[編織訊息架構][netty源碼分析]9 Promise 實作類別DefaultPromise職責與實現

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netty Future是基於jdk Future擴充，以監聽完成任務觸發執行
Promise是對Future修改任務資料
DefaultPromise是重要的模板類，其它不同類型實現基本是一層簡單的封裝，如DefaultChannelPromise
主要是分析await是如何等侍結果的

 

public interface Future<V> extends java.util.concurrent.Future<V> {   Future<V> addListener(GenericFutureListener<? extends Future<? super V>> listener);}public interface Promise<V> extends Future<V> {    Promise<V> setSuccess(V result);    boolean trySuccess(V result);    Promise<V> setFailure(Throwable cause);    boolean tryFailure(Throwable cause);    boolean setUncancellable();}public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {    @Override    public boolean await(long timeout, TimeUnit unit) throws InterruptedException {        return await0(unit.toNanos(timeout), true);    }    private boolean await0(long timeoutNanos, boolean interruptable) throws InterruptedException {        //已完成任務直接忽略        if (isDone()) {            return true;        }        //沒有等侍時間返回處理記錄        if (timeoutNanos <= 0) {            return isDone();        }        //已中止拋異常        if (interruptable && Thread.interrupted()) {            throw new InterruptedException(toString());        }        //checkDeadLock();        //netty 認為是當前線程是死結狀態        EventExecutor e = executor();        if (e != null && e.inEventLoop()) {            throw new BlockingOperationException(toString());        }                long startTime = System.nanoTime();        long waitTime = timeoutNanos;        boolean interrupted = false;         try {            for (;;) {                synchronized (this) {                    if (isDone()) {                        return true;                    }                    //最大檢查次數為 Short.MAX_VALUE                    //很奇怪的邏輯，處理完後又自減                    if (waiters == Short.MAX_VALUE) {                        throw new IllegalStateException("too many waiters: " + this);                    }                    ++waiters;                    try {                        //阻塞的代碼只是一行參數1是milliseconds，參數2是輔助用的大於0時milliseconds+1，如果是0的話會無限制阻塞                        wait(waitTime / 1000000, (int) (waitTime % 1000000));                    } catch (InterruptedException e) {                        if (interruptable) {                            throw e;                        } else {                            interrupted = true;                        }                    } finally {                        waiters--;                    }                }                //這裡是double check跟並發無影響的邏輯放在synchronized外面                if (isDone()) {                    return true;                } else {                    waitTime = timeoutNanos - (System.nanoTime() - startTime);                    if (waitTime <= 0) {                        return isDone();                    }                }            }        } finally {            if (interrupted) {                Thread.currentThread().interrupt();            }        }    }}public class DefaultChannelPromise extends DefaultPromise<Void> implements ChannelPromise, FlushCheckpoint {    private final Channel channel;    public DefaultChannelPromise(Channel channel) {        this.channel = channel;    }    public DefaultChannelPromise(Channel channel, EventExecutor executor) {        super(executor);        this.channel = channel;    }}

 

[編織訊息架構][netty源碼分析]9 Promise 實作類別DefaultPromise職責與實現