New to pyQT, threading question

jdev8000

I am new to Python and pyQT, I am creating a small app that gets the status of various services on a remote server using fabric and ssh. This is causing the pyQT app to freeze. I am told that using a thread is the way to solve this problem but I am having trouble getting it to work.

The service status is shown with a radio button color (red/green) and I use a function for each that runs a service check on the remote server and returns red or green based on the status.

def check_service(service):
    c = Connection('server.com', user="user", connect_kwargs={"key_filename": "/Users/devuser/.ssh/id_rsa",})
    result = c.run('systemctl is-active --quiet service', warn=True)
    if result.exited == 0:
        status = 0 # service running
    elif result.failed:
        status = 1 # service not running
    else:
        status = 2 # status unknown
    return(status)

The status in QT is shown with a radio button:

self.NF_status = QRadioButton()
self.NF_status.setStyleSheet("QRadioButton::indicator {background-color : %s }" % check_service("server-service.service"))
self.NF_status.setCheckable(False)

In order to get it to update status, I used Qtimer to get updates. There are 12 services that I need to check

class MainWindow(QMainWindow):

    def processOneThing(self):
        self.NF_status.setStyleSheet("QRadioButton::indicator {background-color : %s }" % check_service("server-service.service"))

...


timer = QTimer(self)
        timer.timeout.connect(self.processOneThing)  
        timer.setInterval(5000)  # 1000ms = 1s
        timer.start()

It works but things are just bogged down. From what I have read I can use a Worker(Qthread) class to run the service checks and then pull that data into the MainWindow but so far have been unsuccessful. Looking for some help.

jsulm

@jdev8000 You can move all this long lasting checks including the timer in a worker object which is running in another thread. Everytime there is something new in that thread the worker object emits a signal. This signal is connected to a slot in the UI thread. This slots updates the UI. Never touch UI in other threads, only in main/UI thread!
See https://wiki.qt.io/QThreads_general_usage