src: keep reference buffer alive longer (#55)

* src: keep reference buffer alive longer

Keep a buffer written by WritePointer alive
until the finalizers for the buffer to which
the pointer has been run have been executed:

Refs: #54

Signed-off-by: Michael Dawson <mdawson@devrus.com>

* limit change to writePointer

Update to avoid changing behaviour for
_writePointer and limit change to writePointer
where objects were already being associated
with the buffer.

Signed-off-by: Michael Dawson <mdawson@devrus.com>

* remove _attach call in writePointer

remove _attach call in writePointer as
it is no longer needed since a stronger
version is done in the native code
when true is passed as the fourth parameter

lib/ref.js

@@ -746,8 +746,12 @@ exports.writeObject = function writeObject (buf, offset, obj) {
 
 exports.writePointer = function writePointer (buf, offset, ptr) {
   debug('writing pointer to buffer', buf, offset, ptr);
-  exports._writePointer(buf, offset, ptr);
-  exports._attach(buf, ptr);
+  // Passing true as a fourth parameter does an a stronger
+  // version of attach which ensures ptr is only collected after
+  // the finalizer for buf has run. See
+  // https://github.com/node-ffi-napi/ref-napi/issues/54
+  // for why this is necessary
+  exports._writePointer(buf, offset, ptr, true);
 };
 
 /**

src/binding.cc

@@ -355,6 +355,18 @@ void WritePointer(const CallbackInfo& args) {
   if (input.IsNull()) {
     *reinterpret_cast<char**>(ptr) = nullptr;
   } else {
+    if ((args.Length() == 4) && (args[3].As<Boolean>() == true)) {
+      // create a node-api reference and finalizer to ensure that
+      // the buffer whoes pointer is written can only be
+      // collected after the finalizers for the buffer
+      // to which the pointer was written have already run
+      Reference<Value>* ref = new Reference<Value>;
+      *ref = Persistent(args[2]);
+      args[0].As<Object>().AddFinalizer([](Env env, Reference<Value>* ref) {
+        delete ref;
+      }, ref);
+    }
+
     char* input_ptr = GetBufferData(input);
     *reinterpret_cast<char**>(ptr) = input_ptr;
   }