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679 lines
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679 lines
25 KiB
// Copyright 2021 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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#ifndef ABSL_STRINGS_INTERNAL_CORD_INTERNAL_H_ |
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#define ABSL_STRINGS_INTERNAL_CORD_INTERNAL_H_ |
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#include <atomic> |
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#include <cassert> |
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#include <cstddef> |
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#include <cstdint> |
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#include <type_traits> |
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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/internal/endian.h" |
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#include "absl/base/internal/invoke.h" |
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#include "absl/base/optimization.h" |
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#include "absl/container/internal/compressed_tuple.h" |
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#include "absl/meta/type_traits.h" |
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#include "absl/strings/string_view.h" |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace cord_internal { |
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// The overhead of a vtable is too much for Cord, so we roll our own subclasses |
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// using only a single byte to differentiate classes from each other - the "tag" |
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// byte. Define the subclasses first so we can provide downcasting helper |
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// functions in the base class. |
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struct CordRep; |
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struct CordRepConcat; |
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struct CordRepExternal; |
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struct CordRepFlat; |
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struct CordRepSubstring; |
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struct CordRepCrc; |
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class CordRepRing; |
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class CordRepBtree; |
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class CordzInfo; |
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// Default feature enable states for cord ring buffers |
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enum CordFeatureDefaults { |
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kCordEnableRingBufferDefault = false, |
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kCordShallowSubcordsDefault = false |
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}; |
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extern std::atomic<bool> cord_ring_buffer_enabled; |
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extern std::atomic<bool> shallow_subcords_enabled; |
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// `cord_btree_exhaustive_validation` can be set to force exhaustive validation |
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// in debug assertions, and code that calls `IsValid()` explicitly. By default, |
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// assertions should be relatively cheap and AssertValid() can easily lead to |
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// O(n^2) complexity as recursive / full tree validation is O(n). |
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extern std::atomic<bool> cord_btree_exhaustive_validation; |
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inline void enable_cord_ring_buffer(bool enable) { |
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cord_ring_buffer_enabled.store(enable, std::memory_order_relaxed); |
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} |
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inline void enable_shallow_subcords(bool enable) { |
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shallow_subcords_enabled.store(enable, std::memory_order_relaxed); |
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} |
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enum Constants { |
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// The inlined size to use with absl::InlinedVector. |
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// |
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// Note: The InlinedVectors in this file (and in cord.h) do not need to use |
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// the same value for their inlined size. The fact that they do is historical. |
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// It may be desirable for each to use a different inlined size optimized for |
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// that InlinedVector's usage. |
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// |
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// TODO(jgm): Benchmark to see if there's a more optimal value than 47 for |
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// the inlined vector size (47 exists for backward compatibility). |
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kInlinedVectorSize = 47, |
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// Prefer copying blocks of at most this size, otherwise reference count. |
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kMaxBytesToCopy = 511 |
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}; |
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// Emits a fatal error "Unexpected node type: xyz" and aborts the program. |
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ABSL_ATTRIBUTE_NORETURN void LogFatalNodeType(CordRep* rep); |
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// Compact class for tracking the reference count and state flags for CordRep |
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// instances. Data is stored in an atomic int32_t for compactness and speed. |
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class RefcountAndFlags { |
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public: |
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constexpr RefcountAndFlags() : count_{kRefIncrement} {} |
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struct Immortal {}; |
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explicit constexpr RefcountAndFlags(Immortal) : count_(kImmortalFlag) {} |
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// Increments the reference count. Imposes no memory ordering. |
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inline void Increment() { |
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count_.fetch_add(kRefIncrement, std::memory_order_relaxed); |
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} |
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// Asserts that the current refcount is greater than 0. If the refcount is |
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// greater than 1, decrements the reference count. |
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// |
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// Returns false if there are no references outstanding; true otherwise. |
