base/observer_list_unittest.cc - chromium/src - Git at Google

 // Copyright 2012 The Chromium Authors
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "base/observer_list.h"

 #include <memory>

 #include "base/memory/raw_ptr.h"
 #include "base/strings/string_piece.h"
 #include "base/test/gtest_util.h"
 #include "base/threading/simple_thread.h"
 #include "build/build_config.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/abseil-cpp/absl/types/optional.h"

 namespace base {
 namespace {

 class CheckedBase : public CheckedObserver {
  public:
   virtual void Observe(int x) = 0;
   ~CheckedBase() override = default;
   virtual int GetValue() const { return 0; }
 };

 class UncheckedBase {
  public:
   virtual void Observe(int x) = 0;
   virtual ~UncheckedBase() = default;
   virtual int GetValue() const { return 0; }
 };

 // Helper for TYPED_TEST_SUITE machinery to pick the ObserverList under test.
 // Keyed off the observer type since ObserverList has too many template args and
 // it gets ugly.
 template <class Foo>
 struct PickObserverList {};
 template <>
 struct PickObserverList<CheckedBase> {
   template <class TypeParam,
             bool check_empty = false,
             bool allow_reentrancy = true>
   using ObserverListType =
       ObserverList<TypeParam, check_empty, allow_reentrancy>;
 };
 template <>
 struct PickObserverList<UncheckedBase> {
   template <class TypeParam,
             bool check_empty = false,
             bool allow_reentrancy = true>
   using ObserverListType = typename ObserverList<TypeParam,
                                                  check_empty,
                                                  allow_reentrancy>::Unchecked;
 };

 template <class Foo>
 class AdderT : public Foo {
  public:
   explicit AdderT(int scaler) : total(0), scaler_(scaler) {}
   ~AdderT() override = default;

   void Observe(int x) override { total += x * scaler_; }
   int GetValue() const override { return total; }

   int total;

  private:
   int scaler_;
 };

 template <class ObserverListType,
           class Foo = typename ObserverListType::value_type>
 class DisrupterT : public Foo {
  public:
   DisrupterT(ObserverListType* list, Foo* doomed, bool remove_self)
       : list_(list), doomed_(doomed), remove_self_(remove_self) {}
   DisrupterT(ObserverListType* list, Foo* doomed)
       : DisrupterT(list, doomed, false) {}
   DisrupterT(ObserverListType* list, bool remove_self)
       : DisrupterT(list, nullptr, remove_self) {}

   ~DisrupterT() override = default;

   void Observe(int x) override {
     if (remove_self_)
       list_->RemoveObserver(this);
     if (doomed_)
       list_->RemoveObserver(doomed_.get());
   }

   void SetDoomed(Foo* doomed) { doomed_ = doomed; }

  private:
   raw_ptr<ObserverListType> list_;
   raw_ptr<Foo> doomed_;
   bool remove_self_;
 };

 template <class ObserverListType,
           class Foo = typename ObserverListType::value_type>
 class AddInObserve : public Foo {
  public:
   explicit AddInObserve(ObserverListType* observer_list)
       : observer_list(observer_list), to_add_() {}

   void SetToAdd(Foo* to_add) { to_add_ = to_add; }

   void Observe(int x) override {
     if (to_add_) {
       observer_list->AddObserver(to_add_.get());
       to_add_ = nullptr;
     }
   }

   raw_ptr<ObserverListType> observer_list;
   raw_ptr<Foo> to_add_;
 };

 template <class ObserverListType>
 class ObserverListCreator : public DelegateSimpleThread::Delegate {
  public:
   std::unique_ptr<ObserverListType> Create(
       absl::optional<base::ObserverListPolicy> policy = absl::nullopt) {
     policy_ = policy;
     DelegateSimpleThread thread(this, "ListCreator");
     thread.Start();
     thread.Join();
     return std::move(observer_list_);
   }

  private:
   void Run() override {
     if (policy_) {
       observer_list_ = std::make_unique<ObserverListType>(*policy_);
     } else {
       observer_list_ = std::make_unique<ObserverListType>();
     }
   }

   std::unique_ptr<ObserverListType> observer_list_;
   absl::optional<base::ObserverListPolicy> policy_;
 };

