[WIP] Deadline algorithm

Sources/AsyncAlgorithms/Deadline.swift

@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
+public struct TimeoutError<C: Clock>: Error {
+  public let deadline: C.Instant
+  public let clock: C
+
+  public init(_ deadline: C.Instant, _ clock: C) {
+    self.deadline = deadline
+    self.clock = clock
+  }
+}
+
+@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
+public func withDeadline<C: Clock, T: Sendable>(
+  _ deadline: C.Instant,
+  clock: C,
+  _ operation: @Sendable () async throws -> T
+) async throws -> T {
+  return try await withoutActuallyEscaping(operation) { operation in
+    try await withThrowingTaskGroup(of: T.self) { group in
+      group.addTask(operation: operation)
+      group.addTask {
+        try await Task.sleep(until: deadline, clock: clock)
+        throw TimeoutError(deadline, clock)
+      }
+      defer { group.cancelAll() }
+      return try await group.next()!
+    }
+  }
+}
+
+@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
+public func withTimeout<C: Clock, T: Sendable>(
+  in duration: C.Duration,
+  clock: C,
+  _ operation: @Sendable () async throws -> T
+) async throws -> T {
+  try await withDeadline(
+    clock.now.advanced(by: duration),
+    clock: clock,
+    operation)
+}
+
+@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
+public func withTimeout<T: Sendable>(
+  in duration: Duration,
+  _ operation: @Sendable () async throws -> T
+) async throws -> T {
+  try await withTimeout(in: duration, clock: .continuous, operation)
+}