[tracing] Implement composable memory usage estimators.

base/trace_event/estimate_memory_usage.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_ESTIMATE_MEMORY_USAGE_H_
+#define BASE_TRACE_EVENT_ESTIMATE_MEMORY_USAGE_H_
+
+#include <array>
+#include <list>
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
+#include <type_traits>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "base/template_util.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 type's namespace
+//    (or as a last resort, in base::trace_event namespace).
+//
+// 2. As 'size_t T::EstimateMemoryUsage() const' method. In this case global
+//    EstimateMemoryUsage(T) function in base::trace_event namespace is
+//    provided automatically.
+//
+// Here is an example implementation:
+//
+// size_t foo::bar::MyClass::EstimateMemoryUsage() const {
+//   using base::trace_event::EstimateMemoryUsage;
+//   return EstimateMemoryUsage(name_) +
+//          EstimateMemoryUsage(id_) +
+//          EstimateMemoryUsage(items_);
+// }
+//
+// Two things to note:
+//
+// 1. It starts with 'using' declaration. This makes everything defined in
+//    this file (i.e. all EstimateMemoryUsage variants) available for compiler
+//    to choose from.
+//
+// 2. It just calls EstimateMemoryUsage() on all (suitable) members.
+//    The pattern is simple: first call EstimateMemoryUsage() on all members,
+//    then 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>
+size_t EstimateMemoryUsage(const std::unique_ptr<T>& ptr);
+
+template <class T>
+size_t EstimateMemoryUsage(const std::unique_ptr<T[]>& array,
+                           size_t array_length);
+
+// 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, 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);
+
+// TODO(dskiba):
+//   std::forward_list
+//   std::deque
+//   std::queue
+//   std::stack
+//   std::queue
+//   std::priority_queue
+
+// Definitions
+
+namespace internal {
+
+// HasEMU<T>(0) returns true if EstimateMemoryUsage(T) is available.
+// The function is constexpr, and can be used in templates.
+template <class T>
+constexpr bool HasEMU(long) {
+  return false;
+}
+
+template <class T>
+constexpr auto HasEMU(int)
+    -> decltype(EstimateMemoryUsage(std::declval<const T&>()), bool()) {
+  static_assert(
+    std::is_same<decltype(EstimateMemoryUsage(std::declval<const T&>())),
+                 size_t>::value,
+    "EstimateMemoryUsage(T) must return size_t.");
+  return true;
+}
+
+// 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 {
+  static_assert(
+      std::is_same<T, X>::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>(0)>::type> {
+  static size_t Call(const T& value) {
+    return EstimateMemoryUsage(value);
+  }
+};
+
+template <class T>
+struct EMUCaller<
+    T,
+    typename std::enable_if<
+        !HasEMU<T>(0) && is_trivially_destructible<T>::value
+    >::type> {
+  static size_t Call(const T& value) {
+    return 0;
+  }
+};
+
+}  // 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;
+#if defined(__GLIBCXX__) && _GLIBCXX_USE_CXX11_ABI == 0
+  // libstdc++ with COW std::string - each string allocates a header
+  // (see std::basic_string::_Rep). We don't take into account number
+  // of references, but we do handle 'empty string' case.
+  struct Header {
+    typename string_type::size_type length;
+    typename string_type::size_type capacity;
+    int refcount;
+  };
+  // There is one shared empty string, which we estimate to 0.
+  static const char* empty_cstr = nullptr;
+  if (!empty_cstr) empty_cstr = std::string().c_str();
+  return (string.c_str() == empty_cstr) ?
+      0 :
+      sizeof(Header) + (string.capacity() + 1) * sizeof(value_type);
+#else
+  // 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 char* cstr = reinterpret_cast<const char*>(string.c_str());
+  const char* inline_cstr = reinterpret_cast<const char*>(&string);
+  if (cstr >= inline_cstr && cstr < inline_cstr + sizeof(string)) {
+    // SSO string
+    return 0;
+  }
+  return (string.capacity() + 1) * sizeof(value_type);
+#endif
+}
+
+// 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>
+size_t EstimateMemoryUsage(const std::unique_ptr<T>& ptr) {
+  return ptr ? (sizeof(T) + EstimateItemMemoryUsage(*ptr)) : 0;
+}
+
+template <class T>
+size_t EstimateMemoryUsage(const std::unique_ptr<T[]>& array,
+                           size_t array_length) {
+  return EstimateMemoryUsage(array.get(), array_length);
+}
+
+// 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);
+}
+
+// Tree containers
+
+template <class V>
+size_t EstimateTreeMemoryUsage(size_t size) {
+#if defined(__GLIBCXX__)
+  // libstdc++: _Rb_tree_node<> from include/bits/stl_tree.h
+  struct Node {
+    bool color;
+    Node* parent;
+    Node* left;
+    Node* right;
+    V value;
+  };
+#else
+  // libc++: __tree_node<> from include/__tree
+  struct Node {
+    Node* left;
+    Node* right;
+    Node* parent;
+    bool is_black;
+    V value;
+  };
+#endif
+  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
+
+template <class V>
+size_t EstimateHashMapMemoryUsage(size_t bucket_count, size_t size) {
+#if defined(__GLIBCXX__)
+  // libstdc++: _Hash_node<T, false> from include/bits/hashtable_policy.h
+  struct Node {
+    V value;
+    Node* next;
+  };
+  using Bucket = Node*;
+  // _Hashtable::_M_allocate_buckets() from include/bits/hashtable.h
+  // allocates one extra bucket.
+  return sizeof(Bucket) * (bucket_count + 1) + sizeof(Node) * size;
+#else
+  // libc++: __hash_node<> from include/__hash_table
+  struct Node {
+    void* next;
+    size_t hash;
+    V value;
+  };
+  using Bucket = void*;
+  return sizeof(Bucket) * bucket_count + sizeof(Node) * size;
+#endif
+}
+
+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);
+}
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_ESTIMATE_MEMORY_USAGE_H_