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: #25927 PR-URL: #25992 Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
nodejs · Feb 7, 2019 · 03ffcf76b7cdee745bb53d4b2144f037f0c3017a · 03ffcf7
1 parent 4c22d6e
commit 03ffcf76b7cdee745bb53d4b2144f037f0c3017a
Unified Split

Showing with 15 additions and 0 deletions.

+15 −0 src/js_native_api_v8.cc
diff --git 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) {