尝试以阻塞模式将QTcpSocket连接到其自己的QTcpServer时，单线程应用程序可能会超时吗？

Question

I need to test a feature in my library that requires usage of sequential QIODevices. I have written code like this:

QTcpServer server;
QVERIFY(server.listen());
quint16 port = server.serverPort();
QTcpSocket socket;
socket.connectToHost(QHostAddress(QHostAddress::LocalHost), port);
QVERIFY(socket.waitForConnected());
QVERIFY(server.waitForNewConnection(30000));
QTcpSocket *client = server.nextPendingConnection();
// send some data to socket
socket.disconnectFromHost();
QVERIFY(socket.waitForDisconnected());
QVERIFY(client->waitForReadyRead());
QByteArray received = client->readAll();
client->close();
// check the data received

So far it seems to work (tested in Win7x64/MSVS2012 and Ubuntu/GCC). However, I am worried about this particular part:

QVERIFY(socket.waitForConnected());
QVERIFY(server.waitForNewConnection(30000));

Can't this thing sort of dead-lock (well, actually, time-out)? As far as I know, waitForConnected() tries to perform a connection in non-blocking mode and then call select() or poll() or whatever to actually get the job done. Meanwhile, on the other side someone has to call accept() for the waitForConnected() call to succeed, right? In this case, this someone is the next line calling waitForNewConnection() . But this line is only executed after the connection is successfully established. As far as I understand it, it works because the OS accepts my connection on the TCP level nevertheless without actually waiting for the accept() call.

Can this behavior be relied upon or it may suddenly time out on some systems? I really don't want to go into the world of slots and signals just for this one test, as it will make it much more complicated.

Answer 1

If you in fact want non-sequential devices, then sockets are entirely the wrong thing to use. You want a QBuffer . Sockets are sequential, not random-access.

If you made a typo and do want a sequential device, then simply subclass QBuffer and override its isSequential method to return true.

Your code as written is correct. You could use QLocalServer and QLocalSocket instead, or even write a simple QIODevice pair yourself.