tvl-depot/absl/flags/internal/registry.cc
Abseil Team aa468ad755 Export of internal Abseil changes.
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78293ba4eb4981991ae7e6edd25eb9245fcd7515 by Andy Soffer <asoffer@google.com>:

internal changes

PiperOrigin-RevId: 247073879

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7bd97e3aad0c3012b89a39392a6ad3f254e9f3c3 by Derek Mauro <dmauro@google.com>:

Release commandline flags

PiperOrigin-RevId: 247065920

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2a991849fd7b140a43b073076d194b61533fd199 by Tom Manshreck <shreck@google.com>:

Add documentation for built-in usage flags

PiperOrigin-RevId: 247058863

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14157b0de45841706bbd631284191fd94c313db9 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 247058292

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ed67e0a80468596e30540b367727a250fa415b68 by Abseil Team <absl-team@google.com>:

Internal Change.

PiperOrigin-RevId: 246828655

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e1bc8c2aa3f90b3d56c55c5b7244e718c919265d by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 246822325

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907a68f287199f749cb9bdb48571b50bc34731e1 by Eric Fiselier <ericwf@google.com>:

Accept vector<bool>::reference in StrCat and friends.

Converting vector<bool>::reference to alphanum requires
two user defined conversions, which isn't allowed.
In order to accept this, we need a special constructor that
is only enabled for the bool proxy types.

PiperOrigin-RevId: 246626732

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fe4295fa95cc65dee8c881ba12dd8f516e68c40d by Abseil Team <absl-team@google.com>:

Clarify the proper way to define AbslHashValue, and fix confusing indentation.

PiperOrigin-RevId: 246406528

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d7174681a72d4a25c8fd2b4d9f515a0763eff87c by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 246358214

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a7fdc19683cf1a5885e9e1af52fcdb2db1eda53b by Abseil Team <absl-team@google.com>:

Fix sample template instantiation.

PiperOrigin-RevId: 246354617

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29a23c6835f872948d09b24d890385bf195bc995 by Abseil Team <absl-team@google.com>:

Fix incorrectly copy-pasted static_assert in absl::optional::value_or

The static_assert for a move-constructible type previously said the type must be copy-constructible.

PiperOrigin-RevId: 246313827

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41884d5872d4ea2c67875b00144b8c8a5859a295 by Greg Falcon <gfalcon@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 245418790

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7f90a7f94cdd5e21232c749efe952a750b5c43a2 by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 245412658

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730a329cf047d54b46971fce1781edd857208c2a by Greg Falcon <gfalcon@google.com>:

internal change

PiperOrigin-RevId: 245293234

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cf0216be6338200cbb18167d3f3b2e98e372be77 by Greg Falcon <gfalcon@google.com>:

Internal change

PiperOrigin-RevId: 245288164
GitOrigin-RevId: 78293ba4eb4981991ae7e6edd25eb9245fcd7515
Change-Id: I5ea9a852c36c722bae2d6be65fb7f72473d94ab6
2019-05-07 16:32:35 -04:00

529 lines
18 KiB
C++

//
// 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