Add delegate to event - thread safety

Question

It is possible to execute the following code from multiple threads simultaneously.

this._sequencer.Completed += OnActivityFinished;

Is it t

Answer 1

It depends on the implementation of the event, to be honest.

The field-like events generated by the C# compiler are thread-safe, but if it's a custom event, who knows?

Note that in a multi-threaded app you should expect a race condition between adding/removing a handler and the event firing... for example, the event may start to fire, you could then unsubscribe, and your handler would still be called after that unsubscription.