convert task scheduling to service

Alchemy/Queue/QueueWorker.swift

@@ -1,10 +1,17 @@
 import AsyncAlgorithms
 
-struct QueueWorker: Service, @unchecked Sendable {
+actor QueueWorker: Service {
     let queue: Queue
-    var channels: [String] = [Queue.defaultChannel]
-    var pollRate: Duration = .seconds(1)
-    var untilEmpty: Bool = false
+    var channels: [String]
+    var pollRate: Duration
+    var untilEmpty: Bool
+
+    init(queue: Queue, channels: [String], pollRate: Duration, untilEmpty: Bool) {
+        self.queue = queue
+        self.channels = channels
+        self.pollRate = pollRate
+        self.untilEmpty = untilEmpty
+    }
 
     private var timer: some AsyncSequence {
         AsyncTimerSequence(interval: pollRate, clock: ContinuousClock())

Alchemy/Scheduler/Frequency.swift

@@ -2,7 +2,7 @@ import Cron
 import Foundation
 
 /// Used to help build schedule frequencies for scheduled tasks.
-public final class Frequency {
+public final class Frequency: AsyncSequence {
     /// A day of the week.
     public enum DayOfWeek: Int, ExpressibleByIntegerLiteral {
         /// Sunday
@@ -71,7 +71,7 @@ public final class Frequency {
     var cron = try! DatePattern("* * * * * * *")
 
     /// The time amount until the next interval, if there is one.
-    func timeUntilNext() -> TimeAmount? {
+    func timeUntilNext() -> Duration? {
         guard let next = cron.next(), let nextDate = next.date else {
             return nil
         }
@@ -170,4 +170,25 @@ public final class Frequency {
             preconditionFailure("Error parsing cron expression '\(expression)': \(error).")
         }
     }
+
+    // MARK: AsyncSequence
+
+    public typealias Element = Foundation.Date
+
+    public func makeAsyncIterator() -> Iterator {
+        Iterator(frequency: self)
+    }
+
+    public struct Iterator: AsyncIteratorProtocol {
+        let frequency: Frequency
+
+        public mutating func next() async throws -> Foundation.Date? {
+            guard let delay = frequency.timeUntilNext() else {
+                return nil
+            }
+
+            try await Task.sleep(for: delay)
+            return Date()
+        }
+    }
 }

Alchemy/Scheduler/Plugins/Schedules.swift

@@ -5,8 +5,4 @@ struct Schedules: Plugin {
         app.container.register(scheduler).singleton()
         app.registerCommand(ScheduleCommand.self)
     }
-
-    func shutdown(app: Application) async throws {
-        try await scheduler.shutdown()
-    }
 }

Alchemy/Scheduler/Scheduler.swift

@@ -1,70 +1,41 @@
+import AsyncAlgorithms
 import NIOCore
 import NIOConcurrencyHelpers
+import Foundation
+import ServiceLifecycle
 
 /// A service for scheduling recurring work, in lieu of a separate cron task
 /// running apart from your server.
 public final class Scheduler {
-    private struct ScheduledTask {
+    private struct Task: Service, @unchecked Sendable {
         let name: String
         let frequency: Frequency
-        let work: () async throws -> Void
-    }
-
-    public private(set) var isStarted: Bool = false
-    private var tasks: [ScheduledTask] = []
-    private var scheduled: [Scheduled<Void>] = []
-    private let lock = NIOLock()
-
-    /// Start scheduling with the given loop.
-    ///
-    /// - Parameter scheduleLoop: A loop to run all tasks on. Defaults to the
-    ///   next available `EventLoop`.
-    public func start(on scheduleLoop: EventLoop = LoopGroup.next()) {
-        guard lock.withLock({
-            guard !isStarted else { return false }
-            isStarted = true
-            return true
-        }) else {
-            Log.warning("This scheduler has already been started.")
-            return
-        }
+        let task: () async throws -> Void
 
-        Log.info("Scheduling \(tasks.count) tasks.")
-        for task in tasks {
-            schedule(task: task, on: scheduleLoop)
-        }
-    }
+        func run() async throws {
+            for try await _ in frequency.cancelOnGracefulShutdown() {
+                do {
+                    Log.info("Scheduling \(name) (\(frequency.cron.string))")
+                    try await task()
+                } catch {
+                    // log an error but don't throw - we don't want to stop all
+                    // scheduling if a single instance of a task results in
+                    // an error.
+                    Log.error("Error scheduling \(name): \(error)")
+                }
+            }
 
-    public func shutdown() async throws {
-        lock.withLock {
-            isStarted = false
-            scheduled.forEach { $0.cancel() }
-            scheduled = []
+            Log.info("Scheduling \(name) complete; there are no future times in the frequency.")
         }
     }
 
-    private func schedule(task: ScheduledTask, on loop: EventLoop) {
-        guard let delay = task.frequency.timeUntilNext() else {
-            Log.info("Scheduling \(task.name) complete; there are no future times in the frequency.")
-            return
-        }
-
-        lock.withLock {
-            guard isStarted else {
-                Log.debug("Not scheduling task \(task.name), this Scheduler is not started.")
-                return
-            }
+    private var tasks: [Task] = []
 
-            let scheduledTask = loop.flatScheduleTask(in: delay) {
-                loop.asyncSubmit {
-                    // Schedule next and run
-                    self.schedule(task: task, on: loop)
-
-                    try await task.work()
-                }
-            }
-
-            scheduled.append(scheduledTask)
+    /// Start scheduling.
+    public func start() {
+        Log.info("Scheduling \(tasks.count) tasks.")
+        for task in tasks {
+            Life.addService(task)
         }
     }
 
@@ -78,18 +49,11 @@ public final class Scheduler {
     /// - Returns: A builder for customizing the scheduling frequency.
     public func task(_ name: String? = nil, _ task: @escaping () async throws -> Void) -> Frequency {
         let frequency = Frequency()
-        let name = name ?? "task_\(tasks.count)"
-        let task = ScheduledTask(name: name, frequency: frequency) {
-            do {
-                Log.info("Scheduling \(name) (\(frequency.cron.string))")
-                try await task()
-            } catch {
-                Log.error("Error scheduling \(name): \(error)")
-                throw error
-            }
-        }
-
-        tasks.append(task)
+        tasks.append(
+            Task(name: name ?? "task_\(tasks.count)",
+                 frequency: frequency,
+                 task: task)
+        )
         return frequency
     }
 
@@ -100,7 +64,9 @@ public final class Scheduler {
     ///   - queue: The queue to schedule it on.
     ///   - channel: The queue channel to schedule it on.
     /// - Returns: A builder for customizing the scheduling frequency.
-    public func job<J: Job>(_ job: @escaping @autoclosure () -> J, queue: Queue = Q, channel: String = Queue.defaultChannel) -> Frequency {
+    public func job<J: Job>(_ job: @escaping @autoclosure () -> J,
+                            queue: Queue = Q,
+                            channel: String = Queue.defaultChannel) -> Frequency {
 
         // Register the job, just in case the user forgot.
         Jobs.register(J.self)