From 1a401e4aa3de4efa28bf23a4e93977b569689e96 Mon Sep 17 00:00:00 2001
From: Bryan English <bryan@bryanenglish.com>
Date: Sat, 19 Jun 2021 13:47:43 -0400
Subject: [PATCH 1/3] async_hooks: check for empty contexts before removing

This way we don't end up attempting to SetPromiseHooks on contexts that
have already been collected.

Fixes: https://github.com/nodejs/node/issues/39019
---
 src/env-inl.h                           |  7 ++++++-
 test/parallel/test-async-hooks-vm-gc.js | 15 +++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 test/parallel/test-async-hooks-vm-gc.js

diff --git a/src/env-inl.h b/src/env-inl.h
index 6fb8f137c37569..1c0afb20736ab8 100644
--- a/src/env-inl.h
+++ b/src/env-inl.h
@@ -256,8 +256,13 @@ inline void AsyncHooks::RemoveContext(v8::Local<v8::Context> ctx) {
   v8::Isolate* isolate = env()->isolate();
   v8::HandleScope handle_scope(isolate);
   for (auto it = contexts_.begin(); it != contexts_.end(); it++) {
+    if (it->IsEmpty()) {
+      contexts_.erase(it);
+      it--;
+      continue;
+    }
     v8::Local<v8::Context> saved_context =
-      PersistentToLocal::Weak(env()->isolate(), *it);
+      PersistentToLocal::Weak(isolate, *it);
     if (saved_context == ctx) {
       it->Reset();
       contexts_.erase(it);
diff --git a/test/parallel/test-async-hooks-vm-gc.js b/test/parallel/test-async-hooks-vm-gc.js
new file mode 100644
index 00000000000000..da95e3579dcca4
--- /dev/null
+++ b/test/parallel/test-async-hooks-vm-gc.js
@@ -0,0 +1,15 @@
+// Flags: --expose-gc
+'use strict';
+
+require('../common');
+const asyncHooks = require('async_hooks');
+const vm = require('vm');
+
+// This is a regression test for https://github.com/nodejs/node/issues/39019
+//
+// It should not segfault.
+
+const hook = asyncHooks.createHook({ init() {} }).enable();
+vm.createContext();
+globalThis.gc();
+hook.disable();

From 979bd0b4500dbb833d80fbc0dbf2b974653c3bef Mon Sep 17 00:00:00 2001
From: Bryan English <bryan@bryanenglish.com>
Date: Sun, 20 Jun 2021 23:01:58 -0400
Subject: [PATCH 2/3] fixup! review feedback

Co-authored-by: Anna Henningsen <github@addaleax.net>
---
 src/env-inl.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/env-inl.h b/src/env-inl.h
index 1c0afb20736ab8..a0fcdfacdf4efc 100644
--- a/src/env-inl.h
+++ b/src/env-inl.h
@@ -257,7 +257,7 @@ inline void AsyncHooks::RemoveContext(v8::Local<v8::Context> ctx) {
   v8::HandleScope handle_scope(isolate);
   for (auto it = contexts_.begin(); it != contexts_.end(); it++) {
     if (it->IsEmpty()) {
-      contexts_.erase(it);
+      it = contexts_.erase(it);
       it--;
       continue;
     }

From 9acb32fbbdb3ff6613e810fda5effc065f8e3e43 Mon Sep 17 00:00:00 2001
From: Bryan English <bryan@bryanenglish.com>
Date: Mon, 21 Jun 2021 14:52:35 -0400
Subject: [PATCH 3/3] fixup! check for empty contexts in SetJSPromiseHooks too

---
 src/env-inl.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/env-inl.h b/src/env-inl.h
index a0fcdfacdf4efc..b3b1ea908253b9 100644
--- a/src/env-inl.h
+++ b/src/env-inl.h
@@ -104,6 +104,11 @@ inline void AsyncHooks::SetJSPromiseHooks(v8::Local<v8::Function> init,
   js_promise_hooks_[2].Reset(env()->isolate(), after);
   js_promise_hooks_[3].Reset(env()->isolate(), resolve);
   for (auto it = contexts_.begin(); it != contexts_.end(); it++) {
+    if (it->IsEmpty()) {
+      it = contexts_.erase(it);
+      it--;
+      continue;
+    }
     PersistentToLocal::Weak(env()->isolate(), *it)
         ->SetPromiseHooks(init, before, after, resolve);
   }