base/no_destructor_unittest.cc

   1 // Copyright 2018 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/no_destructor.h"
   6
   7 #include <memory>
   8 #include <string>
   9 #include <utility>
  10 #include <vector>
  11
  12 #include "base/atomicops.h"
  13 #include "base/barrier_closure.h"
  14 #include "base/check.h"
  15 #include "base/functional/bind.h"
  16 #include "base/system/sys_info.h"
  17 #include "base/threading/platform_thread.h"
  18 #include "base/threading/simple_thread.h"
  19 #include "build/build_config.h"
  20 #include "testing/gtest/include/gtest/gtest.h"
  21
  22 namespace base {
  23
  24 namespace {
  25
  26 static_assert(!std::is_trivially_destructible_v<std::string>);
  27 static_assert(
  28     std::is_trivially_destructible_v<base::NoDestructor<std::string>>);
  29
  30 struct CheckOnDestroy {
  31   ~CheckOnDestroy() { CHECK(false); }
  32 };
  33
  34 TEST(NoDestructorTest, SkipsDestructors) {
  35   NoDestructor<CheckOnDestroy> destructor_should_not_run;
  36 }
  37
  38 struct UncopyableUnmovable {
  39   UncopyableUnmovable() = default;
  40   explicit UncopyableUnmovable(int value) : value(value) {}
  41
  42   UncopyableUnmovable(const UncopyableUnmovable&) = delete;
  43   UncopyableUnmovable& operator=(const UncopyableUnmovable&) = delete;
  44
  45   int value = 1;
  46   std::string something_with_a_nontrivial_destructor;
  47 };
  48
  49 struct CopyOnly {
  50   CopyOnly() = default;
  51
  52   CopyOnly(const CopyOnly&) = default;
  53   CopyOnly& operator=(const CopyOnly&) = default;
  54
  55   CopyOnly(CopyOnly&&) = delete;
  56   CopyOnly& operator=(CopyOnly&&) = delete;
  57 };
  58
  59 struct MoveOnly {
  60   MoveOnly() = default;
  61
  62   MoveOnly(const MoveOnly&) = delete;
  63   MoveOnly& operator=(const MoveOnly&) = delete;
  64
  65   MoveOnly(MoveOnly&&) = default;
  66   MoveOnly& operator=(MoveOnly&&) = default;
  67 };
  68
  69 struct ForwardingTestStruct {
  70   ForwardingTestStruct(const CopyOnly&, MoveOnly&&) {}
  71
  72   std::string something_with_a_nontrivial_destructor;
  73 };
  74
  75 TEST(NoDestructorTest, UncopyableUnmovable) {
  76   static NoDestructor<UncopyableUnmovable> default_constructed;
  77   EXPECT_EQ(1, default_constructed->value);
  78
  79   static NoDestructor<UncopyableUnmovable> constructed_with_arg(-1);
  80   EXPECT_EQ(-1, constructed_with_arg->value);
  81 }
  82
  83 TEST(NoDestructorTest, ForwardsArguments) {
  84   CopyOnly copy_only;
  85   MoveOnly move_only;
  86
  87   static NoDestructor<ForwardingTestStruct> test_forwarding(
  88       copy_only, std::move(move_only));
  89 }
  90
  91 TEST(NoDestructorTest, Accessors) {
  92   static NoDestructor<std::string> awesome("awesome");
  93
  94   EXPECT_EQ("awesome", *awesome);
  95   EXPECT_EQ(0, awesome->compare("awesome"));
  96   EXPECT_EQ(0, awesome.get()->compare("awesome"));
  97 }
  98
  99 // Passing initializer list to a NoDestructor like in this test
 100 // is ambiguous in GCC.
 101 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84849
 102 #if !defined(COMPILER_GCC) && !defined(__clang__)
 103 TEST(NoDestructorTest, InitializerList) {
 104   static NoDestructor<std::vector<std::string>> vector({"a", "b", "c"});
 105 }
 106 #endif
 107 }  // namespace
 108
 109 namespace {
 110
 111 // A class whose constructor busy-loops until it is told to complete
 112 // construction.
 113 class BlockingConstructor {
 114  public:
 115   BlockingConstructor() {
 116     EXPECT_FALSE(WasConstructorCalled());
 117     subtle::NoBarrier_Store(&constructor_called_, 1);
 118     EXPECT_TRUE(WasConstructorCalled());
 119     while (!subtle::NoBarrier_Load(&complete_construction_))
 120       PlatformThread::YieldCurrentThread();
 121     done_construction_ = true;
 122   }
 123   BlockingConstructor(const BlockingConstructor&) = delete;
 124   BlockingConstructor& operator=(const BlockingConstructor&) = delete;
 125   ~BlockingConstructor() = delete;
 126
 127   // Returns true if BlockingConstructor() was entered.
