Close blocking QLocalServer from other thread

Question

I am running a blocking QLocalServer in a thread:

void QThread::stopServer()
{
    m_abort = true;
    m_server.close(); // QSocketNotifier: Socket notifiers cannot be enabled or disabled from another thread 
}

void QThread::run()
{
    m_server = new QLocalServer();
    m_server->Listen("PipeName");
    while (!m_abort)
    {
        if (m_server->waitForNewConnection())
        {
            // handle the connection
        }
    }
    delete m_server;
}

How can the server be closed from another thread? Or is the only way to use non-blocking events?

Regards,

Why are you using a thread at all? Just create the `QLocalServer` on the main/GUI thread and connect to its [`newConnection`](https://doc.qt.io/qt-5/qlocalserver.html#newConnection) signal. — G.M., May 10 '20 at 09:55
The ``QLocalServer`` is used in an application which is not based on ``QCoreApplication``. — Hyndrix, May 10 '20 at 10:48

Vladimir Bershov · Answer 1 · 2020-05-10T21:18:03.463

Why just not wait until run() closes or deletes the connection itself, after m_abort will be set?

void QThread::stopServer()
{
    m_abort = true; // shall be thread-safe (std::atomic<bool>, etc)
    wait(); // It’s optional to use it here
}

void QThread::run()
{
    m_server = new QLocalServer();
    m_server->Listen("PipeName");
    while (!m_abort)
    {
        if (m_server->waitForNewConnection())
        {
            /* Most likely you cannot handle the connection
            which was closed in another place, therefore сlose (delete)
            it after leaving here */
        }
    }
    delete m_server;
}

Please note you can use the standard QThread::requestInterruption and isInterruptionRequested() methods instead of creating own m_abort variable.

From the doc:

This function can be used to make long running tasks cleanly interruptible. Never checking or acting on the value returned by this function is safe, however it is advisable do so regularly in long running functions. Take care not to call it too often, to keep the overhead low.

So you can write:

void QThread::stopServer()
{
    requestInterruption();
    wait(); // It’s optional to use it here
}

void QThread::run()
{
    m_server = new QLocalServer();
    m_server->Listen("PipeName");
    while (!isInterruptionRequested())
    {
        if (m_server->waitForNewConnection(100)) // 100 ms for not to call too often
        {
            /* Most likely you cannot handle the connection
            which was closed in another place, therefore сlose (delete)
            it after leaving here */
        }
    }
    delete m_server;
}

Close blocking QLocalServer from other thread

1 Answers1