Events are a very useful, but also a very simple form of communication between multiple threads running concurrently. With events, one thread would, typically, signal that an event has occurred while other threads are actively listening for this signal.
Events are, essentially, objects that feature an internal flag that is either true or false. Within our threads, we can continuously poll this event object to check what state it is in, and then choose to act in whatever manner we want when that flag changes state.
In the previous chapter, we talked about how there were no real mechanisms to kill threads natively in Python, and that's still true. However, we could utilize these event objects and have our threads run only so long as our event object remains unset. While this isn't as useful at the point where a SIGKILL signal is sent, it could, however, be useful in certain situations where you need to gracefully shut down, but where you can wait for a thread to finish what it's doing before it terminates.
An Event has four public functions with which we can modify and utilize it:
- isSet(): This checks to see if the event has been set
- set(): This sets the event
- clear(): This resets our event object
- wait(): This blocks until the internal flag is set to true
