base/trace_event/memory_usage_estimator.h

// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_TRACE_EVENT_MEMORY_USAGE_ESTIMATOR_H_
#define BASE_TRACE_EVENT_MEMORY_USAGE_ESTIMATOR_H_

#include <stdint.h>

#include <array>
#include <deque>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#include "base/base_export.h"
#include "base/containers/linked_list.h"
#include "base/strings/string16.h"

// Composable memory usage estimators.
//
// This file defines set of EstimateMemoryUsage(object) functions that return
// approximate memory usage of their argument.
//
// The ultimate goal is to make memory usage estimation for a class simply a
// matter of aggregating EstimateMemoryUsage() results over all fields.
//
// That is achieved via composability: if EstimateMemoryUsage() is defined
// for T then EstimateMemoryUsage() is also defined for any combination of
// containers holding T (e.g. std::map<int, std::vector<T>>).
//
// There are two ways of defining EstimateMemoryUsage() for a type:
//
// 1. As a global function 'size_t EstimateMemoryUsage(T)' in
//    in base::trace_event namespace.
//
// 2. As 'size_t T::EstimateMemoryUsage() const' method. In this case
//    EstimateMemoryUsage(T) function in base::trace_event namespace is
//    provided automatically.
//
// Here is an example implementation:
//
// size_t foo::bar::MyClass::EstimateMemoryUsage() const {
//   return base::trace_event::EstimateMemoryUsage(name_) +
//          base::trace_event::EstimateMemoryUsage(id_) +
//          base::trace_event::EstimateMemoryUsage(items_);
// }
//
// The approach is simple: first call EstimateMemoryUsage() on all members,
// then recursively fix compilation errors that are caused by types not
// implementing EstimateMemoryUsage().

namespace base {
namespace trace_event {

// Declarations

// If T declares 'EstimateMemoryUsage() const' member function, then
// global function EstimateMemoryUsage(T) is available, and just calls
// the member function.
template <class T>
auto EstimateMemoryUsage(const T& object)
    -> decltype(object.EstimateMemoryUsage());

// String

template <class C, class T, class A>
size_t EstimateMemoryUsage(const std::basic_string<C, T, A>& string);

// Arrays

template <class T, size_t N>
size_t EstimateMemoryUsage(const std::array<T, N>& array);

template <class T, size_t N>
size_t EstimateMemoryUsage(T (&array)[N]);

template <class T>
size_t EstimateMemoryUsage(const T* array, size_t array_length);

// std::unique_ptr

template <class T, class D>
size_t EstimateMemoryUsage(const std::unique_ptr<T, D>& ptr);

template <class T, class D>
size_t EstimateMemoryUsage(const std::unique_ptr<T[], D>& array,
                           size_t array_length);

// std::shared_ptr

template <class T>
size_t EstimateMemoryUsage(const std::shared_ptr<T>& ptr);

// Containers

template <class F, class S>
size_t EstimateMemoryUsage(const std::pair<F, S>& pair);

template <class T, class A>
size_t EstimateMemoryUsage(const std::vector<T, A>& vector);

template <class T, class A>
size_t EstimateMemoryUsage(const std::list<T, A>& list);

template <class T>
size_t EstimateMemoryUsage(const base::LinkedList<T>& list);

template <class T, class C, class A>
size_t EstimateMemoryUsage(const std::set<T, C, A>& set);

template <class T, class C, class A>
size_t EstimateMemoryUsage(const std::multiset<T, C, A>& set);

template <class K, class V, class C, class A>
size_t EstimateMemoryUsage(const std::map<K, V, C, A>& map);

template <class K, class V, class C, class A>
size_t EstimateMemoryUsage(const std::multimap<K, V, C, A>& map);

template <class T, class H, class KE, class A>
size_t EstimateMemoryUsage(const std::unordered_set<T, H, KE, A>& set);

template <class T, class H, class KE, class A>
size_t EstimateMemoryUsage(const std::unordered_multiset<T, H, KE, A>& set);

template <class K, class V, class H, class KE, class A>
size_t EstimateMemoryUsage(const std::unordered_map<K, V, H, KE, A>& map);

template <class K, class V, class H, class KE, class A>
size_t EstimateMemoryUsage(const std::unordered_multimap<K, V, H, KE, A>& map);

template <class T, class A>
size_t EstimateMemoryUsage(const std::deque<T, A>& deque);

template <class T, class C>
size_t EstimateMemoryUsage(const std::queue<T, C>& queue);

template <class T, class C>
size_t EstimateMemoryUsage(const std::priority_queue<T, C>& queue);

template <class T, class C>
size_t EstimateMemoryUsage(const std::stack<T, C>& stack);