 }  // namespace

 class ObserverListTestBase {
  public:
   ObserverListTestBase() = default;
   ObserverListTestBase(const ObserverListTestBase&) = delete;
   ObserverListTestBase& operator=(const ObserverListTestBase&) = delete;

   template <class T>
   const decltype(T::list_.get()) list(const T& iter) {
     return iter.list_.get();
   }

   template <class T>
   typename T::value_type* GetCurrent(T* iter) {
     return iter->GetCurrent();
   }

   // Override GetCurrent() for CheckedObserver. When StdIteratorRemoveFront
   // tries to simulate a sequence to see if it "would" crash, CheckedObservers
   // do, actually, crash with a DCHECK(). Note this check is different to the
   // check during an observer _iteration_. Hence, DCHECK(), not CHECK().
   CheckedBase* GetCurrent(ObserverList<CheckedBase>::iterator* iter) {
     EXPECT_DCHECK_DEATH(return iter->GetCurrent());
     return nullptr;
   }
 };

 // Templatized test fixture that can pick between CheckedBase and UncheckedBase.
 template <class ObserverType>
 class ObserverListTest : public ObserverListTestBase, public ::testing::Test {
  public:
   template <class T>
   using ObserverList =
       typename PickObserverList<ObserverType>::template ObserverListType<T>;

   using iterator = typename ObserverList<ObserverType>::iterator;
   using const_iterator = typename ObserverList<ObserverType>::const_iterator;

   ObserverListTest() = default;
   ObserverListTest(const ObserverListTest&) = delete;
   ObserverListTest& operator=(const ObserverListTest&) = delete;
 };

 using ObserverTypes = ::testing::Types<CheckedBase, UncheckedBase>;
 TYPED_TEST_SUITE(ObserverListTest, ObserverTypes);

 // TYPED_TEST causes the test parent class to be a template parameter, which
 // makes the syntax for referring to the types awkward. Create aliases in local
 // scope with clearer names. Unfortunately, we also need some trailing cruft to
 // avoid "unused local type alias" warnings.
 #define DECLARE_TYPES                                                       \
   using Foo = TypeParam;                                                    \
   using ObserverListFoo =                                                   \
       typename PickObserverList<TypeParam>::template ObserverListType<Foo>; \
   using Adder = AdderT<Foo>;                                                \
   using Disrupter = DisrupterT<ObserverListFoo>;                            \
   using const_iterator = typename TestFixture::const_iterator;              \
   using iterator = typename TestFixture::iterator;                          \
   (void)reinterpret_cast<Disrupter*>(0);                                    \
   (void)reinterpret_cast<Adder*>(0);                                        \
   (void)reinterpret_cast<const_iterator*>(0);                               \
   (void)reinterpret_cast<iterator*>(0)

 TYPED_TEST(ObserverListTest, BasicTest) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   const ObserverListFoo& const_observer_list = observer_list;

   {
     const const_iterator it1 = const_observer_list.begin();
     EXPECT_EQ(it1, const_observer_list.end());
     // Iterator copy.
     const const_iterator it2 = it1;
     EXPECT_EQ(it2, it1);
     // Iterator assignment.
     const_iterator it3;
     it3 = it2;
     EXPECT_EQ(it3, it1);
     EXPECT_EQ(it3, it2);
     // Self assignment.
     it3 = *&it3;  // The *& defeats Clang's -Wself-assign warning.
     EXPECT_EQ(it3, it1);
     EXPECT_EQ(it3, it2);
   }

