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本篇內(nèi)容介紹了“Netty NioEventLoop啟動過程是怎樣的”的有關(guān)知識,在實際案例的操作過程中,不少人都會遇到這樣的困境,接下來就讓小編帶領(lǐng)大家學(xué)習(xí)一下如何處理這些情況吧!希望大家仔細(xì)閱讀,能夠?qū)W有所成!
分析NioEventLoop的execute()接口,主要邏輯如下:
添加任務(wù)隊列
綁定當(dāng)前線程到EventLoop上
調(diào)用EventLoop的run()方法
private static void doBind0( final ChannelFuture regFuture, final Channel channel, final SocketAddress localAddress, final ChannelPromise promise) { // 通過eventLoop來執(zhí)行channel綁定的Task channel.eventLoop().execute(new Runnable() { @Override public void run() { if (regFuture.isSuccess()) { // channel綁定 channel.bind(localAddress, promise).addListener(ChannelFutureListener.CLOSE_ON_FAILURE); } else { promise.setFailure(regFuture.cause()); } } }); }
往下追蹤到 SingleThreadEventExecutor 中 execute 接口,如下:
@Overridepublic void execute(Runnable task) { if (task == null) { throw new NullPointerException("task"); } // 判斷當(dāng)前運行時線程是否與EventLoop中綁定的線程一致 // 這里還未綁定Thread,所以先返回false boolean inEventLoop = inEventLoop(); // 將任務(wù)添加任務(wù)隊列,也就是我們前面講EventLoop創(chuàng)建時候提到的 MpscQueue. addTask(task); if (!inEventLoop) { // 啟動線程 startThread(); if (isShutdown() && removeTask(task)) { reject(); } } if (!addTaskWakesUp && wakesUpForTask(task)) { wakeup(inEventLoop); } }
啟動線程接口:
private void startThread() { // 狀態(tài)比較,最開始時state = 1 ,為true if (state == ST_NOT_STARTED) { // cs操作后,state狀態(tài)設(shè)置為 2 if (STATE_UPDATER.compareAndSet(this, ST_NOT_STARTED, ST_STARTED)) { try { // 啟動接口 doStartThread(); } catch (Throwable cause) { STATE_UPDATER.set(this, ST_NOT_STARTED); PlatformDependent.throwException(cause); } } } }// 執(zhí)行線程啟動方法private void doStartThread() { // 斷言判斷 SingleThreadEventExecutor 還未綁定 Thread assert thread == null; // executor 執(zhí)行任務(wù) executor.execute(new Runnable() { @Override public void run() { // 將 SingleThreadEventExecutor(在我們的案例中就是NioEventLoop) 與 當(dāng)前線程進(jìn)行綁定 thread = Thread.currentThread(); if (interrupted) { thread.interrupt(); } // 設(shè)置狀態(tài)為 false boolean success = false; // 更新最近一次任務(wù)的執(zhí)行時間 updateLastExecutionTime(); try { // 往下調(diào)用 NioEventLoop 的 run 方法,執(zhí)行 SingleThreadEventExecutor.this.run(); success = true; } catch (Throwable t) { logger.warn("Unexpected exception from an event executor: ", t); } finally { ... } } }); }
往下調(diào)用到 NioEventLoop 中的 run 方法,通過無限for循環(huán),主要做以下三件事情:
輪循I/O事件:select(wakenUp.getAndSet(false))
處理I/O事件:processSelectedKeys
運行Task任務(wù):runAllTasks
@Overrideprotected void run() { for (;;) { try { switch (selectStrategy.calculateStrategy(selectNowSupplier, hasTasks())) { case SelectStrategy.CONTINUE: continue; case SelectStrategy.SELECT: // 輪訓(xùn)檢測I/O事件 // wakenUp為了標(biāo)記selector是否是喚醒狀態(tài),每次select操作,都設(shè)置為false,也就是未喚醒狀態(tài)。 select(wakenUp.getAndSet(false)); // 'wakenUp.compareAndSet(false, true)' 總是在調(diào)用 'selector.wakeup()' 之前進(jìn)行評估,以減少喚醒的開銷 // (Selector.wakeup() 是非常耗性能的操作.) // 但是,這種方法存在競爭條件。當(dāng)「wakeup」太早設(shè)置為true時觸發(fā)競爭條件 // 在下面兩種情況下,「wakenUp」會過早設(shè)置為true: // 1)Selector 在 'wakenUp.set(false)' 與 'selector.select(...)' 之間被喚醒。