskWakesUp) {
if (threadFactory == null) {
throw new NullPointerException("threadFactory");
}
this.parent = parent;
this.addTaskWakesUp = addTaskWakesUp;
thread = threadFactory.newThread(new Runnable() {
@Override
public void run() {
boolean success = false;
updateLastExecutionTime();
try {
SingleThreadEventExecutor.this.run();
success = true;
} catch (Throwable t) {
logger.warn("Unexpected exception from an event executor: ", t);
} finally {
for (;;) {
int oldState = STATE_UPDATER.get(SingleThreadEventExecutor.this);
if (oldState >= ST_SHUTTING_DOWN || STATE_UPDATER.compareAndSet(
SingleThreadEventExecutor.this, oldState, ST_SHUTTING_DOWN)) {
break;
}
}
// Check if confirmShutdown() was called at the end of the loop.
if (success && gracefulShutdownStartTime == 0) {
logger.error(
"Buggy " + EventExecutor.class.getSimpleName() + " implementation; " +
SingleThreadEventExecutor.class.getSimpleName() + ".confirmShutdown() must be called " +
"before run() implementation terminates.");
}
try {
// Run all remaining tasks and shutdown hooks.
for (;;) {
if (confirmShutdown()) {
break;
}
}
} finally {
try {
cleanup();
} finally {
STATE_UPDATER.set(SingleThreadEventExecutor.this, ST_TERMINATED);
threadLock.release();
if (!taskQueue.isEmpty()) {
logger.warn(
"An event executor terminated with " +
"non-empty task queue (" + taskQueue.size() + ')');
}
terminationFuture.setSuccess(null);
}
}
}
}
});
taskQueue = newTaskQueue();
}
這裡的重點就是在這裡生成了一個線程賦給了thread成員,也就是說每一個eventloop都與一個線程綁定,生命周期同步,由此可見,每一個channel對應的處理的線程,恰恰就是這裡的thread成員,線上程中,直接調用了該eventLoop的run()方法,這裡的run()方法實作在了NioEventLoop當中。
在完成了線程的建立之後,則生成一個新的阻塞連結清單隊列作為正在排隊等待完成task隊列。
是以,在這裡生成的線程的run()方法真正的實作在NioEventLoop當中。
在channel向eventLoopGroup注冊的時候,就會打開這裡的線程。可以看到注冊的時候的代碼。
在當channel的注冊走到unsafe的時候的register()方法的時候。
public final void register(EventLoop eventLoop, final ChannelPromise promise) {
if (eventLoop == null) {
throw new NullPointerException("eventLoop");
}
if (isRegistered()) {
promise.setFailure(new IllegalStateException("registered to an event loop already"));
return;
}
if (!isCompatible(eventLoop)) {
promise.setFailure(
new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName()));
return;
}
AbstractChannel.this.eventLoop = eventLoop;
if (eventLoop.inEventLoop()) {
register0(promise);
} else {
try {
eventLoop.execute(new OneTimeTask() {
@Override
public void run() {
register0(promise);
}
});
} catch (Throwable t) {
logger.warn(
"Force-closing a channel whose registration task was not accepted by an event loop: {}",
AbstractChannel.this, t);
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise, t);
}
}
}
首先,在這裡通過給channel的eventLoop的指派,完成了channel與一個eventLoop的綁定,但此時,eventLoop中的selector還未礽與channel綁定,需要在register0()繼續這個操作,但是,這裡有一個inEventLoop()方法的判斷,這個方法很簡單,隻是判斷目前線程是不是就是eventLoop在構造方法中建立的時候的那個線程,顯然,這裡的線程應該仍舊是在netty啟動中的主線程,顯然不是eventLoop所綁定的線程,那麼将會調用eventLoop的execute()方法,顯然這裡的execute()方法與線程池的方法不一樣,實作在了SingleThreadEventExecutor裡面。
public void execute(Runnable task) {
if (task == null) {
throw new NullPointerException("task");
}
boolean inEventLoop = inEventLoop();
if (inEventLoop) {
addTask(task);
} else {
startThread();
addTask(task);
if (isShutdown() && removeTask(task)) {
reject();
}
}
if (!addTaskWakesUp && wakesUpForTask(task)) {
wakeup(inEventLoop);
}
}
在剛剛的注冊channel場景下,這裡傳入的是是注冊task實作的是register0()方法。這裡仍舊會通過inEventLoop()方法去判斷,但顯然結果與剛才一樣。那麼将會執行startThread()方法,在startThread()中,在構造方法實作的線程終于被開啟,而剛剛作為參數傳入的注冊task也會在開啟線程之後交給阻塞隊列完成。
那麼,就可以把目光放到NioEventLoop對于線程的run()方法的實作,也就是重點。
protected void run() {
for (;;) {
boolean oldWakenUp = wakenUp.getAndSet(false);
try {
if (hasTasks()) {
selectNow();
} else {
select(oldWakenUp);
if (wakenUp.get()) {
selector.wakeup();
}
}
cancelledKeys = 0;
needsToSelectAgain = false;
final int ioRatio = this.ioRatio;
if (ioRatio == 100) {
processSelectedKeys();
runAllTasks();
} else {
final long ioStartTime = System.nanoTime();
processSelectedKeys();
final long ioTime = System.nanoTime() - ioStartTime;
runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
}
if (isShuttingDown()) {
closeAll();
if (confirmShutdown()) {
break;
}
}
} catch (Throwable t) {
logger.warn("Unexpected exception in the selector loop.", t);
// Prevent possible consecutive immediate failures that lead to
// excessive CPU consumption.