   {
     const iterator it1 = observer_list.begin();
     EXPECT_EQ(it1, observer_list.end());
     // Iterator copy.
     const iterator it2 = it1;
     EXPECT_EQ(it2, it1);
     // Iterator assignment.
     iterator it3;
     it3 = it2;
     EXPECT_EQ(it3, it1);
     EXPECT_EQ(it3, it2);
     // Self assignment.
     it3 = *&it3;  // The *& defeats Clang's -Wself-assign warning.
     EXPECT_EQ(it3, it1);
     EXPECT_EQ(it3, it2);
   }

   Adder a(1), b(-1), c(1), d(-1), e(-1);
   Disrupter evil(&observer_list, &c);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);

   EXPECT_TRUE(const_observer_list.HasObserver(&a));
   EXPECT_FALSE(const_observer_list.HasObserver(&c));

   {
     const const_iterator it1 = const_observer_list.begin();
     EXPECT_NE(it1, const_observer_list.end());
     // Iterator copy.
     const const_iterator it2 = it1;
     EXPECT_EQ(it2, it1);
     EXPECT_NE(it2, const_observer_list.end());
     // Iterator assignment.
     const_iterator it3;
     it3 = it2;
     EXPECT_EQ(it3, it1);
     EXPECT_EQ(it3, it2);
     // Self assignment.
     it3 = *&it3;  // The *& defeats Clang's -Wself-assign warning.
     EXPECT_EQ(it3, it1);
     EXPECT_EQ(it3, it2);
     // Iterator post increment.
     const_iterator it4 = it3++;
     EXPECT_EQ(it4, it1);
     EXPECT_EQ(it4, it2);
     EXPECT_NE(it4, it3);
   }

   {
     const iterator it1 = observer_list.begin();
     EXPECT_NE(it1, observer_list.end());
     // Iterator copy.
     const iterator it2 = it1;
     EXPECT_EQ(it2, it1);
     EXPECT_NE(it2, observer_list.end());
     // Iterator assignment.
     iterator it3;
     it3 = it2;
     EXPECT_EQ(it3, it1);
     EXPECT_EQ(it3, it2);
     // Self assignment.
     it3 = *&it3;  // The *& defeats Clang's -Wself-assign warning.
     EXPECT_EQ(it3, it1);
     EXPECT_EQ(it3, it2);
     // Iterator post increment.
     iterator it4 = it3++;
     EXPECT_EQ(it4, it1);
     EXPECT_EQ(it4, it2);
     EXPECT_NE(it4, it3);
   }

   for (auto& observer : observer_list)
     observer.Observe(10);

   observer_list.AddObserver(&evil);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   // Removing an observer not in the list should do nothing.
   observer_list.RemoveObserver(&e);

   for (auto& observer : observer_list)
     observer.Observe(10);

   EXPECT_EQ(20, a.total);
   EXPECT_EQ(-20, b.total);
   EXPECT_EQ(0, c.total);
   EXPECT_EQ(-10, d.total);
   EXPECT_EQ(0, e.total);
 }

 TYPED_TEST(ObserverListTest, CreatedAndUsedOnDifferentThreads) {
   DECLARE_TYPES;

   ObserverListCreator<ObserverListFoo> list_creator;
   Adder a(1);
   // Check with default constructor
   {
     std::unique_ptr<ObserverListFoo> observer_list = list_creator.Create();
     observer_list->AddObserver(&a);
     for (auto& observer : *observer_list) {
       observer.Observe(1);
     }
     EXPECT_EQ(1, a.GetValue());
   }

   // Check with constructor taking explicit policy
   {
     std::unique_ptr<ObserverListFoo> observer_list =
         list_creator.Create(base::ObserverListPolicy::EXISTING_ONLY);
     observer_list->AddObserver(&a);
     for (auto& observer : *observer_list) {
       observer.Observe(1);
     }
     EXPECT_EQ(2, a.GetValue());
   }
 }

 TYPED_TEST(ObserverListTest, CompactsWhenNoActiveIterator) {
   DECLARE_TYPES;
   using ObserverListConstFoo =
       typename TestFixture::template ObserverList<const Foo>;

