/* Copyright 2018 The TensorFlow Authors. All Rights Reserved.

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 TENSORFLOW_CORE_COMMON_RUNTIME_SCOPED_ALLOCATOR_H_
#define TENSORFLOW_CORE_COMMON_RUNTIME_SCOPED_ALLOCATOR_H_

#include "tensorflow/core/framework/allocator.h"
#include "tensorflow/core/framework/tensor.h"
#include "tensorflow/core/lib/core/refcount.h"
#include "tensorflow/core/platform/mutex.h"

namespace tensorflow {
class ScopedAllocatorContainer;
class ScopedAllocatorInstance;

// Manages a single backing tensor and a collection of aliases.
class ScopedAllocator {
 public:
  static const int32 kInvalidId = 0;
  static const size_t kMaxAlignment = 64;

  // A subrange of the TensorBuffer associated with this object that
  // will be the backing memory for one aliased tensor.
  struct Field {
    int32 scope_id;
    size_t offset;
    size_t bytes;
  };
  // Field index that refers to backing tensor, not any aliased field.
  static const int32 kBackingIndex = -1;

  // backing_tensor is expected to be newly allocated by a ScopedAllocatorOp
  // instance.  It must be large enough to back all of the specified
  // (offset, byte) ranges of the fields.
  ScopedAllocator(const Tensor& backing_tensor, int32 scope_id,
                  const string& name, const gtl::ArraySlice<Field>& fields,
                  int32 expected_call_count,
                  ScopedAllocatorContainer* container);

  // Automatically deletes when last use expires, or when
  // ScopedAllocatorContainer decides to delete.
  ~ScopedAllocator() LOCKS_EXCLUDED(mu_);

  // For debugging: returns true iff p is a pointer that could have
  // been returned by AllocateRaw.
  bool VerifyPointer(const void* p);
  bool VerifyTensor(const Tensor* t);

  const Tensor& tensor() const { return backing_tensor_; }

  const string& name() const { return name_; }

 private:
  friend class ScopedAllocatorInstance;
  // Only ScopedAllocatorInstances can call AllocateRaw and DeallocateRaw on a
  // ScopedAllocator
  void* AllocateRaw(int32 field_index, size_t num_bytes) LOCKS_EXCLUDED(mu_);
  void DeallocateRaw(void* p) LOCKS_EXCLUDED(mu_);
  Tensor backing_tensor_;
  TensorBuffer* tbuf_;
  int32 id_;
  string name_;
  ScopedAllocatorContainer* container_;
  std::vector<Field> fields_;
  mutex mu_;
  int32 expected_call_count_ GUARDED_BY(mu_);
  int32 live_alloc_count_ GUARDED_BY(mu_);
};

// An Allocator that will return a pointer into the backing buffer of
// a previously allocated tensor, allowing creation of an alias
// tensor.  There is a one-to-one mapping between the fields of a
// ScopedAllocator and ScopedAllocatorInstances.  There is also a one-to-one
// mapping between scope_ids and ScopedAllocatorInstances.  It should be
// discarded immediately after a single use.
class ScopedAllocatorInstance : public Allocator {
 public:
  explicit ScopedAllocatorInstance(ScopedAllocator* sa, int32 field_index);

 private:
  ~ScopedAllocatorInstance() { VLOG(1) << "~ScopedAllocatorInstance " << this; }

 public:
  // When a ScopedAllocatorContainer "Drops" a scope_id, it calls DropFromTable
  // on the underlying ScopedAllocatorInstance.  If this instance has already
  // deallocated the tensor slice, we can safely delete this.
  void DropFromTable() LOCKS_EXCLUDED(mu_);
  void* AllocateRaw(size_t alignment, size_t num_bytes)
      LOCKS_EXCLUDED(mu_) override;
  void* AllocateRaw(size_t alignment, size_t num_bytes,
                    const AllocationAttributes& allocator_attr) override {
    return AllocateRaw(alignment, num_bytes);
  }
  void DeallocateRaw(void* p) LOCKS_EXCLUDED(mu_) override;
  bool TracksAllocationSizes() override { return false; }
  bool ShouldAllocateEmptyTensors() override { return false; }
  size_t RequestedSize(const void* ptr) override { return 0; }
  size_t AllocatedSize(const void* ptr) override { return 0; }
  int64 AllocationId(const void* ptr) override { return 0; }
  size_t AllocatedSizeSlow(const void* ptr) override { return 0; }
  string Name() override;

 private:
  mutex mu_;
  ScopedAllocator* scoped_allocator_;
  int32 field_index_;
  bool allocated_ GUARDED_BY(mu_);
  bool deallocated_ GUARDED_BY(mu_);
  bool in_table_ GUARDED_BY(mu_);
};

}  // namespace tensorflow
#endif  // TENSORFLOW_CORE_COMMON_RUNTIME_SCOPED_ALLOCATOR_H_