// TODO(dskiba):
//   std::forward_list

// Definitions

namespace internal {

// HasEMU<T>::value is true iff EstimateMemoryUsage(T) is available.
// (This is the default version, which is false.)
template <class T, class X = void>
struct HasEMU : std::false_type {};

// This HasEMU specialization is only picked up if there exists function
// EstimateMemoryUsage(const T&) that returns size_t. Simpler ways to
// achieve this don't work on MSVC.
template <class T>
struct HasEMU<
    T,
    typename std::enable_if<std::is_same<
        size_t,
        decltype(EstimateMemoryUsage(std::declval<const T&>()))>::value>::type>
    : std::true_type {};

// EMUCaller<T> does three things:
// 1. Defines Call() method that calls EstimateMemoryUsage(T) if it's
//    available.
// 2. If EstimateMemoryUsage(T) is not available, but T has trivial dtor
//    (i.e. it's POD, integer, pointer, enum, etc.) then it defines Call()
//    method that returns 0. This is useful for containers, which allocate
//    memory regardless of T (also for cases like std::map<int, MyClass>).
// 3. Finally, if EstimateMemoryUsage(T) is not available, then it triggers
//    a static_assert with a helpful message. That cuts numbers of errors
//    considerably - if you just call EstimateMemoryUsage(T) but it's not
//    available for T, then compiler will helpfully list *all* possible
//    variants of it, with an explanation for each.
template <class T, class X = void>
struct EMUCaller {
  // std::is_same<> below makes static_assert depend on T, in order to
  // prevent it from asserting regardless instantiation.
  static_assert(std::is_same<T, std::false_type>::value,
                "Neither global function 'size_t EstimateMemoryUsage(T)' "
                "nor member function 'size_t T::EstimateMemoryUsage() const' "
                "is defined for the type.");

  static size_t Call(const T&) { return 0; }
};

template <class T>
struct EMUCaller<T, typename std::enable_if<HasEMU<T>::value>::type> {
  static size_t Call(const T& value) { return EstimateMemoryUsage(value); }
};

template <class T>
struct EMUCaller<
    T,
    typename std::enable_if<!HasEMU<T>::value &&
                            std::is_trivially_destructible<T>::value>::type> {
  static size_t Call(const T& value) { return 0; }
};

// Returns reference to the underlying container of a container adapter.
// Works for std::stack, std::queue and std::priority_queue.
template <class A>
const typename A::container_type& GetUnderlyingContainer(const A& adapter) {
  struct ExposedAdapter : A {
    using A::c;
  };
  return adapter.*&ExposedAdapter::c;
}

}  // namespace internal

// Proxy that deducts T and calls EMUCaller<T>.
// To be used by EstimateMemoryUsage() implementations for containers.
template <class T>
size_t EstimateItemMemoryUsage(const T& value) {
  return internal::EMUCaller<T>::Call(value);
}

template <class I>
size_t EstimateIterableMemoryUsage(const I& iterable) {
  size_t memory_usage = 0;
  for (const auto& item : iterable) {
    memory_usage += EstimateItemMemoryUsage(item);
  }
  return memory_usage;
}

// Global EstimateMemoryUsage(T) that just calls T::EstimateMemoryUsage().
template <class T>
auto EstimateMemoryUsage(const T& object)
    -> decltype(object.EstimateMemoryUsage()) {
  static_assert(
      std::is_same<decltype(object.EstimateMemoryUsage()), size_t>::value,
      "'T::EstimateMemoryUsage() const' must return size_t.");
  return object.EstimateMemoryUsage();
}

// String

template <class C, class T, class A>
size_t EstimateMemoryUsage(const std::basic_string<C, T, A>& string) {
  using string_type = std::basic_string<C, T, A>;
  using value_type = typename string_type::value_type;
  // C++11 doesn't leave much room for implementors - std::string can
  // use short string optimization, but that's about it. We detect SSO
  // by checking that c_str() points inside |string|.
  const uint8_t* cstr = reinterpret_cast<const uint8_t*>(string.c_str());
  const uint8_t* inline_cstr = reinterpret_cast<const uint8_t*>(&string);
  if (cstr >= inline_cstr && cstr < inline_cstr + sizeof(string)) {
    // SSO string
    return 0;
  }
  return (string.capacity() + 1) * sizeof(value_type);
}

// Use explicit instantiations from the .cc file (reduces bloat).
extern template BASE_EXPORT size_t EstimateMemoryUsage(const std::string&);
extern template BASE_EXPORT size_t EstimateMemoryUsage(const string16&);

