Add DirectExecutor

PiperOrigin-RevId: 474671922

Package.swift

@@ -505,6 +505,7 @@ let package = Package(
         "internal/platform/cancellation_flag_test.cc",
         "internal/platform/bluetooth_adapter_test.cc",
         "internal/platform/byte_utils_test.cc",
+        "internal/platform/direct_executor_test.cc",
         // simulation
         "connections/implementation/offline_simulation_user.cc",
         "connections/implementation/simulation_user.cc",

internal/platform/BUILD

@@ -309,6 +309,7 @@ cc_library(
         "condition_variable.h",
         "count_down_latch.h",
         "crypto.h",
+        "direct_executor.h",
         "file.h",
         "future.h",
         "lockable.h",
@@ -411,6 +412,7 @@ cc_test(
         "count_down_latch_test.cc",
         "credential_storage_impl_test.cc",
         "crypto_test.cc",
+        "direct_executor_test.cc",
         "future_test.cc",
         "logging_test.cc",
         "multi_thread_executor_test.cc",

internal/platform/direct_executor.h

@@ -0,0 +1,52 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+#ifndef THIRD_PARTY_NEARBY_INTERNAL_PLATFORM_DIRECT_EXECUTOR_H_
+#define THIRD_PARTY_NEARBY_INTERNAL_PLATFORM_DIRECT_EXECUTOR_H_
+
+#include "absl/base/thread_annotations.h"
+#include "internal/platform/implementation/executor.h"
+#include "internal/platform/submittable_executor.h"
+
+namespace location {
+namespace nearby {
+
+// An Executor that executes the tasks immediately on the thread calling
+// `Execute()`.
+//
+// DirectExecutor is suitable for running fast, trivial runnables.
+class ABSL_LOCKABLE DirectExecutor final : public api::Executor {
+ public:
+  DirectExecutor(const DirectExecutor &) = delete;
+  DirectExecutor &operator=(const DirectExecutor &) = delete;
+  static DirectExecutor &GetInstance() {
+    // DirectExecutor isn't technically trivially-destructible because it has a
+    // virtual destructor, but the class is final, the destructor is default
+    // (the base class is an interface) and there are no member fields.
+    // NOLINTNEXTLINE(google3-runtime-global-variables)
+    static DirectExecutor instance;
+    return instance;
+  }
+
+  void Execute(Runnable &&runnable) override { runnable(); }
+
+  void Shutdown() override {}
+
+ private:
+  DirectExecutor() = default;
+};
+
+}  // namespace nearby
+}  // namespace location
+
+#endif  // THIRD_PARTY_NEARBY_INTERNAL_PLATFORM_DIRECT_EXECUTOR_H_

internal/platform/direct_executor_test.cc

@@ -0,0 +1,32 @@
+
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "internal/platform/direct_executor.h"
+
+#include "gtest/gtest.h"
+
+namespace location {
+namespace nearby {
+
+TEST(DirectExecutorTest, ExecutesRunnable) {
+  int call_count = 0;
+
+  DirectExecutor::GetInstance().Execute([&]() { call_count++; });
+
+  EXPECT_EQ(call_count, 1);
+}
+
+}  // namespace nearby
+}  // namespace location