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Kenneth Reitz
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1.7 KiB
ReStructuredText
39 lines
1.7 KiB
ReStructuredText
`|Redis Documentation| <index.html>`_
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**EventLibray: Contents**
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`Event Library <#Event%20Library>`_
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`Why is an Event Library needed at all? <#Why%20is%20an%20Event%20Library%20needed%20at%20all?>`_
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EventLibray
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===========
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Event Library
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=============
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Why is an Event Library needed at all?
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--------------------------------------
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Let us figure it out through a series of Q&As.
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Q: What do you expect a network server to be doing all the time?
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<br/> A: Watch for inbound connections on the port its listening
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and accept them.
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Q: Calling `accept <http://man.cx/accept(2)>`_ yields a descriptor.
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What do I do with it?<br/> A: Save the descriptor and do a
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non-blocking read/write operation on it.
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Q: Why does the read/write have to be non-blocking?<br/> A: If the
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file operation ( even a socket in Unix is a file ) is blocking how
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could the server for example accept other connection requests when
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its blocked in a file I/O operation.
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Q: I guess I have to do many such non-blocking operations on the
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socket to see when it's ready. Am I right?<br/> A: Yes. That is
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what an event library does for you. Now you get it.
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Q: How do Event Libraries do what they do?<br/> A: They use the
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operating system's
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`polling <http://www.devshed.com/c/a/BrainDump/Linux-Files-and-the-Event-Poll-Interface/>`_
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facility along with timers.
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Q: So are there any open source event libraries that do what you
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just described? <br/> A: Yes. Libevent and Libev are two such event
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libraries that I can recall off the top of my head.
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Q: Does Redis use such open source event libraries for handling
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socket I/O?<br/> A: No. For various
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`reasons <http://groups.google.com/group/redis-db/browse_thread/thread/b52814e9ef15b8d0/>`_
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Redis uses its own event library.
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.. |Redis Documentation| image:: redis.png |