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//
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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 "absl/base/optimization.h"
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#include "absl/synchronization/mutex.h"
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namespace absl {
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namespace flags_internal {
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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(const CommandLineFlag& flag) {
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#define DONT_VALIDATE(T) \
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if (flag.IsOfType<T>()) return false;
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ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(DONT_VALIDATE)
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DONT_VALIDATE(std::string)
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DONT_VALIDATE(std::vector<std::string>)
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#undef DONT_VALIDATE
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return true;
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}
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} // namespace
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void FlagImpl::Init() {
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ABSL_CONST_INIT static absl::Mutex init_lock(absl::kConstInit);
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{
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absl::MutexLock lock(&init_lock);
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if (locks_ == nullptr) { // Must initialize Mutexes for this flag.
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locks_ = new FlagImpl::CommandLineFlagLocks;
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}
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}
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absl::MutexLock lock(&locks_->primary_mu);
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if (def_ != nullptr) {
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inited_.store(true, std::memory_order_release);
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} else {
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// Need to initialize def and cur fields.
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def_ = (*initial_value_gen_)();
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cur_ = Clone(op_, def_);
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StoreAtomic();
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inited_.store(true, std::memory_order_release);
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InvokeCallback();
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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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ABSL_LOCK_RETURNED(locks_->primary_mu) {
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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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// All fields initialized; locks_ is therefore safe to read.
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return &locks_->primary_mu;
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}
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void FlagImpl::Destroy() const {
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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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if (def_) Delete(op_, def_);
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}
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delete locks_;
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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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return Unparse(marshalling_op_, def_);
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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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callback_ = mutation_callback;
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InvokeCallback();
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}
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void FlagImpl::InvokeCallback() const
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ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu) {
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if (!callback_) return;
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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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DataGuard()->Unlock();
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{
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absl::MutexLock lock(&locks_->callback_mu);
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callback_();
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}
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DataGuard()->Lock();
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}
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bool FlagImpl::RestoreState(const CommandLineFlag& flag, const void* value,
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bool modified, bool on_command_line,
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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(flag, 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 stores the parsed value in
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// 'dst' assuming it is a pointer to the flag's value type. In case if any error
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// is encountered in either step, the error message is stored in 'err'
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bool FlagImpl::TryParse(const CommandLineFlag& flag, void* dst,
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absl::string_view value, std::string* err) const
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ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu) {
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void* tentative_value = Clone(op_, def_);
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std::string parse_err;
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if (!Parse(marshalling_op_, value, tentative_value, &parse_err)) {
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auto type_name = flag.Typename();
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absl::string_view err_sep = parse_err.empty() ? "" : "; ";
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absl::string_view typename_sep = type_name.empty() ? "" : " ";
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*err = absl::StrCat("Illegal value '", value, "' specified for",
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typename_sep, type_name, " flag '", flag.Name(), "'",
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err_sep, parse_err);
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Delete(op_, tentative_value);
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return false;
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}
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Copy(op_, tentative_value, dst);
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Delete(op_, tentative_value);
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return true;
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}
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void FlagImpl::Read(const CommandLineFlag& flag, void* dst,
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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 '", 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() ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu) {
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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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atomic_.store(t, std::memory_order_release);
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}
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}
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void FlagImpl::Write(const CommandLineFlag& flag, const void* src,
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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 '", 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(flag)) {
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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,
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absl::StrCat("Attempt to set flag '", 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(const CommandLineFlag& flag,
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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(flag, 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(flag, 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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// modify the flag's default-value
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if (!TryParse(flag, def_, value, err)) return false;
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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_, def_, 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(
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const CommandLineFlag& flag) const {
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std::string v = DefaultValue();
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absl::MutexLock lock(DataGuard());
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void* dst = Clone(op_, def_);
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std::string error;
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if (!flags_internal::Parse(marshalling_op_, v, dst, &error)) {
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ABSL_INTERNAL_LOG(
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FATAL,
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absl::StrCat("Flag ", flag.Name(), " (from ", flag.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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Delete(op_, dst);
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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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void* obj = Clone(op_, def_);
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std::string ignored_error;
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const bool result =
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flags_internal::Parse(marshalling_op_, value, obj, &ignored_error);
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Delete(op_, obj);
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return result;
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}
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} // namespace flags_internal
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} // namespace absl
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