adoption of sendable (#252)

motivation: adopt to sendable requirments in swift 5.6

changes:
* define sendable shims for protocols and structs that may be used in async context
* adjust tests
* add a test to make sure no warning are emitted

Sources/AWSLambdaRuntimeCore/LambdaContext.swift

@@ -12,9 +12,15 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if compiler(>=5.6)
+@preconcurrency import Dispatch
+@preconcurrency import Logging
+@preconcurrency import NIOCore
+#else
 import Dispatch
 import Logging
 import NIOCore
+#endif
 
 // MARK: - InitializationContext
 
@@ -23,7 +29,7 @@ extension Lambda {
     /// The Lambda runtime generates and passes the `InitializationContext` to the Handlers
     /// ``ByteBufferLambdaHandler/makeHandler(context:)`` or ``LambdaHandler/init(context:)``
     /// as an argument.
-    public struct InitializationContext {
+    public struct InitializationContext: _AWSLambdaSendable {
         /// `Logger` to log with
         ///
         /// - note: The `LogLevel` can be configured using the `LOG_LEVEL` environment variable.
@@ -67,17 +73,17 @@ extension Lambda {
 
 /// Lambda runtime context.
 /// The Lambda runtime generates and passes the `Context` to the Lambda handler as an argument.
-public struct LambdaContext: CustomDebugStringConvertible {
-    final class _Storage {
-        var requestID: String
-        var traceID: String
-        var invokedFunctionARN: String
-        var deadline: DispatchWallTime
-        var cognitoIdentity: String?
-        var clientContext: String?
-        var logger: Logger
-        var eventLoop: EventLoop
-        var allocator: ByteBufferAllocator
+public struct LambdaContext: CustomDebugStringConvertible, _AWSLambdaSendable {
+    final class _Storage: _AWSLambdaSendable {
+        let requestID: String
+        let traceID: String
+        let invokedFunctionARN: String
+        let deadline: DispatchWallTime
+        let cognitoIdentity: String?
+        let clientContext: String?
+        let logger: Logger
+        let eventLoop: EventLoop
+        let allocator: ByteBufferAllocator
 
         init(
             requestID: String,

Sources/AWSLambdaRuntimeCore/LambdaHandler.swift

@@ -58,13 +58,30 @@ extension LambdaHandler {
 
     public func handle(_ event: Event, context: LambdaContext) -> EventLoopFuture<Output> {
         let promise = context.eventLoop.makePromise(of: Output.self)
+        // using an unchecked sendable wrapper for the handler
+        // this is safe since lambda runtime is designed to calls the handler serially
+        let handler = UncheckedSendableHandler(underlying: self)
         promise.completeWithTask {
-            try await self.handle(event, context: context)
+            try await handler.handle(event, context: context)
         }
         return promise.futureResult
     }
 }
 
+/// unchecked sendable wrapper for the handler
+/// this is safe since lambda runtime is designed to calls the handler serially
+@available(macOS 12, iOS 15, tvOS 15, watchOS 8, *)
+fileprivate struct UncheckedSendableHandler<Underlying: LambdaHandler, Event, Output>: @unchecked Sendable where Event == Underlying.Event, Output == Underlying.Output {
+    let underlying: Underlying
+
+    init(underlying: Underlying) {
+        self.underlying = underlying
+    }
+
+    func handle(_ event: Event, context: LambdaContext) async throws -> Output {
+        try await self.underlying.handle(event, context: context)
+    }
+}
 #endif
 
 // MARK: - EventLoopLambdaHandler

Sources/AWSLambdaRuntimeCore/LambdaRuntime.swift

@@ -63,10 +63,17 @@ public final class LambdaRuntime<Handler: ByteBufferLambdaHandler> {
 
     /// Start the `LambdaRuntime`.
     ///
-    /// - Returns: An `EventLoopFuture` that is fulfilled after the Lambda hander has been created and initiliazed, and a first run has been scheduled.
-    ///
-    /// - note: This method must be called  on the `EventLoop` the `LambdaRuntime` has been initialized with.
+    /// - Returns: An `EventLoopFuture` that is fulfilled after the Lambda hander has been created and initialized, and a first run has been scheduled.
     public func start() -> EventLoopFuture<Void> {
+        if self.eventLoop.inEventLoop {
+            return self._start()
+        } else {
+            return self.eventLoop.flatSubmit { self._start() }
+        }
+    }
+
+    private func _start() -> EventLoopFuture<Void> {
+        // This method must be called on the `EventLoop` the `LambdaRuntime` has been initialized with.
         self.eventLoop.assertInEventLoop()
 
         logger.info("lambda runtime starting with \(self.configuration)")
@@ -189,3 +196,8 @@ public final class LambdaRuntime<Handler: ByteBufferLambdaHandler> {
         }
     }
 }
+
+/// This is safe since lambda runtime synchronizes by dispatching all methods to a single `EventLoop`
+#if compiler(>=5.5) && canImport(_Concurrency)
+extension LambdaRuntime: @unchecked Sendable {}
+#endif

