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+//
+// Copyright 2019 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 "absl/flags/internal/registry.h"
+
+#include "absl/base/call_once.h"
+#include "absl/base/dynamic_annotations.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/flags/config.h"
+#include "absl/flags/usage_config.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/string_view.h"
+#include "absl/synchronization/mutex.h"
+
+// --------------------------------------------------------------------
+// FlagRegistry implementation
+// A FlagRegistry holds all flag objects indexed
+// by their names so that if you know a flag's name you can access or
+// set it.
+
+namespace absl {
+namespace flags_internal {
+namespace {
+
+void DestroyFlag(CommandLineFlag* flag) NO_THREAD_SAFETY_ANALYSIS {
+ // Values are heap allocated for retired and Abseil Flags.
+ if (flag->IsRetired() || flag->IsAbseilFlag()) {
+ if (flag->cur) Delete(flag->op, flag->cur);
+ if (flag->def) Delete(flag->op, flag->def);
+ }
+
+ delete flag->locks;
+
+ // CommandLineFlag handle object is heap allocated for non Abseil Flags.
+ if (!flag->IsAbseilFlag()) {
+ delete flag;
+ }
+}
+
+// --------------------------------------------------------------------
+// FlagRegistry
+// A FlagRegistry singleton object holds all flag objects indexed
+// by their names so that if you know a flag's name (as a C
+// string), you can access or set it. If the function is named
+// FooLocked(), you must own the registry lock before calling
+// the function; otherwise, you should *not* hold the lock, and
+// the function will acquire it itself if needed.
+// --------------------------------------------------------------------
+
+// A map from flag pointer to CommandLineFlag*. Used when registering
+// validators.
+class FlagPtrMap {
+ public:
+ void Register(CommandLineFlag* flag) {
+ auto& vec = buckets_[BucketForFlag(flag->cur)];
+ if (vec.size() == vec.capacity()) {
+ // Bypass default 2x growth factor with 1.25 so we have fuller vectors.
+ // This saves 4% memory compared to default growth.
+ vec.reserve(vec.size() * 1.25 + 0.5);
+ }
+ vec.push_back(flag);
+ }
+
+ CommandLineFlag* FindByPtr(const void* flag_ptr) {
+ const auto& flag_vector = buckets_[BucketForFlag(flag_ptr)];
+ for (CommandLineFlag* entry : flag_vector) {
+ if (entry->cur == flag_ptr) {
+ return entry;
+ }
+ }
+ return nullptr;
+ }
+
+ private:
+ // Instead of std::map, we use a custom hash table where each bucket stores
+ // flags in a vector. This reduces memory usage 40% of the memory that would
+ // have been used by std::map.
+ //
+ // kNumBuckets was picked as a large enough prime. As of writing this code, a
+ // typical large binary has ~8k (old-style) flags, and this would gives
+ // buckets with roughly 50 elements each.
+ //
+ // Note that reads to this hash table are rare: exactly as many as we have
+ // flags with validators. As of writing, a typical binary only registers 52
+ // validated flags.
+ static constexpr size_t kNumBuckets = 163;
+ std::vector<CommandLineFlag*> buckets_[kNumBuckets];
+
+ static int BucketForFlag(const void* ptr) {
+ // Modulo a prime is good enough here. On a real program, bucket size stddev
+ // after registering 8k flags is ~5 (mean size at 51).
+ return reinterpret_cast<uintptr_t>(ptr) % kNumBuckets;
+ }
+};
+constexpr size_t FlagPtrMap::kNumBuckets;
+
+} // namespace
+
+class FlagRegistry {
+ public:
+ FlagRegistry() = default;
+ ~FlagRegistry() {
+ for (auto& p : flags_) {
+ DestroyFlag(p.second);
+ }
+ }
+
+ // Store a flag in this registry. Takes ownership of *flag.
+ // If ptr is non-null, the flag can later be found by calling
+ // FindFlagViaPtrLocked(ptr).
+ void RegisterFlag(CommandLineFlag* flag, const void* ptr);
+
+ void Lock() EXCLUSIVE_LOCK_FUNCTION(lock_) { lock_.Lock(); }
+ void Unlock() UNLOCK_FUNCTION(lock_) { lock_.Unlock(); }
+
+ // 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);
+
+ // Returns the flag object whose current-value is stored at flag_ptr.
