Don't need @finished, don't call unblock if cancelled.

lib/async/work_pool.rb

@@ -12,9 +12,9 @@ def initialize(scheduler, fiber, work)
 				@scheduler = scheduler
 				@fiber = fiber
 				@work = work
-				@thread = nil
 
-				@finished = false
+				# The thread, if any, that is doing the work:
+				@thread = nil
 
 				@result = nil
 				@error = nil
@@ -29,8 +29,10 @@ def call
 			rescue => @error
 			ensure
 				@thread = nil
-				@finished = true
-				@scheduler.unblock(self, @fiber)
+
+				if @fiber
+					@scheduler.unblock(self, @fiber)
+				end
 			end
 
 			def wait
@@ -45,6 +47,7 @@ def wait
 
 			def cancel!
 				@work = nil
+				@fiber = nil # Don't call unblock.
 				@thread&.raise(Interrupt)
 			end
 		end