(BAD) // 2)Selector 在 'selector.select(...)' 與 'if (wakenUp.get()) { ... }' 之間被喚醒。(OK) // 在第一種情況下,'wakenUp'設(shè)置為true,后面的'selector.select(...)'將立即喚醒。 直到'wakenUp'在下一輪中再次設(shè)置為false,'wakenUp.compareAndSet(false,true)'將失敗,因此任何喚醒選擇器的嘗試也將失敗,從而導(dǎo)致以下'selector.select(。 ..)'呼吁阻止不必要的。 // 要解決這個問題,如果在selector.select(...)操作之后wakenUp立即為true,我們會再次喚醒selector。 它是低效率的,因為它喚醒了第一種情況(BAD - 需要喚醒)和第二種情況(OK - 不需要喚醒)的選擇器。 if (wakenUp.get()) { selector.wakeup(); } // fall through default: } cancelledKeys = 0; needsToSelectAgain = false; // ioRatio 表示處理I/O事件與執(zhí)行具體任務(wù)事件之間所耗時間的比值。 // ioRatio 默認(rèn)為50 final int ioRatio = this.ioRatio; if (ioRatio == 100) { try { // 處理I/O事件 processSelectedKeys(); } finally { // 處理任務(wù)隊列 runAllTasks(); } } else { // 處理IO事件的開始時間 final long ioStartTime = System.nanoTime(); try { // 處理I/O事件 processSelectedKeys(); } finally { // 記錄io所耗時間 final long ioTime = System.nanoTime() - ioStartTime; // 處理任務(wù)隊列,設(shè)置最大的超時時間 runAllTasks(ioTime * (100 - ioRatio) / ioRatio); } } } catch (Throwable t) { handleLoopException(t); } // Always handle shutdown even if the loop processing threw an exception. try { if (isShuttingDown()) { closeAll(); if (confirmShutdown()) { return; } } } catch (Throwable t) { handleLoopException(t); } } }
private void select(boolean oldWakenUp) throws IOException { Selector selector = this.selector; try { // select操作計數(shù) int selectCnt = 0; // 記錄當(dāng)前系統(tǒng)時間 long currentTimeNanos = System.nanoTime(); // delayNanos方法用于計算定時任務(wù)隊列,最近一個任務(wù)的截止時間 // selectDeadLineNanos 表示當(dāng)前select操作所不能超過的最大截止時間 long selectDeadLineNanos = currentTimeNanos + delayNanos(currentTimeNanos); for (;;) { // 計算超時時間,判斷是否超時 long timeoutMillis = (selectDeadLineNanos - currentTimeNanos + 500000L) / 1000000L; // 如果 timeoutMillis <= 0, 表示超時,進(jìn)行一個非阻塞的 select 操作。設(shè)置 selectCnt 為 1. 并終止本次循環(huán)。 if (timeoutMillis <= 0) { if (selectCnt == 0) { selector.selectNow(); selectCnt = 1; } break; } // 當(dāng)wakenUp為ture時,恰好有task被提交,這個task將無法獲得調(diào)用的機會 // Selector#wakeup. 因此,在執(zhí)行select操作之前,需要再次檢查任務(wù)隊列 // 如果不這么做,這個Task將一直掛起,直到select操作超時 // 如果 pipeline 中存在 IdleStateHandler ,那么Task將一直掛起直到 空閑超時。 if (hasTasks() && wakenUp.compareAndSet(false, true)) { // 調(diào)用非阻塞方法 selector.selectNow(); selectCnt = 1; break; } // 如果當(dāng)前任務(wù)隊列為空,并且超時時間未到,則進(jìn)行一個阻塞式的selector操作。timeoutMillis 為最大的select時間 int selectedKeys = selector.select(timeoutMillis); // 操作計數(shù) +1 selectCnt ++; // 存在以下情況,本次selector則終止 if (selectedKeys != 0 || oldWakenUp || wakenUp.get() || hasTasks() || hasScheduledTasks()) { // - 輪訓(xùn)到了事件(Selected something,) // - 被用戶喚醒(waken up by user,) // - 已有任務(wù)隊列(the task queue has a pending task.) // - 已有定時任務(wù)(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; } // 記錄當(dāng)前時間 long time = System.nanoTime(); // 如果time > currentTimeNanos + timeoutMillis(超時時間),則表明已經(jīng)執(zhí)行過一次select操作 if (time - TimeUnit.MILLISECONDS.toNanos(timeoutMillis) >= currentTimeNanos) { // timeoutMillis elapsed without anything selected. selectCnt = 1; } // 如果 time <= currentTimeNanos + timeoutMillis,表示觸發(fā)了空輪訓(xùn) // 如果空輪訓(xùn)的次數(shù)超過 SELECTOR_AUTO_REBUILD_THRESHOLD (512),則重建一個新的selctor,避免空輪訓(xùn) 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, selector); // 重建創(chuàng)建一個新的selector rebuildSelector(); selector = this.selector; // Select again to populate selectedKeys. // 對重建后的selector進(jìn)行一次非阻塞調(diào)用,用于獲取最新的selectedKeys selector.selectNow(); // 設(shè)置select計數(shù) selectCnt = 1; break; } currentTimeNanos = time; } if (selectCnt > MIN_PREMATURE_SELECTOR_RETURNS) { if (logger.isDebugEnabled()) { logger.debug("Selector.select() returned prematurely {} times in a row for Selector {}.", selectCnt - 1, selector); } } } catch (CancelledKeyException e) { if (logger.isDebugEnabled()) { logger.debug(CancelledKeyException.class.getSimpleName() + " raised by a Selector {} - JDK bug?", selector, e); } // Harmless exception - log anyway } }
該方法的主要邏輯就是:
創(chuàng)建一個新的selector
將老的selector上的 selectKey注冊到新的 selector 上
public void rebuildSelector() { if (!inEventLoop()) { execute(new Runnable() { @Override public void run() { rebuildSelector0(); } }); return; } rebuildSelector0(); }// 重新創(chuàng)建selectorprivate void rebuildSelector0() { // 暫存老的selector final Selector oldSelector = selector; final SelectorTuple newSelectorTuple; if (oldSelector == null) { return; } try { // 創(chuàng)建一個新的 SelectorTuple // openSelector()在之前分析過了 newSelectorTuple = openSelector(); } catch (Exception e) { logger.warn("Failed to create a new Selector.", e); return; } // Register all channels to the new Selector. // 記錄select上注冊的channel數(shù)量 int nChannels = 0; // 遍歷老的 selector 上的 SelectionKey for (SelectionKey key: oldSelector.keys()) { // 獲取 attachment,這里的attachment就是我們前面在講 Netty Channel注冊時,select會將channel賦值到 attachment 變量上。 // 獲取老的selector上注冊的channel Object a = key.attachment(); try { if (!key.isValid() || key.channel().keyFor(newSelectorTuple.unwrappedSelector) != null) { continue; } // 獲取興趣集 int interestOps = key.interestOps(); // 取消 SelectionKey key.cancel(); // 將老的興趣集重新注冊到前面新創(chuàng)建的selector上 SelectionKey newKey = key.channel().register(newSelectorTuple.unwrappedSelector, interestOps, a); if (a instanceof AbstractNioChannel) { // Update SelectionKey ((AbstractNioChannel) a).selectionKey = newKey; } // nChannels計數(shù) + 1 nChannels ++; } catch (Exception e) { logger.warn("Failed to re-register a Channel to the new Selector.", e); if (a instanceof AbstractNioChannel) { AbstractNioChannel ch = (AbstractNioChannel) a; ch.unsafe().close(ch.unsafe().voidPromise()); } else { @SuppressWarnings("unchecked") NioTask<SelectableChannel> task = (NioTask<SelectableChannel>) a; invokeChannelUnregistered(task, key, e); } } } // 設(shè)置新的 selector selector = newSelectorTuple.selector; // 設(shè)置新的 unwrappedSelector unwrappedSelector = newSelectorTuple.unwrappedSelector; try { // time to close the old selector as everything else is registered to the new one // 關(guān)閉老的seleclor oldSelector.close(); } catch (Throwable t) { if (logger.isWarnEnabled()) { logger.warn("Failed to close the old Selector.", t); } } if (logger.isInfoEnabled()) { logger.info("Migrated " + nChannels + " channel(s) to the new Selector."); } }
