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
Backport-PR-URL: https://github.com/nodejs/node/pull/26060
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/node_api.cc b/src/node_api.cc
index 196f5512c9..ec477e1d23 100644
--- a/src/node_api.cc
+++ b/src/node_api.cc
@@ -448,10 +448,25 @@ 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();
+
     // Check before calling the finalize callback, because the callback might
     // delete it.
     bool delete_self = reference->_delete_self;