merge(3p/absl): subtree merge of Abseil up to e19260f r/1889

... notably, this includes Abseil's own StatusOr type, which
conflicted with our implementation (that was taken from TensorFlow).

Change-Id: Ie7d6764b64055caaeb8dc7b6b9d066291e6b538f

1 files changed, 91 insertions, 62 deletions

diff --git a/third_party/abseil_cpp/absl/flags/reflection.cc b/third_party/abseil_cpp/absl/flags/reflection.cc
index 5fc945f23767..c976d4679601 100644
--- a/third_party/abseil_cpp/absl/flags/reflection.cc
+++ b/third_party/abseil_cpp/absl/flags/reflection.cc
@@ -17,6 +17,7 @@
 
 #include <assert.h>
 
+#include <atomic>
 #include <map>
 #include <string>
 
@@ -56,25 +57,23 @@ class FlagRegistry {
 
   // Returns the flag object for the specified name, or nullptr if not found.
   // Will emit a warning if a 'retired' flag is specified.
-  CommandLineFlag* FindFlagLocked(absl::string_view name);
-
-  // Returns the retired flag object for the specified name, or nullptr if not
-  // found or not retired.  Does not emit a warning.
-  CommandLineFlag* FindRetiredFlagLocked(absl::string_view name);
+  CommandLineFlag* FindFlag(absl::string_view name);
 
   static FlagRegistry& GlobalRegistry();  // returns a singleton registry
 
  private:
   friend class flags_internal::FlagSaverImpl;  // reads all the flags in order
                                                // to copy them
-  friend void ForEachFlagUnlocked(
-      std::function<void(CommandLineFlag&)> visitor);
+  friend void ForEachFlag(std::function<void(CommandLineFlag&)> visitor);
+  friend void FinalizeRegistry();
 
-  // The map from name to flag, for FindFlagLocked().
+  // The map from name to flag, for FindFlag().
   using FlagMap = std::map<absl::string_view, CommandLineFlag*>;
   using FlagIterator = FlagMap::iterator;
   using FlagConstIterator = FlagMap::const_iterator;
   FlagMap flags_;
+  std::vector<CommandLineFlag*> flat_flags_;
+  std::atomic<bool> finalized_flags_{false};
 
   absl::Mutex lock_;
 
@@ -83,29 +82,6 @@ class FlagRegistry {
   FlagRegistry& operator=(const FlagRegistry&);
 };
 
-CommandLineFlag* FlagRegistry::FindFlagLocked(absl::string_view name) {
-  FlagConstIterator i = flags_.find(name);
-  if (i == flags_.end()) {
-    return nullptr;
-  }
-
-  if (i->second->IsRetired()) {
-    flags_internal::ReportUsageError(
-        absl::StrCat("Accessing retired flag '", name, "'"), false);
-  }
-
-  return i->second;
-}
-
-CommandLineFlag* FlagRegistry::FindRetiredFlagLocked(absl::string_view name) {
-  FlagConstIterator i = flags_.find(name);
-  if (i == flags_.end() || !i->second->IsRetired()) {
-    return nullptr;
-  }
-
-  return i->second;
-}
-
 namespace {
 
 class FlagRegistryLock {
@@ -117,12 +93,26 @@ class FlagRegistryLock {
   FlagRegistry& fr_;
 };
 
-void DestroyRetiredFlag(CommandLineFlag& flag);
-
 }  // namespace
 
+CommandLineFlag* FlagRegistry::FindFlag(absl::string_view name) {
+  if (finalized_flags_.load(std::memory_order_acquire)) {
+    // We could save some gcus here if we make `Name()` be non-virtual.
+    // We could move the `const char*` name to the base class.
+    auto it = std::partition_point(
+        flat_flags_.begin(), flat_flags_.end(),
+        [=](CommandLineFlag* f) { return f->Name() < name; });
+    if (it != flat_flags_.end() && (*it)->Name() == name) return *it;
+  }
+
+  FlagRegistryLock frl(*this);
+  auto it = flags_.find(name);
+  return it != flags_.end() ? it->second : nullptr;
+}
+
 void FlagRegistry::RegisterFlag(CommandLineFlag& flag) {
   FlagRegistryLock registry_lock(*this);
+
   std::pair<FlagIterator, bool> ins =
       flags_.insert(FlagMap::value_type(flag.Name(), &flag));
   if (ins.second == false) {  // means the name was already in the map
@@ -143,8 +133,6 @@ void FlagRegistry::RegisterFlag(CommandLineFlag& flag) {
                        old_flag.Filename(), "' and '", flag.Filename(), "'."),
           true);
     } else if (old_flag.IsRetired()) {
-      // Retired flag can just be deleted.
-      DestroyRetiredFlag(flag);
       return;
     } else if (old_flag.Filename() != flag.Filename()) {
       flags_internal::ReportUsageError(
@@ -155,7 +143,7 @@ void FlagRegistry::RegisterFlag(CommandLineFlag& flag) {
     } else {
       flags_internal::ReportUsageError(
           absl::StrCat(
-              "Something wrong with flag '", flag.Name(), "' in file '",
+              "Something is wrong with flag '", flag.Name(), "' in file '",
               flag.Filename(), "'. One possibility: file '", flag.Filename(),
               "' is being linked both statically and dynamically into this "
               "executable. e.g. some files listed as srcs to a test and also "
@@ -174,18 +162,15 @@ FlagRegistry& FlagRegistry::GlobalRegistry() {
 
