Node.js worker thread API

.editorconfig

@@ -156,6 +156,9 @@ csharp_space_between_square_brackets = false
 dotnet_diagnostic.CA1510.severity = none
 dotnet_diagnostic.CA1513.severity = none
 
+# Stream APIs with Memory parameters are not available in .NET Framework
+dotnet_diagnostic.CA1835.severity = none
+
 dotnet_diagnostic.IDE0290.severity = none # Use primary constructor
 dotnet_diagnostic.IDE0065.severity = none # Using directives must be placed outside of namespace
 

docs/.vitepress/config.mts

@@ -42,8 +42,9 @@ export default defineConfig({
           { text: 'JS / .NET Marshalling', link: '/features/js-dotnet-marshalling' },
           { text: 'JS types in .NET', link: '/features/js-types-in-dotnet' },
           { text: 'JS value scopes', link: '/features/js-value-scopes' },
-          { text: 'JS threading & async', link: '/features/js-threading-async' },
           { text: 'JS references', link: '/features/js-references' },
+          { text: 'JS threading & async', link: '/features/js-threading-async' },
+          { text: 'Node worker threads', link: '/features/node-workers' },
           { text: '.NET Native AOT', link: '/features/dotnet-native-aot' },
           { text: 'Performance', link: '/features/performance' },
         ]

docs/features/node-workers.md

@@ -0,0 +1,65 @@
+# Node Worker Threads
+
+[Node worker threads](https://nodejs.org/api/worker_threads.html) enable parallel execution of
+JavaScript in the same process. They are ideal for CPU-intensive JavaScript operations. They are
+less suited to I/O-intensive work, where the Node.js built-in asynchronous I/O operations are more
+efficient than Workers.
+
+The [NodeWorker](../reference/dotnet/Microsoft.JavaScript.NodeApi.Interop/NodeWorker) class enables
+C# code to create Node worker threads in the same process, and communicate with them.
+
+## JS worker threads
+
+To create a worker, construct a new `NodeWorker` instance with the path to the worker JavaScript
+file:
+
+```C#
+var worker = new NodeWorker(@".\myWorker.js", new NodeWorker.Options());
+```
+
+Or provide the worker script directly as a string, using the `Eval` option:
+```C#
+var worker = new NodeWorker(@"
+    const assert = require('node:assert');
+    const { isMainThread } = require('node:worker_threads');
+    assert(!isMainThread); // This script is running as a worker.
+    ", new NodeWorker.Options { Eval = true });
+```
+
+Messages (any serializable JS values) can be passed back and forth between the C# host and the JS
+worker:
+```C#
+var worker = new NodeWorker(@"
+    const { parentPort } = require('node:worker_threads');
+    parentPort.on('message', (msg) => {
+        parentPort.postMessage(msg); // echo
+    });
+    ", new NodeWorker.Options { Eval = true });
+
+// Wait for the worker to start before sending a message.
+TaskCompletionSource<bool> onlineCompletion = new();
+worker.Online += (sender, e) => onlineCompletion.TrySetResult(true);
+worker.Error += (sender, e) => onlineCompletion.TrySetException(new JSException(e.Error));
+await onlineCompletion.Task;
+
+// Send a message and verify the response.
+TaskCompletionSource<string> echoCompletion = new();
+worker.Message += (_, e) => echoCompletion.TrySetResult((string)e.Value);
+worker.Error += (_, e) => echoCompletion.TrySetException(
+    new JSException(e.Error));
+worker.Exit += (_, e) => echoCompletion.TrySetException(
+    new InvalidOperationException("Worker exited without echoing!"));
+worker.PostMessage("hello");
+string echo = await echoCompletion.Task;
+Assert.Equal("hello", echo);
+```
+
+## C# worker threads
+
+::: warning :construction: COMING SOON
+This functionality is not available yet, but is coming soon.
+:::
+
+Instead of starting a worker with a JavaScript file, it will be possible to provide a C# delegate.
+The delegate callback will be invoked on the JS worker thread; then it can orchestrate importing
+JavaScript packages, callilng JS functions, or whatever is needed to do the work on the thread.