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// Inserts barriers to ensure that state written before this method returns |
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// false will be visible to a thread that just observed this method returning |
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// false. Always returns false when the immortal bit is set. |
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inline bool Decrement() { |
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int32_t refcount = count_.load(std::memory_order_acquire) & kRefcountMask; |
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assert(refcount > 0 || refcount & kImmortalFlag); |
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return refcount != kRefIncrement && |
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(count_.fetch_sub(kRefIncrement, std::memory_order_acq_rel) & |
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kRefcountMask) != kRefIncrement; |
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} |
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// Same as Decrement but expect that refcount is greater than 1. |
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inline bool DecrementExpectHighRefcount() { |
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int32_t refcount = |
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count_.fetch_sub(kRefIncrement, std::memory_order_acq_rel) & |
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kRefcountMask; |
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assert(refcount > 0 || refcount & kImmortalFlag); |
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return refcount != kRefIncrement; |
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} |
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// Returns the current reference count using acquire semantics. |
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inline size_t Get() const { |
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return static_cast<size_t>(count_.load(std::memory_order_acquire) >> |
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kNumFlags); |
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} |
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// Returns whether the atomic integer is 1. |
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// If the reference count is used in the conventional way, a |
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// reference count of 1 implies that the current thread owns the |
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// reference and no other thread shares it. |
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// This call performs the test for a reference count of one, and |
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// performs the memory barrier needed for the owning thread |
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// to act on the object, knowing that it has exclusive access to the |
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// object. Always returns false when the immortal bit is set. |
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inline bool IsOne() { |
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return (count_.load(std::memory_order_acquire) & kRefcountMask) == |
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kRefIncrement; |
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} |
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bool IsImmortal() const { |
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return (count_.load(std::memory_order_relaxed) & kImmortalFlag) != 0; |
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} |
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private: |
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// We reserve the bottom bits for flags. |
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// kImmortalBit indicates that this entity should never be collected; it is |
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// used for the StringConstant constructor to avoid collecting immutable |
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// constant cords. |
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// kReservedFlag is reserved for future use. |
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enum Flags { |
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kNumFlags = 2, |
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kImmortalFlag = 0x1, |
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kReservedFlag = 0x2, |
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kRefIncrement = (1 << kNumFlags), |
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// Bitmask to use when checking refcount by equality. This masks out |
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// all flags except kImmortalFlag, which is part of the refcount for |
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// purposes of equality. (A refcount of 0 or 1 does not count as 0 or 1 |
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// if the immortal bit is set.) |
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kRefcountMask = ~kReservedFlag, |
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}; |
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std::atomic<int32_t> count_; |
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}; |
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// Various representations that we allow |
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enum CordRepKind { |
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UNUSED_0 = 0, |
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SUBSTRING = 1, |
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CRC = 2, |
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BTREE = 3, |
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RING = 4, |
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EXTERNAL = 5, |
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// We have different tags for different sized flat arrays, |
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// starting with FLAT, and limited to MAX_FLAT_TAG. The below values map to an |
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// allocated range of 32 bytes to 256 KB. The current granularity is: |
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// - 8 byte granularity for flat sizes in [32 - 512] |
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// - 64 byte granularity for flat sizes in (512 - 8KiB] |
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// - 4KiB byte granularity for flat sizes in (8KiB, 256 KiB] |
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// If a new tag is needed in the future, then 'FLAT' and 'MAX_FLAT_TAG' should |
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// be adjusted as well as the Tag <---> Size mapping logic so that FLAT still |
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// represents the minimum flat allocation size. (32 bytes as of now). |
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FLAT = 6, |
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MAX_FLAT_TAG = 248 |
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}; |
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// There are various locations where we want to check if some rep is a 'plain' |
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// data edge, i.e. an external or flat rep. By having FLAT == EXTERNAL + 1, we |
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// can perform this check in a single branch as 'tag >= EXTERNAL' |
