Add timeout support to Condition#wait

fixtures/async/a_condition.rb

@@ -84,6 +84,25 @@ module Async
 			expect(condition.waiting_count).to be == 0
 		end
 
+		it "can timeout while waiting" do
+			expect do
+				condition.wait(timeout: 0.01)
+			end.to raise_exception(Async::TimeoutError)
+
+			expect(condition.waiting_count).to be == 0
+		end
+
+		it "can receive nil before the timeout" do
+			task = reactor.async do
+				condition.wait(timeout: 1)
+			end
+
+			expect(condition.waiting_count).to be == 1
+			condition.signal
+
+			expect(task.wait).to be_nil
+		end
+
 		with "timeout" do
 			let(:ready) {Async::Variable.new(condition)}
 			let(:waiting) {Async::Variable.new(subject.new)}

lib/async/condition.rb

@@ -6,21 +6,31 @@
 # Copyright, 2026, by Robert Mosolgo.
 
 require "fiber"
+require_relative "error"
 require_relative "list"
 
 module Async
 	# A synchronization primitive, which allows fibers to wait until a particular condition is (edge) triggered.
 	# @public Since *Async v1*.
 	class Condition
+		Entry = Struct.new(:value)
+		private_constant :Entry
+
 		# Create a new condition.
 		def initialize
 			@ready = ::Thread::Queue.new
 		end
 
-		# Queue up the current fiber and wait on yielding the task.
+		# Queue up the current fiber and wait until the condition is signalled.
+		# @parameter timeout [Numeric | Nil] The maximum time to wait, or `nil` to wait indefinitely.
 		# @returns [Object]
-		def wait
-			@ready.pop
+		# @raises [Async::TimeoutError] If the timeout expires before the condition is signalled.
+		def wait(timeout: nil)
+			if entry = @ready.pop(timeout: timeout)
+				return entry.value
+			else
+				raise TimeoutError, "Timeout while waiting for condition!"
+			end
 		end
 
 		# @returns [Boolean] If there are no fibers waiting on this condition.
@@ -44,9 +54,10 @@ def signal(value = nil)
 			return if empty?
 
 			ready = self.exchange
+			entry = Entry.new(value)
 
 			ready.num_waiting.times do
-				ready.push(value)
+				ready.push(entry)
 			end
 
 			ready.close

lib/async/notification.rb

@@ -26,8 +26,10 @@ def alive?
 			end
 
 			def transfer
+				entry = Entry.new(value)
+
 				ready.num_waiting.times do
-					ready.push(value)
+					ready.push(entry)
 				end
 
 				ready.close

releases.md

@@ -1,5 +1,9 @@
 # Releases
 
+## Unreleased
+
+  - Added `Async::Condition#wait(timeout:)`, inherited by `Async::Notification`, which raises `Async::TimeoutError` if the condition is not signalled before the timeout expires.
+
 ## v2.45.1
 
   - Fixed `Scheduler#io_wait` returning `nil` instead of `false` when an explicit timeout expired. Native callers such as `Socket#connect` with `connect_timeout:` distinguish a timeout by checking for `false`, so the `nil` caused `TypeError: no implicit conversion from nil to integer` instead of the intended `IO::TimeoutError`.