private void processSelectedKeysOptimized() { for (int i = 0; i < selectedKeys.size; ++i) { final SelectionKey k = selectedKeys.keys[i]; // 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 // 設(shè)置為null,有利于GC回收 selectedKeys.keys[i] = null; // 獲取 SelectionKey 中的 attachment, 我們這里就是 NioChannel final Object a = k.attachment(); if (a instanceof AbstractNioChannel) { // 處理 SelectedKey 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 selectedKeys.reset(i + 1); selectAgain(); i = -1; } } }// 處理 SelectedKeyprivate void processSelectedKey(SelectionKey k, AbstractNioChannel ch) { // 獲取Netty Channel中的 NioUnsafe 對象,用于后面的IO操作 final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe(); // 判斷 SelectedKey 的有效性,如果無效,則直接返回并關(guān)閉channel if (!k.isValid()) { final EventLoop eventLoop; try { eventLoop = ch.eventLoop(); } catch (Throwable ignored) { // If the channel implementation throws an exception because there is no event loop, we ignore this // because we are only trying to determine if ch is registered to this event loop and thus has authority // to close ch. return; } // Only close ch if ch is still registered to this EventLoop. ch could have deregistered from the event loop // and thus the SelectionKey could be cancelled as part of the deregistration process, but the channel is // still healthy and should not be closed. // See https://github.com/netty/netty/issues/5125 if (eventLoop != this || eventLoop == null) { return; } // close the channel if the key is not valid anymore // 關(guān)閉channel unsafe.close(unsafe.voidPromise()); return; } try { // 獲取 SelectionKey 中所有準(zhǔn)備就緒的操作集 int readyOps = k.readyOps(); // We first need to call finishConnect() before try to trigger a read(...) or write(...) as otherwise // the NIO JDK channel implementation may throw a NotYetConnectedException. // 在調(diào)用處理READ與WRITE事件之間,先調(diào)用finishConnect()接口,避免異常 NotYetConnectedException 發(fā)生。 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(); } // Process OP_WRITE first as we may be able to write some queued buffers and so free memory. // 處理 WRITE 事件 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(); } // Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead // to a spin loop // 處理 ACCEPT 與 READ 事件 // 如果當(dāng)前的EventLoop是WorkGroup,則表示有 READ 事件 // 如果當(dāng)前的EventLoop是BossGroup,則表示有 ACCEPT 事件,有新連接進(jìn)來了 if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) { // 讀取數(shù)據(jù) unsafe.read(); } } catch (CancelledKeyException ignored) { unsafe.close(unsafe.voidPromise()); } }
關(guān)于
unsafe.read()
的分析,請看 后文
接下來,我們了解一下執(zhí)行具體Task任務(wù)的接口:runAllTasks。在EventLoop中,待執(zhí)行的任務(wù)隊列分為兩種:一種是普通任務(wù)隊列,一種是定時任務(wù)隊列。
前面 我們講 EventLoop 創(chuàng)建時提到過NioEventLoop中 taskQueue 的創(chuàng)建,是一個MpscQueue,關(guān)于高效率的MpscQueue 后面單獨寫文章進(jìn)行介紹:
