Netty is an asynchronous event-driven network application framework for Java. It provides an asynchronous model with non-blocking I/O based on Java NIO. To create an HTTP server with Netty, one sets up thread pools for handling connections and requests, provides a ChannelFactory and PipelineFactory, and puts it all together with a Bootstrap. The server can then be started to listen for connections. Custom handlers can be added to the pipeline to process requests. Channels are gathered and closed to release resources when the server is shut down. TCP options like keepAlive and noDelay can be configured but their effects should be measured for each application.

1. Netty
List("Asynchronous", "data", "transfer")
::: List("practical", "aspects")
Victor Cherkassky
"vcherkassky@gmail.com"

2. What is Netty
IO library
IO
cat Files > Networking

3. What is Netty
IO library
asynchronous
ChannelFuture future = channel.write(message)
future.addListener(WRITE_COMPLETE_LISTENER)

4. What is Netty
IO library
asynchronous
non-blocking
/**
* This method blocks until input data is available
*/
InputStream.read()

5. What is Netty
IO library
asynchronous
non-blocking
multi-protocol
HTTP | WebSocket | Protobuf
| Binary
TCP | UDP

6. blocking vs non-blocking
blocking (OIO)
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nuSra s e ienuSra(iptbn)
itbt =i.ed) / crettra wisfrrsl o err
n ye sra(; / urn hed at o eut r ro
non-blocking (NIO)
wie(re {
hl tu)
slco.eet) / rqetn eet fo mlil canl
eetrslc(; / eusig vns rm utpe hnes
Ieao i =slco.eetdes)ieao(;
trtr t eetrslceKy(.trtr)
wie(thset) {
hl i.aNx()
SlcoKyky=(eetoKy i.et)
eetre e Slcine) tnx(;
hnlKyky;
adee(e)
i.eoe)
trmv(;
}
}

7. blocking vs non-blocking
Hardware blocking write

8. blocking vs non-blocking
Hardware non-blocking write: DMA

9. blocking vs non-blocking
OS
select()/poll() - traditional POSIX polling O(n)
epoll() - event-based polling O(1), Linux 2.5.44+
kqueue - FreeBSD, Mac OS X
I/O Completion Ports - Windows NT 3.5+, Solaris 10+

10. blocking vs non-blocking
Java
SelectableChannel.register(selector) - blocking operation,
registers an "interest" for IO events
Selector.select - non-blocking operation, checks for
occurred events

11. blocking vs non-blocking
Java OS
select() / poll() / kqueue
Channel.register & Selector.select I/O Completion Ports
epoll() - Java 1.6+

12. Thread model
Tomcat
1 request = 1 thread
fast for ~1000 clients
too much memory

13. Thread model
Node.js
all requests = 1 thread
super scalable
limited error handling

14. Thread model
Netty
many requests = 1 thread
flexible model

15. Netty web Server

16. Netty web Client

17. Channel Pipeline

18. All terms together
Channel (socket read/write)
channel Buffer (byte array)
channel Event (message)
channel Pipeline (message bus)
channel Handler (message handler)
Upstream Event (from socket)
Downstream Event (to socket)

19. Creating an HTTP server
Set up thread pools
boss pool for handling incoming connections
worker pool for processing IO
piaefnlEeuo bsPo =Eeuosnwahdhedol)
rvt ia xctr osol xctr.eCceTraPo(
;
piaefnlEeuo wrePo =Eeuosnwahdhedol
rvt ia xctr okrol xctr.eCceTraPo
(;
)

20. Creating an HTTP server
Provide ChannelFactory
piaefnlCanlatr canlatr =
rvt ia hneFcoy hneFcoy
nwNoevrokthneFcoybsPo,wrePo)
e iSreSceCanlatr(osol okrol;

