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![Ryan Macnak](/assets/img/avatar_default.png)
TEST=local build Change-Id: I9503dfbb1b9ba6ef2b5fb8423c13d5066e5af98b Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/206140 Commit-Queue: Ryan Macnak <rmacnak@google.com> Reviewed-by: Tess Strickland <sstrickl@google.com>
232 lines
7.8 KiB
C++
232 lines
7.8 KiB
C++
// Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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#ifndef RUNTIME_VM_BITFIELD_H_
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#define RUNTIME_VM_BITFIELD_H_
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#include <type_traits>
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#include "platform/atomic.h"
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#include "platform/globals.h"
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#include "platform/thread_sanitizer.h"
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namespace dart {
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class AtomicBitFieldContainerBase {
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private:
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AtomicBitFieldContainerBase() = delete; // Only used for std::is_base_of.
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};
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template <typename T>
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class AtomicBitFieldContainer : AtomicBitFieldContainerBase {
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static_assert(sizeof(std::atomic<T>) == sizeof(T),
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"Size of type changes when made atomic");
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public:
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using ContainedType = T;
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AtomicBitFieldContainer() : field_(0) {}
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operator T() const { return field_.load(std::memory_order_relaxed); }
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T operator=(T tags) {
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field_.store(tags, std::memory_order_relaxed);
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return tags;
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}
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T load(std::memory_order order) const { return field_.load(order); }
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void store(T value, std::memory_order order) { field_.store(value, order); }
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bool compare_exchange_weak(T old_tags, T new_tags, std::memory_order order) {
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return field_.compare_exchange_weak(old_tags, new_tags, order);
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}
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template <class TargetBitField,
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std::memory_order order = std::memory_order_relaxed>
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typename TargetBitField::Type Read() const {
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return TargetBitField::decode(field_.load(order));
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}
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template <class TargetBitField>
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NO_SANITIZE_THREAD typename TargetBitField::Type ReadIgnoreRace() const {
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return TargetBitField::decode(*reinterpret_cast<const T*>(&field_));
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}
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template <class TargetBitField,
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std::memory_order order = std::memory_order_relaxed>
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void UpdateBool(bool value) {
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if (value) {
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field_.fetch_or(TargetBitField::encode(true), order);
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} else {
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field_.fetch_and(~TargetBitField::encode(true), order);
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}
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}
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template <class TargetBitField>
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void FetchOr(typename TargetBitField::Type value) {
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field_.fetch_or(TargetBitField::encode(value), std::memory_order_relaxed);
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}
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template <class TargetBitField>
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void Update(typename TargetBitField::Type value) {
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T old_field = field_.load(std::memory_order_relaxed);
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T new_field;
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do {
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new_field = TargetBitField::update(value, old_field);
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} while (!field_.compare_exchange_weak(old_field, new_field,
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std::memory_order_relaxed));
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}
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template <class TargetBitField>
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void UpdateUnsynchronized(typename TargetBitField::Type value) {
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field_.store(
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TargetBitField::update(value, field_.load(std::memory_order_relaxed)),
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std::memory_order_relaxed);
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}
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template <class TargetBitField>
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typename TargetBitField::Type UpdateConditional(
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typename TargetBitField::Type value_to_be_set,
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typename TargetBitField::Type conditional_old_value) {
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T old_field = field_.load(std::memory_order_relaxed);
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while (true) {
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// This operation is only performed if the condition is met.
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auto old_value = TargetBitField::decode(old_field);
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if (old_value != conditional_old_value) {
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return old_value;
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}
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T new_tags = TargetBitField::update(value_to_be_set, old_field);
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if (field_.compare_exchange_weak(old_field, new_tags,
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std::memory_order_relaxed)) {
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return value_to_be_set;
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}
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// [old_tags] was updated to it's current value.
