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Events in General

Events in General. Agenda. Post/wait technique I/O multiplexing Asynchronous I/O Signal-driven I/O Database events Publish/subscribe model Local vs. distributed events. Post/wait technique. Operating systems and some DBMSes Wait for an event to happen

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Events in General

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  1. Events in General

  2. Agenda • Post/wait technique • I/O multiplexing • Asynchronous I/O • Signal-driven I/O • Database events • Publish/subscribe model • Local vs. distributed events

  3. Post/wait technique • Operating systems and some DBMSes • Wait for an event to happen • Post an event; i.e., make it happen • Problems • multiple listeners not usually possible • waiting for different types of events not possible without multiple threads • posting before waiting/waiting for non-event

  4. Quick Review User Space System Call Data Transfer Kernel Space Device I/O Char/Block transfer Hardware

  5. Blocking and Non-blocking I/O • Blocking • send request and wait for completion • Non-blocking • send request and check later for completion • Check later: • periodically (polling) • occasionally • deferred wait

  6. I/O Multiplexing • Unix select() kernel function • Send I/O requests and continue executing • Wait for one or more of multiple events • and/or a timeout to occur • events are read, write or exception • kernel notifies caller when I/O initiates • Demultiplex event and handle it • handler copies data from kernel space to user space

  7. Asynchronous I/O • Register handler function, send I/O request to kernel and continue executing • Kernel notifies handler function • after I/O has completed • kernel copies data from kernel space to user space • Not really in most Unixes • it’s a POSIX thing

  8. Signal-driven I/O • Register handler function for signal, send I/O request and continue executing • Kernel notifies (signals) handler function • after I/O has initiated • Handler copies data from kernel space to user space

  9. Database Events • InterBase’s mechanism • Post/wait technique • Named events • Applications can register for multiple events • synchronous or asynchronous • Events under transaction control • Multiple postings of same event yields only one event

  10. Publish/Subscribe Model • Interested parties subscribe to service • consumers (listeners) • Publisher of service provides information • supplier (source) • Push: send out information • Pull: request information • Java Event Model: • supplier pushes GUI events to consumer

  11. Event Channels • Familiar push model: one-to-many • Channels allow: • push or pull • many-to-many Consumer 1 Supplier 1 Channel Consumer 2 Supplier 2 Consumer 3

  12. Event Channels: Advantages • Multiple suppliers and multiple consumers • Could: • buffer incoming events for later delivery • ensure quality of service • hide communication models • filter events • route events • make events persist

  13. Local vs. Distributed Events • Most event models don’t consider distribution • Why is this? • Industry solutions: • CORBA • ACE

  14. Blocking I/O Example

  15. Non-blocking I/O (Poll) Example

  16. Non-blocking I/O (Select) Example

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