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// Likewise, we have some locations where we check for 'ring or external/flat', |
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// so likewise align RING to EXTERNAL. |
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// Note that we can leave this optimization to the compiler. The compiler will |
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// DTRT when it sees a condition like `tag == EXTERNAL || tag >= FLAT`. |
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static_assert(RING == BTREE + 1, "BTREE and RING not consecutive"); |
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static_assert(EXTERNAL == RING + 1, "BTREE and EXTERNAL not consecutive"); |
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static_assert(FLAT == EXTERNAL + 1, "EXTERNAL and FLAT not consecutive"); |
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struct CordRep { |
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// Result from an `extract edge` operation. Contains the (possibly changed) |
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// tree node as well as the extracted edge, or {tree, nullptr} if no edge |
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// could be extracted. |
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// On success, the returned `tree` value is null if `extracted` was the only |
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// data edge inside the tree, a data edge if there were only two data edges in |
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// the tree, or the (possibly new / smaller) remaining tree with the extracted |
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// data edge removed. |
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struct ExtractResult { |
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CordRep* tree; |
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CordRep* extracted; |
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}; |
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CordRep() = default; |
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constexpr CordRep(RefcountAndFlags::Immortal immortal, size_t l) |
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: length(l), refcount(immortal), tag(EXTERNAL), storage{} {} |
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// The following three fields have to be less than 32 bytes since |
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// that is the smallest supported flat node size. |
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size_t length; |
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RefcountAndFlags refcount; |
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// If tag < FLAT, it represents CordRepKind and indicates the type of node. |
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// Otherwise, the node type is CordRepFlat and the tag is the encoded size. |
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uint8_t tag; |
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// `storage` provides two main purposes: |
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// - the starting point for FlatCordRep.Data() [flexible-array-member] |
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// - 3 bytes of additional storage for use by derived classes. |
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// The latter is used by CordrepConcat and CordRepBtree. CordRepConcat stores |
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// a 'depth' value in storage[0], and the (future) CordRepBtree class stores |
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// `height`, `begin` and `end` in the 3 entries. Otherwise we would need to |
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// allocate room for these in the derived class, as not all compilers reuse |
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// padding space from the base class (clang and gcc do, MSVC does not, etc) |
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uint8_t storage[3]; |
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// Returns true if this instance's tag matches the requested type. |
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constexpr bool IsRing() const { return tag == RING; } |
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constexpr bool IsSubstring() const { return tag == SUBSTRING; } |
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constexpr bool IsCrc() const { return tag == CRC; } |
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constexpr bool IsExternal() const { return tag == EXTERNAL; } |
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constexpr bool IsFlat() const { return tag >= FLAT; } |
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constexpr bool IsBtree() const { return tag == BTREE; } |
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inline CordRepRing* ring(); |
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inline const CordRepRing* ring() const; |
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inline CordRepSubstring* substring(); |
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inline const CordRepSubstring* substring() const; |
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inline CordRepCrc* crc(); |
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inline const CordRepCrc* crc() const; |
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inline CordRepExternal* external(); |
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inline const CordRepExternal* external() const; |
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inline CordRepFlat* flat(); |
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inline const CordRepFlat* flat() const; |
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inline CordRepBtree* btree(); |
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inline const CordRepBtree* btree() const; |
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// -------------------------------------------------------------------- |
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// Memory management |
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// Destroys the provided `rep`. |
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static void Destroy(CordRep* rep); |
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// Increments the reference count of `rep`. |
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// Requires `rep` to be a non-null pointer value. |
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static inline CordRep* Ref(CordRep* rep); |
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// Decrements the reference count of `rep`. Destroys rep if count reaches |
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// zero. Requires `rep` to be a non-null pointer value. |
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static inline void Unref(CordRep* rep); |
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}; |
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struct CordRepSubstring : public CordRep { |
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size_t start; // Starting offset of substring in child |
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CordRep* child; |
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// Creates a substring on `child`, adopting a reference on `child`. |
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// Requires `child` to be either a flat or external node, and `pos` and `n` to |