   ObserverListConstFoo ol;
   const ObserverListConstFoo& col = ol;

   const Adder a(1);
   const Adder b(2);
   const Adder c(3);

   ol.AddObserver(&a);
   ol.AddObserver(&b);

   EXPECT_TRUE(col.HasObserver(&a));
   EXPECT_FALSE(col.HasObserver(&c));

   EXPECT_TRUE(!col.empty());

   using It = typename ObserverListConstFoo::const_iterator;

   {
     It it = col.begin();
     EXPECT_NE(it, col.end());
     It ita = it;
     EXPECT_EQ(ita, it);
     EXPECT_NE(++it, col.end());
     EXPECT_NE(ita, it);
     It itb = it;
     EXPECT_EQ(itb, it);
     EXPECT_EQ(++it, col.end());

     EXPECT_TRUE(!col.empty());
     EXPECT_EQ(&*ita, &a);
     EXPECT_EQ(&*itb, &b);

     ol.RemoveObserver(&a);
     EXPECT_TRUE(!col.empty());
     EXPECT_FALSE(col.HasObserver(&a));
     EXPECT_EQ(&*itb, &b);

     ol.RemoveObserver(&b);
     EXPECT_FALSE(!col.empty());
     EXPECT_FALSE(col.HasObserver(&a));
     EXPECT_FALSE(col.HasObserver(&b));

     it = It();
     ita = It();
     EXPECT_FALSE(!col.empty());
     ita = itb;
     itb = It();
     EXPECT_FALSE(!col.empty());
     ita = It();
     EXPECT_FALSE(!col.empty());
   }

   ol.AddObserver(&a);
   ol.AddObserver(&b);
   EXPECT_TRUE(!col.empty());
   ol.Clear();
   EXPECT_FALSE(!col.empty());

   ol.AddObserver(&a);
   ol.AddObserver(&b);
   EXPECT_TRUE(!col.empty());
   {
     const It it = col.begin();
     ol.Clear();
     EXPECT_FALSE(!col.empty());
   }
   EXPECT_FALSE(!col.empty());
 }

 TYPED_TEST(ObserverListTest, DisruptSelf) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter evil(&observer_list, true);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);

   for (auto& observer : observer_list)
     observer.Observe(10);

   observer_list.AddObserver(&evil);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   for (auto& observer : observer_list)
     observer.Observe(10);

   EXPECT_EQ(20, a.total);
   EXPECT_EQ(-20, b.total);
   EXPECT_EQ(10, c.total);
   EXPECT_EQ(-10, d.total);
 }

 TYPED_TEST(ObserverListTest, DisruptBefore) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter evil(&observer_list, &b);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&evil);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   for (auto& observer : observer_list)
     observer.Observe(10);
   for (auto& observer : observer_list)
     observer.Observe(10);

   EXPECT_EQ(20, a.total);
   EXPECT_EQ(-10, b.total);
   EXPECT_EQ(20, c.total);
   EXPECT_EQ(-20, d.total);
 }

 TYPED_TEST(ObserverListTest, Existing) {
   DECLARE_TYPES;
   ObserverListFoo observer_list(ObserverListPolicy::EXISTING_ONLY);
   Adder a(1);
   AddInObserve<ObserverListFoo> b(&observer_list);
   Adder c(1);
   b.SetToAdd(&c);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);

   for (auto& observer : observer_list)
     observer.Observe(1);

   EXPECT_FALSE(b.to_add_);
   // B's adder should not have been notified because it was added during
   // notification.
   EXPECT_EQ(0, c.total);

   // Notify again to make sure b's adder is notified.
   for (auto& observer : observer_list)
     observer.Observe(1);
   EXPECT_EQ(1, c.total);
 }

 template <class ObserverListType,
           class Foo = typename ObserverListType::value_type>
 class AddInClearObserve : public Foo {
  public:
   explicit AddInClearObserve(ObserverListType* list)
       : list_(list), added_(false), adder_(1) {}

   void Observe(int /* x */) override {
     list_->Clear();
     list_->AddObserver(&adder_);
     added_ = true;
   }

   bool added() const { return added_; }
   const AdderT<Foo>& adder() const { return adder_; }

  private:
   const raw_ptr<ObserverListType> list_;

   bool added_;
   AdderT<Foo> adder_;
 };