 // --------------------------------------------------------------------
 
-void ForEachFlagUnlocked(std::function<void(CommandLineFlag&)> visitor) {
+void ForEachFlag(std::function<void(CommandLineFlag&)> visitor) {
   FlagRegistry& registry = FlagRegistry::GlobalRegistry();
-  for (FlagRegistry::FlagConstIterator i = registry.flags_.begin();
-       i != registry.flags_.end(); ++i) {
-    visitor(*i->second);
+
+  if (registry.finalized_flags_.load(std::memory_order_acquire)) {
+    for (const auto& i : registry.flat_flags_) visitor(*i);
   }
-}
 
-void ForEachFlag(std::function<void(CommandLineFlag&)> visitor) {
-  FlagRegistry& registry = FlagRegistry::GlobalRegistry();
   FlagRegistryLock frl(registry);
-  ForEachFlagUnlocked(visitor);
+  for (const auto& i : registry.flags_) visitor(*i.second);
 }
 
 // --------------------------------------------------------------------
@@ -195,6 +180,21 @@ bool RegisterCommandLineFlag(CommandLineFlag& flag) {
   return true;
 }
 
+void FinalizeRegistry() {
+  auto& registry = FlagRegistry::GlobalRegistry();
+  FlagRegistryLock frl(registry);
+  if (registry.finalized_flags_.load(std::memory_order_relaxed)) {
+    // Was already finalized. Ignore the second time.
+    return;
+  }
+  registry.flat_flags_.reserve(registry.flags_.size());
+  for (const auto& f : registry.flags_) {
+    registry.flat_flags_.push_back(f.second);
+  }
+  registry.flags_.clear();
+  registry.finalized_flags_.store(true, std::memory_order_release);
+}
+
 // --------------------------------------------------------------------
 
 namespace {
@@ -206,16 +206,34 @@ class RetiredFlagObj final : public CommandLineFlag {
 
  private:
   absl::string_view Name() const override { return name_; }
-  std::string Filename() const override { return "RETIRED"; }
+  std::string Filename() const override {
+    OnAccess();
+    return "RETIRED";
+  }
   FlagFastTypeId TypeId() const override { return type_id_; }
-  std::string Help() const override { return ""; }
+  std::string Help() const override {
+    OnAccess();
+    return "";
+  }
   bool IsRetired() const override { return true; }
-  bool IsSpecifiedOnCommandLine() const override { return false; }
-  std::string DefaultValue() const override { return ""; }
-  std::string CurrentValue() const override { return ""; }
+  bool IsSpecifiedOnCommandLine() const override {
+    OnAccess();
+    return false;
+  }
+  std::string DefaultValue() const override {
+    OnAccess();
+    return "";
+  }
+  std::string CurrentValue() const override {
+    OnAccess();
+    return "";
+  }
 
   // Any input is valid
-  bool ValidateInputValue(absl::string_view) const override { return true; }
+  bool ValidateInputValue(absl::string_view) const override {
+    OnAccess();
+    return true;
+  }
 
   std::unique_ptr<flags_internal::FlagStateInterface> SaveState() override {
     return nullptr;
@@ -223,29 +241,32 @@ class RetiredFlagObj final : public CommandLineFlag {
 
   bool ParseFrom(absl::string_view, flags_internal::FlagSettingMode,
                  flags_internal::ValueSource, std::string&) override {
+    OnAccess();
     return false;
   }
 
-  void CheckDefaultValueParsingRoundtrip() const override {}
+  void CheckDefaultValueParsingRoundtrip() const override { OnAccess(); }
+
+  void Read(void*) const override { OnAccess(); }
 
-  void Read(void*) const override {}
+  void OnAccess() const {
+    flags_internal::ReportUsageError(
+        absl::StrCat("Accessing retired flag '", name_, "'"), false);
+  }
 
   // Data members
   const char* const name_;
   const FlagFastTypeId type_id_;
 };
 
-void DestroyRetiredFlag(CommandLineFlag& flag) {
-  assert(flag.IsRetired());
-  delete static_cast<RetiredFlagObj*>(&flag);
-}
-
 }  // namespace
 
-bool Retire(const char* name, FlagFastTypeId type_id) {
-  auto* flag = new flags_internal::RetiredFlagObj(name, type_id);
+void Retire(const char* name, FlagFastTypeId type_id, char* buf) {
+  static_assert(sizeof(RetiredFlagObj) == kRetiredFlagObjSize, "");
+  static_assert(alignof(RetiredFlagObj) == kRetiredFlagObjAlignment, "");
+  auto* flag = ::new (static_cast<void*>(buf))
+      flags_internal::RetiredFlagObj(name, type_id);
   FlagRegistry::GlobalRegistry().RegisterFlag(*flag);
-  return true;
 }
 
 // --------------------------------------------------------------------
@@ -299,9 +320,17 @@ CommandLineFlag* FindCommandLineFlag(absl::string_view name) {
   if (name.empty()) return nullptr;
   flags_internal::FlagRegistry& registry =
       flags_internal::FlagRegistry::GlobalRegistry();
-  flags_internal::FlagRegistryLock frl(registry);
+  return registry.FindFlag(name);
+}
+
+// --------------------------------------------------------------------
 
-  return registry.FindFlagLocked(name);
+absl::flat_hash_map<absl::string_view, absl::CommandLineFlag*> GetAllFlags() {
+  absl::flat_hash_map<absl::string_view, absl::CommandLineFlag*> res;
+  flags_internal::ForEachFlag([&](CommandLineFlag& flag) {
+    if (!flag.IsRetired()) res.insert({flag.Name(), &flag});
+  });
+  return res;
 }
 
 ABSL_NAMESPACE_END