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redis
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<b>EventLibray: Contents</b><br>&nbsp;&nbsp;<a href="#Event Library">Event Library</a><br>&nbsp;&nbsp;&nbsp;&nbsp;<a href="#Why is an Event Library needed at all?">Why is an Event Library needed at all?</a>
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<h1><a name="Event Library">Event Library</a></h1><h2><a name="Why is an Event Library needed at all?">Why is an Event Library needed at all?</a></h2>Let us figure it out through a series of Q&amp;As.<br/><br/>Q: What do you expect a network server to be doing all the time? &lt;br/&gt;
A: Watch for inbound connections on the port its listening and accept them.<br/><br/>Q: Calling <a href="http://man.cx/accept%282%29" target="_blank">accept</a> yields a descriptor. What do I do with it?&lt;br/&gt;
A: Save the descriptor and do a non-blocking read/write operation on it.<br/><br/>Q: Why does the read/write have to be non-blocking?&lt;br/&gt;
A: If the file operation ( even a socket in Unix is a file ) is blocking how could the server for example accept other connection requests when its blocked in a file I/O operation.<br/><br/>Q: I guess I have to do many such non-blocking operations on the socket to see when it's ready. Am I right?&lt;br/&gt;
A: Yes. That is what an event library does for you. Now you get it.<br/><br/>Q: How do Event Libraries do what they do?&lt;br/&gt;
A: They use the operating system's <a href="http://www.devshed.com/c/a/BrainDump/Linux-Files-and-the-Event-Poll-Interface/" target="_blank">polling</a> facility along with timers.<br/><br/>Q: So are there any open source event libraries that do what you just described? &lt;br/&gt;
A: Yes. Libevent and Libev are two such event libraries that I can recall off the top of my head.<br/><br/>Q: Does Redis use such open source event libraries for handling socket I/O?&lt;br/&gt;
A: No. For various <a href="http://groups.google.com/group/redis-db/browse_thread/thread/b52814e9ef15b8d0/" target="_blank">reasons</a> Redis uses its own event library.
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