Publish-subscribe, Event brokers
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description
Publish-subscribe, Event brokers. INF 123 – Software architecture [email protected]. Outline. Pubsub Event brokers. pubsub. Newspaper distribution. Newspaper companies publish newspapers Readers (un)subscribe to a company for a newspaper Company sends newspaper to its subscribers. - PowerPoint PPT Presentation
Transcript of Publish-subscribe, Event brokers
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Outline
• Pubsub• Event brokers
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PUBSUB
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Newspaper distribution
• Newspaper companies publish newspapers• Readers (un)subscribe to a company for a
newspaper• Company sends newspaper to its subscribers
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Newspaper distribution
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Stock exchange
• Jobs wants to buy AAPL below $30• Gates wants to buy MSFT below $40• Buffett wants to sell MSFT and AAPL for $35• Traders are intermediaries– Publication and subscription are decoupled – Buffett does not know who he sold to– Gates does not know who he bought from
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Stock exchange 2
• NYSE provides feed of stock updates– Humongous, fast
• Traders are only interested in parts of it– Need filtering
8Eugster 2003: The many faces of publish/subscribe
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Constraints
• Subscribers register their interest– Interest in a publisher, an event, or a content
• Publishers generate events– Sometimes through intermediaries called message
broker, or message bus, or even proxy• Usually asynchronous– Publishers don’t wait for subscribers to publish– Subscribers give a callback to be notified
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Gains
• Scalable one-way communication– Usually over the network– “Well adapted to the loosely coupled nature of
distributed large-scale applications” [Eugster03]• Can decouple subscribers from publishers– Decoupling– Privacy
• Content filtering
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Request-reply vs pubsub
Request-reply• Implies client-server
– Medium coupling
• Pull info
Pubsub • Less coupled
• Push info
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More about pubsub
• AKA producer-consumer– Implies message queues
• Pubsub != client-server
Criteria Pubsub Client-server
Message passing One-way Two-way
Request-reply Impossible Possible
Information flow Publishers push to subscribers
Clients pull from server
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Pubsub + space partitioning = scale
http://www.cescg.org/CESCG-2000/JKrivanek/
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But …
• What if everyone subscribes to one item?– BarackObama: 43M followers on Twitter– Bandwidth limits, slower updates– Can/should cache
• What if everyone subscribes to everything?– Then Pubsub is probably not the right style
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Apple Push Notifications
http://www.raywenderlich.com/32960/apple-push-notification-services-in-ios-6-tutorial-part-1
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Apple Push Notifications
• Subscription– Device token = content of interest– Delivered by APNS, for security – why?
• Notification– APNS intermediary between appServer and
appClient– For privacy – why?
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Zoom-in/out
• Zoom on a region of the board– Useful with a million small pieces
• Originally client-side– The server sends all piece movement events– Most events that the client receives are not rendered,
and could be ignored• Then server-side pubsub– Only receive events near me– Client subscription == client view– Client model = subset of server model
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“Near me”
• Current view: x, y, w, h• Subscribe to [x: x+w, y: y+h]• Subscribe to [x-d: x+w+d, y-d: y+h+d]• Partition the world statically in cells– Subscribe to the cells that my view overlap with
User-oriented software development for real time online applications, Gorlatch 2008
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EVENT BROKERS
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Event broker vs pubsub
• Event broker = pubsub– With an intermediary – Where subscribers publish– And publishers subscribe– And usually with function callbacks rather than
over the network
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Mini-map
• Receive player position message• Change player position on main screen• Change player position on mini-map
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Mini-map
• Main view and mini-map view• Both subscribe to:– My movements– Quest markers
• The main view subscribes to:– Other players movement
• The mini-map subscribes to:– Zoom clicks
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Widgets
• GUI widgets• N widgets interested in an event• A widget may fire another event in response– Enqueue new event?– Or dispatch it right away?
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Publish events
http://ezide.com/games/writing-games.html
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Dispatch events
http://ezide.com/games/writing-games.html
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If you’re interested …
• http://msdn.microsoft.com/en-us/library/ff650653.aspx
• http://ezide.com/games/writing-games.html• The Many Faces of Publish/Subscribe, Eugster
et al. 2003• http://code.google.com/p/pubsubhubbub/• http://www.capitalware.com/dl/docs/intro_p
ub_sub.pdf