 TYPED_TEST(ObserverListTest, ClearNotifyAll) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   AddInClearObserve<ObserverListFoo> a(&observer_list);

   observer_list.AddObserver(&a);

   for (auto& observer : observer_list)
     observer.Observe(1);
   EXPECT_TRUE(a.added());
   EXPECT_EQ(1, a.adder().total)
       << "Adder should observe once and have sum of 1.";
 }

 TYPED_TEST(ObserverListTest, ClearNotifyExistingOnly) {
   DECLARE_TYPES;
   ObserverListFoo observer_list(ObserverListPolicy::EXISTING_ONLY);
   AddInClearObserve<ObserverListFoo> a(&observer_list);

   observer_list.AddObserver(&a);

   for (auto& observer : observer_list)
     observer.Observe(1);
   EXPECT_TRUE(a.added());
   EXPECT_EQ(0, a.adder().total)
       << "Adder should not observe, so sum should still be 0.";
 }

 template <class ObserverListType,
           class Foo = typename ObserverListType::value_type>
 class ListDestructor : public Foo {
  public:
   explicit ListDestructor(ObserverListType* list) : list_(list) {}
   ~ListDestructor() override = default;

   void Observe(int x) override { delete list_.ExtractAsDangling(); }

  private:
   raw_ptr<ObserverListType> list_;
 };

 TYPED_TEST(ObserverListTest, IteratorOutlivesList) {
   DECLARE_TYPES;
   ObserverListFoo* observer_list = new ObserverListFoo;
   ListDestructor<ObserverListFoo> a(observer_list);
   observer_list->AddObserver(&a);

   for (auto& observer : *observer_list)
     observer.Observe(0);

   // There are no EXPECT* statements for this test, if we catch
   // use-after-free errors for observer_list (eg with ASan) then
   // this test has failed.  See http://crbug.com/85296.
 }

 TYPED_TEST(ObserverListTest, BasicStdIterator) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;

   // An optimization: begin() and end() do not involve weak pointers on
   // empty list.
   EXPECT_FALSE(this->list(observer_list.begin()));
   EXPECT_FALSE(this->list(observer_list.end()));

   // Iterate over empty list: no effect, no crash.
   for (auto& i : observer_list)
     i.Observe(10);

   Adder a(1), b(-1), c(1), d(-1);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   for (iterator i = observer_list.begin(), e = observer_list.end(); i != e; ++i)
     i->Observe(1);

   EXPECT_EQ(1, a.total);
   EXPECT_EQ(-1, b.total);
   EXPECT_EQ(1, c.total);
   EXPECT_EQ(-1, d.total);

   // Check an iteration over a 'const view' for a given container.
   const ObserverListFoo& const_list = observer_list;
   for (const_iterator i = const_list.begin(), e = const_list.end(); i != e;
        ++i) {
     EXPECT_EQ(1, std::abs(i->GetValue()));
   }

   for (const auto& o : const_list)
     EXPECT_EQ(1, std::abs(o.GetValue()));
 }

 TYPED_TEST(ObserverListTest, StdIteratorRemoveItself) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter disrupter(&observer_list, true);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&disrupter);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   for (auto& o : observer_list)
     o.Observe(1);

   for (auto& o : observer_list)
     o.Observe(10);

   EXPECT_EQ(11, a.total);
   EXPECT_EQ(-11, b.total);
   EXPECT_EQ(11, c.total);
   EXPECT_EQ(-11, d.total);
 }

 TYPED_TEST(ObserverListTest, StdIteratorRemoveBefore) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter disrupter(&observer_list, &b);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&disrupter);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   for (auto& o : observer_list)
     o.Observe(1);

   for (auto& o : observer_list)
     o.Observe(10);

