Default device backendintf (#3695)

* Implement default device type and ordinal for backend interface

* torch_pin

* lazy init defailt device

* init xlaBackend in test

* Delete .torch_pin

Author: JackCaoG

test/cpp/torch_xla_test.cpp

@@ -8,19 +8,13 @@
 #include "torch_xla/csrc/device.h"
 #include "torch_xla/csrc/helpers.h"
 #include "torch_xla/csrc/tensor.h"
-
-namespace at {
-// This function is defined in the codegenerated RegisterDispatchKey.cpp file.
-extern TORCH_API void RegisterXLAXLANativeFunctions();
-extern TORCH_API void RegisterXLAAutogradXLANativeFunctions();
-}  // namespace at
+#include "torch_xla/csrc/xla_backend_impl.h"
 
 namespace torch_xla {
 namespace cpp_test {
 
 void XlaTest::SetUp() {
-  at::RegisterXLAXLANativeFunctions();
-  at::RegisterXLAAutogradXLANativeFunctions();
+  InitXlaBackend();
   at::manual_seed(42);
   XLATensor::SetRngSeed(GetCurrentDevice(), 42);
   start_msnap_ = absl::make_unique<MetricsSnapshot>();

torch_xla/csrc/xla_backend_impl.cpp

@@ -22,6 +22,30 @@ namespace torch_xla {
 class XlaBackendImpl : public torch::lazy::BackendImplInterface {
  public:
   XlaBackendImpl() {}
+
+  bool InitDefaultDeviceType() {
+    if (!default_device_type_inited_) {
+      // GetDefaultDevice will trigger the runtime device init, should
+      // not do it during class init time.
+      torch::lazy::BackendDevice default_device = *GetDefaultDevice();
+      default_device_type_ = std::make_shared<DeviceType>(
+          static_cast<XlaDeviceType>(default_device.type()));
+      default_device_type_inited_ = true;
+    }
+    return true;
+  }
+
+  bool InitDefaultDeviceOrdinal() {
+    if (!default_device_ordinal_inited_) {
+      // GetDefaultDevice will trigger the runtime device init, should
+      // not do it during class init time.
+      torch::lazy::BackendDevice default_device = *GetDefaultDevice();
+      default_device_ordinal_ = default_device.ordinal();
+      default_device_ordinal_inited_ = true;
+    }
+    return true;
+  }
+
   void PrepareToExit() const override { XLA_ERROR() << "Not implemented yet"; }
 
   void SetRngSeed(size_t seed) const override {
@@ -150,18 +174,31 @@ class XlaBackendImpl : public torch::lazy::BackendImplInterface {
 
   std::shared_ptr<torch::lazy::BackendDeviceType> GetDefaultDeviceType()
       const override {
-    // want to reuse the getDefualtDeviceTypelogic
-    torch::lazy::BackendDevice default_device = *GetDefaultDevice();
-    return std::make_shared<DeviceType>(
-        static_cast<XlaDeviceType>(default_device.type()));
+    // lazily init default device type, we only need to init once.
+    static bool init =
+        const_cast<XlaBackendImpl*>(this)->InitDefaultDeviceType();
+    return default_device_type_;
   }
 
-  at::DeviceType EagerFallbackDeviceType() const override {
-    return at::DeviceType::CPU;
+  void SetDefaultDeviceType(int8_t type) override {
+    default_device_type_ =
+        std::make_shared<DeviceType>(static_cast<XlaDeviceType>(type));
+    default_device_type_inited_ = true;
   }
 
-  void SetDefaultDeviceType(std::string type) override {
-    default_device_type_ = XlaDeviceType(c10::Device(type).type());
+  int64_t GetDefaultDeviceOrdinal() const override {
+    // lazily init default device ordinal, we only need to init once.
+    static bool init =
+        const_cast<XlaBackendImpl*>(this)->InitDefaultDeviceOrdinal();
+    return default_device_ordinal_;
+  }
+  void SetDefaultDeviceOrdinal(int64_t ordinal) override {
+    default_device_ordinal_ = ordinal;
+    default_device_ordinal_inited_ = true;
+  }
+
+  at::DeviceType EagerFallbackDeviceType() const override {
+    return at::DeviceType::CPU;
   }
 
   std::vector<torch::lazy::BackendDevice> GetBackendDevices() const override {
@@ -180,7 +217,10 @@ class XlaBackendImpl : public torch::lazy::BackendImplInterface {
   }
 
  private:
-  DeviceType default_device_type_;
+  bool default_device_type_inited_ = false;
+  bool default_device_ordinal_inited_ = false;
+  std::shared_ptr<torch::lazy::BackendDeviceType> default_device_type_;
+  int64_t default_device_ordinal_;
 };
 
 torch::lazy::BackendImplInterface* GetXlaBackendImpl() {