Limit default concurrency to prevent allocation overshoot. Fixes #23.

Author: ioquatix

lib/async/pool/controller.rb

@@ -27,9 +27,9 @@ def self.wrap(**options, &block)
 			#
 			# @parameter constructor [Proc] A block which creates a new resource.
 			# @parameter limit [Integer | Nil] The maximum number of resources that this pool can have at any given time. If nil, the pool can have an unlimited number of resources.
-			# @parameter concurrency [Integer] The maximum number of concurrent tasks that can be creating a new resource.
+			# @parameter concurrency [Integer] The maximum number of concurrent tasks that can be creating a new resource. Defaults to 1 to ensure the pool limit is enforced. Higher values may result in more resources being created than the limit under high load.
 			# @parameter policy [Policy] The pool policy.
-			def initialize(constructor, limit: nil, concurrency: (limit || 1), policy: nil, tags: nil)
+			def initialize(constructor, limit: nil, concurrency: 1, policy: nil, tags: nil)
 				@constructor = constructor
 				@limit = limit
 

test/async/pool/controller.rb

@@ -443,4 +443,47 @@ def failures(repeats: 500, time_scale: 0.001, &block)
 			expect(pool.resources).to be(:empty?)
 		end
 	end
+	
+	with "high concurrency with limit" do
+		it "does not exceed the configured limit" do
+			# Track the maximum pool size we observe
+			max_size = 0
+			mutex = Thread::Mutex.new
+			
+			constructor = proc do
+				# Introduce a small delay during resource creation to widen the race window
+				sleep(0.001)
+				Async::Pool::Resource.new
+			end
+			
+			# Default concurrency is limit (10), which is the issue
+			pool = subject.new(constructor, limit: 10)
+			
+			tasks = []
+			
+			# Create many concurrent tasks that all try to acquire at once
+			100.times do
+				tasks << Async do
+					pool.acquire do |resource|
+						# Track the maximum size of the pool thread-safely
+						mutex.synchronize do
+							current_size = pool.size
+							max_size = current_size if current_size > max_size
+						end
+						
+						# Simulate brief work
+						sleep(0.001)
+					end
+				end
+			end
+			
+			# Wait for all tasks to complete
+			tasks.each(&:wait)
+			
+			# The pool should never have exceeded the limit
+			expect(max_size).to be <= 10
+			
+			pool.close
+		end
+	end
 end