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// form a non-empty partial sub range of `'child`, i.e.: |
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// `n > 0 && n < length && n + pos <= length` |
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static inline CordRepSubstring* Create(CordRep* child, size_t pos, size_t n); |
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// Creates a substring of `rep`. Does not adopt a reference on `rep`. |
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// Requires `IsDataEdge(rep) && n > 0 && pos + n <= rep->length`. |
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// If `n == rep->length` then this method returns `CordRep::Ref(rep)` |
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// If `rep` is a substring of a flat or external node, then this method will |
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// return a new substring of that flat or external node with `pos` adjusted |
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// with the original `start` position. |
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static inline CordRep* Substring(CordRep* rep, size_t pos, size_t n); |
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}; |
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// Type for function pointer that will invoke the releaser function and also |
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// delete the `CordRepExternalImpl` corresponding to the passed in |
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// `CordRepExternal`. |
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using ExternalReleaserInvoker = void (*)(CordRepExternal*); |
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// External CordReps are allocated together with a type erased releaser. The |
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// releaser is stored in the memory directly following the CordRepExternal. |
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struct CordRepExternal : public CordRep { |
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CordRepExternal() = default; |
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explicit constexpr CordRepExternal(absl::string_view str) |
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: CordRep(RefcountAndFlags::Immortal{}, str.size()), |
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base(str.data()), |
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releaser_invoker(nullptr) {} |
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const char* base; |
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// Pointer to function that knows how to call and destroy the releaser. |
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ExternalReleaserInvoker releaser_invoker; |
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// Deletes (releases) the external rep. |
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// Requires rep != nullptr and rep->IsExternal() |
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static void Delete(CordRep* rep); |
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}; |
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struct Rank1 {}; |
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struct Rank0 : Rank1 {}; |
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template <typename Releaser, typename = ::absl::base_internal::invoke_result_t< |
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Releaser, absl::string_view>> |
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void InvokeReleaser(Rank0, Releaser&& releaser, absl::string_view data) { |
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::absl::base_internal::invoke(std::forward<Releaser>(releaser), data); |
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} |
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template <typename Releaser, |
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typename = ::absl::base_internal::invoke_result_t<Releaser>> |
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void InvokeReleaser(Rank1, Releaser&& releaser, absl::string_view) { |
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::absl::base_internal::invoke(std::forward<Releaser>(releaser)); |
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} |
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// We use CompressedTuple so that we can benefit from EBCO. |
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template <typename Releaser> |
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struct CordRepExternalImpl |
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: public CordRepExternal, |
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public ::absl::container_internal::CompressedTuple<Releaser> { |
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// The extra int arg is so that we can avoid interfering with copy/move |
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// constructors while still benefitting from perfect forwarding. |
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template <typename T> |
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CordRepExternalImpl(T&& releaser, int) |
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: CordRepExternalImpl::CompressedTuple(std::forward<T>(releaser)) { |
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this->releaser_invoker = &Release; |
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} |
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~CordRepExternalImpl() { |
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InvokeReleaser(Rank0{}, std::move(this->template get<0>()), |
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absl::string_view(base, length)); |
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} |
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static void Release(CordRepExternal* rep) { |
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delete static_cast<CordRepExternalImpl*>(rep); |
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} |
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}; |
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inline CordRepSubstring* CordRepSubstring::Create(CordRep* child, size_t pos, |
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size_t n) { |
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assert(child != nullptr); |
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assert(n > 0); |
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assert(n < child->length); |
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assert(pos < child->length); |
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assert(n <= child->length - pos); |
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// TODO(b/217376272): Harden internal logic. |
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// Move to strategical places inside the Cord logic and make this an assert. |
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if (ABSL_PREDICT_FALSE(!(child->IsExternal() || child->IsFlat()))) { |
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LogFatalNodeType(child); |
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} |
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CordRepSubstring* rep = new CordRepSubstring(); |
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rep->length = n; |
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rep->tag = SUBSTRING; |
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rep->start = pos; |