public abstract class SingleThreadEventExecutor extends AbstractScheduledEventExecutor implements OrderedEventExecutor { ... // 存放普通任務(wù)的隊列 private final Queue<Runnable> taskQueue; ... protected SingleThreadEventExecutor(EventExecutorGroup parent, Executor executor, boolean addTaskWakesUp, int maxPendingTasks, RejectedExecutionHandler rejectedHandler) { super(parent); this.addTaskWakesUp = addTaskWakesUp; this.maxPendingTasks = Math.max(16, maxPendingTasks); this.executor = ObjectUtil.checkNotNull(executor, "executor"); // 創(chuàng)建TaskQueue taskQueue = newTaskQueue(this.maxPendingTasks); rejectedExecutionHandler = ObjectUtil.checkNotNull(rejectedHandler, "rejectedHandler"); } ... }public final class NioEventLoop extends SingleThreadEventLoop { ... // NioEventLoop 創(chuàng)建TaskQueue隊列 @Override protected Queue<Runnable> newTaskQueue(int maxPendingTasks) { // This event loop never calls takeTask() return maxPendingTasks == Integer.MAX_VALUE ? PlatformDependent.<Runnable>newMpscQueue() : PlatformDependent.<Runnable>newMpscQueue(maxPendingTasks); } ... }
存放定時任務(wù)的隊列在 AbstractScheduledEventExecutor 中,成員變量為 scheduledTaskQueue,代碼如下:
public abstract class AbstractScheduledEventExecutor extends AbstractEventExecutor { // 優(yōu)先級隊列的比較器 private static final Comparator<ScheduledFutureTask<?>> SCHEDULED_FUTURE_TASK_COMPARATOR = new Comparator<ScheduledFutureTask<?>>() { @Override public int compare(ScheduledFutureTask<?> o1, ScheduledFutureTask<?> o2) { return o1.compareTo(o2); } }; // 存放定時任務(wù)的優(yōu)先級隊列 PriorityQueue<ScheduledFutureTask<?>> scheduledTaskQueue; // 創(chuàng)建定時任務(wù)隊列 PriorityQueue<ScheduledFutureTask<?>> scheduledTaskQueue() { if (scheduledTaskQueue == null) { scheduledTaskQueue = new DefaultPriorityQueue<ScheduledFutureTask<?>>( SCHEDULED_FUTURE_TASK_COMPARATOR, // Use same initial capacity as java.util.PriorityQueue 11); } return scheduledTaskQueue; } // 保存定時任務(wù) @Override public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) { ObjectUtil.checkNotNull(command, "command"); ObjectUtil.checkNotNull(unit, "unit"); if (delay < 0) { delay = 0; } validateScheduled0(delay, unit); return schedule(new ScheduledFutureTask<Void>( this, command, null, ScheduledFutureTask.deadlineNanos(unit.toNanos(delay)))); } // 保存定時任務(wù) @Override public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) { ObjectUtil.checkNotNull(callable, "callable"); ObjectUtil.checkNotNull(unit, "unit"); if (delay < 0) { delay = 0; } validateScheduled0(delay, unit); return schedule(new ScheduledFutureTask<V>( this, callable, ScheduledFutureTask.deadlineNanos(unit.toNanos(delay)))); } // 保存定時任務(wù) <V> ScheduledFuture<V> schedule(final ScheduledFutureTask<V> task) { // 判斷是否為當(dāng)前線程 if (inEventLoop()) { // 添加定時任務(wù)隊列 scheduledTaskQueue().add(task); } else { execute(new Runnable() { @Override public void run() { // 添加定時任務(wù)隊列 scheduledTaskQueue().add(task); } }); } return task; } }
Netty存放定時任務(wù)隊列為 DefaultPriorityQueue ,定時任務(wù)的封裝對象為 ScheduledFutureTask ,在隊列中的優(yōu)先按照它們的截止時間進(jìn)行排序,其次在按照id進(jìn)行排序。
