Integrate zhouwang/pr1441 into master

Source/CNTKv2LibraryDll/API/CNTKLibrary.h

@@ -1744,7 +1744,7 @@ private:
 
         CNTK_API static Variable Deserialize(const Dictionary& dictionary, const ::CNTK::DeviceDescriptor& device = DeviceDescriptor::UseDefaultDevice());
 
-        void SetOwner(Function* ownerFunction);
+        void SetOwner(const std::weak_ptr<Function>& ownerFunction);
 
         Variable CompositePreservingCopy(const std::shared_ptr<const Function>& composite) const;
 

Source/CNTKv2LibraryDll/Function.cpp

@@ -22,9 +22,9 @@ namespace CNTK
             for (auto outputVar : outputs)
             {
                 if (outputVar.IsOutput() && !outputVar.Owner())
-                    outputVar.SetOwner(this);
+                    outputVar.SetOwner(shared_from_this());
 
-                if (m_rootFunction == nullptr && outputVar.IsOutput() && outputVar.m_dataFields->m_ownerFunction == this)
+                if (m_rootFunction == nullptr && outputVar.IsOutput() && outputVar.Owner().get() == this)
                 {
                     // in case of a primitive function, set uid of output vars to owner function uid + "_Output_" + output index.
                     outputVar.m_dataFields->m_uid = m_uid + L"_" + VariableKindName(outputVar.Kind()) + L"_" + std::to_wstring(m_outputs.size());

Source/CNTKv2LibraryDll/Utils.cpp

@@ -133,9 +133,6 @@ namespace CNTK
         return !(*this == other);    
     }
 
-    
-
-
     Dictionary::Dictionary()
         : m_dictionaryData(new unordered_map <wstring, DictionaryValue>)
     {
@@ -425,7 +422,6 @@ namespace CNTK
         return fd;
     }
 
-
     std::string ToString(const std::wstring& wstring)
     {
 #ifdef _MSC_VER
@@ -518,6 +514,7 @@ namespace CNTK
 
         return std::pair<size_t, size_t>(maxNumTimeSteps, numSequences);
     }
+
     /*static*/ void Utils::VerifyVariableValueCompatibility(const Variable& var, const ValuePtr& value)
     {
         if (var.GetDataType() != value->GetDataType())

Source/CNTKv2LibraryDll/Utils.h

@@ -30,6 +30,15 @@ namespace CNTK
             NOT_IMPLEMENTED;
     }
 
+    template <typename T>
+    inline bool IsObjectExpired(std::weak_ptr<T> ptrToObject)
+    {
+        if ((ptrToObject.owner_before(std::weak_ptr<T>{}) || std::weak_ptr<T>{}.owner_before(ptrToObject)) && ptrToObject.expired())
+            return true;
+        else
+            return false;
+    }
+
     inline DEVICEID_TYPE AsCNTKImplDeviceId(const DeviceDescriptor& device)
     {
         if (device.Type() == DeviceKind::CPU)

Source/CNTKv2LibraryDll/Variable.cpp

@@ -72,10 +72,7 @@ namespace CNTK
 
     FunctionPtr Variable::Owner() const 
     {
-        if (m_dataFields->m_ownerFunction != nullptr)
+        return m_dataFields->Owner();
-            return m_dataFields->m_ownerFunction->shared_from_this();
-        else
-            return nullptr;
     }
 
     Variable Variable::CompositePreservingCopy(const std::shared_ptr<const Function>& composite) const
@@ -94,12 +91,12 @@ namespace CNTK
         return copy;
     }
 
-    void Variable::SetOwner(Function* ownerFunction)
+    void Variable::SetOwner(const std::weak_ptr<Function>& ownerFunction)
     {
         if (Kind() != VariableKind::Output)
             LogicError("Variable '%S' SetOwner: Owner can only be set for Output Variables", AsString().c_str());
 