   EXPECT_EQ(11, a.total);
   EXPECT_EQ(-1, b.total);
   EXPECT_EQ(11, c.total);
   EXPECT_EQ(-11, d.total);
 }

 TYPED_TEST(ObserverListTest, StdIteratorRemoveAfter) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter disrupter(&observer_list, &c);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&disrupter);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   for (auto& o : observer_list)
     o.Observe(1);

   for (auto& o : observer_list)
     o.Observe(10);

   EXPECT_EQ(11, a.total);
   EXPECT_EQ(-11, b.total);
   EXPECT_EQ(0, c.total);
   EXPECT_EQ(-11, d.total);
 }

 TYPED_TEST(ObserverListTest, StdIteratorRemoveAfterFront) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter disrupter(&observer_list, &a);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&disrupter);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   for (auto& o : observer_list)
     o.Observe(1);

   for (auto& o : observer_list)
     o.Observe(10);

   EXPECT_EQ(1, a.total);
   EXPECT_EQ(-11, b.total);
   EXPECT_EQ(11, c.total);
   EXPECT_EQ(-11, d.total);
 }

 TYPED_TEST(ObserverListTest, StdIteratorRemoveBeforeBack) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter disrupter(&observer_list, &d);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&disrupter);
   observer_list.AddObserver(&d);

   for (auto& o : observer_list)
     o.Observe(1);

   for (auto& o : observer_list)
     o.Observe(10);

   EXPECT_EQ(11, a.total);
   EXPECT_EQ(-11, b.total);
   EXPECT_EQ(11, c.total);
   EXPECT_EQ(0, d.total);
 }

 TYPED_TEST(ObserverListTest, StdIteratorRemoveFront) {
   DECLARE_TYPES;
   using iterator = typename TestFixture::iterator;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter disrupter(&observer_list, true);

   observer_list.AddObserver(&disrupter);
   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   bool test_disruptor = true;
   for (iterator i = observer_list.begin(), e = observer_list.end(); i != e;
        ++i) {
     i->Observe(1);
     // Check that second call to i->Observe() would crash here.
     if (test_disruptor) {
       EXPECT_FALSE(this->GetCurrent(&i));
       test_disruptor = false;
     }
   }

   for (auto& o : observer_list)
     o.Observe(10);

   EXPECT_EQ(11, a.total);
   EXPECT_EQ(-11, b.total);
   EXPECT_EQ(11, c.total);
   EXPECT_EQ(-11, d.total);
 }

 TYPED_TEST(ObserverListTest, StdIteratorRemoveBack) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter disrupter(&observer_list, true);

   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);
   observer_list.AddObserver(&disrupter);

   for (auto& o : observer_list)
     o.Observe(1);

   for (auto& o : observer_list)
     o.Observe(10);

   EXPECT_EQ(11, a.total);
   EXPECT_EQ(-11, b.total);
   EXPECT_EQ(11, c.total);
   EXPECT_EQ(-11, d.total);
 }

 TYPED_TEST(ObserverListTest, NestedLoop) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1), c(1), d(-1);
   Disrupter disrupter(&observer_list, true);

   observer_list.AddObserver(&disrupter);
   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
   observer_list.AddObserver(&c);
   observer_list.AddObserver(&d);

   for (auto& observer : observer_list) {
     observer.Observe(10);

     for (auto& nested_observer : observer_list)
       nested_observer.Observe(1);
   }

   EXPECT_EQ(15, a.total);
   EXPECT_EQ(-15, b.total);
   EXPECT_EQ(15, c.total);
   EXPECT_EQ(-15, d.total);
 }

 TYPED_TEST(ObserverListTest, NonCompactList) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1);

   Disrupter disrupter2(&observer_list, true);  // Must outlive `disrupter1`.
   Disrupter disrupter1(&observer_list, true);