final class ScheduledFutureTask<V> extends PromiseTask<V> implements ScheduledFuture<V>, PriorityQueueNode { ... // 比較 ScheduledFutureTask 之間的排序 @Override public int compareTo(Delayed o) { if (this == o) { return 0; } ScheduledFutureTask<?> that = (ScheduledFutureTask<?>) o; long d = deadlineNanos() - that.deadlineNanos(); if (d < 0) { return -1; } else if (d > 0) { return 1; } else if (id < that.id) { return -1; } else if (id == that.id) { throw new Error(); } else { return 1; } } ... }
再來看看任務(wù)的執(zhí)行邏輯,首先將定時任務(wù)取出,聚合到普通任務(wù)隊列中,再去for循環(huán)運行每個Task。
protected boolean runAllTasks(long timeoutNanos) { // 將定時任務(wù)從定時隊列中取出,放入普通隊列中 fetchFromScheduledTaskQueue(); // 從隊列中取出任務(wù) Runnable task = pollTask(); if (task == null) { afterRunningAllTasks(); return false; } // 計算任務(wù)執(zhí)行的最大超時時間 final long deadline = ScheduledFutureTask.nanoTime() + timeoutNanos; // 任務(wù)計數(shù) long runTasks = 0; // 最近一次任務(wù)執(zhí)行的時間 long lastExecutionTime; for (;;) { // 執(zhí)行任務(wù) safeExecute(task); // 任務(wù)計數(shù) +1 runTasks ++; // Check timeout every 64 tasks because nanoTime() is relatively expensive. // XXX: Hard-coded value - will make it configurable if it is really a problem. // 由于nanoTime() 是非常好性能的操作,因此每64次就對比一下 定時任務(wù)的執(zhí)行時間與 deadline, // 如果 lastExecutionTime >= deadline,則表示任務(wù)超時了,需要中斷退出 if ((runTasks & 0x3F) == 0) { lastExecutionTime = ScheduledFutureTask.nanoTime(); if (lastExecutionTime >= deadline) { break; } } // 獲取任務(wù) task = pollTask(); if (task == null) { lastExecutionTime = ScheduledFutureTask.nanoTime(); break; } } afterRunningAllTasks(); // 記錄最后一次的執(zhí)行時間 this.lastExecutionTime = lastExecutionTime; return true; }// 取出任務(wù)protected Runnable pollTask() { assert inEventLoop(); return pollTaskFrom(taskQueue); }// 從隊列中取出任務(wù)protected static Runnable pollTaskFrom(Queue<Runnable> taskQueue) { for (;;) { Runnable task = taskQueue.poll(); if (task == WAKEUP_TASK) { continue; } return task; } }// 將定時任務(wù)從定時隊列中取出,聚合到普通隊列中:private boolean fetchFromScheduledTaskQueue() { // 得到nanoTime = 當(dāng)前時間 - ScheduledFutureTask的START_TIME(開始時間) long nanoTime = AbstractScheduledEventExecutor.nanoTime(); // 獲得截止時間小于nanoTime的定時任務(wù) Runnable scheduledTask = pollScheduledTask(nanoTime); while (scheduledTask != null) { // 將定時任務(wù)放入普通隊列中,以備運行 if (!taskQueue.offer(scheduledTask)) { // No space left in the task queue add it back to the scheduledTaskQueue so we pick it up again. // 如果 taskQueue 沒有足夠的空間,導(dǎo)致添加失敗,則將其返回定時任務(wù)隊列中 scheduledTaskQueue().add((ScheduledFutureTask<?>) scheduledTask); return false; } scheduledTask = pollScheduledTask(nanoTime); } return true; }// 獲得截止時間小于nanoTime的定時任務(wù)protected final Runnable pollScheduledTask(long nanoTime) { assert inEventLoop(); // 獲取定時任務(wù)隊列 Queue<ScheduledFutureTask<?>> scheduledTaskQueue = this.scheduledTaskQueue; // 獲取第一個定時任務(wù) ScheduledFutureTask<?> scheduledTask = scheduledTaskQueue == null ? null : scheduledTaskQueue.peek(); if (scheduledTask == null) { return null; } // 如果該定時任務(wù)的截止時間 <= nanoTime ,則返回 if (scheduledTask.deadlineNanos() <= nanoTime) { scheduledTaskQueue.remove(); return scheduledTask; } return null; }
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