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}
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}
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template <class TargetBitField>
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bool TryAcquire() {
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T mask = TargetBitField::encode(true);
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T old_field = field_.fetch_or(mask, std::memory_order_relaxed);
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return !TargetBitField::decode(old_field);
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}
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template <class TargetBitField>
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bool TryClear() {
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T mask = ~TargetBitField::encode(true);
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T old_field = field_.fetch_and(mask, std::memory_order_relaxed);
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return TargetBitField::decode(old_field);
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}
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private:
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std::atomic<T> field_;
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};
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static const uword kUwordOne = 1U;
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// BitField is a template for encoding and decoding a value of type T
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// inside a storage of type S.
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template <typename S,
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typename T,
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int position,
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int size = (sizeof(S) * kBitsPerByte) - position,
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bool sign_extend = false,
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typename Enable = void>
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class BitField {
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public:
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typedef T Type;
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static_assert((sizeof(S) * kBitsPerByte) >= (position + size),
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"BitField does not fit into the type.");
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static_assert(!sign_extend || std::is_signed<T>::value,
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"Should only sign extend signed bitfield types");
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static const intptr_t kNextBit = position + size;
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// Tells whether the provided value fits into the bit field.
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static constexpr bool is_valid(T value) {
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return decode(encode_unchecked(value)) == value;
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}
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// Returns a S mask of the bit field.
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static constexpr S mask() { return (kUwordOne << size) - 1; }
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// Returns a S mask of the bit field which can be applied directly to
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// to the raw unshifted bits.
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static constexpr S mask_in_place() { return mask() << position; }
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// Returns the shift count needed to right-shift the bit field to
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// the least-significant bits.
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static constexpr int shift() { return position; }
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// Returns the size of the bit field.
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static constexpr int bitsize() { return size; }
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// Returns an S with the bit field value encoded.
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static constexpr S encode(T value) {
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assert(is_valid(value));
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return encode_unchecked(value);
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}
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// Extracts the bit field from the value.
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static constexpr T decode(S value) {
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// Ensure we slide down the sign bit if the value in the bit field is signed
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// and negative. We use 64-bit ints inside the expression since we can have
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// both cases: sizeof(S) > sizeof(T) or sizeof(S) < sizeof(T).
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if constexpr (sign_extend) {
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auto const u = static_cast<uint64_t>(value);
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return static_cast<T>((static_cast<int64_t>(u << (64 - kNextBit))) >>
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(64 - size));
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} else {
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auto const u = static_cast<typename std::make_unsigned<S>::type>(value);
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return static_cast<T>((u >> position) & mask());
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}
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}
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// Returns an S with the bit field value encoded based on the
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// original value. Only the bits corresponding to this bit field
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// will be changed.
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static constexpr S update(T value, S original) {
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return encode(value) | (~mask_in_place() & original);
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}
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private:
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// Returns an S with the bit field value encoded.
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static constexpr S encode_unchecked(T value) {
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auto const u = static_cast<typename std::make_unsigned<S>::type>(value);
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return (u & mask()) << position;
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}
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};
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// Partial instantiations to avoid having to change BitField declarations if
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// S is decltype(field_) and the type of field_ is changed to be wrapped in an
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// AtomicBitFieldContainer.
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template <typename S, typename T, int position, int size, bool sign_extend>
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class BitField<S,
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T,
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position,
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size,
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sign_extend,
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typename std::enable_if<
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std::is_base_of<AtomicBitFieldContainerBase, S>::value,
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void>::type> : public BitField<typename S::ContainedType,
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T,
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position,
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size,
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sign_extend> {};
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template <typename S, typename T, int position, int size>
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class BitField<S,
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T,
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position,
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size,
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false,
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typename std::enable_if<
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std::is_base_of<AtomicBitFieldContainerBase, S>::value,
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void>::type>
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: public BitField<typename S::ContainedType, T, position, size, false> {};
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} // namespace dart
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#endif // RUNTIME_VM_BITFIELD_H_
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