refactor(napi): use get_uv_event_loop instead of uv_default_loop

Using the uv_loop_s from napi_env is safer as it's possible that
there are multiple Workers, and therefore multiple uv_loop_s.

napi/src/env.rs

@@ -533,6 +533,17 @@ impl Env {
       .map_err(|e| Error::new(Status::InvalidArg, format!("{}", e)))
   }
 
+  #[cfg(napi2)]
+  #[inline]
+  pub fn get_uv_event_loop(&self) -> Result<*mut sys::uv_loop_s> {
+    let mut uv_loop: *mut sys::uv_loop_s = ptr::null_mut();
+    Ok(unsafe {
+      let status = sys::napi_get_uv_event_loop(self.0, &mut uv_loop);
+      check_status(status)?;
+      uv_loop
+    })
+  }
+
   #[cfg(all(feature = "libuv", napi4))]
   #[inline]
   pub fn execute<
@@ -553,7 +564,7 @@ impl Env {
       check_status(status)?;
     }
 
-    let event_loop = unsafe { sys::uv_default_loop() };
+    let event_loop = self.get_uv_event_loop()?;
     let future_promise = promise::FuturePromise::create(self.0, raw_deferred, Box::from(resolver))?;
     let future_to_execute = promise::resolve_from_future(future_promise.start()?, deferred);
     uv::execute(event_loop, Box::pin(future_to_execute))?;

test_module/__test__/napi4/uv.spec.js

@@ -1,10 +1,18 @@
 const test = require('ava')
-const { join } = require('path')
+const { join, resolve } = require('path')
 const { readFileSync } = require('fs')
 
 const bindings = require('../../index.node')
 const napiVersion = require('../napi-version')
 
+let threadMod
+
+try {
+  threadMod = require('worker_threads')
+} catch (err) {
+  //
+}
+
 const filepath = join(__dirname, './example.txt')
 
 test('should execute future on libuv thread pool', async (t) => {
@@ -16,3 +24,21 @@ test('should execute future on libuv thread pool', async (t) => {
   t.true(Buffer.isBuffer(fileContent))
   t.deepEqual(readFileSync(filepath), fileContent)
 })
+
+test('should execute future on libuv thread pool of "Worker"', async (t) => {
+  // Test in threads if current Node.js supports "worker_threads".`
+  if (!threadMod || napiVersion < 4) {
+    return
+  }
+
+  const { Worker } = threadMod
+  const script = resolve(__dirname, './uv_worker.js')
+  const worker = new Worker(script)
+  const success = await new Promise((resolve) => {
+    worker.on('message', (success) => {
+      resolve(success)
+    })
+  })
+
+  t.is(success, true)
+})

test_module/__test__/napi4/uv_worker.js

@@ -0,0 +1,16 @@
+const { isMainThread, parentPort } = require('worker_threads')
+const { join } = require('path')
+const { readFileSync } = require('fs')
+const bindings = require('../../index.node')
+
+const filepath = join(__dirname, './example.txt')
+
+if (!isMainThread) {
+  ;(async () => {
+    const fileContent = await bindings.uvReadFile(filepath)
+    const success =
+      Buffer.isBuffer(fileContent) &&
+      readFileSync(filepath).toString('utf8') === fileContent.toString('utf8')
+    parentPort.postMessage(success)
+  })()
+}