src/NodeApi.DotNetHost/JSMarshaller.cs

@@ -3163,8 +3163,12 @@ private IEnumerable<Expression> BuildFromJSToCollectionInterfaceExpressions(
              *         (key) => (JSValue)key,
              *         (value) => (JSValue)value);
              */
-            MethodInfo asDictionaryMethod = typeof(JSCollectionExtensions).GetStaticMethod(
-                nameof(JSCollectionExtensions.AsDictionary))!.MakeGenericMethod(keyType, valueType);
+            MethodInfo asDictionaryMethod = typeof(JSCollectionExtensions)
+                .GetMethods(BindingFlags.Public | BindingFlags.Static)
+                .Where((m) => m.Name == nameof(JSCollectionExtensions.AsDictionary) &&
+                    m.GetParameters()[0].ParameterType == typeof(JSMap))
+                .Single()
+                .MakeGenericMethod(keyType, valueType);
             MethodInfo asJSMapMethod = typeof(JSMap).GetExplicitConversion(
                 typeof(JSValue), typeof(JSMap));
             yield return Expression.Coalesce(
@@ -3189,9 +3193,12 @@ private IEnumerable<Expression> BuildFromJSToCollectionInterfaceExpressions(
              *         (value) => (TValue)value,
              *         (key) => (JSValue)key);
              */
-            MethodInfo asDictionaryMethod = typeof(JSCollectionExtensions).GetStaticMethod(
-                nameof(JSCollectionExtensions.AsReadOnlyDictionary))
-                !.MakeGenericMethod(keyType, valueType);
+            MethodInfo asDictionaryMethod = typeof(JSCollectionExtensions)
+                .GetMethods(BindingFlags.Public | BindingFlags.Static)
+                .Where((m) => m.Name == nameof(JSCollectionExtensions.AsReadOnlyDictionary) &&
+                    m.GetParameters()[0].ParameterType == typeof(JSMap))
+                .Single()
+                .MakeGenericMethod(keyType, valueType);
             MethodInfo asJSMapMethod = typeof(JSMap).GetExplicitConversion(
                 typeof(JSValue), typeof(JSMap));
             yield return Expression.Coalesce(
@@ -3248,71 +3255,6 @@ private IEnumerable<Expression> BuildFromJSToCollectionClassExpressions(
                         Expression.Convert(valueExpression, jsIterableType, asJSIterableMethod),
                         GetFromJSValueExpression(elementType))));
         }
-        else if (typeDefinition == typeof(Dictionary<,>))
-        {
-            Type keyType = elementType;
-            Type valueType = toType.GenericTypeArguments[1];
-
-            /*
-             * value.TryUnwrap() as Dictionary<TKey, TValue> ??
-             *     new Dictionary<TKey, TValue>(((JSMap)value).AsDictionary<TKey, TValue>(
-             *         (key) => (TKey)key,
-             *         (value) => (TValue)value,
-             *         (key) => (JSValue)key,
-             *         (value) => (JSValue)value);
-             */
-            MethodInfo asDictionaryMethod = typeof(JSCollectionExtensions).GetStaticMethod(
-                nameof(JSCollectionExtensions.AsDictionary))!.MakeGenericMethod(
-                    keyType, valueType);
-            MethodInfo asJSMapMethod = typeof(JSMap).GetExplicitConversion(
-                typeof(JSValue), typeof(JSMap));
-            ConstructorInfo dictionaryConstructor = toType.GetConstructor(
-                new[] { typeof(IDictionary<,>).MakeGenericType(keyType, valueType) })!;
-            yield return Expression.Coalesce(
-                Expression.TypeAs(Expression.Call(valueExpression, s_tryUnwrap), toType),
-                Expression.New(
-                    dictionaryConstructor,
-                    Expression.Call(
-                        asDictionaryMethod,
-                        Expression.Convert(valueExpression, typeof(JSMap), asJSMapMethod),
-                        GetFromJSValueExpression(keyType),
-                        GetFromJSValueExpression(valueType),
-                        GetToJSValueExpression(keyType),
-                        GetToJSValueExpression(valueType))));
-        }
-        else if (typeDefinition == typeof(SortedDictionary<,>))
-        {
-            Type keyType = elementType;
-            Type valueType = toType.GenericTypeArguments[1];
-
-            /*
-             * value.TryUnwrap() as SortedDictionary<TKey, TValue> ??
-             *     new SortedDictionary<TKey, TValue>(((JSMap)value).AsDictionary<TKey, TValue>(
-             *         (key) => (TKey)key,
-             *         (value) => (TValue)value,
-             *         (key) => (JSValue)key,
-             *         (value) => (JSValue)value));
-             */
-            MethodInfo asDictionaryMethod = typeof(JSCollectionExtensions).GetStaticMethod(
-                nameof(JSCollectionExtensions.AsDictionary))!.MakeGenericMethod(
-                    keyType, valueType);
-            MethodInfo asJSMapMethod = typeof(JSMap).GetExplicitConversion(
-                typeof(JSValue), typeof(JSMap));
-            // SortedDictionary doesn't have a constructor that takes IEnumerable<KeyValuePair<>>.
-            ConstructorInfo dictionaryConstructor = toType.GetConstructor(
-                new[] { typeof(IDictionary<,>).MakeGenericType(keyType, valueType) })!;
-            yield return Expression.Coalesce(
-                Expression.TypeAs(Expression.Call(valueExpression, s_tryUnwrap), toType),
-                Expression.New(
-                    dictionaryConstructor,
-                    Expression.Call(
-                        asDictionaryMethod,
-                        Expression.Convert(valueExpression, typeof(JSMap), asJSMapMethod),
-                        GetFromJSValueExpression(keyType),
-                        GetFromJSValueExpression(valueType),
-                        GetToJSValueExpression(keyType),
-                        GetToJSValueExpression(valueType))));
-        }
         else if (typeDefinition == typeof(Collection<>) ||
             typeDefinition == typeof(ReadOnlyCollection<>))
         {
@@ -3342,21 +3284,27 @@ private IEnumerable<Expression> BuildFromJSToCollectionClassExpressions(
                         GetToJSValueExpression(elementType))));
 