21. Creating an HTTP server
Set up PipelineFactory
piaefnlCanlieieatr pplnFcoy=
rvt ia hnePplnFcoy ieieatr
nwCanlieieatr( {
e hnePplnFcoy)
@vrie
Oerd
pbi Canlieiegtieie)trw Ecpin{
ulc hnePpln ePpln( hos xeto
Canlieiep=Canl.ieie)
hnePpln hnesppln(;
padat"tpevroe" nwHtSreCdc);
.dLs(htSreCdc, e tpevroe()
padat"ade" nwCsoRqetade(lCanl);
.dLs(hnlr, e utmeusHnlralhnes)
rtr p
eun ;
}
};

22. Creating an HTTP server
Put all together with Bootstrap
piaefnlSreBosrpbosrp=nwSreBosrpca
rvt ia evrotta otta e evrotta(h
neFcoy;
nlatr)
...
bosrpstieieatr(ieieatr)
otta.ePplnFcoypplnFcoy;
/ Otosfraprn canl-i acpscnetos
/ pin o aet hne t cet oncin
bosrpstpin"oaAdes,nwIeSceAdespr);
otta.eOto(lcldrs" e ntoktdrs(ot)
bosrpstpin"esAdes,tu)
otta.eOto(ruedrs" re;
/ Otosfriscide -te poesI
/ pin o t hlrn hy rcs O
bosrpstpin"hl.cNDly,tu)
otta.eOto(cidtpoea" re;
bosrpstpin"hl.eplv" fle;
otta.eOto(cidkeAie, as)

23. Creating an HTTP server
Writing a custom handler
casCsoHnlretnsSmlCanlptemade {
ls utmade xed ipehneUsraHnlr
...
@vrie
Oerd
pbi vi msaeeevdCanladeCnetcx Msae
ulc od esgRcie(hneHnlrotx t, esgE
vn e trw Ecpin{
et ) hos xeto
HtRqetrq=(tpeus)egtesg(;
tpeus e HtRqet .eMsae)
/ pouersos adwiei t acanl
/ rdc epne n rt t o hne
HtRsos rs=nwDfuttpepneHT__,O)
tpepne e e ealHtRsos(TP11 K;
Canluueftr =Canl.rt(t.eCanl) rs;
hneFtr uue hneswiecxgthne(, e)
ftr.dLsee(hneFtrLsee.LS)
uueaditnrCanluueitnrCOE;
}
}

24. Creating an HTTP server
Gather channels for future closing
piaefnlCanlru alhnes=nwDfuthneGop
rvt ia hneGop lCanl e ealCanlru(
)
...
/ aanisd orcso hnlr
/ gi nie u utm ade
casCsoHnlretnsSmlCanlptemade {
ls utmade xed ipehneUsraHnlr
...
@vrie
Oerd
pbi vi canlpnCanladeCnetcx Canltt
ulc od hneOe(hneHnlrotx t, hneSae
Eete trw Ecpin{
vn ) hos xeto
Canlcanl=egthne(;
hne hne .eCanl)
alhnesadcanl;
lCanl.d(hne)
}
}

25. Creating an HTTP server
Release resources
close gathered channels
release external resources
alhnescoe)aatnnerpil(;
lCanl.ls(.wiUitrutby)
bosrprlaexenleore(;
otta.eesEtraRsucs)

26. TCPnodelay, TCPkeepalive
Remember that bootstrap code?
/ Otosfriscide -te poesI
/ pin o t hlrn hy rcs O
bosrpstpin"hl.cNDly,tu)
otta.eOto(cidtpoea" re;
bosrpstpin"hl.eplv" fle;
otta.eOto(cidkeAie, as)
What do these options mean?

27. TCP keepAlive
prolongs each TCP connection
makes NAT router happy

28. TCP noDelay
Nagle's algorithm
glues up small TCP packets
tries to reduce bandwidth
increases latency

29. TCPnodelay, TCPkeepalive
To use,
or not to use?

30. Don't ask,
measure!

31. Thank you
Additional resources
netty @ github
introductory article