+ CommandLineFlag* FindFlagViaPtrLocked(const void* flag_ptr);
+
+ static FlagRegistry* GlobalRegistry(); // returns a singleton registry
+
+ private:
+ friend class FlagSaverImpl; // reads all the flags in order to copy them
+ friend void ForEachFlagUnlocked(
+ std::function<void(CommandLineFlag*)> visitor);
+
+ // The map from name to flag, for FindFlagLocked().
+ using FlagMap = std::map<absl::string_view, CommandLineFlag*>;
+ using FlagIterator = FlagMap::iterator;
+ using FlagConstIterator = FlagMap::const_iterator;
+ FlagMap flags_;
+
+ FlagPtrMap flag_ptr_map_;
+
+ static FlagRegistry* global_registry_; // a singleton registry
+
+ static absl::once_flag global_registry_once_;
+
+ static void InitGlobalRegistry();
+
+ absl::Mutex lock_;
+
+ // Disallow
+ FlagRegistry(const FlagRegistry&);
+ FlagRegistry& operator=(const FlagRegistry&);
+};
+
+// Get the singleton FlagRegistry object
+FlagRegistry* FlagRegistry::global_registry_ = nullptr;
+absl::once_flag FlagRegistry::global_registry_once_;
+
+void FlagRegistry::InitGlobalRegistry() { global_registry_ = new FlagRegistry; }
+
+FlagRegistry* FlagRegistry::GlobalRegistry() {
+ absl::call_once(global_registry_once_, &InitGlobalRegistry);
+
+ return global_registry_;
+}
+
+namespace {
+
+class FlagRegistryLock {
+ public:
+ explicit FlagRegistryLock(FlagRegistry* fr) : fr_(fr) { fr_->Lock(); }
+ ~FlagRegistryLock() { fr_->Unlock(); }
+
+ private:
+ FlagRegistry* const fr_;
+};
+
+} // namespace
+
+void FlagRegistry::RegisterFlag(CommandLineFlag* flag, const void* ptr) {
+ 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
+ CommandLineFlag* old_flag = ins.first->second;
+ if (flag->IsRetired() != old_flag->IsRetired()) {
+ // All registrations must agree on the 'retired' flag.
+ flags_internal::ReportUsageError(
+ absl::StrCat(
+ "Retired flag '", flag->Name(),
+ "' was defined normally in file '",
+ (flag->IsRetired() ? old_flag->Filename() : flag->Filename()),
+ "'."),
+ true);
+ } else if (flag->op != old_flag->op) {
+ flags_internal::ReportUsageError(
+ absl::StrCat("Flag '", flag->Name(),
+ "' was defined more than once but with "
+ "differing types. Defined in files '",
+ old_flag->Filename(), "' and '", flag->Filename(),
+ "' with types '", old_flag->Typename(), "' and '",
+ flag->Typename(), "', respectively."),
+ true);
+ } else if (old_flag->IsRetired()) {
+ // Retired definitions are idempotent. Just keep the old one.
+ DestroyFlag(flag);
+ return;
+ } else if (old_flag->Filename() != flag->Filename()) {
+ flags_internal::ReportUsageError(
+ absl::StrCat("Flag '", flag->Name(),
+ "' was defined more than once (in files '",
+ old_flag->Filename(), "' and '", flag->Filename(),
+ "')."),
+ true);
+ } else {
+ flags_internal::ReportUsageError(
+ absl::StrCat(
+ "Something 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 "
+ "listed as srcs of some shared lib deps of the same test."),
+ true);
+ }
+ // All cases above are fatal, except for the retired flags.
+ std::exit(1);
+ }
+
+ if (ptr != nullptr) {
+ // This must be the first time we're seeing this flag.
+ flag_ptr_map_.Register(flag);
+ }
+}
+
+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;
+}
+
+CommandLineFlag* FlagRegistry::FindFlagViaPtrLocked(const void* flag_ptr) {
+ return flag_ptr_map_.FindByPtr(flag_ptr);
+}
+
+// --------------------------------------------------------------------
+// FlagSaver
+// FlagSaverImpl
+// This class stores the states of all flags at construct time,
+// and restores all flags to that state at destruct time.
+// Its major implementation challenge is that it never modifies
+// pointers in the 'main' registry, so global FLAG_* vars always
+// point to the right place.
+// --------------------------------------------------------------------
+
+class FlagSaverImpl {
+ public:
+ // Constructs an empty FlagSaverImpl object.
