Add 'third_party/abseil_cpp/' from commit '768eb2ca28'

git-subtree-dir: third_party/abseil_cpp
git-subtree-mainline: ffb2ae54be
git-subtree-split: 768eb2ca28

third_party/abseil_cpp/absl/synchronization/lifetime_test.cc

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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <cstdlib>
+#include <thread>  // NOLINT(build/c++11), Abseil test
+#include <type_traits>
+
+#include "absl/base/attributes.h"
+#include "absl/base/const_init.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/thread_annotations.h"
+#include "absl/synchronization/mutex.h"
+#include "absl/synchronization/notification.h"
+
+namespace {
+
+// A two-threaded test which checks that Mutex, CondVar, and Notification have
+// correct basic functionality.  The intent is to establish that they
+// function correctly in various phases of construction and destruction.
+//
+// Thread one acquires a lock on 'mutex', wakes thread two via 'notification',
+// then waits for 'state' to be set, as signalled by 'condvar'.
+//
+// Thread two waits on 'notification', then sets 'state' inside the 'mutex',
+// signalling the change via 'condvar'.
+//
+// These tests use ABSL_RAW_CHECK to validate invariants, rather than EXPECT or
+// ASSERT from gUnit, because we need to invoke them during global destructors,
+// when gUnit teardown would have already begun.
+void ThreadOne(absl::Mutex* mutex, absl::CondVar* condvar,
+               absl::Notification* notification, bool* state) {
+  // Test that the notification is in a valid initial state.
+  ABSL_RAW_CHECK(!notification->HasBeenNotified(), "invalid Notification");
+  ABSL_RAW_CHECK(*state == false, "*state not initialized");
+
+  {
+    absl::MutexLock lock(mutex);
+
+    notification->Notify();
+    ABSL_RAW_CHECK(notification->HasBeenNotified(), "invalid Notification");
+
+    while (*state == false) {
+      condvar->Wait(mutex);
+    }
+  }
+}
+
+void ThreadTwo(absl::Mutex* mutex, absl::CondVar* condvar,
+               absl::Notification* notification, bool* state) {
+  ABSL_RAW_CHECK(*state == false, "*state not initialized");
+
+  // Wake thread one
+  notification->WaitForNotification();
+  ABSL_RAW_CHECK(notification->HasBeenNotified(), "invalid Notification");
+  {
+    absl::MutexLock lock(mutex);
+    *state = true;
+    condvar->Signal();
+  }
+}
+
+// Launch thread 1 and thread 2, and block on their completion.
+// If any of 'mutex', 'condvar', or 'notification' is nullptr, use a locally
+// constructed instance instead.
+void RunTests(absl::Mutex* mutex, absl::CondVar* condvar) {
+  absl::Mutex default_mutex;
+  absl::CondVar default_condvar;
+  absl::Notification notification;
+  if (!mutex) {
+    mutex = &default_mutex;
+  }
+  if (!condvar) {
+    condvar = &default_condvar;
+  }
+  bool state = false;
+  std::thread thread_one(ThreadOne, mutex, condvar, &notification, &state);
+  std::thread thread_two(ThreadTwo, mutex, condvar, &notification, &state);
+  thread_one.join();
+  thread_two.join();
+}
+
+void TestLocals() {
+  absl::Mutex mutex;
+  absl::CondVar condvar;
+  RunTests(&mutex, &condvar);
+}
+
+// Normal kConstInit usage
+ABSL_CONST_INIT absl::Mutex const_init_mutex(absl::kConstInit);
+void TestConstInitGlobal() { RunTests(&const_init_mutex, nullptr); }
+
+// Global variables during start and termination
+//
+// In a translation unit, static storage duration variables are initialized in
+// the order of their definitions, and destroyed in the reverse order of their
+// definitions.  We can use this to arrange for tests to be run on these objects
+// before they are created, and after they are destroyed.
+
+using Function = void (*)();
+
+class OnConstruction {
+ public:
+  explicit OnConstruction(Function fn) { fn(); }
+};
+
+class OnDestruction {
+ public:
+  explicit OnDestruction(Function fn) : fn_(fn) {}
+  ~OnDestruction() { fn_(); }
+ private:
+  Function fn_;
+};
+
+// These tests require that the compiler correctly supports C++11 constant
+// initialization... but MSVC has a known regression since v19.10:
+// https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html
+// TODO(epastor): Limit the affected range once MSVC fixes this bug.
+#if defined(__clang__) || !(defined(_MSC_VER) && _MSC_VER > 1900)
+// kConstInit
+// Test early usage.  (Declaration comes first; definitions must appear after
+// the test runner.)
+extern absl::Mutex early_const_init_mutex;
+// (Normally I'd write this +[], to make the cast-to-function-pointer explicit,
+// but in some MSVC setups we support, lambdas provide conversion operators to
+// different flavors of function pointers, making this trick ambiguous.)
+OnConstruction test_early_const_init([] {
+  RunTests(&early_const_init_mutex, nullptr);
+});
+// This definition appears before test_early_const_init, but it should be
+// initialized first (due to constant initialization).  Test that the object
+// actually works when constructed this way.
+ABSL_CONST_INIT absl::Mutex early_const_init_mutex(absl::kConstInit);
+
+// Furthermore, test that the const-init c'tor doesn't stomp over the state of
+// a Mutex.  Really, this is a test that the platform under test correctly
+// supports C++11 constant initialization.  (The constant-initialization
+// constructors of globals "happen at link time"; memory is pre-initialized,
+// before the constructors of either grab_lock or check_still_locked are run.)
+extern absl::Mutex const_init_sanity_mutex;
+OnConstruction grab_lock([]() ABSL_NO_THREAD_SAFETY_ANALYSIS {
+  const_init_sanity_mutex.Lock();
+});
+ABSL_CONST_INIT absl::Mutex const_init_sanity_mutex(absl::kConstInit);
+OnConstruction check_still_locked([]() ABSL_NO_THREAD_SAFETY_ANALYSIS {
+  const_init_sanity_mutex.AssertHeld();
+  const_init_sanity_mutex.Unlock();
+});
+#endif  // defined(__clang__) || !(defined(_MSC_VER) && _MSC_VER > 1900)
+
+// Test shutdown usage.  (Declarations come first; definitions must appear after
+// the test runner.)
+extern absl::Mutex late_const_init_mutex;
+// OnDestruction is being used here as a global variable, even though it has a
+// non-trivial destructor.  This is against the style guide.  We're violating
+// that rule here to check that the exception we allow for kConstInit is safe.
+// NOLINTNEXTLINE
+OnDestruction test_late_const_init([] {
+  RunTests(&late_const_init_mutex, nullptr);
+});
+ABSL_CONST_INIT absl::Mutex late_const_init_mutex(absl::kConstInit);
+
+}  // namespace
+
+int main() {
+  TestLocals();
+  TestConstInitGlobal();
+  // Explicitly call exit(0) here, to make it clear that we intend for the
+  // above global object destructors to run.
+  std::exit(0);
+}