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// Ignore.
}
}
}
}
在run()方法中是一個死循環,在循環得到一開始,首先會通過hasTasks()判斷這時在阻塞隊列中是否還有未完成的任務。如果隊列中仍舊存在,則會直接調用selectNow,否則會通過select()方法去取得io資訊。selectNow()與select()的差別在于selectNow()沒有tiemout,及時channel沒有已經就緒的資訊也會立即傳回,這也符合隊列中仍舊還有未完成的task任務的場景。而如果阻塞隊列已空,則會直接調用nioEventLoop的select()方法。
private void select(boolean oldWakenUp) throws IOException {
Selector selector = this.selector;
try {
int selectCnt = 0;
long currentTimeNanos = System.nanoTime();
long selectDeadLineNanos = currentTimeNanos + delayNanos(currentTimeNanos);
for (;;) {
long timeoutMillis = (selectDeadLineNanos - currentTimeNanos + 500000L) / 1000000L;
if (timeoutMillis <= 0) {
if (selectCnt == 0) {
selector.selectNow();
selectCnt = 1;
}
break;
}
int selectedKeys = selector.select(timeoutMillis);
selectCnt ++;
if (selectedKeys != 0 || oldWakenUp || wakenUp.get() || hasTasks() || hasScheduledTasks()) {
// - Selected something,
// - waken up by user, or
// - the task queue has a pending task.
// - a scheduled task is ready for processing
break;
}
if (Thread.interrupted()) {
// Thread was interrupted so reset selected keys and break so we not run into a busy loop.
// As this is most likely a bug in the handler of the user or it's client library we will
// also log it.
//
// See https://github.com/netty/netty/issues/2426
if (logger.isDebugEnabled()) {
logger.debug("Selector.select() returned prematurely because " +
"Thread.currentThread().interrupt() was called. Use " +
"NioEventLoop.shutdownGracefully() to shutdown the NioEventLoop.");
}
selectCnt = 1;
break;
}
long time = System.nanoTime();
if (time - TimeUnit.MILLISECONDS.toNanos(timeoutMillis) >= currentTimeNanos) {
// timeoutMillis elapsed without anything selected.
selectCnt = 1;
} else if (SELECTOR_AUTO_REBUILD_THRESHOLD > 0 &&
selectCnt >= SELECTOR_AUTO_REBUILD_THRESHOLD) {
// The selector returned prematurely many times in a row.
// Rebuild the selector to work around the problem.
logger.warn(
"Selector.select() returned prematurely {} times in a row; rebuilding selector.",
selectCnt);
rebuildSelector();
selector = this.selector;
// Select again to populate selectedKeys.
