netty-FileRegion.write

最新推荐文章于 2024-05-14 10:26:53 发布

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本文深入探讨了NioSocketChannel的写操作机制，包括doWrite和flush类型的循环spin写入过程，以及FileRegion的transferTo零拷贝写方法。通过分析writeSpinCount配置和region.transferred状态，揭示了NioSocketChannel内部高效的数据传输策略。

NioSocketChannel.doWrite(ChannelOutboundBuffer in)
和flush类型，循环spin次一直write，只是write的方法调用不一样

 } else if (msg instanceof FileRegion) {
      FileRegion region = (FileRegion) msg;
        boolean done = region.transferred() >= region.count();

        if (!done) {
            long flushedAmount = 0;
            if (writeSpinCount == -1) {
                writeSpinCount = config().getWriteSpinCount();
            }

            for (int i = writeSpinCount - 1; i >= 0; i--) {
                long localFlushedAmount = doWriteFileRegion(region);
                if (localFlushedAmount == 0) {
                    setOpWrite = true;
                    break;
                }

                flushedAmount += localFlushedAmount;
                if (region.transferred() >= region.count()) {
                    done = true;
                    break;
                }
            }

            in.progress(flushedAmount);
        }

        if (done) {
            in.remove();
        } else {
            // Break the loop and so incompleteWrite(...) is called.
            break;
        }
    }

fileRegion的write方法是调用transferTo，零拷贝

   @Override
    protected long doWriteFileRegion(FileRegion region) throws Exception {
        final long position = region.transferred();
        return region.transferTo(javaChannel(), position);
    }