// Arrays

template <class T, size_t N>
size_t EstimateMemoryUsage(const std::array<T, N>& array) {
  return EstimateIterableMemoryUsage(array);
}

template <class T, size_t N>
size_t EstimateMemoryUsage(T (&array)[N]) {
  return EstimateIterableMemoryUsage(array);
}

template <class T>
size_t EstimateMemoryUsage(const T* array, size_t array_length) {
  size_t memory_usage = sizeof(T) * array_length;
  for (size_t i = 0; i != array_length; ++i) {
    memory_usage += EstimateItemMemoryUsage(array[i]);
  }
  return memory_usage;
}

// std::unique_ptr

template <class T, class D>
size_t EstimateMemoryUsage(const std::unique_ptr<T, D>& ptr) {
  return ptr ? (sizeof(T) + EstimateItemMemoryUsage(*ptr)) : 0;
}

template <class T, class D>
size_t EstimateMemoryUsage(const std::unique_ptr<T[], D>& array,
                           size_t array_length) {
  return EstimateMemoryUsage(array.get(), array_length);
}

// std::shared_ptr

template <class T>
size_t EstimateMemoryUsage(const std::shared_ptr<T>& ptr) {
  auto use_count = ptr.use_count();
  if (use_count == 0) {
    return 0;
  }
  // Model shared_ptr after libc++,
  // see __shared_ptr_pointer from include/memory
  struct SharedPointer {
    void* vtbl;
    long shared_owners;
    long shared_weak_owners;
    T* value;
  };
  // If object of size S shared N > S times we prefer to (potentially)
  // overestimate than to return 0.
  return sizeof(SharedPointer) +
         (EstimateItemMemoryUsage(*ptr) + (use_count - 1)) / use_count;
}

// std::pair

template <class F, class S>
size_t EstimateMemoryUsage(const std::pair<F, S>& pair) {
  return EstimateItemMemoryUsage(pair.first) +
         EstimateItemMemoryUsage(pair.second);
}

// std::vector

template <class T, class A>
size_t EstimateMemoryUsage(const std::vector<T, A>& vector) {
  return sizeof(T) * vector.capacity() + EstimateIterableMemoryUsage(vector);
}

// std::list

template <class T, class A>
size_t EstimateMemoryUsage(const std::list<T, A>& list) {
  using value_type = typename std::list<T, A>::value_type;
  struct Node {
    Node* prev;
    Node* next;
    value_type value;
  };
  return sizeof(Node) * list.size() +
         EstimateIterableMemoryUsage(list);
}

template <class T>
size_t EstimateMemoryUsage(const base::LinkedList<T>& list) {
  size_t memory_usage = 0u;
  for (base::LinkNode<T>* node = list.head(); node != list.end();
       node = node->next()) {
    // Since we increment by calling node = node->next() we know that node
    // isn't nullptr.
    memory_usage += EstimateMemoryUsage(*node->value()) + sizeof(T);
  }
  return memory_usage;
}

// Tree containers

template <class V>
size_t EstimateTreeMemoryUsage(size_t size) {
  // Tree containers are modeled after libc++
  // (__tree_node from include/__tree)
  struct Node {
    Node* left;
    Node* right;
    Node* parent;
    bool is_black;
    V value;
  };
  return sizeof(Node) * size;
}

template <class T, class C, class A>
size_t EstimateMemoryUsage(const std::set<T, C, A>& set) {
  using value_type = typename std::set<T, C, A>::value_type;
  return EstimateTreeMemoryUsage<value_type>(set.size()) +
         EstimateIterableMemoryUsage(set);
}

template <class T, class C, class A>
size_t EstimateMemoryUsage(const std::multiset<T, C, A>& set) {
  using value_type = typename std::multiset<T, C, A>::value_type;
  return EstimateTreeMemoryUsage<value_type>(set.size()) +
         EstimateIterableMemoryUsage(set);
}

template <class K, class V, class C, class A>
size_t EstimateMemoryUsage(const std::map<K, V, C, A>& map) {
  using value_type = typename std::map<K, V, C, A>::value_type;
  return EstimateTreeMemoryUsage<value_type>(map.size()) +
         EstimateIterableMemoryUsage(map);
}

template <class K, class V, class C, class A>
size_t EstimateMemoryUsage(const std::multimap<K, V, C, A>& map) {
  using value_type = typename std::multimap<K, V, C, A>::value_type;
  return EstimateTreeMemoryUsage<value_type>(map.size()) +
         EstimateIterableMemoryUsage(map);
}

// HashMap containers

namespace internal {

// While hashtable containers model doesn't depend on STL implementation, one
// detail still crept in: bucket_count. It's used in size estimation, but its
// value after inserting N items is not predictable.
// This function is specialized by unittests to return constant value, thus
// excluding bucket_count from testing.
template <class V>
size_t HashMapBucketCountForTesting(size_t bucket_count) {
  return bucket_count;
}

