async_hooks: avoid decrementing iterator after erase

decrementing an iterator returned by `std::vector::erase` may have
undefined behaviour and should not be used. Decrementing `end()`
on an empty container is undefined and `.erase()` could leave
the container empty.

Instead, by calling `vec.erase(it--)` we decrement the valid iterator
before the erase operation but after being passed to the erase method.

In case of `AsyncHooks::RemoveContext` perform the cleanup of empty
contexts upfront using `std::remove_if` because the iteration gets
interrupted as soon as the context to be removed has been found.

PR-URL: nodejs#42749
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Mohammed Keyvanzadeh <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Darshan Sen <[email protected]>

src/env-inl.h

@@ -107,8 +107,7 @@ inline void AsyncHooks::SetJSPromiseHooks(v8::Local<v8::Function> init,
   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--;
+      contexts_.erase(it--);
       continue;
     }
     PersistentToLocal::Weak(env()->isolate(), *it)
@@ -251,12 +250,11 @@ inline void AsyncHooks::AddContext(v8::Local<v8::Context> ctx) {
 inline void AsyncHooks::RemoveContext(v8::Local<v8::Context> ctx) {
   v8::Isolate* isolate = env()->isolate();
   v8::HandleScope handle_scope(isolate);
+  contexts_.erase(std::remove_if(contexts_.begin(),
+                                 contexts_.end(),
+                                 [&](auto&& el) { return el.IsEmpty(); }),
+                  contexts_.end());
   for (auto it = contexts_.begin(); it != contexts_.end(); it++) {
-    if (it->IsEmpty()) {
-      it = contexts_.erase(it);
-      it--;
-      continue;
-    }
     v8::Local<v8::Context> saved_context =
       PersistentToLocal::Weak(isolate, *it);
     if (saved_context == ctx) {