Add TfLiteInterpreterOptionsSetOpResolver function to c_api_experimental.h.

This provides adds a new callback-based op registration C API.
This new function would be required in order to implement the TF Tasks Library, or any other C++ API that uses OpResolver parameters, using the TF Lite C API.

PiperOrigin-RevId: 333154110
Change-Id: I6e53edc91ff1271f41c355bb9ad1a48d32bf3e41

tensorflow/lite/BUILD

@@ -181,6 +181,12 @@ cc_library(
     deps = ["//tensorflow/lite/c:common"],
 )
 
+cc_library(
+    name = "builtin_ops",
+    hdrs = ["builtin_ops.h"],
+    compatible_with = get_compatible_with_portable(),
+)
+
 exports_files(["builtin_ops.h"])
 
 cc_library(

tensorflow/lite/c/BUILD

@@ -47,6 +47,7 @@ cc_library(
     visibility = ["//visibility:private"],
     deps = [
         ":common",
+        "//tensorflow/lite:builtin_ops",
         "//tensorflow/lite:framework",
         "//tensorflow/lite/core/api",
     ],
@@ -60,6 +61,7 @@ cc_library(
     deps = [
         ":c_api_internal",
         ":common",
+        "//tensorflow/lite:builtin_ops",
         "//tensorflow/lite:framework",
         "//tensorflow/lite:version",
         "//tensorflow/lite/delegates/nnapi:nnapi_delegate",
@@ -125,6 +127,7 @@ cc_library(
         "common.h",
     ],
     compatible_with = get_compatible_with_portable(),
+    deps = ["//tensorflow/lite:builtin_ops"],
     alwayslink = 1,
 )
 

tensorflow/lite/c/c_api.cc

@@ -16,6 +16,7 @@ limitations under the License.
 
 #include <memory>
 
+#include "tensorflow/lite/builtin_ops.h"
 #include "tensorflow/lite/c/c_api_internal.h"
 #include "tensorflow/lite/delegates/nnapi/nnapi_delegate.h"
 #include "tensorflow/lite/error_reporter.h"
@@ -43,6 +44,44 @@ class CallbackErrorReporter : public tflite::ErrorReporter {
  private:
   TfLiteErrorReporterCallback callback_;
 };
+
+/// `CallbackOpResolver` is a (C++) `tflite::OpResolver` that forwards the
+/// methods to (C ABI) callback functions from a `TfLiteOpResolverCallbacks`
+/// struct.
+///
+/// The SetCallbacks method must be called before calling any of the FindOp
+/// methods.
+class CallbackOpResolver : public ::tflite::OpResolver {
+ public:
+  CallbackOpResolver() {}
+  void SetCallbacks(
+      const struct TfLiteOpResolverCallbacks& op_resolver_callbacks) {
+    op_resolver_callbacks_ = op_resolver_callbacks;
+  }
+  const TfLiteRegistration* FindOp(tflite::BuiltinOperator op,
+                                   int version) const override {
+    if (op_resolver_callbacks_.find_builtin_op == nullptr) {
+      return nullptr;
+    }
+    return op_resolver_callbacks_.find_builtin_op(
+        op_resolver_callbacks_.user_data,
+        static_cast<TfLiteBuiltinOperator>(op), version);
+  }
+  const TfLiteRegistration* FindOp(const char* op, int version) const override {
+    if (op_resolver_callbacks_.find_custom_op == nullptr) {
+      return nullptr;
+    }
+    return op_resolver_callbacks_.find_custom_op(
+        op_resolver_callbacks_.user_data, op, version);
+  }
+
+ private:
+  CallbackOpResolver(const CallbackOpResolver&) = delete;
+  CallbackOpResolver& operator=(const CallbackOpResolver&) = delete;
+
+  struct TfLiteOpResolverCallbacks op_resolver_callbacks_ = {};
+};
+
 }  // namespace
 
 // LINT.IfChange
@@ -210,14 +249,28 @@ TfLiteInterpreter* InterpreterCreateWithOpResolver(
         new CallbackErrorReporter(optional_options->error_reporter_callback));
   }
 