}  // namespace internal

template <class V>
size_t EstimateHashMapMemoryUsage(size_t bucket_count, size_t size) {
  // Hashtable containers are modeled after libc++
  // (__hash_node from include/__hash_table)
  struct Node {
    void* next;
    size_t hash;
    V value;
  };
  using Bucket = void*;
  bucket_count = internal::HashMapBucketCountForTesting<V>(bucket_count);
  return sizeof(Bucket) * bucket_count + sizeof(Node) * size;
}

template <class K, class H, class KE, class A>
size_t EstimateMemoryUsage(const std::unordered_set<K, H, KE, A>& set) {
  using value_type = typename std::unordered_set<K, H, KE, A>::value_type;
  return EstimateHashMapMemoryUsage<value_type>(set.bucket_count(),
                                                set.size()) +
         EstimateIterableMemoryUsage(set);
}

template <class K, class H, class KE, class A>
size_t EstimateMemoryUsage(const std::unordered_multiset<K, H, KE, A>& set) {
  using value_type = typename std::unordered_multiset<K, H, KE, A>::value_type;
  return EstimateHashMapMemoryUsage<value_type>(set.bucket_count(),
                                                set.size()) +
         EstimateIterableMemoryUsage(set);
}

template <class K, class V, class H, class KE, class A>
size_t EstimateMemoryUsage(const std::unordered_map<K, V, H, KE, A>& map) {
  using value_type = typename std::unordered_map<K, V, H, KE, A>::value_type;
  return EstimateHashMapMemoryUsage<value_type>(map.bucket_count(),
                                                map.size()) +
         EstimateIterableMemoryUsage(map);
}

template <class K, class V, class H, class KE, class A>
size_t EstimateMemoryUsage(const std::unordered_multimap<K, V, H, KE, A>& map) {
  using value_type =
      typename std::unordered_multimap<K, V, H, KE, A>::value_type;
  return EstimateHashMapMemoryUsage<value_type>(map.bucket_count(),
                                                map.size()) +
         EstimateIterableMemoryUsage(map);
}

// std::deque

template <class T, class A>
size_t EstimateMemoryUsage(const std::deque<T, A>& deque) {
// Since std::deque implementations are wildly different
// (see crbug.com/674287), we can't have one "good enough"
// way to estimate.

// kBlockSize      - minimum size of a block, in bytes
// kMinBlockLength - number of elements in a block
//                   if sizeof(T) > kBlockSize
#if defined(_LIBCPP_VERSION)
  size_t kBlockSize = 4096;
  size_t kMinBlockLength = 16;
#elif defined(__GLIBCXX__)
  size_t kBlockSize = 512;
  size_t kMinBlockLength = 1;
#elif defined(_MSC_VER)
  size_t kBlockSize = 16;
  size_t kMinBlockLength = 1;
#else
  size_t kBlockSize = 0;
  size_t kMinBlockLength = 1;
#endif

  size_t block_length =
      (sizeof(T) > kBlockSize) ? kMinBlockLength : kBlockSize / sizeof(T);

  size_t blocks = (deque.size() + block_length - 1) / block_length;

#if defined(__GLIBCXX__)
  // libstdc++: deque always has at least one block
  if (!blocks)
    blocks = 1;
#endif

#if defined(_LIBCPP_VERSION)
  // libc++: deque keeps at most two blocks when it shrinks,
  // so even if the size is zero, deque might be holding up
  // to 4096 * 2 bytes. One way to know whether deque has
  // ever allocated (and hence has 1 or 2 blocks) is to check
  // iterator's pointer. Non-zero value means that deque has
  // at least one block.
  if (!blocks && deque.begin().operator->())
    blocks = 1;
#endif

  return (blocks * block_length * sizeof(T)) +
         EstimateIterableMemoryUsage(deque);
}

// Container adapters

template <class T, class C>
size_t EstimateMemoryUsage(const std::queue<T, C>& queue) {
  return EstimateMemoryUsage(internal::GetUnderlyingContainer(queue));
}

template <class T, class C>
size_t EstimateMemoryUsage(const std::priority_queue<T, C>& queue) {
  return EstimateMemoryUsage(internal::GetUnderlyingContainer(queue));
}

template <class T, class C>
size_t EstimateMemoryUsage(const std::stack<T, C>& stack) {
  return EstimateMemoryUsage(internal::GetUnderlyingContainer(stack));
}

}  // namespace trace_event
}  // namespace base

#endif  // BASE_TRACE_EVENT_MEMORY_USAGE_ESTIMATOR_H_