netty-flush

最新推荐文章于 2025-06-30 21:32:57 发布

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DefaultChannelPipeline.flush()

调用unsafe

@Override
public void flush(ChannelHandlerContext ctx) throws Exception {
     unsafe.flush();
 }

AbstractChannel.flush()

调用outboundbuffer.addFlush 然后flush0,

@Override
public final void flush() {
    assertEventLoop();

    ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;
    if (outboundBuffer == null) {
        return;
    }

    outboundBuffer.addFlush();
    flush0();
}

ChannelOutboundBuffer.addFlush()

对unflushedEntry继续计数flushed++
若已经cancel，进行其他处理？？？


/**
* Add a flush to this {@link ChannelOutboundBuffer}. This means all previous added messages are marked as flushed
* and so you will be able to handle them.
*/
public void addFlush() {
	// There is no need to process all entries if there was already a flush before and no new messages
	// where added in the meantime.
	//
	// See https://github.com/netty/netty/issues/2577
	Entry entry = unflushedEntry;
	if (entry != null) {
	    if (flushedEntry == null) {
	        // there is no flushedEntry yet, so start with the entry
	        flushedEntry = entry;
	    }
	    do {
	        flushed ++;
	        if (!entry.promise.setUncancellable()) {
	            // Was cancelled so make sure we free up memory and notify about the freed bytes
	            int pending = entry.cancel();
	            decrementPendingOutboundBytes(pending, false, true);
	        }
	        entry = entry.next;
	    } while (entry != null);
	
	    // All flushed so reset unflushedEntry
	    unflushedEntry = null;
	}
}

flush0()

调用NioSocketChannel.flush0()

@Override
protected final void flush0() {
    // Flush immediately only when there's no pending flush.
    // If there's a pending flush operation, event loop will call forceFlush() later,
    // and thus there's no need to call it now.
    if (isFlushPending()) {
        return;
    }
    super.flush0();
}
//???
private boolean isFlushPending() {
    SelectionKey selectionKey = selectionKey();
    return selectionKey.isValid() && (selectionKey.interestOps() & SelectionKey.OP_WRITE) != 0;
}

NioSocketChannel

主要调用 doWrite(outboundBuffer) 还有其他异常处理

@SuppressWarnings("deprecation")
protected void flush0() {
    if (inFlush0) {
        // Avoid re-entrance
        return;
    }

    final ChannelOutboundBuffer outboundBuffer = this.outboundBuffer;
    if (outboundBuffer == null || outboundBuffer.isEmpty()) {
        return;
    }

    inFlush0 = true;

    // Mark all pending write requests as failure if the channel is inactive.
    if (!isActive()) {
        try {
            if (isOpen()) {
                outboundBuffer.failFlushed(FLUSH0_NOT_YET_CONNECTED_EXCEPTION, true);
            } else {
                // Do not trigger channelWritabilityChanged because the channel is closed already.
                outboundBuffer.failFlushed(FLUSH0_CLOSED_CHANNEL_EXCEPTION, false);
            }
        } finally {
            inFlush0 = false;
        }
        return;
    }

    try {
        doWrite(outboundBuffer);
    } catch (Throwable t) {
        if (t instanceof IOException && config().isAutoClose()) {
            /**
             * Just call {@link #close(ChannelPromise, Throwable, boolean)} here which will take care of
             * failing all flushed messages and also ensure the actual close of the underlying transport
             * will happen before the promises are notified.
             *
             * This is needed as otherwise {@link #isActive()} , {@link #isOpen()} and {@link #isWritable()}
             * may still return {@code true} even if the channel should be closed as result of the exception.
             */
            close(voidPromise(), t, FLUSH0_CLOSED_CHANNEL_EXCEPTION, false);
        } else {
            try {
                shutdownOutput(voidPromise(), t);
            } catch (Throwable t2) {
                close(voidPromise(), t2, FLUSH0_CLOSED_CHANNEL_EXCEPTION, false);
            }
        }
    } finally {
        inFlush0 = false;
    }
}

doWrite()