+  // By default, we use the provided mutable_op_resolver, adding any builtin or
+  // custom ops registered with `TfLiteInterpreterOptionsAddBuiltinOp` and/or
+  // `TfLiteInterpreterOptionsAddCustomOp`.
+  tflite::OpResolver* op_resolver = mutable_resolver;
   if (optional_options) {
-    mutable_resolver->AddAll(optional_options->op_resolver);
+    mutable_resolver->AddAll(optional_options->mutable_op_resolver);
+  }
+  // However, if `TfLiteInterpreterOptionsSetOpResolver` has been called with
+  // a non-null callback parameter, then we instead use a
+  // `CallbackOpResolver` that will forward to the callbacks provided there.
+  CallbackOpResolver callback_op_resolver;
+  if (optional_options &&
+      (optional_options->op_resolver_callbacks.find_builtin_op != nullptr ||
+       optional_options->op_resolver_callbacks.find_custom_op != nullptr)) {
+    callback_op_resolver.SetCallbacks(optional_options->op_resolver_callbacks);
+    op_resolver = &callback_op_resolver;
   }
 
   tflite::ErrorReporter* error_reporter = optional_error_reporter
                                               ? optional_error_reporter.get()
                                               : tflite::DefaultErrorReporter();
-  tflite::InterpreterBuilder builder(model->impl->GetModel(), *mutable_resolver,
+  tflite::InterpreterBuilder builder(model->impl->GetModel(), *op_resolver,
                                      error_reporter);
 
   std::unique_ptr<tflite::Interpreter> interpreter;

tensorflow/lite/c/c_api_experimental.cc

@@ -23,7 +23,6 @@ limitations under the License.
 #include "tensorflow/lite/c/c_api.h"
 #include "tensorflow/lite/c/c_api_internal.h"
 #include "tensorflow/lite/interpreter.h"
-#include "tensorflow/lite/mutable_op_resolver.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -38,8 +37,9 @@ void TfLiteInterpreterOptionsAddBuiltinOp(
     TfLiteInterpreterOptions* options, TfLiteBuiltinOperator op,
     const TfLiteRegistration* registration, int32_t min_version,
     int32_t max_version) {
-  options->op_resolver.AddBuiltin(static_cast<tflite::BuiltinOperator>(op),
-                                  registration, min_version, max_version);
+  options->mutable_op_resolver.AddBuiltin(
+      static_cast<tflite::BuiltinOperator>(op), registration, min_version,
+      max_version);
 }
 
 TfLiteInterpreter* TfLiteInterpreterCreateWithSelectedOps(
@@ -55,7 +55,21 @@ void TfLiteInterpreterOptionsAddCustomOp(TfLiteInterpreterOptions* options,
                                          const TfLiteRegistration* registration,
                                          int32_t min_version,
                                          int32_t max_version) {
-  options->op_resolver.AddCustom(name, registration, min_version, max_version);
+  options->mutable_op_resolver.AddCustom(name, registration, min_version,
+                                         max_version);
+}
+
+void TfLiteInterpreterOptionsSetOpResolver(
+    TfLiteInterpreterOptions* options,
+    const TfLiteRegistration* (*find_builtin_op)(void* user_data,
+                                                 TfLiteBuiltinOperator op,
+                                                 int version),
+    const TfLiteRegistration* (*find_custom_op)(void* user_data, const char* op,
+                                                int version),
+    void* op_resolver_user_data) {
+  options->op_resolver_callbacks.find_builtin_op = find_builtin_op;
+  options->op_resolver_callbacks.find_custom_op = find_custom_op;
+  options->op_resolver_callbacks.user_data = op_resolver_user_data;
 }
 
