在分支过程和客户端之间断开连接

Question

I'm using Qt 5.3 on Linux. I have QCoreApplication server running on Linux, server fork itself when new connection arrives from client.

void Ccbox::incomingConnection(qintptr handle) {
    qDebug()<<"Ccbox::incomingConnection";
    pid_t PID=fork();
    if(PID==0) {
       this->close();
       this->startNetwork(handle);
    } else {
        qDebug()<<"Ccbox::incomingConnection another process started";
    }
}

“this->close()” is to close child process to listen to port like parent, then pointer “handle” is passed to function that creates socket

socket=new QSslSocket(this);
if(!socket->setSocketDescriptor(socketDescriptor)) {
        qDebug() <<"setSocketError:"<<socket->error();
        return;
    }
qDebug()<<"ssl supported:"<<socket->supportsSsl();
qDebug()<<"peerAddress:"<<socket->peerAddress();
socket->addCaCertificates(Zm().sslCA+Zm().sslCACert);
socket->setPrivateKey(Zm().sslFiles+Zm().sslKey);
socket->setLocalCertificate(Zm().sslFiles+Zm().sslCert);
socket->setPeerVerifyMode(QSslSocket::VerifyPeer);
socket->startServerEncryption();

this is QSslSocket, so some cert options are set and connection is encrypted.

The problem is that my forked server always ends up in defunct state “< defunct >” after connection is closed between server and client and server makes qApp->quit();

Connection closing is initiated by a client with disconnectFromHost and on both ends I can see that socket is entering state: QAbstractSocket::UnconnectedState, 5 seconds later forked server makes qApp->quit() and ends up in a defunct state.

I think that what I don't understand is this: When I check with lsof command, right after I start client and fork server it shows that both parent and child server are connected to the client - parent(21347), child(21351):

ccbox-dem 21347   7u  IPv4 2439080      0t0  TCP *:4321 (LISTEN)
ccbox-dem 21347   8u  IPv4 2442399      0t0  TCP localhost:4321->localhost:38669 (ESTABLISHED)
ccbox-big 21349     10u  IPv4 2440519      0t0  TCP localhost:38669->localhost:4321 (ESTABLISHED)
ccbox-dem 21351   8u  IPv4 2442399      0t0  TCP localhost:4321->localhost:38669 (ESTABLISHED)

and after client is closed parent server is still connected to the client waiting in CLOSE_WAIT state

ccbox-dem 21347    7u  IPv4 2439080      0t0  TCP *:4321 (LISTEN)
ccbox-dem 21347    8u  IPv4 2442399      0t0  TCP localhost:4321->localhost:38669 (CLOSE_WAIT)

and "ps ax" commands shows that child process (21351) is in defunct state.

What should I do in parent server to close this connection right after child server has started ? Or is this some other problem? I need to get rid of these defunct processes

Best Regards

Marek

Answer 1

To clean up the defunct processes, you must wait for them. Any of the functions here could do: http://linux.die.net/man/2/wait - the idea is that they are "defunct" because nobody has waited for them to finish, to get their return value. Somebody needs to do that, or the children will be sad and haunt you forever.