What does win32event.SetEvent(self.hWaitStop) do in this python windows service example?

Question

I am looking at following example on how to make a windows service.

'''
SMWinservice
by Davide Mastromatteo

Base class to create winservice in Python
-----------------------------------------

Instructions:

1. Just create a new class that inherits from this base class
2. Define into the new class the variables
   _svc_name_ = "nameOfWinservice"
   _svc_display_name_ = "name of the Winservice that will be displayed in scm"
   _svc_description_ = "description of the Winservice that will be displayed in scm"
3. Override the three main methods:
    def start(self) : if you need to do something at the service initialization.
                      A good idea is to put here the inizialization of the running condition
    def stop(self)  : if you need to do something just before the service is stopped.
                      A good idea is to put here the invalidation of the running condition
    def main(self)  : your actual run loop. Just create a loop based on your running condition
4. Define the entry point of your module calling the method "parse_command_line" of the new class
5. Enjoy
'''

import socket

import win32serviceutil

import servicemanager
import win32event
import win32service


class SMWinservice(win32serviceutil.ServiceFramework):
    '''Base class to create winservice in Python'''

    _svc_name_ = 'pythonService'
    _svc_display_name_ = 'Python Service'
    _svc_description_ = 'Python Service Description'

    @classmethod
    def parse_command_line(cls):
        '''
        ClassMethod to parse the command line
        '''
        win32serviceutil.HandleCommandLine(cls)

    def __init__(self, args):
        '''
        Constructor of the winservice
        '''
        win32serviceutil.ServiceFramework.__init__(self, args)
        self.hWaitStop = win32event.CreateEvent(None, 0, 0, None)
        socket.setdefaulttimeout(60)

    def SvcStop(self):
        '''
        Called when the service is asked to stop
        '''
        self.stop()
        self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
        win32event.SetEvent(self.hWaitStop)

    def SvcDoRun(self):
        '''
        Called when the service is asked to start
        '''
        self.start()
        servicemanager.LogMsg(servicemanager.EVENTLOG_INFORMATION_TYPE,
                              servicemanager.PYS_SERVICE_STARTED,
                              (self._svc_name_, ''))
        self.main()

    def start(self):
        '''
        Override to add logic before the start
        eg. running condition
        '''
        pass

    def stop(self):
        '''
        Override to add logic before the stop
        eg. invalidating running condition
        '''
        pass

    def main(self):
        '''
        Main class to be ovverridden to add logic
        '''
        pass

# entry point of the module: copy and paste into the new module
# ensuring you are calling the "parse_command_line" of the new created class
if __name__ == '__main__':
    SMWinservice.parse_command_line()

Now my question is what does win32event.SetEvent(self.hWaitStop) do exactly? I read about create event and about the set event function. My guess is that the program is trying to signal the ServiceController to wait? but for what? I feel like I'm missing some context here to fully understand the python service example and what exactly the line win32event.SetEvent(self.hWaitStop) does.

VLRoyrenn · Answer 1 · 2019-12-13T20:28:59.607

I think it does nothing. It's in the pywin32 service examples and has been for a good 10 years, but as far as I can tell, no such event is used by the library internally. win32event.SetEvent is supposed to get one thread (in win32event.CreateEvent(None,0,0,None) the first zero means the event will auto-reset as soon as a thread stops waiting, so it's really one thread) waiting for that event to continue, but unless I'm missing something with how services work, nothing ever waits for that event to be fired, so it won't do anything.

Same goes for socket.setdefaulttimeout(60), really, I think someone just forgot to remove it at one point before posting to stackoverflow, and with everyone building on top of what everyone else without, nobody knows why it's there anymore and nobody has ever dared to check. You can just remove the whole __init__ function.

EDIT: See the example from this question

import win32serviceutil 
import win32service 
import win32event

class SmallestPythonService(win32serviceutil.ServiceFramework):
    _svc_name_ = "SmallestPythonService"
    _svc_display_name_ = "display service"

    def __init__(self, args):
        win32serviceutil.ServiceFramework.__init__(self, args)
        self.hWaitStop = win32event.CreateEvent(None, 0, 0, None)

    def SvcStop(self):
        self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
        win32event.SetEvent(self.hWaitStop)

    def SvcDoRun(self):
        win32event.WaitForSingleObject(self.hWaitStop, win32event.INFINITE)

if __name__=='__main__':
    win32serviceutil.HandleCommandLine(SmallestPythonService)

Seems like it's usually meant so you can have an example service that runs until it's stopped.

What does win32event.SetEvent(self.hWaitStop) do in this python windows service example?

1 Answers1