n-api: finalize during second-pass callback

Calling into the engine from a weak callback is unsafe, however, the
engine offers a way to attach a second-pass weak callback which gets
called when it is safe to call into JavaScript. This moves the point
at which the N-API finalize callback gets called to this latter point.

Fixes: https://github.com/nodejs/node/issues/25927
PR-URL: https://github.com/nodejs/node/pull/25992
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/js_native_api_v8.cc b/src/js_native_api_v8.cc
index 9e67e2ca24..287142e265 100644
--- a/src/js_native_api_v8.cc
+++ b/src/js_native_api_v8.cc
@@ -281,10 +281,25 @@ class Reference : private Finalizer {
   }
 
  private:
+  // The N-API finalizer callback may make calls into the engine. V8's heap is
+  // not in a consistent state during the weak callback, and therefore it does
+  // not support calls back into it. However, it provides a mechanism for adding
+  // a finalizer which may make calls back into the engine by allowing us to
+  // attach such a second-pass finalizer from the first pass finalizer. Thus,
+  // we do that here to ensure that the N-API finalizer callback is free to call
+  // into the engine.
   static void FinalizeCallback(const v8::WeakCallbackInfo<Reference>& data) {
     Reference* reference = data.GetParameter();
+
+    // The reference must be reset during the first pass.
     reference->_persistent.Reset();
 
+    data.SetSecondPassCallback(SecondPassCallback);
+  }
+
+  static void SecondPassCallback(const v8::WeakCallbackInfo<Reference>& data) {
+    Reference* reference = data.GetParameter();
+
     napi_env env = reference->_env;
 
     if (reference->_finalize_callback != nullptr) {