 128   static bool WasConstructorCalled() {
 129     return subtle::NoBarrier_Load(&constructor_called_);
 130   }
 131
 132   // Instructs BlockingConstructor() that it may now unblock its construction.
 133   static void CompleteConstructionNow() {
 134     subtle::NoBarrier_Store(&complete_construction_, 1);
 135   }
 136
 137   bool done_construction() const { return done_construction_; }
 138
 139  private:
 140   // Use Atomic32 instead of AtomicFlag for them to be trivially initialized.
 141   static subtle::Atomic32 constructor_called_;
 142   static subtle::Atomic32 complete_construction_;
 143
 144   bool done_construction_ = false;
 145 };
 146
 147 // static
 148 subtle::Atomic32 BlockingConstructor::constructor_called_ = 0;
 149 // static
 150 subtle::Atomic32 BlockingConstructor::complete_construction_ = 0;
 151
 152 // A SimpleThread running at |thread_type| which invokes |before_get| (optional)
 153 // and then invokes thread-safe scoped-static-initializationconstruction on its
 154 // NoDestructor instance.
 155 class BlockingConstructorThread : public SimpleThread {
 156  public:
 157   BlockingConstructorThread(ThreadType thread_type, OnceClosure before_get)
 158       : SimpleThread("BlockingConstructorThread", Options(thread_type)),
 159         before_get_(std::move(before_get)) {}
 160   BlockingConstructorThread(const BlockingConstructorThread&) = delete;
 161   BlockingConstructorThread& operator=(const BlockingConstructorThread&) =
 162       delete;
 163
 164   void Run() override {
 165     if (before_get_)
 166       std::move(before_get_).Run();
 167
 168     static NoDestructor<BlockingConstructor> instance;
 169     EXPECT_TRUE(instance->done_construction());
 170   }
 171
 172  private:
 173   OnceClosure before_get_;
 174 };
 175
 176 }  // namespace
 177
 178 // Tests that if the thread assigned to construct the local-static
 179 // initialization of the NoDestructor runs at background priority : the
 180 // foreground threads will yield to it enough for it to eventually complete
 181 // construction. While local-static thread-safe initialization isn't specific to
 182 // NoDestructor, it is tested here as NoDestructor is set to replace
 183 // LazyInstance and this is an important regression test for it
 184 // (https://crbug.com/797129).
 185 TEST(NoDestructorTest, PriorityInversionAtStaticInitializationResolves) {
 186   TimeTicks test_begin = TimeTicks::Now();
 187
 188   // Construct BlockingConstructor from a thread that is lower priority than the
 189   // other threads that will be constructed. This thread used to be BACKGROUND
 190   // priority but that caused it to be starved by other simultaneously running
 191   // test processes, leading to false-positive failures.
 192   BlockingConstructorThread background_getter(ThreadType::kDefault,
 193                                               OnceClosure());
 194   background_getter.Start();
 195
 196   while (!BlockingConstructor::WasConstructorCalled())
 197     PlatformThread::Sleep(Milliseconds(1));
 198
 199   // Spin 4 foreground thread per core contending to get the already under
 200   // construction NoDestructor. When they are all running and poking at it :
 201   // allow the background thread to complete its work.
 202   const int kNumForegroundThreads = 4 * SysInfo::NumberOfProcessors();
 203   std::vector<std::unique_ptr<SimpleThread>> foreground_threads;
 204   RepeatingClosure foreground_thread_ready_callback =
 205       BarrierClosure(kNumForegroundThreads,
 206                      BindOnce(&BlockingConstructor::CompleteConstructionNow));
 207   for (int i = 0; i < kNumForegroundThreads; ++i) {
 208     // Create threads that are higher priority than background_getter. See above
 209     // for why these particular priorities are chosen.
 210     foreground_threads.push_back(std::make_unique<BlockingConstructorThread>(
 211         ThreadType::kDisplayCritical, foreground_thread_ready_callback));
 212     foreground_threads.back()->Start();
 213   }
 214
 215   // This test will hang if the foreground threads become stuck in
 216   // NoDestructor's construction per the background thread never being scheduled
 217   // to complete construction.
 218   for (auto& foreground_thread : foreground_threads)
 219     foreground_thread->Join();
 220   background_getter.Join();
 221
 222   // Fail if this test takes more than 5 seconds (it takes 5-10 seconds on a
 223   // Z840 without https://crrev.com/527445 but is expected to be fast (~30ms)
 224   // with the fix).
 225   EXPECT_LT(TimeTicks::Now() - test_begin, Seconds(5));
 226 }
 227
 228 }  // namespace base