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POPersistent Qt Local Socket IPC
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  1. POPersistent Qt Local Socket IPC
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    copied!<p>I'm developing an application that uses IPC between a local server and a client application. There is nothing particular to it, as it's structured like the Qt documentation and examples.</p> <p>The problem is that the client sends packets frequently and connecting/disconnecting from the server local socket (named pipe on NT) is very slow. So what I'm trying to achieve is a "persistent" connection between the two applications.</p> <p>The client application connects to the local server (QLocalServer) without any problem:</p> <pre><code>void IRtsClientImpl::ConnectToServer(const QString&amp; name) { connect(_socket, SIGNAL(connected()), this, SIGNAL(connected())); _blockSize = 0; _socket-&gt;abort(); _socket-&gt;connectToServer(name, QIODevice::ReadWrite); } </code></pre> <p>And sends requests also in the traditional Qt manner:</p> <pre><code>void IRtsClientImpl::SendRequest( quint8 cmd, const QVariant* const param_array, unsigned int cParams ) { // Send data through socket QByteArray hdr(PROTO_BLK_HEADER_PROJ); QByteArray dataBlock; QDataStream out(&amp;dataBlock, QIODevice::WriteOnly); out.setVersion(QDataStream::Qt_4_5); quint8 command = cmd; out &lt;&lt; blocksize_t(0) // block size &lt;&lt; hdr // header &lt;&lt; quint32(PROTO_VERSION_PROJ) // protocol version &lt;&lt; command // command &lt;&lt; cParams; // number of valid parameters for (unsigned int i = 0; i &lt; cParams; ++i) out &lt;&lt; param_array[i]; // Write the current block size out.device()-&gt;seek(0); out &lt;&lt; dataBlock.size() - sizeof(blocksize_t); _socket-&gt;write(dataBlock); } </code></pre> <p>No problem. But the trick resides on the readyRead() signal in the server-side. Here's the current implementation of the readyRead() handling slot:</p> <pre><code>void IRtsServerImpl::onReadyRead() { QDataStream in(_lsock); in.setVersion(QDataStream::Qt_4_5); if (_blocksize == 0) { qDebug("Bytes Available on socket: %d", _lsock-&gt;bytesAvailable()); if (_lsock-&gt;bytesAvailable() &lt; sizeof(blocksize_t)) return; in &gt;&gt; _blocksize; } // We need more data? if (_lsock-&gt;bytesAvailable() &lt; _blocksize) return; ReadRequest(in); // Reset _blocksize = 0; } </code></pre> <p>Without setting <code>_blocksize</code> to zero I could not receive more data, only the first block group (I would expect an entire block to arrive without segmentation since this is through a pipe, but it does not, go figure). I expect that behavior, sure, since the _blocksize does not represent the current stream flow anymore. All right, resetting _blocksize does the trick, but I can't resend another packet from the client without getting an increasing array of bytes on the socket. What I want is to process the request in ReadRequest and receive the next data blocks without resorting to connecting/reconnecting the applications involved.</p> <p>Maybe I should 'regulate' the rate of the incoming data?</p> <p>Thank you very much.</p>
 

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