base/supports_user_data.cc

   1 // Copyright 2012 The Chromium Authors
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/supports_user_data.h"
   6
   7 #include "base/feature_list.h"
   8 #include "base/sequence_checker.h"
   9
  10 namespace base {
  11
  12 std::unique_ptr<SupportsUserData::Data> SupportsUserData::Data::Clone() {
  13   return nullptr;
  14 }
  15
  16 SupportsUserData::SupportsUserData() {
  17   // Harmless to construct on a different execution sequence to subsequent
  18   // usage.
  19   DETACH_FROM_SEQUENCE(sequence_checker_);
  20 }
  21
  22 SupportsUserData::SupportsUserData(SupportsUserData&&) = default;
  23 SupportsUserData& SupportsUserData::operator=(SupportsUserData&&) = default;
  24
  25 SupportsUserData::Data* SupportsUserData::GetUserData(const void* key) const {
  26   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  27   // Avoid null keys; they are too vulnerable to collision.
  28   DCHECK(key);
  29   auto found = user_data_.find(key);
  30   if (found != user_data_.end()) {
  31     return found->second.get();
  32   }
  33   return nullptr;
  34 }
  35
  36 std::unique_ptr<SupportsUserData::Data> SupportsUserData::TakeUserData(
  37     const void* key) {
  38   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  39   // Null keys are too vulnerable to collision.
  40   CHECK(key);
  41   auto found = user_data_.find(key);
  42   if (found != user_data_.end()) {
  43     std::unique_ptr<SupportsUserData::Data> deowned;
  44     deowned.swap(found->second);
  45     user_data_.erase(key);
  46     return deowned;
  47   }
  48   return nullptr;
  49 }
  50
  51 void SupportsUserData::SetUserData(const void* key,
  52                                    std::unique_ptr<Data> data) {
  53   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  54   CHECK(!in_destructor_) << "Calling SetUserData() when SupportsUserData is "
  55                             "being destroyed is not supported.";
  56   // Avoid null keys; they are too vulnerable to collision.
  57   DCHECK(key);
  58   if (data.get()) {
  59     user_data_[key] = std::move(data);
  60   } else {
  61     RemoveUserData(key);
  62   }
  63 }
  64
  65 void SupportsUserData::RemoveUserData(const void* key) {
  66   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
  67   auto it = user_data_.find(key);
  68   if (it != user_data_.end()) {
  69     // Remove the entry from the map before deleting `owned_data` to avoid
  70     // reentrancy issues when `owned_data` owns `this`. Otherwise:
  71     //
  72     // 1. `RemoveUserData()` calls `erase()`.
  73     // 2. `erase()` deletes `owned_data`.
  74     // 3. `owned_data` deletes `this`.
  75     //
  76     // At this point, `erase()` is still on the stack even though the
  77     // backing map (owned by `this`) has already been destroyed, and it
  78     // may simply crash, cause a use-after-free, or any other number of
  79     // interesting things.
  80     auto owned_data = std::move(it->second);
  81     user_data_.erase(it);
  82   }
  83 }
  84
  85 void SupportsUserData::DetachFromSequence() {
  86   DETACH_FROM_SEQUENCE(sequence_checker_);
  87 }
  88
  89 void SupportsUserData::CloneDataFrom(const SupportsUserData& other) {
  90   for (const auto& data_pair : other.user_data_) {
  91     auto cloned_data = data_pair.second->Clone();
  92     if (cloned_data) {
  93       SetUserData(data_pair.first, std::move(cloned_data));
  94     }
  95   }
  96 }
  97
  98 SupportsUserData::~SupportsUserData() {
  99   if (!user_data_.empty()) {
 100     DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 101   }
 102   in_destructor_ = true;
 103   absl::flat_hash_map<const void*, std::unique_ptr<Data>> user_data;
 104   user_data_.swap(user_data);
 105   // Now this->user_data_ is empty, and any destructors called transitively from
 106   // the destruction of |local_user_data| will see it that way instead of
 107   // examining a being-destroyed object.
 108 }
 109
 110 void SupportsUserData::ClearAllUserData() {
 111   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 112   user_data_.clear();
 113 }
 114
 115 }  // namespace base