re-add the check on unique Handler and remove the @unchecked on LambdaRuntime !

Author: sebsto

Sources/AWSLambdaRuntime/LambdaRuntime.swift

@@ -13,7 +13,6 @@
 //===----------------------------------------------------------------------===//
 
 import Logging
-import NIOConcurrencyHelpers
 import NIOCore
 import Synchronization
 
@@ -27,10 +26,10 @@ import Foundation
 // We use an Atomic here to ensure thread safety
 private let _isRunning = Atomic<Bool>(false)
 
-// we use unchecked here because Handler are not Sendable
-public final class LambdaRuntime<Handler>: @unchecked Sendable where Handler: StreamingLambdaHandler {
+public final class LambdaRuntime<Handler>: Sendable where Handler: StreamingLambdaHandler {
     @usableFromInline
-    let handler: Handler
+    /// we protect the handler behind a Mutex to ensure that we only ever have one copy of it
+    let handlerMutex: SendingStorage<Handler>
     @usableFromInline
     let logger: Logger
     @usableFromInline
@@ -41,7 +40,7 @@ public final class LambdaRuntime<Handler>: @unchecked Sendable where Handler: St
         eventLoop: EventLoop = Lambda.defaultEventLoop,
         logger: Logger = Logger(label: "LambdaRuntime")
     ) {
-        self.handler = handler
+        self.handlerMutex = SendingStorage(handler)
         self.eventLoop = eventLoop
 
         // by setting the log level here, we understand it can not be changed dynamically at runtime
@@ -80,6 +79,12 @@ public final class LambdaRuntime<Handler>: @unchecked Sendable where Handler: St
             _isRunning.store(false, ordering: .releasing)
         }
 
+        // The handler can be non-sendable, we want to ensure we only ever have one copy of it
+        let handler = try? self.handlerMutex.get()
+        guard let handler else {
+            throw LambdaRuntimeError(code: .runtimeCanOnlyBeStartedOnce)
+        }
+
         // are we running inside an AWS Lambda runtime environment ?
         // AWS_LAMBDA_RUNTIME_API is set when running on Lambda
         // https://docs.aws.amazon.com/lambda/latest/dg/runtimes-api.html
@@ -118,7 +123,7 @@ public final class LambdaRuntime<Handler>: @unchecked Sendable where Handler: St
                 ) { runtimeClient in
                     try await Lambda.runLoop(
                         runtimeClient: runtimeClient,
-                        handler: self.handler,
+                        handler: handler,
                         logger: self.logger
                     )
                 }

Sources/AWSLambdaRuntime/Utils.swift

@@ -13,8 +13,11 @@
 //===----------------------------------------------------------------------===//
 
 import Dispatch
+import NIOConcurrencyHelpers
 import NIOPosix
 
+// import Synchronization
+
 enum Consts {
     static let apiPrefix = "/2018-06-01"
     static let invocationURLPrefix = "\(apiPrefix)/runtime/invocation"
@@ -132,3 +135,34 @@ extension AmazonHeaders {
         return "\(version)-\(datePadding)\(dateValue)-\(identifier)"
     }
 }
+
+/// Temporary storage for value being sent from one isolation domain to another
+// use NIOLockedValueBox instead of Mutex to avoid compiler crashes on 6.0
+// see https://github.com/swiftlang/swift/issues/78048
+@usableFromInline
+struct SendingStorage<Value>: ~Copyable, @unchecked Sendable {
+    @usableFromInline
+    struct ValueAlreadySentError: Error {
+        @usableFromInline
+        init() {}
+    }
+
+    @usableFromInline
+    // let storage: Mutex<Value?>
+    let storage: NIOLockedValueBox<Value?>
+
+    @inlinable
+    init(_ value: sending Value) {
+        self.storage = .init(value)
+    }
+
+    @inlinable
+    func get() throws -> Value {
+        // try self.storage.withLock {
+        try self.storage.withLockedValue {
+            guard let value = $0 else { throw ValueAlreadySentError() }
+            $0 = nil
+            return value
+        }
+    }
+}