真正写。对不同的nioBufferCnt用不同的写方法
写完后会调用ChannelOutboundBuffer.removeBytes(writtenBytes)

@Override
protected void doWrite(ChannelOutboundBuffer in) throws Exception {
	for (;;) {
	    int size = in.size();
	    if (size == 0) {
	        // All written so clear OP_WRITE
	        clearOpWrite();
	        break;
	    }
	    long writtenBytes = 0;
	    boolean done = false;
	    boolean setOpWrite = false;
	
	    // Ensure the pending writes are made of ByteBufs only.
	    ByteBuffer[] nioBuffers = in.nioBuffers();
	    int nioBufferCnt = in.nioBufferCount();
	    long expectedWrittenBytes = in.nioBufferSize();
	    SocketChannel ch = javaChannel();
	
	    // Always us nioBuffers() to workaround data-corruption.
	    // See https://github.com/netty/netty/issues/2761
	    switch (nioBufferCnt) {
	        case 0:
	            // We have something else beside ByteBuffers to write so fallback to normal writes.
	            super.doWrite(in);
	            return;
	        case 1:
	            // Only one ByteBuf so use non-gathering write
	            ByteBuffer nioBuffer = nioBuffers[0];
	            for (int i = config().getWriteSpinCount() - 1; i >= 0; i --) {
	                final int localWrittenBytes = ch.write(nioBuffer);
	                if (localWrittenBytes == 0) {
	                    setOpWrite = true;
	                    break;
	                }
	                expectedWrittenBytes -= localWrittenBytes;
	                writtenBytes += localWrittenBytes;
	                if (expectedWrittenBytes == 0) {
	                    done = true;
	                    break;
	                }
	            }
	            break;
	        default:
	            for (int i = config().getWriteSpinCount() - 1; i >= 0; i --) {
	                final long localWrittenBytes = ch.write(nioBuffers, 0, nioBufferCnt);
	                if (localWrittenBytes == 0) {
	                    setOpWrite = true;
	                    break;
	                }
	                expectedWrittenBytes -= localWrittenBytes;
	                writtenBytes += localWrittenBytes;
	                if (expectedWrittenBytes == 0) {
	                    done = true;
	                    break;
	                }
	            }
	            break;
	    }
	
	    // Release the fully written buffers, and update the indexes of the partially written buffer.
	    in.removeBytes(writtenBytes);
	
	    if (!done) {
	        // Did not write all buffers completely.
	        incompleteWrite(setOpWrite);
	        break;
	    }
	}
}

ChannelOutboundBuffer.removeBytes()

记录写的progress，若current()的buffer写完，会调用remove();
最后调用clearNioBuffers();

/**
* Removes the fully written entries and update the reader index of the partially written entry.
* This operation assumes all messages in this buffer is {@link ByteBuf}.
*/
public void removeBytes(long writtenBytes) {
	for (;;) {
	    Object msg = current();
	    if (!(msg instanceof ByteBuf)) {
	        assert writtenBytes == 0;
	        break;
	    }
	
	    final ByteBuf buf = (ByteBuf) msg;
	    final int readerIndex = buf.readerIndex();
	    final int readableBytes = buf.writerIndex() - readerIndex;
	
	    if (readableBytes <= writtenBytes) {
	        if (writtenBytes != 0) {
	            progress(readableBytes);
	            writtenBytes -= readableBytes;
	        }
	        remove();
	    } else { // readableBytes > writtenBytes
	        if (writtenBytes != 0) {
	            buf.readerIndex(readerIndex + (int) writtenBytes);
	            progress(writtenBytes);
	        }
	        break;
	    }
	}
	clearNioBuffers();
}

remove()

调用removeEntry(e)

/**
* Will remove the current message, mark its {@link ChannelPromise} as success and return {@code true}. If no
* flushed message exists at the time this method is called it will return {@code false} to signal that no more
* messages are ready to be handled.
*/
public boolean remove() {
	Entry e = flushedEntry;
	if (e == null) {
	    clearNioBuffers();
	    return false;
	}
	Object msg = e.msg;
	
