Use Mutex instead of NIOLockedValueBox (swift-server#394)

* Use Mutex instead of NIOLockedValueBox

* fix format

---------

Co-authored-by: Sébastien Stormacq <sebastien.stormacq@gmail.com>

Author: fabianfett

Sources/AWSLambdaRuntimeCore/LambdaRuntime.swift

@@ -14,15 +14,11 @@
 
 import Foundation
 import Logging
-import NIOConcurrencyHelpers
 import NIOCore
+import Synchronization
 
-// We need `@unchecked` Sendable here, as `NIOLockedValueBox` does not understand `sending` today.
-// We don't want to use `NIOLockedValueBox` here anyway. We would love to use Mutex here, but this
-// sadly crashes the compiler today.
-public final class LambdaRuntime<Handler>: @unchecked Sendable where Handler: StreamingLambdaHandler {
-    // TODO: We want to change this to Mutex as soon as this doesn't crash the Swift compiler on Linux anymore
-    let handlerMutex: NIOLockedValueBox<Handler?>
+public final class LambdaRuntime<Handler>: Sendable where Handler: StreamingLambdaHandler {
+    let handlerMutex: Mutex<Handler?>
     let logger: Logger
     let eventLoop: EventLoop
 
@@ -31,7 +27,7 @@ public final class LambdaRuntime<Handler>: @unchecked Sendable where Handler: St
         eventLoop: EventLoop = Lambda.defaultEventLoop,
         logger: Logger = Logger(label: "LambdaRuntime")
     ) {
-        self.handlerMutex = NIOLockedValueBox(handler)
+        self.handlerMutex = Mutex(handler)
         self.eventLoop = eventLoop
         self.logger = logger
     }
@@ -45,7 +41,7 @@ public final class LambdaRuntime<Handler>: @unchecked Sendable where Handler: St
         let ip = String(ipAndPort[0])
         guard let port = Int(ipAndPort[1]) else { throw LambdaRuntimeError(code: .invalidPort) }
 
-        let handler = self.handlerMutex.withLockedValue { handler in
+        let handler = self.handlerMutex.withLock { handler in
             let result = handler
             handler = nil
             return result