Allow Interrupt to retry the run loop after issuing #stop. (#297)

* Add Ruby v3.1 to coverage workflow.

.github/workflows/coverage.yaml

@@ -20,6 +20,7 @@ jobs:
           - ubuntu
 
         ruby:
+          - "3.1"
           - "3.2"
           - "ruby-head"
 

lib/async/scheduler.rb

@@ -306,17 +306,22 @@ def run(...)
 
 			initial_task = self.async(...) if block_given?
 
-			# In theory, we could use Exception here to be a little bit safer, but we've only shown the case for SignalException to be a problem, so let's not over-engineer this.
-			Thread.handle_interrupt(SignalException => :never) do
-				while true
-					# If we are interrupted, we need to exit:
-					break if self.interrupted?
-
-					# If we are finished, we need to exit:
-					break unless self.run_once
+			begin
+				# In theory, we could use Exception here to be a little bit safer, but we've only shown the case for SignalException to be a problem, so let's not over-engineer this.
+				Thread.handle_interrupt(SignalException => :never) do
+					while true
+						# If we are interrupted, we need to exit:
+						break if self.interrupted?
+
+						# If we are finished, we need to exit:
+						break unless self.run_once
+					end
 				end
+			rescue Interrupt
+				self.stop
+				retry
 			end
-
+				
 			return initial_task
 		ensure
 			Console.logger.debug(self) {"Exiting run-loop because #{$! ? $! : 'finished'}."}

test/async/scheduler.rb

@@ -87,6 +87,43 @@
 			scheduler.close
 			scheduler.interrupt
 		end
+
+		it "can interrupt a scheduler from a different thread" do
+			finished = false
+			sleeping = Thread::Queue.new
+
+			thread = Thread.new do
+				scheduler = Async::Scheduler.new
+				Fiber.set_scheduler(scheduler)
+
+				scheduler.run do |task|
+					sleeping.push(true)
+					sleep
+				ensure
+					begin
+						sleeping.push(true)
+						sleep
+					ensure
+						finished = true
+					end
+				end
+			# rescue Interrupt
+			# 	# Ignore.
+			end
+
+			expect(sleeping.pop).to be == true
+			expect(finished).to be == false
+
+			thread.raise(Interrupt)
+
+			expect(sleeping.pop).to be == true
+			expect(finished).to be == false
+
+			thread.raise(Interrupt)
+			thread.join
+
+			expect(finished).to be == true
+		end
 	end
 
 	with '#block' do