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