         }
-        else if (typeDefinition == typeof(ReadOnlyDictionary<,>))
+        else if (typeDefinition == typeof(Dictionary<,>) ||
+            typeDefinition == typeof(SortedDictionary<,>) ||
+            typeDefinition == typeof(ReadOnlyDictionary<,>))
         {
             Type keyType = elementType;
             Type valueType = toType.GenericTypeArguments[1];
 
             /*
-             * value.TryUnwrap() as ReadOnlyDictionary<TKey, TValue> ??
+             * value.TryUnwrap() as Dictionary<TKey, TValue> ??
              *     new Dictionary<TKey, TValue>(((JSMap)value).AsDictionary<TKey, TValue>(
              *         (key) => (TKey)key,
              *         (value) => (TValue)value,
              *         (key) => (JSValue)key,
              *         (value) => (JSValue)value));
              */
-            MethodInfo asDictionaryMethod = typeof(JSCollectionExtensions).GetStaticMethod(
-                nameof(JSCollectionExtensions.AsDictionary))!.MakeGenericMethod(keyType, valueType);
+            MethodInfo asDictionaryMethod = typeof(JSCollectionExtensions)
+                .GetMethods(BindingFlags.Public | BindingFlags.Static)
+                .Where((m) => m.Name == nameof(JSCollectionExtensions.AsDictionary) &&
+                    m.GetParameters()[0].ParameterType == typeof(JSMap))
+                .Single()
+                .MakeGenericMethod(keyType, valueType);
             MethodInfo asJSMapMethod = typeof(JSMap).GetExplicitConversion(
                 typeof(JSValue), typeof(JSMap));
             ConstructorInfo dictionaryConstructor = toType.GetConstructor(

src/NodeApi.DotNetHost/ManagedHost.cs

@@ -113,7 +113,10 @@ JSValue removeListener(JSCallbackArgs args)
             JSPropertyDescriptor.Function("load", LoadAssembly),
 
             JSPropertyDescriptor.Function("addListener", addListener),
-            JSPropertyDescriptor.Function("removeListener", removeListener));
+            JSPropertyDescriptor.Function("removeListener", removeListener),
+
+            JSPropertyDescriptor.Function("runWorker", RunWorker));
+
 
         // Create a marshaller instance for the current thread. The marshaller dynamically
         // generates adapter delegates for calls to and from JS, for assemblies that were not
@@ -560,6 +563,27 @@ private Assembly LoadAssembly(string assemblyNameOrFilePath, bool allowNativeLib
         return assembly;
     }
 
+    private JSValue RunWorker(JSCallbackArgs args)
+    {
+        nint callbackHandleValue = (nint)args[0].ToBigInteger();
+        Trace($"> ManagedHost.RunWorker({callbackHandleValue})");
+
+        GCHandle callbackHandle = GCHandle.FromIntPtr(callbackHandleValue);
+        Action callback = (Action)callbackHandle.Target!;
+        callbackHandle.Free();
+
+        try
+        {
+            // Worker data and argv are available to the callback as NodejsWorker static properties.
+            callback();
+            return JSValue.Undefined;
+        }
+        finally
+        {
+            Trace($"< ManagedHost.RunWorker({callbackHandleValue})");
+        }
+    }
+
     protected override void Dispose(bool disposing)
     {
         if (disposing)