Abseil Common Libraries (C++) (grcp 依赖)
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425 lines
13 KiB
425 lines
13 KiB
// |
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// Copyright 2019 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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#include "absl/flags/internal/flag.h" |
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#include <stddef.h> |
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#include <stdint.h> |
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#include <string.h> |
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#include <atomic> |
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#include <memory> |
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#include <string> |
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#include <vector> |
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#include "absl/base/attributes.h" |
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#include "absl/base/config.h" |
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#include "absl/base/const_init.h" |
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#include "absl/base/optimization.h" |
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#include "absl/flags/internal/commandlineflag.h" |
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#include "absl/flags/usage_config.h" |
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#include "absl/strings/str_cat.h" |
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#include "absl/strings/string_view.h" |
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#include "absl/synchronization/mutex.h" |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace flags_internal { |
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// The help message indicating that the commandline flag has been |
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// 'stripped'. It will not show up when doing "-help" and its |
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// variants. The flag is stripped if ABSL_FLAGS_STRIP_HELP is set to 1 |
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// before including absl/flags/flag.h |
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const char kStrippedFlagHelp[] = "\001\002\003\004 (unknown) \004\003\002\001"; |
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namespace { |
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// Currently we only validate flag values for user-defined flag types. |
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bool ShouldValidateFlagValue(FlagOpFn flag_type_id) { |
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#define DONT_VALIDATE(T) \ |
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if (flag_type_id == &flags_internal::FlagOps<T>) return false; |
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ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(DONT_VALIDATE) |
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#undef DONT_VALIDATE |
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return true; |
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} |
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// RAII helper used to temporarily unlock and relock `absl::Mutex`. |
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// This is used when we need to ensure that locks are released while |
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// invoking user supplied callbacks and then reacquired, since callbacks may |
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// need to acquire these locks themselves. |
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class MutexRelock { |
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public: |
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explicit MutexRelock(absl::Mutex* mu) : mu_(mu) { mu_->Unlock(); } |
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~MutexRelock() { mu_->Lock(); } |
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MutexRelock(const MutexRelock&) = delete; |
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MutexRelock& operator=(const MutexRelock&) = delete; |
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private: |
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absl::Mutex* mu_; |
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}; |
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// This global lock guards the initialization and destruction of data_guard_, |
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// which is used to guard the other Flag data. |
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ABSL_CONST_INIT static absl::Mutex flag_mutex_lifetime_guard(absl::kConstInit); |
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} // namespace |
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void FlagImpl::Init() { |
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{ |
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absl::MutexLock lock(&flag_mutex_lifetime_guard); |
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// Must initialize data guard for this flag. |
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if (!is_data_guard_inited_) { |
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new (&data_guard_) absl::Mutex; |
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is_data_guard_inited_ = true; |
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} |
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} |
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absl::MutexLock lock(reinterpret_cast<absl::Mutex*>(&data_guard_)); |
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if (cur_ != nullptr) { |
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inited_.store(true, std::memory_order_release); |
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} else { |
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// Need to initialize cur field. |
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cur_ = MakeInitValue().release(); |
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StoreAtomic(); |
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inited_.store(true, std::memory_order_release); |
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} |
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} |
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// Ensures that the lazily initialized data is initialized, |
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// and returns pointer to the mutex guarding flags data. |
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absl::Mutex* FlagImpl::DataGuard() const { |
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if (ABSL_PREDICT_FALSE(!inited_.load(std::memory_order_acquire))) { |
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const_cast<FlagImpl*>(this)->Init(); |
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} |
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// data_guard_ is initialized. |
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return reinterpret_cast<absl::Mutex*>(&data_guard_); |
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} |
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void FlagImpl::Destroy() { |
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{ |
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absl::MutexLock l(DataGuard()); |
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// Values are heap allocated for Abseil Flags. |
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if (cur_) Delete(op_, cur_); |
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// Release the dynamically allocated default value if any. |
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if (def_kind_ == FlagDefaultSrcKind::kDynamicValue) { |
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Delete(op_, default_src_.dynamic_value); |
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} |
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// If this flag has an assigned callback, release callback data. |
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if (callback_data_) delete callback_data_; |
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} |
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absl::MutexLock l(&flag_mutex_lifetime_guard); |
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DataGuard()->~Mutex(); |
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is_data_guard_inited_ = false; |
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} |
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std::unique_ptr<void, DynValueDeleter> FlagImpl::MakeInitValue() const { |
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void* res = nullptr; |
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if (def_kind_ == FlagDefaultSrcKind::kDynamicValue) { |
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res = Clone(op_, default_src_.dynamic_value); |
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} else { |
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res = (*default_src_.gen_func)(); |
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} |
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return {res, DynValueDeleter{op_}}; |
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} |
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absl::string_view FlagImpl::Name() const { return name_; } |
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std::string FlagImpl::Filename() const { |
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return flags_internal::GetUsageConfig().normalize_filename(filename_); |
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} |
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std::string FlagImpl::Help() const { |
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return help_source_kind_ == FlagHelpSrcKind::kLiteral ? help_.literal |