	ChannelPromise promise = e.promise;
	int size = e.pendingSize;
	
	removeEntry(e);
	
	if (!e.cancelled) {
	    // only release message, notify and decrement if it was not canceled before.
	    ReferenceCountUtil.safeRelease(msg);
	    safeSuccess(promise);//回调
	    decrementPendingOutboundBytes(size, false, true);//小于低水位，设置write快速再写
	}
	
	// recycle the entry 回收
	e.recycle();
	
	return true;
}

removeEntry()

–flushed
若flushed为0flushedEntity设置null
否则把next设置给flushed

private void removeEntry(Entry e) {
        if (-- flushed == 0) {
            // processed everything
            flushedEntry = null;
            if (e == tailEntry) {
                tailEntry = null;
                unflushedEntry = null;
            }
        } else {
            flushedEntry = e.next;
        }
    }

//小于低水位，设置write快速再写
private void decrementPendingOutboundBytes(long size, boolean invokeLater, boolean notifyWritability) {
	if (size == 0) {
	    return;
	}
	
	long newWriteBufferSize = TOTAL_PENDING_SIZE_UPDATER.addAndGet(this, -size);
	if (notifyWritability && newWriteBufferSize < channel.config().getWriteBufferLowWaterMark()) {
	    setWritable(invokeLater);
	}
}


private void setWritable(boolean invokeLater) {
	for (;;) {
	    final int oldValue = unwritable;
	    final int newValue = oldValue & ~1;
	    if (UNWRITABLE_UPDATER.compareAndSet(this, oldValue, newValue)) {
	        if (oldValue != 0 && newValue == 0) {
	            fireChannelWritabilityChanged(invokeLater);
	        }
	        break;
	    }
	}
}

clearNioBuffers()

把线程中分配的BUF设置为null

 // Clear all ByteBuffer from the array so these can be GC'ed.
    // See https://github.com/netty/netty/issues/3837
    private void clearNioBuffers() {
        int count = nioBufferCount;
        if (count > 0) {
            nioBufferCount = 0;
            Arrays.fill(NIO_BUFFERS.get(), 0, count, null);
        }
    }
  private static final FastThreadLocal<ByteBuffer[]> NIO_BUFFERS = new FastThreadLocal<ByteBuffer[]>() {
        @Override
        protected ByteBuffer[] initialValue() throws Exception {
            return new ByteBuffer[1024];
        }
    };

AbstractNioByteChannel.incompleteWrite()

网咯拥塞的时候（writeBytes返回0）设置write,加速写

protected final void incompleteWrite(boolean setOpWrite) {
	// Did not write completely.
	if (setOpWrite) {
	    setOpWrite();
	} else {
	    // Schedule flush again later so other tasks can be picked up in the meantime
	    Runnable flushTask = this.flushTask;
	    if (flushTask == null) {
	        flushTask = this.flushTask = new Runnable() {
	            @Override
	            public void run() {
	                flush();
	            }
	        };
	    }
	    eventLoop().execute(flushTask);
	}
}

setOpWrite()

  protected final void setOpWrite() {
        final SelectionKey key = selectionKey();
        // Check first if the key is still valid as it may be canceled as part of the deregistration
        // from the EventLoop
        // See https://github.com/netty/netty/issues/2104
        if (!key.isValid()) {
            return;
        }
        final int interestOps = key.interestOps();
        if ((interestOps & SelectionKey.OP_WRITE) == 0) {
            key.interestOps(interestOps | SelectionKey.OP_WRITE);
        }
    }

clearOpWrite()

protected final void clearOpWrite() {
	final SelectionKey key = selectionKey();
	// Check first if the key is still valid as it may be canceled as part of the deregistration
	// from the EventLoop
	// See https://github.com/netty/netty/issues/2104
	if (!key.isValid()) {
	    return;
	}
	final int interestOps = key.interestOps();
	if ((interestOps & SelectionKey.OP_WRITE) != 0) {
	    key.interestOps(interestOps & ~SelectionKey.OP_WRITE);
	}
}