add backend is available (pytorch#8738)

Summary:

Add a pybind API to see if the backend is available

Differential Revision: D69810445

Author: cccclai

extension/pybindings/portable_lib.py

@@ -27,7 +27,6 @@
 # related libs, ensuring that the pybindings lib can resolve those runtime
 # dependencies.
 import torch as _torch
-
 # Let users import everything from the C++ _portable_lib extension as if this
 # python file defined them. Although we could import these dynamically, it
 # wouldn't preserve the static type annotations.
@@ -37,6 +36,7 @@
     # Disable "imported but unused" (F401) checks.
     _create_profile_block,  # noqa: F401
     _dump_profile_results,  # noqa: F401
+    _is_available,  # noqa: F401
     _get_operator_names,  # noqa: F401
     _get_registered_backend_names,  # noqa: F401
     _load_bundled_program_from_buffer,  # noqa: F401

extension/pybindings/pybindings.cpp

@@ -88,10 +88,12 @@ using ::executorch::extension::BufferDataLoader;
 using ::executorch::extension::MallocMemoryAllocator;
 using ::executorch::extension::MmapDataLoader;
 using ::executorch::runtime::ArrayRef;
+using ::executorch::runtime::BackendInterface;
 using ::executorch::runtime::DataLoader;
 using ::executorch::runtime::Error;
 using ::executorch::runtime::EValue;
 using ::executorch::runtime::EventTracerDebugLogLevel;
+using ::executorch::runtime::get_backend_class;
 using ::executorch::runtime::get_backend_name;
 using ::executorch::runtime::get_num_registered_backends;
 using ::executorch::runtime::get_registered_kernels;
@@ -990,6 +992,14 @@ py::list get_registered_backend_names() {
   return res;
 }
 
+py::bool_ is_available(const std::string& target_backend_name) {
+  BackendInterface* backend = get_backend_class(target_backend_name.c_str());
+  if (backend == nullptr) {
+    return false;
+  }
+  return backend->is_available();
+}
+
 } // namespace
 
 PYBIND11_MODULE(EXECUTORCH_PYTHON_MODULE_NAME, m) {
@@ -1048,6 +1058,7 @@ PYBIND11_MODULE(EXECUTORCH_PYTHON_MODULE_NAME, m) {
       &get_registered_backend_names,
       call_guard);
   m.def("_get_operator_names", &get_operator_names);
+  m.def("_is_available", &is_available, py::arg("backend_name"), call_guard);
   m.def("_create_profile_block", &create_profile_block, call_guard);
   m.def(
       "_reset_profile_results",

extension/pybindings/pybindings.pyi

@@ -211,6 +211,17 @@ def _load_bundled_program_from_buffer(
     """
     ...
 
+
+@experimental("This API is experimental and subject to change without notice.")
+def _is_available(backend_name: str) -> bool:
+    """
+    .. warning::
+
+        This API is experimental and subject to change without notice.
+    """
+    ...
+
+
 @experimental("This API is experimental and subject to change without notice.")
 def _get_operator_names() -> List[str]:
     """

extension/pybindings/test/test_backend_pybinding.py

@@ -1,6 +1,7 @@
 import unittest
 
 from executorch.runtime import Runtime
+from executorch.extension.pybindings.portable_lib import _is_available
 
 
 class TestBackendsPybinding(unittest.TestCase):
@@ -12,3 +13,12 @@ def test_backend_name_list(
         registered_backend_names = runtime.backend_registry.registered_backend_names
         self.assertGreaterEqual(len(registered_backend_names), 1)
         self.assertIn("XnnpackBackend", registered_backend_names)
+
+    def test_backend_is_available(
+        self, 
+    ) -> None:
+        # XnnpackBackend is available
+        runtime = Runtime.get()
+        self.assertTrue(runtime.backend_registry.is_available(backend_name="XnnpackBackend"))
+        # NonExistBackend doesn't exist and not available
+        self.assertFalse(runtime.backend_registry.is_available(backend_name="NonExistBackend"))

runtime/__init__.py

@@ -140,6 +140,13 @@ def registered_backend_names(self) -> List[str]:
         return self._legacy_module._get_registered_backend_names()
 
 
+    def is_available(self, backend_name: str) -> bool:
+        """
+        Returns the names of all registered backends as a list of strings.
+        """
+        return self._legacy_module._is_available(backend_name)
+
+
 class OperatorRegistry:
     """The registry of operators that are available to the runtime."""