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netty源码学习-课堂5

2012-11-22 21:53 363 查看

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"watermarkindicatedthesafelevel,thatwhentheamountofbytesqueuedtobesentwentunderthisvaluewriting
couldresume(isWriteable()=true).

"high"watermarkwouldindicatethedangerlevel,thanwhentheamountofbytesqueuedtobesentwentoverthisvaluethenwritingshouldstop(isWriteable()=false).Thedocumentationsaystheinverseofthis.

>1.Ifwehadpreviouslyexceededthehighwatermark(counter>0)and
>wearestillabovethelowwatermark,writeremainsdisabled.
>2.Ifwehadpreviouslyexceededthehighwatermark(counter>0)and
>wearenowbelowthelowwatermark,writeisenabled.
>3.Ifwewerebeneaththehighwatermark(counter<=0)andweare
>stillbelowthehighwatermark,writeremainsenabled.
>4.Ifwewerebeneaththehighwatermark(counter<=0)andwearenow
>abovethehighwatermark,writeisdisabled.

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

[b][b]1.【不安全】如果危险系数比较低（counter<=0），[b]且目前写任务的个数>高水位，那么只能排队；容易理解[/b][/b][/b]
2.【安全】如果危险系数比较高（counter>0），[b]且目前写任务的个数<低水位，那么可以往外[/b]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[b]排队；　容易理解[/b]
4.【安全】如果危险系数比较低（counter<=0），[b]且目前写任务的个数<高水位，那么可以往外写；容易理解
[/b]

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。
.........................................TOBECONTINUED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

Channel

hasapropertycalled

interestOps

whichissimilartothatof

NIOSelectionKey

.Itisrepresentedasabitfieldwhichiscomposedofthetwoflags.

OP_READ

-Ifset,amessagesentbyaremotepeerwillbereadimmediately.Ifunset,themessagefromtheremotepeerwillnotbereaduntilthe

OP_READ

flagissetagain(i.e.readsuspension).

OP_WRITE

-Ifset,awriterequestwillnotbesenttoaremotepeeruntilthe

OP_WRITE

flagisclearedandthewriterequestwillbependinginaqueue.Ifunset,thewriterequestwillbeflushedoutassoonaspossiblefromthequeue.

OP_READ_WRITE

-Thisisacombinationof

OP_READ

and

OP_WRITE

,whichmeansonlywriterequestsaresuspended.

OP_NONE

-Thisisacombinationof(NOT

OP_READ

)and(NOT

OP_WRITE

),whichmeansonlyreadoperationissuspended.

Youcansetorclearthe

OP_READ

flagtosuspendandresumereadoperationvia

setReadable(boolean)

.

Pleasenotethatyoucannotsuspendorresumewriteoperationjustlikeyoucansetorclear

OP_READ

.The

OP_WRITE

flagisreadonlyandprovidedsimplyasameantotellyouifthesizeofpendingwriterequestsexceededacertainthresholdornotsothatyoudon'tissuetoomanypendingwritesthatleadtoan

OutOfMemoryError

.Forexample,theNIOsockettransportusesthe

writeBufferLowWaterMark

and

writeBufferHighWaterMark

propertiesin

NioSocketChannelConfig

todeterminewhentosetorclearthe

OP_WRITE

flag.

http://wenku.baidu.com/view/5d3d6dfd910ef12d2af9e7c6.html
http://wenku.baidu.com/view/7765bc2db4daa58da0114a4c.html

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