src: restrict unloading addons to Worker threads

src/env.cc

@@ -276,9 +276,16 @@ Environment::~Environment() {
   TRACE_EVENT_NESTABLE_ASYNC_END0(
     TRACING_CATEGORY_NODE1(environment), "Environment", this);
 
-  // Dereference all addons that were loaded into this environment.
-  for (binding::DLib& addon : loaded_addons_) {
-    addon.Close();
+  // Do not unload addons on the main thread. Some addons need to retain memory
+  // beyond the Environment's lifetime, and unloading them early would break
+  // them; with Worker threads, we have the opportunity to be stricter.
+  // Also, since the main thread usually stops just before the process exits,
+  // this is far less relevant here.
+  if (!is_main_thread()) {
+    // Dereference all addons that were loaded into this environment.
+    for (binding::DLib& addon : loaded_addons_) {
+      addon.Close();
+    }
   }
 }
 

test/addons/worker-addon/binding.cc

@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <v8.h>
+#include <uv.h>
 
 using v8::Context;
 using v8::HandleScope;
@@ -41,6 +42,17 @@ void Initialize(Local<Object> exports,
       const_cast<void*>(static_cast<const void*>("cleanup")));
   node::AddEnvironmentCleanupHook(context->GetIsolate(), Dummy, nullptr);
   node::RemoveEnvironmentCleanupHook(context->GetIsolate(), Dummy, nullptr);
+
+  if (getenv("addExtraItemToEventLoop") != nullptr) {
+    // Add an item to the event loop that we do not clean up in order to make
+    // sure that for the main thread, this addon's memory persists even after
+    // the Environment instance has been destroyed.
+    static uv_async_t extra_async;
+    uv_loop_t* loop = node::GetCurrentEventLoop(context->GetIsolate());
+    int err = uv_async_init(loop, &extra_async, [](uv_async_t*) {});
+    assert(err == 0);
+    uv_unref(reinterpret_cast<uv_handle_t*>(&extra_async));
+  }
 }
 
 NODE_MODULE_CONTEXT_AWARE(NODE_GYP_MODULE_NAME, Initialize)

test/addons/worker-addon/test.js

@@ -6,12 +6,19 @@ const path = require('path');
 const { Worker } = require('worker_threads');
 const binding = path.resolve(__dirname, `./build/${common.buildType}/binding`);
 
-if (process.argv[2] === 'child') {
+if (process.argv[2] === 'worker') {
   new Worker(`require(${JSON.stringify(binding)});`, { eval: true });
-} else {
+  return;
+} else if (process.argv[2] === 'main-thread') {
+  process.env.addExtraItemToEventLoop = 'yes';
+  require(binding);
+  return;
+}
+
+for (const test of ['worker', 'main-thread']) {
   const proc = child_process.spawnSync(process.execPath, [
     __filename,
-    'child'
+    test
   ]);
   assert.strictEqual(proc.stderr.toString(), '');
   assert.strictEqual(proc.stdout.toString(), 'ctor cleanup dtor');