// Copyright 2019 The TCMalloc Authors
//
// 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 TCMALLOC_INTERNAL_MINCORE_H_
#define TCMALLOC_INTERNAL_MINCORE_H_

#include <stddef.h>

namespace tcmalloc {
namespace tcmalloc_internal {

// Class to wrap mincore so that we can replace it for testing.
class MInCoreInterface {
 public:
  MInCoreInterface() {}
  virtual ~MInCoreInterface() {}
  virtual int mincore(void* addr, size_t length, unsigned char* result) = 0;

 private:
  MInCoreInterface(const MInCoreInterface&) = delete;
  MInCoreInterface& operator=(const MInCoreInterface&) = delete;
};

// The MInCore class through the function residence(addr, size) provides
// a convenient way to report the residence of an arbitrary memory region.
// This is a wrapper for the ::mincore() function. The ::mincore() function has
// the constraint of requiring the base address to be page aligned.
class MInCore {
 public:
  MInCore() {}
  // For a region of memory return the number of bytes that are
  // actually resident in memory. Note that the address and size
  // do not need to be a multiple of the system page size.
  static size_t residence(void* addr, size_t size);

 private:
  // Separate out the implementation to make the code easier to test.
  static size_t residence_impl(void* addr, size_t size,
                               MInCoreInterface* mincore);

  // Size of the array used to gather results from mincore().
  static constexpr int kArrayLength = 4096;
  // Friends required for testing
  friend class MInCoreTest;
};

}  // namespace tcmalloc_internal
}  // namespace tcmalloc

#endif  // TCMALLOC_INTERNAL_MINCORE_H_
