Blocked waiting for a asynchronous Qt signal

Question

Hello!

I know, there are some similar questions to the following out there, but I couldn't find a concrete answer that helps me. So here's my problem:

I work on an application that does some gui-initialisations on start up. One of the things I have to do, is calling

NetworkConfigurationManager::updateConfigurations ()

This is a asynchronous call, which emits the updateCompleted() signal, when it is finished. The problem is, that all my other gui-initialisations have to wait until the updateConfigurations() is finished.

So what I could do would be something like this:

MyApp::MyApp(QWidget *parent) : ....
{
   doSomeInits();
   //Now connect the signal we have to wait for
   connect(configManager, SIGNAL(updateCompleted()), this, SLOT(networkConfigurationUpdated()));
   configManager->updateConfigurations(); //call the async function
}

void MyApp::networkConfigurationUpdated()
{
   doSomething();
   doReaminingInitsThatHadToWaitForConfigMgr();
}

To split up the initialisation doesn't seem a good way to me. I think it makes the code much harder to read - inits should remain together. The other thing is: Because updateConfiguration() is asynchronous, the user will be able to use the GUI, which doesn't give him any informations yet, cause we are waiting for updateCompleted().

So is there a way that to wait for the updateCompleted() signal, before the application continues?

like:

MyApp::MyApp(QWidget *parent) : ....
{
   doSomeInits();
   //Now connect the signal we have to wait for
   connect(configManager, SIGNAL(updateCompleted()), this, SLOT(doSomething()));
   ???? //wait until doSomething() is done.
   doRemainingInitsThatHadToWaitForConfigMgr();
}

In some APIs the are blocking alternatives to asynchronous functions, but not in this case.

I appreciate any help. Thanks!

Answer 1

MyApp::MyApp(QWidget *parent) : ....
{
    doSomeInits();
    {
        QEventLoop loop;
        loop.connect(configManager, SIGNAL(updateCompleted()), SLOT(quit()));
        configManager->updateConfigurations(); 
        loop.exec();
    }
    doReaminingInitsThatHadToWaitForConfigMgr();
}

Note: I haven't event compiled this snippet, but IMHO local QEventLoop is a way to go.

Answer 2

Working from chalup's answer, if you are going to be waiting for a user-noticeable time, you might want to show a progress bar instead (or a splash screen, perhaps).

MyApp::MyApp(QWidget *parent) : ....
{
    doSomeInits();
    {
        QSpashScreen splash;
        splash.connect(configManager, SIGNAL(updateCompleted()), SLOT(close()));
        configManager->updateConfigurations(); 
        splash.exec();
    }
    doReaminingInitsThatHadToWaitForConfigMgr();
}