 void TfLiteInterpreterOptionsSetUseNNAPI(TfLiteInterpreterOptions* options,

tensorflow/lite/c/c_api_experimental.h

@@ -36,6 +36,9 @@ TFL_CAPI_EXPORT extern TfLiteStatus TfLiteInterpreterResetVariableTensors(
 /// so the caller should ensure that its contents (function pointers, etc...)
 /// remain valid for the duration of the interpreter's lifetime. A common
 /// practice is making the provided `TfLiteRegistration` instance static.
+///
+/// Code that uses this function should NOT call
+/// `TfLiteInterpreterOptionsSetOpResolver' on the same options object.
 TFL_CAPI_EXPORT void TfLiteInterpreterOptionsAddBuiltinOp(
     TfLiteInterpreterOptions* options, TfLiteBuiltinOperator op,
     const TfLiteRegistration* registration, int32_t min_version,
@@ -50,16 +53,41 @@ TFL_CAPI_EXPORT void TfLiteInterpreterOptionsAddBuiltinOp(
 /// so the caller should ensure that its contents (function pointers, etc...)
 /// remain valid for the duration of any created interpreter's lifetime. A
 /// common practice is making the provided `TfLiteRegistration` instance static.
+///
+/// Code that uses this function should NOT call
+/// `TfLiteInterpreterOptionsSetOpResolver' on the same options object.
 TFL_CAPI_EXPORT void TfLiteInterpreterOptionsAddCustomOp(
     TfLiteInterpreterOptions* options, const char* name,
     const TfLiteRegistration* registration, int32_t min_version,
     int32_t max_version);
 
+/// Registers callbacks for resolving builtin or custom operators.
+///
+/// The `TfLiteInterpreterOptionsSetOpResolver` function provides an alternative
+/// method for registering builtin ops and/or custom ops, by providing operator
+/// resolver callbacks.  Unlike using `TfLiteInterpreterOptionsAddBuiltinOp`
+/// and/or `TfLiteInterpreterOptionsAddAddCustomOp`, these let you register all
+/// the operators in a single call.
+///
+/// Code that uses this function should NOT call
+/// `TfLiteInterpreterOptionsAddBuiltin' or
+/// `TfLiteInterpreterOptionsAddCustomOp' on the same options object.
+void TfLiteInterpreterOptionsSetOpResolver(
+    TfLiteInterpreterOptions* options,
+    const TfLiteRegistration* (*find_builtin_op)(void* user_data,
+                                                 TfLiteBuiltinOperator op,
+                                                 int version),
+    const TfLiteRegistration* (*find_custom_op)(void* user_data,
+                                                const char* custom_op,
+                                                int version),
+    void* op_resolver_user_data);
+
 /// Returns a new interpreter using the provided model and options, or null on
 /// failure, where the model uses only the operators explicitly added to the
 /// options.  This is the same as `TFLiteInterpreterCreate` from `c_api.h`,
 /// except that the only operators that are supported are the ones registered
-/// in `options` via calls to `TfLiteInterpreterOptionsAddBuiltinOp` and/or
+/// in `options` via calls to `TfLiteInterpreterOptionsSetOpResolver`,
+/// `TfLiteInterpreterOptionsAddBuiltinOp`, and/or
 /// `TfLiteInterpreterOptionsAddCustomOp`.
 ///
 /// * `model` must be a valid model instance. The caller retains ownership of

tensorflow/lite/c/c_api_experimental_test.cc

@@ -110,6 +110,55 @@ TEST(CApiExperimentalTest, MissingBuiltin) {
   TfLiteModelDelete(model);
 }
 
+struct OpResolverData {
+  bool called_for_add = false;
+};
+
+const TfLiteRegistration* MyFindBuiltinOp(void* user_data,
+                                          TfLiteBuiltinOperator op,
+                                          int version) {
+  OpResolverData* my_data = static_cast<OpResolverData*>(user_data);
+  if (op == kTfLiteBuiltinAdd && version == 1) {
+    my_data->called_for_add = true;
+    return GetDummyRegistration();
+  }
+  return nullptr;
+}
+
+const TfLiteRegistration* MyFindCustomOp(void*, const char* custom_op,
+                                         int version) {
+  if (absl::string_view(custom_op) == "foo" && version == 1) {
+    return GetDummyRegistration();
+  }
+  return nullptr;
+}
+
+// Test using TfLiteInterpreterCreateWithSelectedOps.
+TEST(CApiExperimentalTest, SetOpResolver) {
+  TfLiteModel* model =
+      TfLiteModelCreateFromFile("tensorflow/lite/testdata/add.bin");
+  ASSERT_NE(model, nullptr);
+
+  TfLiteInterpreterOptions* options = TfLiteInterpreterOptionsCreate();
+
+  OpResolverData my_data;
+  TfLiteInterpreterOptionsSetOpResolver(options, MyFindBuiltinOp,
+                                        MyFindCustomOp, &my_data);
+  EXPECT_FALSE(my_data.called_for_add);
+
+  TfLiteInterpreter* interpreter =
+      TfLiteInterpreterCreateWithSelectedOps(model, options);
+  ASSERT_NE(interpreter, nullptr);
+  ASSERT_EQ(TfLiteInterpreterAllocateTensors(interpreter), kTfLiteOk);
+  EXPECT_EQ(TfLiteInterpreterResetVariableTensors(interpreter), kTfLiteOk);
+  EXPECT_EQ(TfLiteInterpreterInvoke(interpreter), kTfLiteOk);
+  EXPECT_TRUE(my_data.called_for_add);
+
+  TfLiteInterpreterDelete(interpreter);
+  TfLiteInterpreterOptionsDelete(options);
+  TfLiteModelDelete(model);
+}
+
 }  // namespace
 
