要学的东西，还很多，例如：
1）详细写过程write
2）bytebuffer设计
3）upstream/downstream各种设计与handler维护
4）各种协议，大架子
喘口气，我们不可能一口气吃下个胖子哈，那么好，我们书接上回，谈谈这详细的写过程。
在写的时候，channel的getInterestOps()，会根据目前的“写情况”来自动更新OP_WRITE相关的interestops，换句话说，OP_WRITE完全由netty自己get/set，业务层无法显式set的。前面刚提到，根据目前的“写情况”，那究竟如何标识写情况呢，我们不得不拎出这两个变量来打量一番。关于highwatermark和lowwatermark这两个变量：
"low" water mark indicated the safe level, that when the amount of bytes queued to be sent went under this value writing could resume (isWriteable() = true)."high" water mark would indicate the danger level, than when the amount of bytes queued to be sent went over this value then writing should stop (isWriteable() = false). The documentation says the inverse of this.> 1. If we had previously exceeded the high water mark (counter > 0) and > we are still above the low water mark, write remains disabled. > 2. If we had previously exceeded the high water mark (counter > 0) and > we are now below the low water mark, write is enabled. > 3. If we were beneath the high water mark (counter <= 0) and we are > still below the high water mark, write remains enabled. > 4. If we were beneath the high water mark (counter <= 0) and we are now > above the high water mark, write is disabled.
也就是说，
【安全】low水位以下，isWriteable=true 可以往外写
【不安全】high水位以上，isWritable=false 只能排队
1. 【不安全】如果危险系数比较低（counter<=0），且目前写任务的个数>高水位，那么只能排队； 容易理解
2. 【安全】如果危险系数比较高（counter>0），且目前写任务的个数<低水位，那么可以往外写； 容易理解
3. 【不安全】如果危险系数比较高（counter>0），且目前写任务的个数>低水位，那么只能排队； 容易理解
4. 【安全】如果危险系数比较低（counter<=0），且目前写任务的个数<高水位，那么可以往外写； 容易理解
那详细的写过程，又是什么样子的呢？nioworker怎么就把数据写到socket里了？遭遇超超大数据会怎样？我们一起来看。
.........................................TO BE CONTINUED 超超大数据基于流来写？
附录：
channel的interestops，究竟应该如何理解呢？
InterestOps
A
Channelhas a property calledinterestOpswhich is similar to that ofNIO SelectionKey. It is represented as a bit field which is composed of the two flags.
OP_READ- If set, a message sent by a remote peer will be read immediately. If unset, the message from the remote peer will not be read until theOP_READflag is set again (i.e. read suspension).OP_WRITE- If set, a write request will not be sent to a remote peer until theOP_WRITEflag is cleared and the write request will be pending in a queue. If unset, the write request will be flushed out as soon as possible from the queue.OP_READ_WRITE- This is a combination ofOP_READandOP_WRITE, which means only write requests are suspended.OP_NONE- This is a combination of (NOTOP_READ) and (NOTOP_WRITE), which means only read operation is suspended.You can set or clear the
OP_READflag to suspend and resume read operation viasetReadable(boolean).Please note that you cannot suspend or resume write operation just like you can set or clearOP_READ. TheOP_WRITEflag is read only and provided simply as a mean to tell you if the size of pending write requests exceeded a certain threshold or not so that you don't issue too many pending writes that lead to anOutOfMemoryError. For example, the NIO socket transport uses thewriteBufferLowWaterMarkandwriteBufferHighWaterMarkproperties inNioSocketChannelConfigto determine when to set or clear theOP_WRITEflag.