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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html><head>
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<title>liboop: on_fd(), cancel_fd()</title>
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<link rel="stylesheet" type="text/css" href="style.css">
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</head><body>
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<h2>on_fd(), cancel_fd()</h2>
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<pre>
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#include &lt;oop.h&gt;
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/* <em>Types of file descriptor activity.</em> */
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typedef enum {
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        OOP_READ,
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        OOP_WRITE,
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        OOP_EXCEPTION<a href="#note-exception">*</a>,
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} oop_event;
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/* <em>Callback function prototype.</em> */
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typedef void *oop_call_fd(oop_source *source,int fd,oop_event event,void *user);
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/* <em>Register and unregister file descriptor activity event sinks.</em> */
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void (*on_fd)(oop_source *source,int fd,oop_event event,oop_call_fd *call,void *user);
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void (*cancel_fd)(oop_source *source,int fd,oop_event event);
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</pre>
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<h3>Arguments.</h3>
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<dl>
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<dt><b>oop_source *source</b>
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<dd>The event source to register or unregister the event sink with.  This must
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be the same event source you got the function pointer from:
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"src-&gt;on_fd(src,...);".<p>
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<dt><b>int fd</b>
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<dd>The file descriptor to watch (or stop watching).<p>
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<dt><b>oop_event event</b>
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<dd>The kind of activity to watch for (or stop watching for).  Must be one of
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OOP_READ (triggered when data is available for reading on the specified file
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descriptor), OOP_WRITE (triggered when buffer space is available to write on
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the specified file descriptor), or OOP_EXCEPTION<a href="#note-exception">*</a>
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(triggered on any number of "exceptional" events, such as TCP urgent data
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or system error).<p>
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<dt><b>oop_call_fd *call</b>
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<dd>The callback function (event sink) to add (or remove).<p>
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<dt><b>void *user</b>
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<dd>User data passed through to the callback function.<p>
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</dl>
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<h3>Description.</h3>
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Note that these are not global functions, but function pointers supplied
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by the event source (in the <em>oop_source</em> structure) or by the user.
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<dl>
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<dt><b>on_fd</b>
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<dd>After this function is called, whenever the source's event loop detects
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the condition indicated by <em>event</em> (OOP_READ, OOP_WRITE, or
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OOP_EXCEPTION<a href="#note-exception">*</a>) on the file descriptor
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<em>fd</em>, it will call the function
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<em>call</em>, passing it a pointer to the event source, the file descriptor,
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the event type, and the same opaque <em>user</em> pointer passed to on_fd.  
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This callback will be called repeatedly as long as the condition persists and
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it is not deactivated (see below).  Only one callback may be registered per
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(event,fd) pair.<p>
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<dt><b>cancel_fd</b>
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<dd>Deactivate an event sink callback registered using on_fd (above).  
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Any callback associated with the (event,fd) pair in question is removed.<p>
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<dt><b>oop_call_fd</b>
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<dd>Called when the event is triggered.  Performs a user_specific action.
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Should return OOP_CONTINUE if the event loop should continue operating; any
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other value (including OOP_HALT) will cause termination of the event loop.
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</dl>
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<hr>
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<p><a name="note-exception">*</a> <b>Compatibility note:</b> OOP_EXCEPTION
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is only available in version 0.7 or newer.</p>
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