Add IdGenerator am: 69d75b47

        "repeating_timer_unittest.cc",

        "state_machine_unittest.cc",

        "time_util_unittest.cc",

        "id_generator_unittest.cc",

    ],

    shared_libs: [

        "libprotobuf-cpp-lite",

/*

 * Copyright 2019 The Android Open Source Project

 *

 * 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

 *

 *      http://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.

 */

#pragma once

#include <array>

/* Helper class generating N unique ids, from 0 to N-1 */

template <std::size_t N>

class IdGenerator {

 public:

  static int ALL_USED;

  IdGenerator() : in_use_{} {}

  /* Returns next free id, or ALL_USED if no ids left */

  int GetNext() {

    for (std::size_t i = 0; i < N; i++) {

      if (!in_use_[i]) {

        in_use_[i] = true;

        return i;

      }

    }

    return ALL_USED;

  }

  /* Release given ID */

  void Release(int id) { in_use_[id] = false; }

 private:

  std::array<bool, N> in_use_;

};

template <std::size_t N>

int IdGenerator<N>::ALL_USED = -1;

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/*

 * Copyright 2019 The Android Open Source Project

 *

 * 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

 *

 *      http://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 "common/id_generator.h"

#include <gtest/gtest.h>

TEST(IdGeneratorTest, sanity_test) {

  IdGenerator<5> generator;

  ASSERT_EQ(0, generator.GetNext());

  ASSERT_EQ(1, generator.GetNext());

  ASSERT_EQ(2, generator.GetNext());

  ASSERT_EQ(3, generator.GetNext());

  ASSERT_EQ(4, generator.GetNext());

  ASSERT_EQ(generator.ALL_USED, generator.GetNext());

  generator.Release(3);

  ASSERT_EQ(3, generator.GetNext());

  generator.Release(0);

  generator.Release(2);

  ASSERT_EQ(0, generator.GetNext());

  ASSERT_EQ(2, generator.GetNext());

}

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