c++ - Avoiding GUI freezing on multithreaded operations -


i have qt gui class preferenceswindow that, obviously, responsible handling user preferences. have fields manage connection database server. when field left, dbschanged() method called. below code managed write:

void preferenceswindow::dbschanged() {     qfuture<qstringlist> loader = run(this, &preferenceswindow::get_databases);     qstringlist databases = loader.result();      if (databases.length()) {         this->ui.database->show();         this->ui.nodb_label->hide();         this->ui.database->clear();         this->ui.database->additems(databases);         this->ui.okbutton->setdisabled(false);         this->ui.validationstatus->setpixmap(qpixmap(":/icon/tick.png"));     } else {         this->ui.database->hide();         this->ui.nodb_label->show();         this->ui.okbutton->setdisabled(true);         this->ui.validationstatus->setpixmap(qpixmap(":/icon/error.png"));     } } qstringlist preferenceswindow::get_databases() {     qsqldatabase test_connection;     if (qsqldatabase::contains("preferemces_live_test_connection"))         test_connection = qsqldatabase::database("preferemces_live_test_connection");     else test_connection = qsqldatabase::adddatabase("qmysql", "preferemces_live_test_connection");     test_connection.sethostname(this->ui.serveraddress->text());     test_connection.setusername(this->ui.username->text());     test_connection.setpassword(this->ui.password->text());     test_connection.setdatabasename(this->ui.database->currenttext());     test_connection.setport(this->ui.serverport->value());      test_connection.open();     qdebug() << "error: " << test_connection.lasterror();     qsqlquery show_databases = test_connection.exec("show databases");     qstringlist databases;     while (show_databases.next()) {         databases.append(show_databases.value(0).tostring());     }     qsqldatabase::removedatabase("preferences_live_test_connection");     return databases; }

since get_databases can take long time, thought putting in on separate thread can see in these 2 lines:

qfuture<qstringlist> loader = run(this, &preferenceswindow::get_databases); qstringlist databases = loader.result();

could solve problem. runs on separate thread, still freezes gui (while working).

how should rewrite entire process? though of solutions, not sure performance, , don't want work uselessly...

it freezes gui because though get_databases call in separate thread, still wait results causes freeze.

i don't know how in qt, normal thing open dialog saying "please wait" or cancel button, , have worker thread send signal parent (gui) thread when done.


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