src: unregister Isolate with platform before disposing

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

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() {

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)

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();
   }

test/cctest/test_platform.cc

@@ -101,6 +101,6 @@ TEST_F(NodeZeroIsolateTestFixture, IsolatePlatformDelegateTest) {
 
   // Graceful shutdown
   delegate->Shutdown();
-  isolate->Dispose();
   platform->UnregisterIsolate(isolate);
+  isolate->Dispose();
 }