Update on "Enforce const on PyRRef functions"

Shen Li · Shen Li · commit be2be27eac09 · 2020-05-13T15:05:02.000-07:00
Differential Revision: [D21554722](https://our.internmc.facebook.com/intern/diff/D21554722) [ghstack-poisoned]
diff --git a/torch/csrc/distributed/rpc/py_rref.cpp b/torch/csrc/distributed/rpc/py_rref.cpp
@@ -111,6 +111,9 @@ PyRRef::PyRRef(const py::object& value, const py::object& type_hint)
         // jit::toIValue takes a py::handle as the first argument, and it calls
         // py::handle.cast<py::object>() to incref of provided value. The
         // returned ivalue will keep the reference alive.
+        // NB: the first argument const py::object& value must be kept alive
+        // until the following jit::toIValue returns (i.e., incref done). That's
+        // why this ctor can only be called while holding GIL.
         IValue ivalue = jit::toIValue(value, elem_type);
         rref->setValue(std::move(ivalue));
         return rref;
diff --git a/torch/csrc/distributed/rpc/py_rref.h b/torch/csrc/distributed/rpc/py_rref.h
@@ -14,6 +14,8 @@ enum RRefProxyType { RPC_SYNC, RPC_ASYNC, REMOTE };
 // pickle and unpickle.
 class PyRRef {
  public:
+  // The first ctor can only be called while holding GIL. See its implementation
+  // for more explanations.
   explicit PyRRef(const py::object& value, const py::object& type_hint);
   explicit PyRRef(c10::intrusive_ptr<RRef> rref);
 
