Signals and communicating between actors

In Writing actors, we covered the basics of writing your own Actor class. Here, we consider a further complication: How do actors talk with improv and with one another. The most basic mechanism for doing so is through signals.

On Unix-like computing systems, signals are messages sent by the operating system to processes running on the machine. The most well-known of these are SIGINT (“interrupt,” what you get by pressing Ctrl-C at the terminal), SIGTERM (“terminate,” shut the process down, but ask nicely), and SIGKILL (“kill,” and don’t take no for an answer). In Python, handling of these events is done with the signal library.

For communicating between improv’s server and actors, we use both the signal library (internally) and actor.Signal for improv’s own set of messages. In the default Actor class (an alias for ManagedActor), signals are handled by the RunManger class, which calls the relevant class method when it receives a signal. In Correspondences between signals we list the signals defined in Signal along with the Actor methods they call.

Table 1 Correspondences between signals

actor.Signal received	ManagedActor method called
setup	setup
run	runStep
pause	not yet implemented
resume	not yet implemented
reset	not yet implemented
load	not yet implemented
ready	sent by actors to server
kill	handled by server
revive	not yet implemented
stop	stop
stop_success	not yet implemented
quit	handled by server

Note

Users who wish to do their own signal handling (e.g., by inheriting from AbstractActor) will need to test for the presence of actor.Signal messages in the connection to the server within the run function and handle them appropriately.