-        if (m_dataFields->m_ownerFunction != nullptr)
+        if (Owner() != nullptr)
             LogicError("Variable '%S' SetOwner: An Output Variable whose owner has previously been set, cannot be reset.", AsString().c_str());
 
         m_dataFields->m_ownerFunction = ownerFunction;
@@ -213,13 +210,24 @@ namespace CNTK
         return wss.str();
     }
 
+    FunctionPtr VariableFields::Owner() const
+    {
+        if (IsObjectExpired(m_ownerFunction))
+            LogicError("The owner function of Variable '%S' is unexpectedly expired.", AsString().c_str());
+
+        auto ownerFunctionPtr = m_ownerFunction.lock();
+        if (ownerFunctionPtr != nullptr)
+            return ownerFunctionPtr->shared_from_this();
+        else
+            return nullptr;
+    }
+
     std::shared_ptr<VariableFields> VariableFields::Clone() const
     {
-        if (m_ownerFunction != nullptr)
+        if (Owner() != nullptr)
             InvalidArgument("Output variable '%S' cannot be cloned.", AsString().c_str());
 
         // Note: We do not clone m_blockFunctionVariableMapping
-
         auto clone = MakeSharedObject<VariableFields>(m_shape,
             m_varKind,
             m_dataType,
@@ -364,7 +372,7 @@ namespace CNTK
     }
 
     Variable::Variable(const NDShape& shape, VariableKind varType, CNTK::DataType dataType, const NDArrayViewPtr& value, bool needsGradient, const std::vector<Axis>& dynamicAxes, bool isSparse, const std::wstring& name, const std::wstring& uid)
-        : m_dataFields(MakeSharedObject<VariableFields>(shape, varType, dataType, nullptr, value, needsGradient, dynamicAxes, isSparse, name, uid))
+        : m_dataFields(MakeSharedObject<VariableFields>(shape, varType, dataType, std::weak_ptr<Function>(), value, needsGradient, dynamicAxes, isSparse, name, uid))
     {}
 
     template <typename ElementType>

Source/CNTKv2LibraryDll/Variable.h

@@ -19,7 +19,7 @@ namespace CNTK
         NDShape m_shape;
         VariableKind m_varKind;
         ::CNTK::DataType m_dataType;
-        Function* m_ownerFunction; // Variable does not keep the Function alive
+        std::weak_ptr<Function> m_ownerFunction;
         std::unique_ptr<std::once_flag> m_initValueFlag;
         NDArrayViewPtr m_value;
         std::unique_ptr<ParameterInitializer> m_valueInitializer;
@@ -32,7 +32,7 @@ namespace CNTK
         std::atomic<size_t> m_valueTimeStamp;
         Variable m_blockFunctionVariableMapping;
 
-        VariableFields(const NDShape& shape, VariableKind varType, ::CNTK::DataType type, Function* ownerFunction, const NDArrayViewPtr& value, bool needsGradient, const std::vector<Axis>& dynamicAxes, bool isSparse, const std::wstring& name, const std::wstring& uid)
+        VariableFields(const NDShape& shape, VariableKind varType, ::CNTK::DataType type, const std::weak_ptr<Function>& ownerFunction, const NDArrayViewPtr& value, bool needsGradient, const std::vector<Axis>& dynamicAxes, bool isSparse, const std::wstring& name, const std::wstring& uid)
             : m_shape(shape), m_varKind(varType), m_dataType(type), m_ownerFunction(ownerFunction), m_value(value), m_needsGradient(needsGradient), m_dynamicAxes(dynamicAxes), m_isSparse(isSparse), m_name(name), m_uid(uid), m_valueTimeStamp(0)
         {
             if (value && (type != value->GetDataType()))
@@ -59,6 +59,7 @@ namespace CNTK
 
         std::wstring AsString() const;
         std::shared_ptr<VariableFields> Clone() const;
+        FunctionPtr Owner() const;
 
         CNTK_API void SetValueInitialization(const ParameterInitializer& initializationConfig, const DeviceDescriptor& device);