+ FlagSaverImpl() {}
+ ~FlagSaverImpl() {
+ // reclaim memory from each of our CommandLineFlags
+ for (const SavedFlag& src : backup_registry_) {
+ Delete(src.op, src.current);
+ Delete(src.op, src.default_value);
+ }
+ }
+
+ // Saves the flag states from the flag registry into this object.
+ // It's an error to call this more than once.
+ // Must be called when the registry mutex is not held.
+ void SaveFromRegistry() {
+ assert(backup_registry_.empty()); // call only once!
+ SavedFlag saved;
+ flags_internal::ForEachFlag([&](flags_internal::CommandLineFlag* flag) {
+ if (flag->IsRetired()) return;
+
+ saved.name = flag->Name();
+ saved.op = flag->op;
+ saved.marshalling_op = flag->marshalling_op;
+ {
+ absl::MutexLock l(InitFlagIfNecessary(flag));
+ saved.validator = flag->validator;
+ saved.modified = flag->modified;
+ saved.on_command_line = flag->IsSpecifiedOnCommandLine();
+ saved.current = Clone(saved.op, flag->cur);
+ saved.default_value = Clone(saved.op, flag->def);
+ saved.counter = flag->counter;
+ }
+ backup_registry_.push_back(saved);
+ });
+ }
+
+ // Restores the saved flag states into the flag registry. We
+ // assume no flags were added or deleted from the registry since
+ // the SaveFromRegistry; if they were, that's trouble! Must be
+ // called when the registry mutex is not held.
+ void RestoreToRegistry() {
+ FlagRegistry* const global_registry = FlagRegistry::GlobalRegistry();
+ FlagRegistryLock frl(global_registry);
+ for (const SavedFlag& src : backup_registry_) {
+ CommandLineFlag* flag = global_registry->FindFlagLocked(src.name);
+ // If null, flag got deleted from registry.
+ if (!flag) continue;
+
+ bool restored = false;
+ {
+ absl::Mutex* mu = InitFlagIfNecessary(flag);
+ absl::MutexLock l(mu);
+ flag->validator = src.validator;
+ flag->modified = src.modified;
+ flag->on_command_line = src.on_command_line;
+ if (flag->counter != src.counter ||
+ ChangedDirectly(flag, src.default_value, flag->def)) {
+ flag->counter++;
+ Copy(src.op, src.default_value, flag->def);
+ }
+ if (flag->counter != src.counter ||
+ ChangedDirectly(flag, src.current, flag->cur)) {
+ restored = true;
+ flag->counter++;
+ Copy(src.op, src.current, flag->cur);
+ UpdateCopy(flag, mu);
+
+ // Revalidate the flag because the validator might store state based
+ // on the flag's value, which just changed due to the restore.
+ // Failing validation is ignored because it's assumed that the flag
+ // was valid previously and there's little that can be done about it
+ // here, anyway.
+ Validate(flag, flag->cur);
+ }
+ }
+
+ // Log statements must be done when no flag lock is held.
+ if (restored) {
+ ABSL_INTERNAL_LOG(
+ INFO, absl::StrCat("Restore saved value of ", flag->Name(), ": ",
+ Unparse(src.marshalling_op, src.current)));
+ }
+ }
+ }
+
+ private:
+ struct SavedFlag {
+ absl::string_view name;
+ FlagOpFn op;
+ FlagMarshallingOpFn marshalling_op;
+ int64_t counter;
+ bool modified;
+ bool on_command_line;
+ bool (*validator)();
+ const void* current; // nullptr after restore
+ const void* default_value; // nullptr after restore
+ };
+
+ std::vector<SavedFlag> backup_registry_;
+
+ FlagSaverImpl(const FlagSaverImpl&); // no copying!
+ void operator=(const FlagSaverImpl&);
+};
+
+FlagSaver::FlagSaver() : impl_(new FlagSaverImpl()) {
+ impl_->SaveFromRegistry();
+}
+
+void FlagSaver::Ignore() {
+ delete impl_;
+ impl_ = nullptr;
+}
+
+FlagSaver::~FlagSaver() {
+ if (!impl_) return;
+
+ impl_->RestoreToRegistry();
+ delete impl_;
+}
+
+// --------------------------------------------------------------------
+// GetAllFlags()
+// The main way the FlagRegistry class exposes its data. This
+// returns, as strings, all the info about all the flags in
+// the main registry, sorted first by filename they are defined
+// in, and then by flagname.
