WIP

lib/async/pool/controller.rb

@@ -154,20 +154,18 @@ def release(resource)
 				retire(resource) unless processed
 			end
 
+			def drain
+				# Enumerate all existing resources and retire them:
+				while resource = acquire_existing_resource
+					retire(resource)
+				end
+			end
+
 			# Close all resources in the pool.
 			def close
-				@available.clear
-
-				while pair = @resources.shift
-					resource, usage = pair
-
-					if usage > 0
-						Console.warn(self, resource: resource, usage: usage) {"Closing resource while still in use!"}
-					end
-
-					resource.close
-				end
+				self.drain
 
+				@available.clear
 				@gardener&.stop
 			end
 
@@ -224,6 +222,8 @@ def retire(resource)
 			def start_gardener
 				return if @gardener
 
+				@gardener = true
+
 				Async(transient: true, annotation: "#{self.class} Gardener") do |task|
 					@gardener = task
 
@@ -319,7 +319,7 @@ def available_resource
 				resource = nil
 
 				@guard.acquire do
-					resource = get_resource
+					resource = acquire_or_create_resource
 				end
 
 				return resource
@@ -330,7 +330,24 @@ def available_resource
 
 			private
 
-			def get_resource
+			# Acquire an existing resource with zero usage.
+			# If there are resources that are in use, wait until they are released.
+			def acquire_existing_resource
+				while @resources.any?
+					@resources.each do |resource, usage|
+						if usage == 0
+							return resource
+						end
+					end
+
+					@notification.wait
+				end
+
+				# Only when the pool has been completely drained, return nil:
+				return nil
+			end
+
+			def acquire_or_create_resource
 				while resource = @available.last
 					if usage = @resources[resource] and usage < resource.concurrency
 						if resource.viable?

test/async/pool/controller.rb

@@ -274,11 +274,27 @@
 		end
 
 		it "warns if closing while a resource is acquired" do
-			pool.acquire
+			events = []
 
-			expect(Console).to receive(:warn).and_return(nil)
+			child = Async do |task|
+				events << :acquire
+				resource = pool.acquire
+
+				sleep 0.1
+
+				events << :release
+				pool.release(resource)
+			end
+
+			sleep 0.1
 
+			events << :close
 			pool.close
+			events << :closed
+
+			child.wait
+
+			expect(events).to be == [:acquire, :close, :release, :closed]
 		end
 	end