Don't allow creation of a task on a finished parent.

Author: ioquatix

lib/async/task.rb

@@ -113,6 +113,8 @@ def run(*arguments)
 
 		# Run an asynchronous task as a child of the current task.
 		def async(*arguments, **options, &block)
+			raise "Cannot create child task within a task that has finished execution!" if self.finished?
+			
 			task = Task.new(self, **options, &block)
 
 			task.run(*arguments)

test/async/task.rb

@@ -12,7 +12,7 @@
 describe Async::Task do
 	let(:reactor) {Async::Reactor.new}
 
-	describe '.yield' do
+	with '.yield' do
 		it "can yield back to scheduler" do
 			state = nil
 
@@ -142,6 +142,18 @@
 				end
 			end.to raise_exception(SignalException, message: be =~ /TERM/)
 		end
+		
+		it "can't start child task after finishing" do
+			task = reactor.async do |task|
+			end
+			
+			task.wait
+			
+			expect do
+				task.async do |task|
+				end
+			end.to raise_exception(RuntimeError, message: be =~ /finished/)
+		end
 	end
 
 	with '#yield' do