example: add example for calling JS from AsyncWorker::Execute() (#211)

This was asked for in
nodejs/node-addon-api#110 (comment)
and
nodejs/node-addon-api#110 (comment).
The solution was described in text in
nodejs/node-addon-api#110 (comment)
but it would be better to have a code example that folks can refer to.

Signed-off-by: Darshan Sen <[email protected]>

Author: RaisinTen

call-js-from-async-worker-execute/node-addon-api/binding.gyp

@@ -0,0 +1,28 @@
+{
+  "targets": [
+    {
+      "target_name": "dispatcher",
+      "sources": [ "src/binding.cc" ],
+      'cflags!': [ '-fno-exceptions' ],
+      'cflags_cc!': [ '-fno-exceptions' ],
+      'include_dirs': ["<!@(node -p \"require('node-addon-api').include\")"],
+      'dependencies': ["<!(node -p \"require('node-addon-api').gyp\")"],
+      'conditions': [
+        ['OS=="win"', {
+          "msvs_settings": {
+            "VCCLCompilerTool": {
+              "ExceptionHandling": 1
+            }
+          }
+        }],
+        ['OS=="mac"', {
+          "xcode_settings": {
+            "CLANG_CXX_LIBRARY": "libc++",
+            'GCC_ENABLE_CPP_EXCEPTIONS': 'YES',
+            'MACOSX_DEPLOYMENT_TARGET': '10.7'
+          }
+        }]
+      ]
+    }
+  ]
+}

call-js-from-async-worker-execute/node-addon-api/index.js

@@ -0,0 +1,25 @@
+'use strict'
+
+const { EventEmitter } = require('node:events');
+const { dispatch } = require('bindings')('dispatcher');
+
+class Socket extends EventEmitter {
+  constructor () {
+    super();
+    dispatch(this.emit.bind(this));
+  }
+}
+
+const socket = new Socket();
+
+socket.on('open', () => {
+  console.log('opened');
+});
+
+socket.on('message', (message) => {
+  console.log(`message: ${message}`);
+});
+
+socket.on('close', () => {
+  console.log('closed');
+});

call-js-from-async-worker-execute/node-addon-api/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "call-js-from-async-worker-execute",
+  "version": "0.0.0",
+  "description": "Node.js Addons - calls JS from AsyncWorker::Execute",
+  "main": "index.js",
+  "private": true,
+  "gypfile": true,
+  "scripts": {
+    "start": "node index.js"
+  },
+  "dependencies": {
+    "node-addon-api": "*",
+    "bindings": "*"
+  }
+}

call-js-from-async-worker-execute/node-addon-api/src/binding.cc

@@ -0,0 +1,101 @@
+#include <napi.h>
+
+#include <chrono>
+#include <thread>
+
+class Dispatcher : public Napi::AsyncWorker {
+ public:
+  Dispatcher(Napi::Env env, Napi::Function& callback)
+      : Napi::AsyncWorker(env),
+        callback_(callback),
+        tsfn_{
+            Napi::ThreadSafeFunction::New(env, callback, "Dispatcher", 0, 1)} {}
+
+  virtual ~Dispatcher() override { tsfn_.Release(); }
+
+  void Execute() override {
+    // Since this method executes on a thread that is different from the main
+    // thread, we can't directly call into JavaScript. To trigger a call into
+    // JavaScript from this thread, ThreadSafeFunction needs to be used to
+    // communicate with the main thread, so that the main thread can invoke the
+    // JavaScript function.
+
+    napi_status status =
+        tsfn_.BlockingCall([](Napi::Env env, Napi::Function js_callback) {
+          js_callback.Call({Napi::String::New(env, "open")});
+        });
+    if (status != napi_ok) {
+      SetError("Napi::ThreadSafeNapi::Function.BlockingCall() failed");
+      return;
+    }
+
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+    status = tsfn_.BlockingCall([](Napi::Env env, Napi::Function js_callback) {
+      js_callback.Call(
+          {Napi::String::New(env, "message"), Napi::String::New(env, "data1")});
+    });
+    if (status != napi_ok) {
+      SetError("Napi::ThreadSafeNapi::Function.BlockingCall() failed");
+      return;
+    }
+
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+    status = tsfn_.BlockingCall([](Napi::Env env, Napi::Function js_callback) {
+      js_callback.Call(
+          {Napi::String::New(env, "message"), Napi::String::New(env, "data2")});
+    });
+    if (status != napi_ok) {
+      SetError("Napi::ThreadSafeNapi::Function.BlockingCall() failed");
+      return;
+    }
+
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+    status = tsfn_.BlockingCall([](Napi::Env env, Napi::Function js_callback) {
+      js_callback.Call(
+          {Napi::String::New(env, "message"), Napi::String::New(env, "data3")});
+    });
+    if (status != napi_ok) {
+      SetError("Napi::ThreadSafeNapi::Function.BlockingCall() failed");
+      return;
+    }
+
+    status = tsfn_.BlockingCall([](Napi::Env env, Napi::Function js_callback) {
+      js_callback.Call({Napi::String::New(env, "close")});
+    });
+    if (status != napi_ok) {
+      SetError("Napi::ThreadSafeNapi::Function.BlockingCall() failed");
+      return;
+    }
+  }
+
+  void OnError(Napi::Error const& error) override {
+    callback_.Call({Napi::String::New(Env(), "error"), error.Value()});
+  }
+
+ private:
+  Napi::Function callback_;
+  Napi::ThreadSafeFunction tsfn_;
+};
+
+void Dispatch(const Napi::CallbackInfo& info) {
+  Napi::Env env = info.Env();
+
+  if (info.Length() < 1 || !info[0].IsFunction()) {
+    Napi::TypeError::New(
+        env, "The first argument needs to be the callback function.")
+        .ThrowAsJavaScriptException();
+    return;
+  }
+
+  Napi::Function callback = info[0].As<Napi::Function>();
+
+  Dispatcher* dispatcher = new Dispatcher(env, callback);
+  dispatcher->Queue();
+}
+
+Napi::Object Init(Napi::Env env, Napi::Object exports) {
+  exports.Set("dispatch", Napi::Function::New(env, Dispatch));
+  return exports;
+}
+
+NODE_API_MODULE(dispatcher, Init)