Sources/AWSLambdaRuntimeCore/LambdaRuntimeClient.swift

@@ -13,8 +13,13 @@
 //===----------------------------------------------------------------------===//
 
 import Logging
+#if compiler(>=5.6)
+@preconcurrency import NIOCore
+@preconcurrency import NIOHTTP1
+#else
 import NIOCore
 import NIOHTTP1
+#endif
 
 /// An HTTP based client for AWS Runtime Engine. This encapsulates the RESTful methods exposed by the Runtime Engine:
 /// * /runtime/invocation/next

Sources/AWSLambdaRuntimeCore/Sendable.swift

@@ -0,0 +1,21 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftAWSLambdaRuntime open source project
+//
+// Copyright (c) 2022 Apple Inc. and the SwiftAWSLambdaRuntime project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftAWSLambdaRuntime project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+// Sendable bridging types
+
+#if compiler(>=5.6)
+public typealias _AWSLambdaSendable = Sendable
+#else
+public typealias _AWSLambdaSendable = Any
+#endif

Sources/AWSLambdaRuntimeCore/Terminator.swift

@@ -18,7 +18,7 @@ import NIOCore
 /// Lambda terminator.
 /// Utility to manage the lambda shutdown sequence.
 public final class LambdaTerminator {
-    private typealias Handler = (EventLoop) -> EventLoopFuture<Void>
+    fileprivate typealias Handler = (EventLoop) -> EventLoopFuture<Void>
 
     private var storage: Storage
 
@@ -99,7 +99,7 @@ extension LambdaTerminator {
 }
 
 extension LambdaTerminator {
-    private final class Storage {
+    fileprivate final class Storage {
         private let lock: Lock
         private var index: [RegistrationKey]
         private var map: [RegistrationKey: (name: String, handler: Handler)]
@@ -137,3 +137,10 @@ extension LambdaTerminator {
         let underlying: [Error]
     }
 }
+
+// Ideally this would not be @unchecked Sendable, but Sendable checks do not understand locks
+// We can transition this to an actor once we drop support for older Swift versions
+#if compiler(>=5.5) && canImport(_Concurrency)
+extension LambdaTerminator: @unchecked Sendable {}
+extension LambdaTerminator.Storage: @unchecked Sendable {}
+#endif

Tests/AWSLambdaRuntimeCoreTests/LambdaTest.swift

@@ -13,9 +13,14 @@
 //===----------------------------------------------------------------------===//
 
 @testable import AWSLambdaRuntimeCore
+#if compiler(>=5.6)
+@preconcurrency import Logging
+@preconcurrency import NIOPosix
+#else
 import Logging
-import NIOCore
 import NIOPosix
+#endif
+import NIOCore
 import XCTest
 
 class LambdaTest: XCTestCase {
@@ -250,6 +255,47 @@ class LambdaTest: XCTestCase {
         XCTAssertLessThanOrEqual(context.getRemainingTime(), .seconds(1))
         XCTAssertGreaterThan(context.getRemainingTime(), .milliseconds(800))
     }
+
+    #if compiler(>=5.6)
+    func testSendable() async throws {
+        struct Handler: EventLoopLambdaHandler {
+            typealias Event = String
+            typealias Output = String
+
+            static func makeHandler(context: Lambda.InitializationContext) -> EventLoopFuture<Handler> {
+                context.eventLoop.makeSucceededFuture(Handler())
+            }
+
+            func handle(_ event: String, context: LambdaContext) -> EventLoopFuture<String> {
+                context.eventLoop.makeSucceededFuture("hello")
+            }
+        }
+
+        let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
+        defer { XCTAssertNoThrow(try eventLoopGroup.syncShutdownGracefully()) }
+
+        let server = try MockLambdaServer(behavior: Behavior()).start().wait()
+        defer { XCTAssertNoThrow(try server.stop().wait()) }
+
+        let logger = Logger(label: "TestLogger")
+        let configuration = Lambda.Configuration(runtimeEngine: .init(requestTimeout: .milliseconds(100)))
+
+        let handler1 = Handler()
+        let task = Task.detached {
+            print(configuration.description)
+            logger.info("hello")
+            let runner = Lambda.Runner(eventLoop: eventLoopGroup.next(), configuration: configuration)
+
+            try runner.run(logger: logger, handler: handler1).wait()
+
+            try runner.initialize(logger: logger, terminator: LambdaTerminator(), handlerType: Handler.self).flatMap { handler2 in
+                runner.run(logger: logger, handler: handler2)
+            }.wait()
+        }
+
+        try await task.value
+    }
+    #endif
 }
 
 private struct Behavior: LambdaServerBehavior {