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121 lines
6.0 KiB
121 lines
6.0 KiB
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<title>TQDataSource Class</title>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>TQDataSource Class Reference<br><small>[obsolete]</small></h1>
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<p>The TQDataSource class is an asynchronous producer of data.
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<a href="#details">More...</a>
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<p><tt>#include <<a href="qasyncio-h.html">ntqasyncio.h</a>></tt>
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<p>Inherits <a href="ntqasyncio.html">TQAsyncIO</a>.
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<p>Inherited by <a href="tqiodevicesource.html">TQIODeviceSource</a>.
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<p><a href="tqdatasource-members.html">List of all member functions.</a>
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<h2>Public Members</h2>
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<ul>
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<li class=fn>virtual int <a href="#readyToSend"><b>readyToSend</b></a> () = 0</li>
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<li class=fn>virtual void <a href="#sendTo"><b>sendTo</b></a> ( TQDataSink *, int count ) = 0</li>
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<li class=fn>void <a href="#maybeReady"><b>maybeReady</b></a> ()</li>
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<li class=fn>virtual bool <a href="#rewindable"><b>rewindable</b></a> () const</li>
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<li class=fn>virtual void <a href="#enableRewind"><b>enableRewind</b></a> ( bool on )</li>
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<li class=fn>virtual void <a href="#rewind"><b>rewind</b></a> ()</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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<b>This class is obsolete.</b> It is provided to keep old source working. We strongly advise against using it in new code.
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<p> The TQDataSource class is an asynchronous producer of data.
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<p> A data source is an object which provides data from some source in an
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asynchronous manner. This means that at some time not determined by
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the data source, blocks of data will be taken from it for processing.
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The data source is able to limit the maximum size of such blocks which
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it is currently able to provide.
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<p> <p>See also <a href="ntqasyncio.html">TQAsyncIO</a>, <a href="tqdatasink.html">TQDataSink</a>, and <a href="tqdatapump.html">TQDataPump</a>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn>void <a name="enableRewind"></a>TQDataSource::enableRewind ( bool on )<tt> [virtual]</tt>
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</h3>
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If this function is called with <em>on</em> set to TRUE, and <a href="#rewindable">rewindable</a>()
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is TRUE, then the data source must take measures to allow the <a href="#rewind">rewind</a>()
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function to subsequently operate as described. If rewindable() is FALSE,
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the function should call <a href="#enableRewind">TQDataSource::enableRewind</a>(), which aborts with
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a <a href="ntqapplication.html#qFatal">tqFatal</a>() error.
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<p> For example, a network connection may choose to use a disk cache
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of input only if rewinding is enabled before the first buffer-full of
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data is discarded, returning FALSE in rewindable() if that first buffer
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is discarded.
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<p>Reimplemented in <a href="tqiodevicesource.html#enableRewind">TQIODeviceSource</a>.
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<h3 class=fn>void <a name="maybeReady"></a>TQDataSource::maybeReady ()
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</h3>
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This should be called whenever <a href="#readyToSend">readyToSend</a>() might have become non-zero.
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It is merely calls <a href="ntqasyncio.html#ready">TQAsyncIO::ready</a>() if readyToSend() is non-zero.
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<h3 class=fn>int <a name="readyToSend"></a>TQDataSource::readyToSend ()<tt> [pure virtual]</tt>
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</h3>
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<p> The data source should return a value indicating how much data it is ready
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to provide. This may be 0. If the data source knows it will never be
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able to provide any more data (until after a <a href="#rewind">rewind</a>()), it may return -1.
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<p>Reimplemented in <a href="tqiodevicesource.html#readyToSend">TQIODeviceSource</a>.
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<h3 class=fn>void <a name="rewind"></a>TQDataSource::rewind ()<tt> [virtual]</tt>
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</h3>
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This function rewinds the data source. This may only be called if
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<a href="#enableRewind">enableRewind</a>(TRUE) has been previously called.
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<p>Reimplemented in <a href="tqiodevicesource.html#rewind">TQIODeviceSource</a>.
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<h3 class=fn>bool <a name="rewindable"></a>TQDataSource::rewindable () const<tt> [virtual]</tt>
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</h3>
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This function should return TRUE if the data source can be rewound.
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<p> The default returns FALSE.
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<p>Reimplemented in <a href="tqiodevicesource.html#rewindable">TQIODeviceSource</a>.
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<h3 class=fn>void <a name="sendTo"></a>TQDataSource::sendTo ( <a href="tqdatasink.html">TQDataSink</a> *, int count )<tt> [pure virtual]</tt>
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</h3>
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<p> This function is called to extract data from the source, by sending
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it to the given data sink. The <em>count</em> will be no more than the amount
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indicated by the most recent call to <a href="#readyToSend">readyToSend</a>(). The source must
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use all the provided data, and the sink will be prepared to accept at
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least this much data.
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<p>Reimplemented in <a href="tqiodevicesource.html#sendTo">TQIODeviceSource</a>.
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