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-rw-r--r--absl/flags/internal/commandlineflag.h187
1 files changed, 64 insertions, 123 deletions
diff --git a/absl/flags/internal/commandlineflag.h b/absl/flags/internal/commandlineflag.h
index 528d3106..13a3352e 100644
--- a/absl/flags/internal/commandlineflag.h
+++ b/absl/flags/internal/commandlineflag.h
@@ -16,12 +16,10 @@
#ifndef ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
#define ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
-#include <atomic>
#include <memory>
#include "absl/base/macros.h"
#include "absl/flags/marshalling.h"
-#include "absl/synchronization/mutex.h"
#include "absl/types/optional.h"
namespace absl {
@@ -151,14 +149,6 @@ inline size_t Sizeof(FlagOpFn op) {
op(flags_internal::kSizeof, nullptr, nullptr)));
}
-// The following struct contains the locks in a CommandLineFlag struct.
-// They are in a separate struct that is lazily allocated to avoid problems
-// with static initialization and to avoid multiple allocations.
-struct CommandLineFlagLocks {
- absl::Mutex primary_mu; // protects several fields in CommandLineFlag
- absl::Mutex callback_mu; // used to serialize callbacks
-};
-
// Holds either a pointer to help text or a function which produces it. This is
// needed for supporting both static initialization of Flags while supporting
// the legacy registration framework. We can't use absl::variant<const char*,
@@ -200,25 +190,9 @@ class FlagStateInterface {
// Holds all information for a flag.
class CommandLineFlag {
public:
- constexpr CommandLineFlag(
- const char* name, HelpText help_text, const char* filename,
- const flags_internal::FlagOpFn op,
- const flags_internal::FlagMarshallingOpFn marshalling_op,
- const flags_internal::InitialValGenFunc initial_value_gen, void* def,
- void* cur)
- : name_(name),
- help_(help_text),
- filename_(filename),
- op_(op),
- marshalling_op_(marshalling_op),
- make_init_value_(initial_value_gen),
- inited_(false),
- modified_(false),
- on_command_line_(false),
- def_(def),
- cur_(cur),
- counter_(0),
- locks_(nullptr) {}
+ constexpr CommandLineFlag(const char* name, HelpText help_text,
+ const char* filename)
+ : name_(name), help_(help_text), filename_(filename) {}
// Virtual destructor
virtual void Destroy() const = 0;
@@ -227,60 +201,73 @@ class CommandLineFlag {
CommandLineFlag(const CommandLineFlag&) = delete;
CommandLineFlag& operator=(const CommandLineFlag&) = delete;
- // Access methods.
-
- // Returns true iff this object corresponds to retired flag
- virtual bool IsRetired() const { return false; }
- // Returns true iff this is a handle to an Abseil Flag.
- virtual bool IsAbseilFlag() const { return true; }
-
+ // Non-polymorphic access methods.
absl::string_view Name() const { return name_; }
std::string Help() const { return help_.GetHelpText(); }
- bool IsModified() const;
- void SetModified(bool is_modified);
- bool IsSpecifiedOnCommandLine() const;
-
absl::string_view Typename() const;
std::string Filename() const;
- std::string DefaultValue() const;
- std::string CurrentValue() const;
-
- // Interface to store the value in atomic if one used. This is short term
- // interface. To be reworked once cur_ is moved.
- virtual void StoreAtomic() {}
-
- // Interfaces to operate on validators.
- virtual bool InvokeValidator(const void* /*value*/) const { return true; }
- // Invoke the flag validators for old flags.
- // TODO(rogeeff): implement proper validators for Abseil Flags
- bool ValidateDefaultValue() const;
- bool ValidateInputValue(absl::string_view value) const;
// Return true iff flag has type T.
template <typename T>
inline bool IsOfType() const {
- return op_ == &flags_internal::FlagOps<T>;
+ return TypeId() == &flags_internal::FlagOps<T>;
}
// Attempts to retrieve the flag value. Returns value on success,
// absl::nullopt otherwise.
template <typename T>
absl::optional<T> Get() const {
- if (IsRetired() || flags_internal::FlagOps<T> != op_) return absl::nullopt;
-
- T res;
- Read(&res, flags_internal::FlagOps<T>);
+ if (IsRetired() || !IsOfType<T>()) {
+ return absl::nullopt;
+ }
- return res;
+ // Implementation notes:
+ //
+ // We are wrapping a union around the value of `T` to serve three purposes:
+ //
+ // 1. `U.value` has correct size and alignment for a value of type `T`
+ // 2. The `U.value` constructor is not invoked since U's constructor does
+ // not
+ // do it explicitly.
+ // 3. The `U.value` destructor is invoked since U's destructor does it
+ // explicitly. This makes `U` a kind of RAII wrapper around non default
+ // constructible value of T, which is destructed when we leave the
+ // scope. We do need to destroy U.value, which is constructed by
+ // CommandLineFlag::Read even though we left it in a moved-from state
+ // after std::move.
