event-driven programming
DESCRIPTION
Event-Driven Programming. Vivek Pai Dec 4, 2001. GedankenEvents. Enron – bad news all around What are these numbers: $1B, $100B, $80B, $200M Korean facts Largest on-line game has 3M+ subscribers What’s the comparable figure for the US? What are the populations of the two countries? - PowerPoint PPT PresentationTRANSCRIPT
Event-Driven Programming
Vivek PaiDec 4, 2001
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GedankenEventsGedankenEvents
Enron – bad news all aroundWhat are these numbers: $1B, $100B, $80B, $200M
Korean factsLargest on-line game has 3M+ subscribersWhat’s the comparable figure for the US?What are the populations of the two countries?
How many albums does the Wu Tang Clan have?What is Ginger?
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A Random AsideA Random Aside
What do these companies have in commonVA Linux, Penguin ComputingRLX Technologies, FibercycleHP, CompaqDell, IBM
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MechanicsMechanics
Project 3 grading in progressProject 4 grading in progressAll feedback questions answeredOne mail dropped – extra project proposalsSpeaking of which
We need to agree on a one-page proposal
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Project 5Project 5
Tyranny of the majoritySeveral goals
Performance improvement via cachingDynamic adjustment to loadMaster/slave or symmetric programming
Probably due on Dean’s DateExtra credit: 6 points (15 base)
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Another Random AsideAnother Random Aside
You may want to readFlash: An Efficient and Portable Web ServerAvailable from my home page
Caveat: far more complicated than Project 5
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Official GoalsOfficial Goals
Discuss the difference between standard programming styles and event-driven programming
Show the difference between structuring servers using processes and application-level multiplexing
Discuss the benefits and drawbacks of each approach
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What Is An Event?What Is An Event?
Some kind of notificationInterruptsSignalsPolling (via poll/select/etc)Callback (via function pointer)
Similarities?
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“Reactive” Environments“Reactive” Environments
Windowing systemsNetwork-aware programsDrivers of all sorts
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Traditional EnvironmentsTraditional Environments
One thing going on at a timeFinish that thing, go on to nextAny step can block indefinitelyResumption from blocking is simple – OS
provided
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What Goes On In A Web Browser?
What Goes On In A Web Browser?
Drawing the current pageInline images
Translating machine names to IP addressesLaunching connectionsSending requestsGetting piecemeal responses, drawing images
User clicking to next link
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Threads Versus EventsThreads Versus Events
One stack versus many stacksWhat happens on blocking operationsParallelismShared variablesState
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Let’s Think Of StatesLet’s Think Of States
How many possible states are there?Take all pieces of informationDecide valid range for all piecesEnumerate
Can we reduce states?Some combinations invalidStill, lots of states
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Really Reducing StatesReally Reducing States
Take all major pieces of programAdd extra tags to stateWhat do tags look like?
PositionCount #
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State ExamplesState Examples
If-then-else3 states: start, then-clause, else-clause
For loop1 state + count
Why do we care?Resuming at the right state
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Remember This Diagram?Remember This Diagram?
Read File
Send Data
Accept
Conn
Read
Request
Find
File
Send
Headerend
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Structure of Event-Driven Programs
Structure of Event-Driven Programs
Lots of state machinesMaintaining information about each oneSome way of moving through statesAs few restrictions as possible on timing
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The Real StructureThe Real Structure
While (1)Get eventDispatch event
Or, while loop in libraryEvent handlers in main program
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DelaysDelays
Are delays possible?Interrupt handlers – generally notOtherwise? Depends on event rate
How to avoid delays?More events – asynchronous operationsWhat happens if no async support?
Fake it
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Blocking StepsBlocking Steps
Read File
Send Data
Accept
Conn
Read
Request
Find
File
Send
Headerend
Network Blocking
Disk Blocking
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Overcoming Disk Blocking States
Overcoming Disk Blocking States
Read File
Send Data
Accept
Conn
Read
Request
Find
File
Send
Headerend
Helper Helper
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New Architecture - AMPEDNew Architecture - AMPED
Helpers are threads or processes
Read File
Send Data
Accept
Conn
Read
Request
Find
File
Send
Header
Event Dispatcher
Asymmetric Multiple Process Event Driven
Helper 1 Helper 2 Helper N
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Caches in Flash Web Server
Caches in Flash Web Server
Read File
Send Data
Accept
Conn
Read
Request
Find
File
Send
Headerend
Pathname
Translation
Cache
Helper Helper
Mapped
File
Cache
Response
Header
Cache