From 55768c0079d8381b464b99507b6c7f123729a6e6 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Sat, 19 Jan 2019 00:24:20 +0100
Subject: [PATCH] src: restrict unloading addons to Worker threads

Unloading native addons from the main thread was an (presumably
unintended) significant breaking change, because addons may
rely on their memory being available after an `Environment` exits.

This patch only restricts this to Worker threads, at least for the
time being, and thus matches the behaviour from
https://github.com/nodejs/node/pull/23319.

PR-URL: https://github.com/nodejs/node/pull/25577
Refs: https://github.com/nodejs/node/pull/24861
Refs: https://github.com/nodejs/node/pull/23319
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
---
 src/env.cc                          | 13 ++++++++++---
 test/addons/worker-addon/binding.cc | 12 ++++++++++++
 test/addons/worker-addon/test.js    | 13 ++++++++++---
 3 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/src/env.cc b/src/env.cc
index 2cbbd14e713b9b..f45386dce4a058 100644
--- a/src/env.cc
+++ b/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();
+    }
   }
 }
 
diff --git a/test/addons/worker-addon/binding.cc b/test/addons/worker-addon/binding.cc
index 1fb85ae230eb5f..faf3ba8647e5bc 100644
--- a/test/addons/worker-addon/binding.cc
+++ b/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)
diff --git a/test/addons/worker-addon/test.js b/test/addons/worker-addon/test.js
index b6d962c0868741..7fb7c1a87aa903 100644
--- a/test/addons/worker-addon/test.js
+++ b/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');