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: help_.gen_func(); |
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} |
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bool FlagImpl::IsModified() const { |
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absl::MutexLock l(DataGuard()); |
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return modified_; |
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} |
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bool FlagImpl::IsSpecifiedOnCommandLine() const { |
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absl::MutexLock l(DataGuard()); |
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return on_command_line_; |
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} |
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std::string FlagImpl::DefaultValue() const { |
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absl::MutexLock l(DataGuard()); |
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auto obj = MakeInitValue(); |
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return Unparse(marshalling_op_, obj.get()); |
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} |
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std::string FlagImpl::CurrentValue() const { |
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absl::MutexLock l(DataGuard()); |
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return Unparse(marshalling_op_, cur_); |
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} |
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void FlagImpl::SetCallback( |
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const flags_internal::FlagCallback mutation_callback) { |
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absl::MutexLock l(DataGuard()); |
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if (callback_data_ == nullptr) { |
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callback_data_ = new CallbackData; |
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} |
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callback_data_->func = mutation_callback; |
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InvokeCallback(); |
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} |
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void FlagImpl::InvokeCallback() const { |
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if (!callback_data_) return; |
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// Make a copy of the C-style function pointer that we are about to invoke |
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// before we release the lock guarding it. |
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FlagCallback cb = callback_data_->func; |
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// If the flag has a mutation callback this function invokes it. While the |
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// callback is being invoked the primary flag's mutex is unlocked and it is |
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// re-locked back after call to callback is completed. Callback invocation is |
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// guarded by flag's secondary mutex instead which prevents concurrent |
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// callback invocation. Note that it is possible for other thread to grab the |
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// primary lock and update flag's value at any time during the callback |
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// invocation. This is by design. Callback can get a value of the flag if |
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// necessary, but it might be different from the value initiated the callback |
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// and it also can be different by the time the callback invocation is |
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// completed. Requires that *primary_lock be held in exclusive mode; it may be |
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// released and reacquired by the implementation. |
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MutexRelock relock(DataGuard()); |
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absl::MutexLock lock(&callback_data_->guard); |
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cb(); |
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} |
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bool FlagImpl::RestoreState(const void* value, bool modified, |
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bool on_command_line, int64_t counter) { |
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{ |
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absl::MutexLock l(DataGuard()); |
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if (counter_ == counter) return false; |
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} |
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Write(value, op_); |
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{ |
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absl::MutexLock l(DataGuard()); |
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modified_ = modified; |
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on_command_line_ = on_command_line; |
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} |
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return true; |
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} |
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// Attempts to parse supplied `value` string using parsing routine in the `flag` |
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// argument. If parsing successful, this function replaces the dst with newly |
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// parsed value. In case if any error is encountered in either step, the error |
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// message is stored in 'err' |
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bool FlagImpl::TryParse(void** dst, absl::string_view value, |
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std::string* err) const { |
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auto tentative_value = MakeInitValue(); |
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std::string parse_err; |
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if (!Parse(marshalling_op_, value, tentative_value.get(), &parse_err)) { |
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absl::string_view err_sep = parse_err.empty() ? "" : "; "; |
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*err = absl::StrCat("Illegal value '", value, "' specified for flag '", |
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Name(), "'", err_sep, parse_err); |
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return false; |
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} |
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void* old_val = *dst; |
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*dst = tentative_value.release(); |
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tentative_value.reset(old_val); |
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return true; |
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} |
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void FlagImpl::Read(void* dst, const flags_internal::FlagOpFn dst_op) const { |
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absl::ReaderMutexLock l(DataGuard()); |
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// `dst_op` is the unmarshaling operation corresponding to the declaration |
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// visibile at the call site. `op` is the Flag's defined unmarshalling |
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// operation. They must match for this operation to be well-defined. |
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if (ABSL_PREDICT_FALSE(dst_op != op_)) { |
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ABSL_INTERNAL_LOG( |
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ERROR, |
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absl::StrCat("Flag '", Name(), |
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"' is defined as one type and declared as another")); |
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} |
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CopyConstruct(op_, cur_, dst); |
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} |
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void FlagImpl::StoreAtomic() { |
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size_t data_size = Sizeof(op_); |
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if (data_size <= sizeof(int64_t)) { |
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int64_t t = 0; |
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std::memcpy(&t, cur_, data_size); |
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atomics_.small_atomic.store(t, std::memory_order_release); |
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} |
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#if defined(ABSL_FLAGS_INTERNAL_ATOMIC_DOUBLE_WORD) |
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else if (data_size <= sizeof(FlagsInternalTwoWordsType)) { |
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FlagsInternalTwoWordsType t{0, 0}; |
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std::memcpy(&t, cur_, data_size); |
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atomics_.big_atomic.store(t, std::memory_order_release); |
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} |
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#endif |
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} |
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void FlagImpl::Write(const void* src, const flags_internal::FlagOpFn src_op) { |
