java nio doug_Scalable IO in Java -Doug Lea
【实例简介】
Scalable IO in Java -Doug Lea
描述java nio 和reactor 设计模式之间的关系
Network services
Web services Distributed objects. etc
Most have same basic structure
Read request
Decode request
Process service
Encode repl
ly
Send reply
But differ in nature and cost of each step
XML parsing, File transfer, Web page
generation, computational services
Classic Service Designs
client
ead(decode compute(encode( send
handler
ead)(decode compute (encode( send
client
Server
handler
client
read )(decode compute(encode( send
ha
andler
Each handler may be started in its own thread
Classic Server Socket Loop
Scalability Goals
Graceful degradation under increasing load
(more clients)
Continuous improvement with increasing
resources(CPU, memory, disk, bandwidth)
Also meet availability and performance goals
Short latencⅰes
Meeting peak demand
Tunable quality of service
Divide-and-conquer is usually the best
approach for achieving any scalability goal
Divide and Conquer
Divide processing into small tasks
Each task performs an action without blocking
Execute each task when it is enabled
Here, an lo event usually serves as
handler
Basic mechanisms supported in java nio
Non-blocking reads and writes
Dispatch tasks associated with sensed IO events
Endless variation possible
a family of event-driven designs
Event-driven Designs
Usually more efficient than alternatives
Fewer resources
Don't usually need a thread per client
ess overhead
Less context switching, often less locking
But dispatching can be slower
Must manually bind actions to events
Usually harder to program
Must break up into simple non-blocking actions
Similar to gul event-driven actions
Cannot eliminate all blocking: GC, page faults, etc
Must keep track of logical state of service
Background: Events in AWT
AWT Event Queue
Event
Button
Event
aWT thread
click!
Actionlistener
Event-driven lO uses similar ideas but in different designs
Reactor Pattern
Reactor responds to lO events by dispatching
the appropriate handler
Similar to awt thread
Handlers perform non-blocking actions
Similar to awt actionlisteners
Manage by binding handlers to events
Similar to awt addactionlistener
See schmidt et al. pattern-Oriented software
Architecture, Volume 2(POSA2)
Also Richard stevens s networking books matt
Welsh's seda framework. etc
【实例截图】
【核心代码】