+// --------------------------------------------------------------------
+
+struct FilenameFlagnameLess {
+ bool operator()(const CommandLineFlagInfo& a,
+ const CommandLineFlagInfo& b) const {
+ int cmp = absl::string_view(a.filename).compare(b.filename);
+ if (cmp != 0) return cmp < 0;
+ return a.name < b.name;
+ }
+};
+
+void FillCommandLineFlagInfo(CommandLineFlag* flag,
+ CommandLineFlagInfo* result) {
+ result->name = std::string(flag->Name());
+ result->type = std::string(flag->Typename());
+ result->description = flag->Help();
+ result->filename = flag->Filename();
+
+ UpdateModifiedBit(flag);
+
+ absl::MutexLock l(InitFlagIfNecessary(flag));
+ result->current_value = flag->CurrentValue();
+ result->default_value = flag->DefaultValue();
+ result->is_default = !flag->modified;
+ result->has_validator_fn = (flag->validator != nullptr);
+ result->flag_ptr = flag->IsAbseilFlag() ? nullptr : flag->cur;
+}
+
+// --------------------------------------------------------------------
+
+CommandLineFlag* FindCommandLineFlag(absl::string_view name) {
+ if (name.empty()) return nullptr;
+ FlagRegistry* const registry = FlagRegistry::GlobalRegistry();
+ FlagRegistryLock frl(registry);
+
+ return registry->FindFlagLocked(name);
+}
+
+CommandLineFlag* FindCommandLineV1Flag(const void* flag_ptr) {
+ FlagRegistry* const registry = FlagRegistry::GlobalRegistry();
+ FlagRegistryLock frl(registry);
+
+ return registry->FindFlagViaPtrLocked(flag_ptr);
+}
+
+CommandLineFlag* FindRetiredFlag(absl::string_view name) {
+ FlagRegistry* const registry = FlagRegistry::GlobalRegistry();
+ FlagRegistryLock frl(registry);
+
+ return registry->FindRetiredFlagLocked(name);
+}
+
+// --------------------------------------------------------------------
+
+void ForEachFlagUnlocked(std::function<void(CommandLineFlag*)> visitor) {
+ FlagRegistry* const registry = FlagRegistry::GlobalRegistry();
+ for (FlagRegistry::FlagConstIterator i = registry->flags_.begin();
+ i != registry->flags_.end(); ++i) {
+ visitor(i->second);
+ }
+}
+
+void ForEachFlag(std::function<void(CommandLineFlag*)> visitor) {
+ FlagRegistry* const registry = FlagRegistry::GlobalRegistry();
+ FlagRegistryLock frl(registry);
+ ForEachFlagUnlocked(visitor);
+}
+
+// --------------------------------------------------------------------
+
+void GetAllFlags(std::vector<CommandLineFlagInfo>* OUTPUT) {
+ flags_internal::ForEachFlag([&](CommandLineFlag* flag) {
+ if (flag->IsRetired()) return;
+
+ CommandLineFlagInfo fi;
+ FillCommandLineFlagInfo(flag, &fi);
+ OUTPUT->push_back(fi);
+ });
+
+ // Now sort the flags, first by filename they occur in, then alphabetically
+ std::sort(OUTPUT->begin(), OUTPUT->end(), FilenameFlagnameLess());
+}
+
+// --------------------------------------------------------------------
+
+bool RegisterCommandLineFlag(CommandLineFlag* flag, const void* ptr) {
+ FlagRegistry::GlobalRegistry()->RegisterFlag(flag, ptr);
+ return true;
+}
+
+// --------------------------------------------------------------------
+
+bool Retire(FlagOpFn ops, FlagMarshallingOpFn marshalling_ops,
+ const char* name) {
+ auto* flag = new CommandLineFlag(
+ name,
+ /*help_text=*/absl::flags_internal::HelpText::FromStaticCString(nullptr),
+ /*filename_arg=*/"RETIRED", ops, marshalling_ops,
+ /*initial_value_gen=*/nullptr,
+ /*retired_arg=*/true, nullptr, nullptr);
+ FlagRegistry::GlobalRegistry()->RegisterFlag(flag, nullptr);
+ return true;
+}
+
+// --------------------------------------------------------------------
+
+bool IsRetiredFlag(absl::string_view name, bool* type_is_bool) {
+ assert(!name.empty());
+ CommandLineFlag* flag = flags_internal::FindRetiredFlag(name);
+ if (flag == nullptr) {
+ return false;
+ }
+ assert(type_is_bool);
+ *type_is_bool = flag->IsOfType<bool>();
+ return true;
+}
+
+} // namespace flags_internal
+} // namespace absl