node,timers: fix beforeExit with unrefed timers

src/handle_wrap.h

@@ -53,6 +53,7 @@ class HandleWrap : public AsyncWrap {
  private:
   friend class Environment;
   friend void GetActiveHandles(const v8::FunctionCallbackInfo<v8::Value>&);
+  friend bool HasUnrefedTimerHandles(Environment* env);
   static void OnClose(uv_handle_t* handle);
   ListNode<HandleWrap> handle_wrap_queue_;
   unsigned int flags_;

src/node.cc

@@ -1544,6 +1544,15 @@ void GetActiveHandles(const FunctionCallbackInfo<Value>& args) {
 }
 
 
+bool HasUnrefedTimerHandles(Environment* env) {
+  for (auto w : *env->handle_wrap_queue()) {
+    if (!w->persistent().IsEmpty() && w->flags_ & HandleWrap::kUnref)
+      return true;
+  }
+  return false;
+}
+
+
 static void Abort(const FunctionCallbackInfo<Value>& args) {
   ABORT();
 }
@@ -3969,6 +3978,11 @@ static void StartNodeInstance(void* arg) {
           v8::platform::PumpMessageLoop(default_platform, isolate);
           EmitBeforeExit(env);
 
+          // We need to run an extra event loop turn to purge unrefed handles.
+          bool unrefedTimers = HasUnrefedTimerHandles(env);
+          if (unrefedTimers == true)
+            uv_run(env->event_loop(), UV_RUN_NOWAIT);
+
           // Emit `beforeExit` if the loop became alive either after emitting
           // event, or after running some callbacks.
           more = uv_loop_alive(env->event_loop());

test/parallel/test-timers-unrefed-in-beforeexit.js

@@ -0,0 +1,20 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+var once = 0;
+
+process.on('beforeExit', () => {
+  if (once > 1)
+    throw new RangeError('beforeExit should only have been called once!');
+
+  setTimeout(() => {}, 1).unref();
+  once++;
+});
+
+process.on('exit', (code) => {
+  if (code !== 0) return;
+
+  assert.strictEqual(once, 1);
+});