   // Disrupt itself and another one.
   disrupter1.SetDoomed(&disrupter2);

   observer_list.AddObserver(&disrupter1);
   observer_list.AddObserver(&disrupter2);
   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);

   for (auto& observer : observer_list) {
     // Get the { nullptr, nullptr, &a, &b } non-compact list
     // on the first inner pass.
     observer.Observe(10);

     for (auto& nested_observer : observer_list)
       nested_observer.Observe(1);
   }

   EXPECT_EQ(13, a.total);
   EXPECT_EQ(-13, b.total);
 }

 TYPED_TEST(ObserverListTest, BecomesEmptyThanNonEmpty) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;
   Adder a(1), b(-1);

   Disrupter disrupter2(&observer_list, true);  // Must outlive `disrupter1`.
   Disrupter disrupter1(&observer_list, true);

   // Disrupt itself and another one.
   disrupter1.SetDoomed(&disrupter2);

   observer_list.AddObserver(&disrupter1);
   observer_list.AddObserver(&disrupter2);

   bool add_observers = true;
   for (auto& observer : observer_list) {
     // Get the { nullptr, nullptr } empty list on the first inner pass.
     observer.Observe(10);

     for (auto& nested_observer : observer_list)
       nested_observer.Observe(1);

     if (add_observers) {
       observer_list.AddObserver(&a);
       observer_list.AddObserver(&b);
       add_observers = false;
     }
   }

   EXPECT_EQ(12, a.total);
   EXPECT_EQ(-12, b.total);
 }

 TYPED_TEST(ObserverListTest, AddObserverInTheLastObserve) {
   DECLARE_TYPES;
   ObserverListFoo observer_list;

   AddInObserve<ObserverListFoo> a(&observer_list);
   Adder b(-1);

   a.SetToAdd(&b);
   observer_list.AddObserver(&a);

   auto it = observer_list.begin();
   while (it != observer_list.end()) {
     auto& observer = *it;
     // Intentionally increment the iterator before calling Observe(). The
     // ObserverList starts with only one observer, and it == observer_list.end()
     // should be true after the next line.
     ++it;
     // However, the first Observe() call will add a second observer: at this
     // point, it != observer_list.end() should be true, and Observe() should be
     // called on the newly added observer on the next iteration of the loop.
     observer.Observe(10);
   }

   EXPECT_EQ(-10, b.total);
 }

 class MockLogAssertHandler {
  public:
   MOCK_METHOD4(
       HandleLogAssert,
       void(const char*, int, const base::StringPiece, const base::StringPiece));
 };

 #if DCHECK_IS_ON()
 TYPED_TEST(ObserverListTest, NonReentrantObserverList) {
   DECLARE_TYPES;
   using NonReentrantObserverListFoo = typename PickObserverList<
       Foo>::template ObserverListType<Foo, /*check_empty=*/false,
                                       /*allow_reentrancy=*/false>;
   NonReentrantObserverListFoo non_reentrant_observer_list;
   Adder a(1);
   non_reentrant_observer_list.AddObserver(&a);

   EXPECT_DCHECK_DEATH({
     for (const Foo& observer : non_reentrant_observer_list) {
       for (const Foo& nested_observer : non_reentrant_observer_list) {
         std::ignore = observer;
         std::ignore = nested_observer;
       }
     }
   });
 }

 TYPED_TEST(ObserverListTest, ReentrantObserverList) {
   DECLARE_TYPES;
   using ReentrantObserverListFoo = typename PickObserverList<
       Foo>::template ObserverListType<Foo, /*check_empty=*/false,
                                       /*allow_reentrancy=*/true>;
   ReentrantObserverListFoo reentrant_observer_list;
   Adder a(1);
   reentrant_observer_list.AddObserver(&a);
   bool passed = false;
   for (const Foo& observer : reentrant_observer_list) {
     for (const Foo& nested_observer : reentrant_observer_list) {
       std::ignore = observer;
       std::ignore = nested_observer;
       passed = true;
     }
   }
   EXPECT_TRUE(passed);
 }
 #endif

 class TestCheckedObserver : public CheckedObserver {
  public:
   explicit TestCheckedObserver(int* count) : count_(count) {}
   TestCheckedObserver(const TestCheckedObserver&) = delete;
   TestCheckedObserver& operator=(const TestCheckedObserver&) = delete;

   void Observe() { ++(*count_); }

  private:
   raw_ptr<int> count_;
 };

