YugabyteDB (2.13.0.0-b42, bfc6a6643e7399ac8a0e81d06a3ee6d6571b33ab)

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//   http://www.apache.org/licenses/LICENSE-2.0

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// specific language governing permissions and limitations

// under the License.

//

// The following only applies to changes made to this file as part of YugaByte development.

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// Portions Copyright (c) YugaByte, Inc.

//

// 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.

//

#ifndef YB_UTIL_ONCE_H

#define YB_UTIL_ONCE_H

#include <stddef.h>

#include "yb/gutil/once.h"

#include "yb/util/atomic.h"

#include "yb/util/status.h"

namespace yb {

class YBOnceDynamic;

namespace internal {

// Cheap, single-arg "bound callback" (similar to yb::Callback) for use

// in YBOnceDynamic.

template<typename T>

struct MemberFunc {

  YBOnceDynamic* once;

  T* instance;

  Status (T::*member_func)();

};

template<typename T>

void InitCb(void* arg) {

  MemberFunc<T>* mf = reinterpret_cast<MemberFunc<T>*>(arg);

  mf->once->status_ = (mf->instance->*mf->member_func)();

  mf->once->set_initted();

}

} // namespace internal

// More versatile version of GoogleOnceDynamic, including the following:

// 1. Can be used with single-arg, non-static member functions.

// 2. Retains results and overall initialization state for repeated access.

// 3. Access to initialization state is safe for concurrent use.

class YBOnceDynamic {

 public:

  YBOnceDynamic()

    : initted_(false) {

  }

  // If the underlying GoogleOnceDynamic has yet to be invoked, invokes the

  // provided member function and stores its return value. Otherwise,

  // returns the stored Status.

  //

  // T: the type of the member passed in.

  template<typename T>

  CHECKED_STATUS Init(Status (T::*member_func)(), T* instance) {

    internal::MemberFunc<T> mf = { this, instance, member_func };

    // Clang UBSAN doesn't like it when GoogleOnceDynamic handles the cast

    // of the argument:

    //

    //   runtime error: call to function

    //   yb::cfile::BloomFileReader::InitOnceCb(yb::cfile::BloomFileReader*)

    //   through pointer to incorrect function type 'void (*)(void *)'

    //

    // So let's do the cast ourselves, to void* here and back in InitCb().

    once_.Init(&internal::InitCb<T>, reinterpret_cast<void*>(&mf));

    return status_;

  }

  // kMemOrderAcquire ensures that loads/stores that come after initted()

  // aren't reordered to come before it instead. kMemOrderRelease ensures

  // the opposite (i.e. loads/stores before set_initted() aren't reordered

  // to come after it).

  //

  // Taken together, threads can safely synchronize on initted_.

  bool initted() const { return initted_.Load(kMemOrderAcquire); }

  // Returns the memory usage of this object without the object itself. Should

  // be used when embedded inside another object.

  size_t memory_footprint_excluding_this() const;

  // Returns the memory usage of this object including the object itself.

  // Should be used when allocated on the heap.

  size_t memory_footprint_including_this() const;

 private:

  template<typename T>

  friend void internal::InitCb(void* arg);

  void set_initted() { initted_.Store(true, kMemOrderRelease); }

  AtomicBool initted_;

  GoogleOnceDynamic once_;

  Status status_;

};

} // namespace yb

#endif