 int main(int argc, char** argv) {

tensorflow/lite/c/c_api_internal.h

@@ -20,7 +20,9 @@ limitations under the License.
 #include <memory>
 #include <vector>
 
+#include "tensorflow/lite/builtin_ops.h"
 #include "tensorflow/lite/core/api/error_reporter.h"
+#include "tensorflow/lite/core/api/op_resolver.h"
 #include "tensorflow/lite/interpreter.h"
 #include "tensorflow/lite/model.h"
 #include "tensorflow/lite/mutable_op_resolver.h"
@@ -36,6 +38,30 @@ struct TfLiteModel {
   std::shared_ptr<const tflite::FlatBufferModel> impl;
 };
 
+// The `TfLiteOpResolver` struct is an abstract callback interface that
+// contains function pointers for callbacks that return a
+// `TfLiteRegistration` given an op code or custom op name. This mechanism is
+// used to map ops referenced in the flatbuffer model to executable function
+// pointers (`TfLiteRegistration`s).
+// This struct mirrors the tflite::OpResolver C++ abstract base class.
+struct TfLiteOpResolverCallbacks {
+  // Opaque data that gets passed down to the callback functions.
+  void* user_data = nullptr;
+
+  // Callback that finds the op registration for a builtin operator by enum
+  // code.  The `user_data` parameter will be set to the
+  // `op_resolver_user_data` value that was passed to
+  // `TfLiteInterpreterOptionsSetOpResolver`.
+  const TfLiteRegistration* (*find_builtin_op)(void* user_data,
+                                               TfLiteBuiltinOperator op,
+                                               int version);
+  // Callback that finds the op registration of a custom operator by op name.
+  // The `user_data` parameter will be set to the `op_resolver_user_data` value
+  // that was passed to `TfLiteInterpreterOptionsSetOpResolver`.
+  const TfLiteRegistration* (*find_custom_op)(void* user_data, const char* op,
+                                              int version);
+};
+
 // This struct mirrors the tflite::ErrorResolver C++ abstract base class.
 struct TfLiteErrorReporterCallback {
   // Opaque data that gets passed down to the callback function.
@@ -52,7 +78,9 @@ struct TfLiteInterpreterOptions {
   };
   int num_threads = kDefaultNumThreads;
 
-  tflite::MutableOpResolver op_resolver;
+  tflite::MutableOpResolver mutable_op_resolver;
+
+  TfLiteOpResolverCallbacks op_resolver_callbacks = {};
 
   std::vector<TfLiteDelegate*> delegates;
 
@@ -79,9 +107,9 @@ namespace internal {
 
 // This adds the builtin and/or custom operators specified in options in
 // `optional_options` (if any) to `mutable_resolver`, and then returns a newly
-// created TfLiteInterpreter using `mutable_op_resolver` as the OpResolver, and
-// using any other options in `optional_options`, and using the provided
-// `model`.
+// created TfLiteInterpreter using `mutable_op_resolver` as the default
+// OpResolver, and using any other options in `optional_options`, and using
+// the provided `model`.
 //
 // * `model` must be a valid model instance. The caller retains ownership of the
 //   object, and can destroy it immediately after creating the interpreter; the