 // A second, identical observer, used to test multiple inheritance.
 class TestCheckedObserver2 : public CheckedObserver {
  public:
   explicit TestCheckedObserver2(int* count) : count_(count) {}
   TestCheckedObserver2(const TestCheckedObserver2&) = delete;
   TestCheckedObserver2& operator=(const TestCheckedObserver2&) = delete;

   void Observe() { ++(*count_); }

  private:
   raw_ptr<int> count_;
 };

 using CheckedObserverListTest = ::testing::Test;

 // Test Observers that CHECK() when a UAF might otherwise occur.
 TEST_F(CheckedObserverListTest, CheckedObserver) {
   // See comments below about why this is unique_ptr.
   auto list = std::make_unique<ObserverList<TestCheckedObserver>>();
   int count1 = 0;
   int count2 = 0;
   TestCheckedObserver l1(&count1);
   list->AddObserver(&l1);
   {
     TestCheckedObserver l2(&count2);
     list->AddObserver(&l2);
     for (auto& observer : *list)
       observer.Observe();
     EXPECT_EQ(1, count1);
     EXPECT_EQ(1, count2);
   }
   {
     auto it = list->begin();
     it->Observe();
     // For CheckedObservers, a CHECK() occurs when advancing the iterator. (On
     // calling the observer method would be too late since the pointer would
     // already be null by then).
     EXPECT_CHECK_DEATH(it++);

     // On the non-death fork, no UAF occurs since the deleted observer is never
     // notified, but also the observer list still has |l2| in it. Check that.
     list->RemoveObserver(&l1);
     EXPECT_TRUE(!list->empty());

     // Now (in the non-death fork()) there's a problem. To delete |it|, we need
     // to compact the list, but that needs to iterate, which would CHECK again.
     // We can't remove |l2| (it's null). But we can delete |list|, which makes
     // the weak pointer in the iterator itself null.
     list.reset();
   }
   EXPECT_EQ(2, count1);
   EXPECT_EQ(1, count2);
 }

 class MultiObserver : public TestCheckedObserver,
                       public TestCheckedObserver2,
                       public AdderT<UncheckedBase> {
  public:
   MultiObserver(int* checked_count, int* two_count)
       : TestCheckedObserver(checked_count),
         TestCheckedObserver2(two_count),
         AdderT(1) {}
 };

 // Test that observers behave as expected when observing multiple interfaces
 // with different traits.
 TEST_F(CheckedObserverListTest, MultiObserver) {
   // Observe two checked observer lists. This is to ensure the WeakPtrFactory
   // in CheckedObserver can correctly service multiple ObserverLists.
   ObserverList<TestCheckedObserver> checked_list;
   ObserverList<TestCheckedObserver2> two_list;

   ObserverList<UncheckedBase>::Unchecked unsafe_list;

   int counts[2] = {};

   auto multi_observer = std::make_unique<MultiObserver>(&counts[0], &counts[1]);
   two_list.AddObserver(multi_observer.get());
   checked_list.AddObserver(multi_observer.get());
   unsafe_list.AddObserver(multi_observer.get());

   auto iterate_over = [](auto* list) {
     for (auto& observer : *list)
       observer.Observe();
   };
   iterate_over(&two_list);
   iterate_over(&checked_list);
   for (auto& observer : unsafe_list)
     observer.Observe(10);

   EXPECT_EQ(10, multi_observer->GetValue());
   for (const auto& count : counts)
     EXPECT_EQ(1, count);

   unsafe_list.RemoveObserver(multi_observer.get());  // Avoid a use-after-free.

   multi_observer.reset();
   EXPECT_CHECK_DEATH(iterate_over(&checked_list));

   for (const auto& count : counts)
     EXPECT_EQ(1, count);
 }

 }  // namespace base