Use MainActor to ensure we're running on main queue (#515)

* Use MainActor to ensure we're running on main queue

...and to simplify the code.

* VZVirtualMachine.requestStop() is not asynchronous

Sources/tart/Commands/Run.swift

@@ -427,7 +427,7 @@ struct Run: AsyncParsableCommand {
               Task { try await vm!.virtualMachine.stop() }
             }
             Button("Request Stop") {
-              Task { try await vm!.virtualMachine.requestStop() }
+              Task { try vm!.virtualMachine.requestStop() }
             }
           }
         }

Sources/tart/VM+Recovery.swift

@@ -5,34 +5,26 @@ import Dynamic
 // Kudos to @saagarjha's VirtualApple for finding about _VZVirtualMachineStartOptions
 
 extension VZVirtualMachine {
-  @available(macOS 12, *)
+  @MainActor @available(macOS 12, *)
   func start(_ recovery: Bool) async throws {
     if !recovery {
       // just use the regular API
-      return try await withCheckedThrowingContinuation { continuation in
-        DispatchQueue.main.async {
-          self.start(completionHandler: { result in
-            continuation.resume(with: result)
-          })
-        }
-      }
+      return try await self.start()
     }
 
     // use some private stuff only for recovery
     return try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Void, Error>) in
-      DispatchQueue.main.async {
-        let handler: @convention(block) (_ result: Any?) -> Void = { result in
-          if let error = result as? Error {
-            continuation.resume(throwing: error)
-          } else {
-            continuation.resume(returning: ())
-          }
+      let handler: @convention(block) (_ result: Any?) -> Void = { result in
+        if let error = result as? Error {
+          continuation.resume(throwing: error)
+        } else {
+          continuation.resume(returning: ())
         }
-        // dynamic magic
-        let options = Dynamic._VZVirtualMachineStartOptions()
-        options.bootMacOSRecovery = recovery
-        Dynamic(self)._start(withOptions: options, completionHandler: handler)
       }
+      // dynamic magic
+      let options = Dynamic._VZVirtualMachineStartOptions()
+      options.bootMacOSRecovery = recovery
+      Dynamic(self)._start(withOptions: options, completionHandler: handler)
     }
   }
 }

Sources/tart/VM.swift

@@ -223,24 +223,9 @@ class VM: NSObject, VZVirtualMachineDelegate, ObservableObject {
   func run(_ recovery: Bool) async throws {
     try network.run(sema)
 
-    let startTask = DispatchQueue.main.sync {
-      Task {
-        if #available(macOS 13, *) {
-          // new API introduced in Ventura
-          let startOptions = VZMacOSVirtualMachineStartOptions()
-          startOptions.startUpFromMacOSRecovery = recovery
-          try await virtualMachine.start(options: startOptions)
-        } else {
-          // use method that also available on Monterey
-          try await virtualMachine.start(recovery)
-        }
-      }
-    }
-
-    try await withTaskCancellationHandler(operation: {
-      // Await on VZVirtualMachine.start() result
-      _ = try await startTask.value
+    try await start(recovery)
 
+    await withTaskCancellationHandler(operation: {
       // Wait for the VM to finish running
       // or for the exit condition
       sema.wait()
@@ -249,16 +234,30 @@ class VM: NSObject, VZVirtualMachineDelegate, ObservableObject {
     })
 
     if Task.isCancelled {
-      DispatchQueue.main.sync {
-        Task {
-          try await self.virtualMachine.stop()
-        }
-      }
+      try await stop()
     }
 
     try await network.stop()
   }
 
+  @MainActor
+  private func start(_ recovery: Bool) async throws {
+    if #available(macOS 13, *) {
+      // new API introduced in Ventura
+      let startOptions = VZMacOSVirtualMachineStartOptions()
+      startOptions.startUpFromMacOSRecovery = recovery
+      try await virtualMachine.start(options: startOptions)
+    } else {
+      // use method that also available on Monterey
+      try await virtualMachine.start(recovery)
+    }
+  }
+
+  @MainActor
+  private func stop() async throws {
+    try await self.virtualMachine.stop()
+  }
+
   static func craftConfiguration(
     diskURL: URL,
     nvramURL: URL,