From 27d48ed7ef78a8b5ef2d05b6d2dd503a24e63802 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Wed, 11 Dec 2019 21:48:47 -0500
Subject: [PATCH] src: unregister Isolate with platform before disposing

I previously thought the order of these calls was no longer
relevant. I was wrong.

This commit undoes the changes from 312c02d25e9, adds a comment
explaining why I was wrong, and flips the order of the calls
elsewhere for consistency, the latter having been the goal
of 312c02d25e9.

Fixes: https://github.com/nodejs/node/issues/30846
Refs: https://github.com/nodejs/node/pull/30181
---
 src/node.h                      | 1 +
 src/node_main_instance.cc       | 2 +-
 src/node_worker.cc              | 7 ++++++-
 test/cctest/node_test_fixture.h | 2 +-
 test/cctest/test_platform.cc    | 2 +-
 5 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/node.h b/src/node.h
index f3da4574019254..50f85ae338914e 100644
--- a/src/node.h
+++ b/src/node.h
@@ -298,6 +298,7 @@ class NODE_EXTERN MultiIsolatePlatform : public v8::Platform {
 
   // This function may only be called once per `Isolate`, and discard any
   // pending delayed tasks scheduled for that isolate.
+  // This needs to be called right before calling `Isolate::Dispose()`.
   virtual void UnregisterIsolate(v8::Isolate* isolate) = 0;
 
   // The platform should call the passed function once all state associated
diff --git a/src/node_main_instance.cc b/src/node_main_instance.cc
index eea847725300f0..86a857299f6e90 100644
--- a/src/node_main_instance.cc
+++ b/src/node_main_instance.cc
@@ -99,8 +99,8 @@ NodeMainInstance::~NodeMainInstance() {
   if (!owns_isolate_) {
     return;
   }
-  isolate_->Dispose();
   platform_->UnregisterIsolate(isolate_);
+  isolate_->Dispose();
 }
 
 int NodeMainInstance::Run() {
diff --git a/src/node_worker.cc b/src/node_worker.cc
index 9976ec3f0ac089..46c52731356ddc 100644
--- a/src/node_worker.cc
+++ b/src/node_worker.cc
@@ -189,8 +189,13 @@ class WorkerThreadData {
         *static_cast<bool*>(data) = true;
       }, &platform_finished);
 
-      isolate->Dispose();
+      // The order of these calls is important; if the Isolate is first disposed
+      // and then unregistered, there is a race condition window in which no
+      // new Isolate at the same address can successfully be registered with
+      // the platform.
+      // (Refs: https://github.com/nodejs/node/issues/30846)
       w_->platform_->UnregisterIsolate(isolate);
+      isolate->Dispose();
 
       // Wait until the platform has cleaned up all relevant resources.
       while (!platform_finished)
diff --git a/test/cctest/node_test_fixture.h b/test/cctest/node_test_fixture.h
index c8cb9232978821..44f4466356e1b7 100644
--- a/test/cctest/node_test_fixture.h
+++ b/test/cctest/node_test_fixture.h
@@ -116,8 +116,8 @@ class NodeTestFixture : public NodeZeroIsolateTestFixture {
   void TearDown() override {
     platform->DrainTasks(isolate_);
     isolate_->Exit();
-    isolate_->Dispose();
     platform->UnregisterIsolate(isolate_);
+    isolate_->Dispose();
     isolate_ = nullptr;
     NodeZeroIsolateTestFixture::TearDown();
   }
diff --git a/test/cctest/test_platform.cc b/test/cctest/test_platform.cc
index 73057bb2d8c03a..c56766b5ec8611 100644
--- a/test/cctest/test_platform.cc
+++ b/test/cctest/test_platform.cc
@@ -101,6 +101,6 @@ TEST_F(NodeZeroIsolateTestFixture, IsolatePlatformDelegateTest) {
 
   // Graceful shutdown
   delegate->Shutdown();
-  isolate->Dispose();
   platform->UnregisterIsolate(isolate);
+  isolate->Dispose();
 }