Add UTs for device selection API

Makefile

@@ -422,6 +422,7 @@ CNTKLIBRARY_TESTS_SRC =\
 	Tests/UnitTests/V2LibraryTests/FunctionTests.cpp \
 	Tests/UnitTests/V2LibraryTests/SequenceClassification.cpp \
 	Tests/UnitTests/V2LibraryTests/Seq2Seq.cpp \
+	Tests/UnitTests/V2LibraryTests/DeviceSelectionTests.cpp \
 	Examples/Evaluation/CPPEvalV2Client/EvalMultithreads.cpp \
 
 CNTKLIBRARY_TESTS:=$(BINDIR)/v2librarytests

Source/CNTKv2LibraryDll/Common.cpp

@@ -5,6 +5,7 @@
 
 #include "stdafx.h"
 #include "CNTKLibrary.h"
+#include "Utils.h"
 #include "BestGpu.h"
 #include <mutex>
 #include <algorithm>
@@ -62,8 +63,7 @@ namespace CNTK
         auto selectedDevice = DefaultDevice();
         if (!alreadyFrozen)
         {
-            auto id = selectedDevice.Type() == DeviceKind::CPU ? CPUDEVICE : selectedDevice.Id();
-            Microsoft::MSR::CNTK::OnDeviceSelected(id);
+            Microsoft::MSR::CNTK::OnDeviceSelected(AsCNTKImplDeviceId(selectedDevice));
         }
         return selectedDevice;
     }

Source/CNTKv2LibraryDll/Utils.h

@@ -32,7 +32,7 @@ namespace CNTK
     inline DEVICEID_TYPE AsCNTKImplDeviceId(const DeviceDescriptor& device)
     {
         if (device.Type() == DeviceKind::CPU)
-            return -1;
+            return CPUDEVICE;
         else if (device.Type() == DeviceKind::GPU)
             return device.Id();
         else

Tests/UnitTests/V2LibraryTests/DeviceSelectionTests.cpp

@@ -0,0 +1,46 @@
+#include "CNTKLibrary.h"
+#include "Common.h"
+
+using namespace CNTK;
+
+void DeviceSelectionTests()
+{
+    auto cpuDevice = DeviceDescriptor::CPUDevice();
+    DeviceDescriptor::SetDefaultDevice(cpuDevice);
+
+    assert(DeviceDescriptor::DefaultDevice() == cpuDevice);
+
+    auto bestDevice = DeviceDescriptor::BestDevice();
+    DeviceDescriptor::SetDefaultDevice(bestDevice);
+
+    assert(DeviceDescriptor::DefaultDevice() == bestDevice);
+
+    if (bestDevice != cpuDevice)
+    {
+        DeviceDescriptor::SetDefaultDevice(cpuDevice);
+    }
+    
+    assert(DeviceDescriptor::UseDefaultDevice() == cpuDevice);
+
+    VerifyException([&cpuDevice]() {
+        DeviceDescriptor::SetDefaultDevice(cpuDevice);
+    }, "Was able to invoke SetDefaultDevice() after UseDefaultDevice().");
+
+    // Invoke BestDevice after releasing the lock in UseDefaultDevice().
+    bestDevice = DeviceDescriptor::BestDevice();
+
+    const auto& allDevices = DeviceDescriptor::AllDevices();
+
+#ifdef CPUONLY
+    assert(allDevices.size() == 1);
+#endif
+    auto numGpuDevices = allDevices.size() - 1;
+
+    VerifyException([&numGpuDevices]() {
+        DeviceDescriptor::GPUDevice((unsigned int)numGpuDevices);
+    }, "Was able to create GPU device descriptor with invalid id.");
+
+    assert(find(allDevices.begin(), allDevices.end(), bestDevice) != allDevices.end());
+    assert(allDevices.back() == cpuDevice);
+
+}

Tests/UnitTests/V2LibraryTests/Main.cpp

@@ -15,6 +15,7 @@ void SerializationTests();
 void LearnerTests();
 void TrainSequenceToSequenceTranslator();
 void EvalMultiThreadsWithNewNetwork(const DeviceDescriptor&, const int);
+void DeviceSelectionTests();
 
 int main()
 {
@@ -42,6 +43,8 @@ int main()
     EvalMultiThreadsWithNewNetwork(DeviceDescriptor::GPUDevice(0), 2);
 #endif
 
+    DeviceSelectionTests();
+
     fprintf(stderr, "\nCNTKv2Library tests: Passed\n");
     fflush(stderr);
 }

Tests/UnitTests/V2LibraryTests/NDArrayViewTests.cpp

@@ -1,4 +1,5 @@
 #include "CNTKLibrary.h"
+#include "Common.h"
 #include <functional>
 #include <array>
 
@@ -103,31 +104,18 @@ void TestNDArrayView(size_t numAxes, const DeviceDescriptor& device)
         throw std::runtime_error("The buffers underlying the alias view and the view it is an alias of are different!");
 
     // Test readonliness
-    auto verifyException = [](const std::function<void()>& functionToTest) {
-        bool error = false;
-        try
-        {
-            functionToTest();
-        }
-        catch (const std::exception&)
-        {
-            error = true;
-        }
-
-        if (!error)
-            throw std::runtime_error("Was incorrectly able to get a writable buffer pointer from a readonly view");
-    };
+    auto errorMsg = "Was incorrectly able to get a writable buffer pointer from a readonly view";
 
     // Should not be able to get the WritableDataBuffer for a read-only view
-    verifyException([&aliasView]() {
+    VerifyException([&aliasView]() {
         ElementType* aliasViewBuffer = aliasView->WritableDataBuffer<ElementType>();
         aliasViewBuffer;
-    });
+    }, errorMsg);
 
     // Should not be able to copy into a read-only view
-    verifyException([&aliasView, &dataView]() {
+    VerifyException([&aliasView, &dataView]() {
         aliasView->CopyFrom(*dataView);
-    });
+    }, errorMsg);
 }
 
 template <typename ElementType>

Tests/UnitTests/V2LibraryTests/V2LibraryTests.vcxproj

@@ -111,6 +111,7 @@
   <ItemGroup>
     <ClCompile Include="..\..\..\Examples\Evaluation\CPPEvalV2Client\EvalMultithreads.cpp" />
     <ClCompile Include="CifarResNet.cpp" />
+    <ClCompile Include="DeviceSelectionTests.cpp" />
     <ClCompile Include="LearnerTests.cpp" />
     <ClCompile Include="Seq2Seq.cpp" />
     <ClCompile Include="SerializationTests.cpp" />

Tests/UnitTests/V2LibraryTests/V2LibraryTests.vcxproj.filters

@@ -54,6 +54,9 @@
     <ClCompile Include="..\..\..\Examples\Evaluation\CPPEvalV2Client\EvalMultithreads.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="DeviceSelectionTests.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="Common.h">