feedback: Make scheduleCallback throwing

Author: simonjbeaumont

Benchmarks/Benchmarks/NIOPosixBenchmarks/Benchmarks.swift

@@ -101,7 +101,7 @@ let benchmarks = {
 
         benchmark.startMeasurement()
         for _ in benchmark.scaledIterations {
-            let handle = loop.scheduleCallback(in: .hours(1), handler: timer)
+            let handle = try! loop.scheduleCallback(in: .hours(1), handler: timer)
         }
     }
 }

Sources/NIOCore/EventLoop.swift

@@ -363,15 +363,15 @@ public protocol EventLoop: EventLoopGroup {
     ///         ``scheduleCallback(at:handler:)-5ryox`` and ``cancelScheduledCallback(_:)-1lfz0``. Failure to do so will
     ///         result in a runtime error.
     @discardableResult
-    func scheduleCallback(at deadline: NIODeadline, handler: some NIOScheduledCallbackHandler) -> NIOScheduledCallback
+    func scheduleCallback(at deadline: NIODeadline, handler: some NIOScheduledCallbackHandler) throws -> NIOScheduledCallback
 
     /// Schedule a callback after given time.
     ///
     /// - NOTE: Event loops that provide a custom scheduled callback implementation **must** implement _both_
     ///         ``scheduleCallback(at:handler:)-5ryox`` and ``cancelScheduledCallback(_:)-1lfz0``. Failure to do so will
     ///         result in a runtime error.
     @discardableResult
-    func scheduleCallback(in amount: TimeAmount, handler: some NIOScheduledCallbackHandler) -> NIOScheduledCallback
+    func scheduleCallback(in amount: TimeAmount, handler: some NIOScheduledCallbackHandler) throws -> NIOScheduledCallback
 
     /// Cancel a scheduled callback.
     ///

Sources/NIOCore/NIOScheduledCallback.swift

@@ -86,8 +86,8 @@ extension EventLoop {
     /// Default implementation of `scheduleCallback(in amount:handler:)`: calls `scheduleCallback(at deadline:handler:)`.
     @discardableResult
     @inlinable
-    public func scheduleCallback(in amount: TimeAmount, handler: some NIOScheduledCallbackHandler) -> NIOScheduledCallback {
-        self.scheduleCallback(at: .now() + amount, handler: handler)
+    public func scheduleCallback(in amount: TimeAmount, handler: some NIOScheduledCallbackHandler) throws -> NIOScheduledCallback {
+        try self.scheduleCallback(at: .now() + amount, handler: handler)
     }
 
     /// Default implementation of `cancelScheduledCallback(_:)`: only cancels callbacks scheduled by the default implementation of `scheduleCallback`.

Sources/NIOPosix/SelectableEventLoop.swift

@@ -897,10 +897,10 @@ internal func assertExpression(_ body: () -> Bool) {
 
 extension SelectableEventLoop {
     @inlinable
-    func scheduleCallback(at deadline: NIODeadline, handler: some NIOScheduledCallbackHandler) -> NIOScheduledCallback {
+    func scheduleCallback(at deadline: NIODeadline, handler: some NIOScheduledCallbackHandler) throws -> NIOScheduledCallback {
         let taskID = self.scheduledTaskCounter.loadThenWrappingIncrement(ordering: .relaxed)
         let task = ScheduledTask(id: taskID, handler, deadline)
-        try! self._schedule0(.scheduled(task))
+        try self._schedule0(.scheduled(task))
         return NIOScheduledCallback(self, id: taskID)
     }