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absl::MutexLock l(DataGuard()); |
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// `src_op` is the marshalling operation corresponding to the declaration |
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// visible at the call site. `op` is the Flag's defined marshalling operation. |
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// They must match for this operation to be well-defined. |
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if (ABSL_PREDICT_FALSE(src_op != op_)) { |
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ABSL_INTERNAL_LOG( |
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ERROR, |
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absl::StrCat("Flag '", Name(), |
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"' is defined as one type and declared as another")); |
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} |
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if (ShouldValidateFlagValue(op_)) { |
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void* obj = Clone(op_, src); |
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std::string ignored_error; |
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std::string src_as_str = Unparse(marshalling_op_, src); |
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if (!Parse(marshalling_op_, src_as_str, obj, &ignored_error)) { |
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ABSL_INTERNAL_LOG(ERROR, absl::StrCat("Attempt to set flag '", Name(), |
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"' to invalid value ", src_as_str)); |
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} |
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Delete(op_, obj); |
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} |
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modified_ = true; |
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counter_++; |
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Copy(op_, src, cur_); |
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StoreAtomic(); |
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InvokeCallback(); |
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} |
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// Sets the value of the flag based on specified string `value`. If the flag |
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// was successfully set to new value, it returns true. Otherwise, sets `err` |
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// to indicate the error, leaves the flag unchanged, and returns false. There |
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// are three ways to set the flag's value: |
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// * Update the current flag value |
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// * Update the flag's default value |
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// * Update the current flag value if it was never set before |
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// The mode is selected based on 'set_mode' parameter. |
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bool FlagImpl::SetFromString(absl::string_view value, FlagSettingMode set_mode, |
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ValueSource source, std::string* err) { |
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absl::MutexLock l(DataGuard()); |
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switch (set_mode) { |
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case SET_FLAGS_VALUE: { |
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// set or modify the flag's value |
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if (!TryParse(&cur_, value, err)) return false; |
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modified_ = true; |
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counter_++; |
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StoreAtomic(); |
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InvokeCallback(); |
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if (source == kCommandLine) { |
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on_command_line_ = true; |
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} |
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break; |
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} |
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case SET_FLAG_IF_DEFAULT: { |
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// set the flag's value, but only if it hasn't been set by someone else |
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if (!modified_) { |
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if (!TryParse(&cur_, value, err)) return false; |
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modified_ = true; |
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counter_++; |
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StoreAtomic(); |
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InvokeCallback(); |
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} else { |
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// TODO(rogeeff): review and fix this semantic. Currently we do not fail |
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// in this case if flag is modified. This is misleading since the flag's |
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// value is not updated even though we return true. |
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// *err = absl::StrCat(Name(), " is already set to ", |
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// CurrentValue(), "\n"); |
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// return false; |
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return true; |
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} |
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break; |
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} |
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case SET_FLAGS_DEFAULT: { |
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if (def_kind_ == FlagDefaultSrcKind::kDynamicValue) { |
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if (!TryParse(&default_src_.dynamic_value, value, err)) { |
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return false; |
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} |
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} else { |
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void* new_default_val = nullptr; |
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if (!TryParse(&new_default_val, value, err)) { |
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return false; |
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} |
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default_src_.dynamic_value = new_default_val; |
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def_kind_ = FlagDefaultSrcKind::kDynamicValue; |
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} |
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if (!modified_) { |
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// Need to set both default value *and* current, in this case |
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Copy(op_, default_src_.dynamic_value, cur_); |
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StoreAtomic(); |
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InvokeCallback(); |
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} |
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break; |
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} |
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} |
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return true; |
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} |
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void FlagImpl::CheckDefaultValueParsingRoundtrip() const { |
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std::string v = DefaultValue(); |
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absl::MutexLock lock(DataGuard()); |
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auto dst = MakeInitValue(); |
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std::string error; |
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if (!flags_internal::Parse(marshalling_op_, v, dst.get(), &error)) { |
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ABSL_INTERNAL_LOG( |
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FATAL, |
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absl::StrCat("Flag ", Name(), " (from ", Filename(), |
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"): std::string form of default value '", v, |
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"' could not be parsed; error=", error)); |
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} |
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// We do not compare dst to def since parsing/unparsing may make |
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// small changes, e.g., precision loss for floating point types. |
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} |
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bool FlagImpl::ValidateInputValue(absl::string_view value) const { |
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absl::MutexLock l(DataGuard()); |
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auto obj = MakeInitValue(); |
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std::string ignored_error; |
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return flags_internal::Parse(marshalling_op_, value, obj.get(), |
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&ignored_error); |
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} |
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} // namespace flags_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl
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