selector.selectNow();
selectCnt = 1;
break;
}
currentTimeNanos = time;
}
if (selectCnt > MIN_PREMATURE_SELECTOR_RETURNS) {
if (logger.isDebugEnabled()) {
logger.debug("Selector.select() returned prematurely {} times in a row.", selectCnt - 1);
}
}
} catch (CancelledKeyException e) {
if (logger.isDebugEnabled()) {
logger.debug(CancelledKeyException.class.getSimpleName() + " raised by a Selector - JDK bug?", e);
}
// Harmless exception - log anyway
}
}
在這裡,将會有時間timeout的嘗試去取io資訊,在不斷嘗試取得io資訊的過程中,一旦取到或者阻塞隊列 中又有新的任務或者有了新的定時任務需要執行都會導緻select過程的中斷。
在完成select()方法之後,回到NioEventLoop的run()方法。
可以看到一個ioRatio參數,表示了執行io資訊與執行隊列中的task配置的時間百分比。如果配置了100,那麼執行隊列中的任務會直到處理完資訊之後開始,并直到處理完隊列中的task之後才會繼續嘗試去取得select key,如果不是100,那麼将會給執行隊伍中task任務的時間設為執行io資料時間的(100- ioRatio)/ioRatio百分比的timeout。
首先看到處理io資料的processSelectedKeys()方法,在processSelectedKeys()方法中,如果在剛剛select()方法中取得到了select key,那麼将會直接進入processSelectedKeyOptimized()方法處理剛剛取得到的select key。
private void processSelectedKeysOptimized(SelectionKey[] selectedKeys) {
for (int i = 0;; i ++) {
final SelectionKey k = selectedKeys[i];
if (k == null) {
break;
}
// null out entry in the array to allow to have it GC'ed once the Channel close
// See https://github.com/netty/netty/issues/2363
selectedKeys[i] = null;
final Object a = k.attachment();
if (a instanceof AbstractNioChannel) {
processSelectedKey(k, (AbstractNioChannel) a);
} else {
@SuppressWarnings("unchecked")
NioTask<SelectableChannel> task = (NioTask<SelectableChannel>) a;
processSelectedKey(k, task);
}
if (needsToSelectAgain) {
// null out entries in the array to allow to have it GC'ed once the Channel close
// See https://github.com/netty/netty/issues/2363
for (;;) {
if (selectedKeys[i] == null) {
break;
}
selectedKeys[i] = null;
i++;
}
selectAgain();
// Need to flip the optimized selectedKeys to get the right reference to the array
// and reset the index to -1 which will then set to 0 on the for loop
// to start over again.
//
// See https://github.com/netty/netty/issues/1523
selectedKeys = this.selectedKeys.flip();
i = -1;
}
}
}
這裡會不斷循環全部處理接收到的selectKey。并且 通過取得到selectkey得到相應的channel去繼續在processSelectedKey()方法中進行處理。
private static void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
final NioUnsafe unsafe = ch.unsafe();
if (!k.isValid()) {
// close the channel if the key is not valid anymore
unsafe.close(unsafe.voidPromise());
return;
}
try {
int readyOps = k.readyOps();
// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead
// to a spin loop
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
unsafe.read();
if (!ch.isOpen()) {
// Connection already closed - no need to handle write.
return;
}
}
if ((readyOps & SelectionKey.OP_WRITE) != 0) {
// Call forceFlush which will also take care of clear the OP_WRITE once there is nothing left to write
ch.unsafe().forceFlush();
}
if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
// remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking
// See https://github.com/netty/netty/issues/924
int ops = k.interestOps();
ops &= ~SelectionKey.OP_CONNECT;
k.interestOps(ops);
unsafe.finishConnect();
}
} catch (CancelledKeyException ignored) {
unsafe.close(unsafe.voidPromise());
}
}
這裡将是處理取得到的io資料的重點,通過select key取得他的ops來判斷這次io請求的目的。如果ops為read或者accept,那麼将會直接進入unsafe的read()方法,開始讀取去接收到的byte資料。
其他的write或者connect都與read和accept類似,都是直接通過unsafe開始業務邏輯的操作,并通過pipeline開始自己編寫的業務邏輯對上述情況的操作。
以上就是eventloop對于io資料的操作。
而在完成io操作之後,将會通過runAllTasks()方法開始處理阻塞隊列中的任務。
protected boolean runAllTasks() {
fetchFromDelayedQueue();
Runnable task = pollTask();
if (task == null) {
return false;
}
for (;;) {
try {
task.run();
} catch (Throwable t) {
logger.warn("A task raised an exception.", t);
}
task = pollTask();
if (task == null) {
lastExecutionTime = ScheduledFutureTask.nanoTime();
return true;
}
}
}
首先會通過fetchFromDelayedQueue()方法中嘗試将延時隊列中已經超過deadline時間的定時任務從延遲隊列中取出,保證定時任務的開啟,放入阻塞隊列中準備開始執行。
private void fetchFromDelayedQueue() {
long nanoTime = 0L;
for (;;) {
ScheduledFutureTask<?> delayedTask = delayedTaskQueue.peek();
if (delayedTask == null) {
break;
}
if (nanoTime == 0L) {
nanoTime = ScheduledFutureTask.nanoTime();
}
if (delayedTask.deadlineNanos() <= nanoTime) {
delayedTaskQueue.remove();
taskQueue.add(delayedTask);
} else {
break;
}
}
}
然後在沒有timeout情況下,将不斷從阻塞隊列中擷取任務,直到将隊列中的任務全部處理完成。
以上就是eventloop的功能。