Question

In a program in c# I have 2 threads apart from the main thread. When the user closes the form I want to terminate one of the threads from the main thread. How do I go about doing so?. Please provide me with the code if possible.

Answer 1

Please don’t use Thread.Abort as recommended by the other answers so far, unless you want your program to be in an unknown state (see articles by Ian Griffiths and Chris Sells for more info). If closing the form should actually be killing the app, you’re probably okay – but in that case I’d recommend just using background threads anyway, which will automatically die when all foreground threads have terminated.

From Joe Duffy’s ‘Concurrent Programming in Windows’:

There are two situations in which thread aborts are always safe:

• The main purpose of thread aborts is to tear down threads during CLR AppDomain unloads. […]
• Synchronous thread aborts are safe, provided that callers expect an exception to be thrown from the method. […]

All other uses of thread aborts are questionable at best. […] While thread aborts are theoretically safer than other thread termination mechanisms, they can still occur at inopportune times, leading to instability and corruption if used without care.

(Synchronous thread aborts are when the thread aborts itself, rather than being aborted by another thread.)

For graceful shutdown (without risking getting into odd states) use a flag which is set periodically from the form and checked from the other threads – taking the memory model into account (e.g. either making the flag volatile or using a lock each time you test or set it). See my article on the topic for an example.