If I am having 1 sec timer calling a fucntion,my function will take 2sec to return what will happen?

[engine_motor]

Spoiler

Spoiler

CallbackTimer()//1 sec Timer
{
  Dosomework();//it will take 2 sec to complete
}

[RobertoBozzolo]

The timer callback will be called immediately after returning; the system will be somewhat hung (i.e. it will be possible to interact with it but with significative delays since the OS will have very little time to serve user events).

In such a case, some redesign of the application is needed: for example, it is difficult to imagine you have a function the is busy all that time, there may be some pauses or waits in it. In such a case, passing to a multithreaded approach will grant the system will be able to handle UI and other events during waits in the second thread.