+ //
+ // All of this serves to avoid requiring `T` being default constructible.
+ union U {
+ T value;
+ U() {}
+ ~U() { value.~T(); }
+ };
+ U u;
+
+ Read(&u.value);
+ return std::move(u.value);
}
+ // Polymorphic access methods
+
+ // Returns true iff this object corresponds to retired flag
+ virtual bool IsRetired() const { return false; }
+ // Returns true iff this is a handle to an Abseil Flag.
+ virtual bool IsAbseilFlag() const { return true; }
+ // Returns id of the flag's value type.
+ virtual flags_internal::FlagOpFn TypeId() const = 0;
+ virtual bool IsModified() const = 0;
+ virtual bool IsSpecifiedOnCommandLine() const = 0;
+ virtual std::string DefaultValue() const = 0;
+ virtual std::string CurrentValue() const = 0;
+
+ // Interfaces to operate on validators.
+ virtual bool ValidateInputValue(absl::string_view value) const = 0;
+
// Interface to save flag to some persistent state. Returns current flag state
// or nullptr if flag does not support saving and restoring a state.
virtual std::unique_ptr<FlagStateInterface> SaveState() = 0;
- // Interfaces to overate on callbacks.
- virtual void InvokeCallback() {}
-
// Sets the value of the flag based on specified std::string `value`. If the flag
// was successfully set to new value, it returns true. Otherwise, sets `error`
// to indicate the error, leaves the flag unchanged, and returns false. There
@@ -289,74 +276,28 @@ class CommandLineFlag {
// * 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 SetFromString(absl::string_view value,
- flags_internal::FlagSettingMode set_mode,
- flags_internal::ValueSource source, std::string* error);
+ virtual bool SetFromString(absl::string_view value,
+ flags_internal::FlagSettingMode set_mode,
+ flags_internal::ValueSource source,
+ std::string* error) = 0;
- void CheckDefaultValueParsingRoundtrip() const;
+ // Checks that flags default value can be converted to std::string and back to the
+ // flag's value type.
+ virtual void CheckDefaultValueParsingRoundtrip() const = 0;
// Constant configuration for a particular flag.
protected:
~CommandLineFlag() = default;
- // Thread safe access to mutation counter.
- int64_t MutationCounter() const;
-
- const char* const name_;
- const HelpText help_;
- const char* const filename_;
-
- const FlagOpFn op_; // Type-specific handler
- const FlagMarshallingOpFn marshalling_op_; // Marshalling ops handler
- const InitialValGenFunc make_init_value_; // Makes initial value for the flag
- std::atomic<bool> inited_; // fields have been lazily initialized
-
- // Mutable state (guarded by locks_->primary_mu).
- bool modified_; // Has flag value been modified?
- bool on_command_line_; // Specified on command line.
- void* def_; // Lazily initialized pointer to default value
- void* cur_; // Lazily initialized pointer to current value
- int64_t counter_; // Mutation counter
-
- // Lazily initialized mutexes for this flag value. We cannot inline a
- // SpinLock or Mutex here because those have non-constexpr constructors and
- // so would prevent constant initialization of this type.
- // TODO(rogeeff): fix it once Mutex has constexpr constructor
- struct CommandLineFlagLocks* locks_; // locks, laziliy allocated.
-
- // Ensure that the lazily initialized fields of *flag have been initialized,
- // and return the lock which should be locked when flag's state is mutated.
- absl::Mutex* InitFlagIfNecessary() const ABSL_LOCK_RETURNED(locks_->primary_mu);
-
- // copy construct new value of flag's type in a memory referenced by dst
- // based on current flag's value
- void Read(void* dst, const flags_internal::FlagOpFn dst_op) const;
- // updates flag's value to *src (locked)
- void Write(const void* src, const flags_internal::FlagOpFn src_op);
-
- friend class FlagRegistry;
- friend class FlagPtrMap;
- friend class FlagSaverImpl;
- friend bool TryParseLocked(CommandLineFlag* flag, void* dst,
- absl::string_view value, std::string* err);
- friend absl::Mutex* InitFlag(CommandLineFlag* flag);
-};
+ const char* const name_; // Flags name passed to ABSL_FLAG as second arg.
+ const HelpText help_; // The function generating help message.
+ const char* const filename_; // The file name where ABSL_FLAG resides.
-// Update any copy of the flag value that is stored in an atomic word.
-// In addition if flag has a mutation callback this function invokes it. While
-// 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.
-void UpdateCopy(CommandLineFlag* flag);
-// Return true iff flag value was changed via direct-access.
-bool ChangedDirectly(CommandLineFlag* flag, const void* a, const void* b);
+ private:
+ // Copy-construct a new value of the flag's type in a memory referenced by
+ // the dst based on the current flag's value.
+ virtual void Read(void* dst) const = 0;
+};
// This macro is the "source of truth" for the list of supported flag types we
// expect to perform lock free operations on. Specifically it generates code,