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rep->child = child; |
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return rep; |
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} |
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inline CordRep* CordRepSubstring::Substring(CordRep* rep, size_t pos, |
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size_t n) { |
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assert(rep != nullptr); |
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assert(n != 0); |
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assert(pos < rep->length); |
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assert(n <= rep->length - pos); |
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if (n == rep->length) return CordRep::Ref(rep); |
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if (rep->IsSubstring()) { |
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pos += rep->substring()->start; |
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rep = rep->substring()->child; |
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} |
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CordRepSubstring* substr = new CordRepSubstring(); |
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substr->length = n; |
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substr->tag = SUBSTRING; |
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substr->start = pos; |
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substr->child = CordRep::Ref(rep); |
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return substr; |
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} |
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inline void CordRepExternal::Delete(CordRep* rep) { |
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assert(rep != nullptr && rep->IsExternal()); |
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auto* rep_external = static_cast<CordRepExternal*>(rep); |
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assert(rep_external->releaser_invoker != nullptr); |
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rep_external->releaser_invoker(rep_external); |
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} |
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template <typename Str> |
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struct ConstInitExternalStorage { |
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ABSL_CONST_INIT static CordRepExternal value; |
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}; |
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template <typename Str> |
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ABSL_CONST_INIT CordRepExternal |
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ConstInitExternalStorage<Str>::value(Str::value); |
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enum { |
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kMaxInline = 15, |
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}; |
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constexpr char GetOrNull(absl::string_view data, size_t pos) { |
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return pos < data.size() ? data[pos] : '\0'; |
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} |
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// We store cordz_info as 64 bit pointer value in big endian format. This |
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// guarantees that the least significant byte of cordz_info matches the last |
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// byte of the inline data representation in as_chars_, which holds the inlined |
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// size or the 'is_tree' bit. |
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using cordz_info_t = int64_t; |
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// Assert that the `cordz_info` pointer value perfectly overlaps the last half |
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// of `as_chars_` and can hold a pointer value. |
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static_assert(sizeof(cordz_info_t) * 2 == kMaxInline + 1, ""); |
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static_assert(sizeof(cordz_info_t) >= sizeof(intptr_t), ""); |
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// BigEndianByte() creates a big endian representation of 'value', i.e.: a big |
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// endian value where the last byte in the host's representation holds 'value`, |
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// with all other bytes being 0. |
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static constexpr cordz_info_t BigEndianByte(unsigned char value) { |
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#if defined(ABSL_IS_BIG_ENDIAN) |
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return value; |
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#else |
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return static_cast<cordz_info_t>(value) << ((sizeof(cordz_info_t) - 1) * 8); |
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#endif |
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} |
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class InlineData { |
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public: |
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// DefaultInitType forces the use of the default initialization constructor. |
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enum DefaultInitType { kDefaultInit }; |
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// kNullCordzInfo holds the big endian representation of intptr_t(1) |
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// This is the 'null' / initial value of 'cordz_info'. The null value |
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// is specifically big endian 1 as with 64-bit pointers, the last |
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// byte of cordz_info overlaps with the last byte holding the tag. |
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static constexpr cordz_info_t kNullCordzInfo = BigEndianByte(1); |
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constexpr InlineData() : as_chars_{0} {} |
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explicit InlineData(DefaultInitType) {} |
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explicit constexpr InlineData(CordRep* rep) : as_tree_(rep) {} |
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explicit constexpr InlineData(absl::string_view chars) |
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: as_chars_{ |
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GetOrNull(chars, 0), GetOrNull(chars, 1), |
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GetOrNull(chars, 2), GetOrNull(chars, 3), |
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GetOrNull(chars, 4), GetOrNull(chars, 5), |
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GetOrNull(chars, 6), GetOrNull(chars, 7), |
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GetOrNull(chars, 8), GetOrNull(chars, 9), |
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GetOrNull(chars, 10), GetOrNull(chars, 11), |
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GetOrNull(chars, 12), GetOrNull(chars, 13), |
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GetOrNull(chars, 14), static_cast<char>((chars.size() << 1))} {} |
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// Returns true if the current instance is empty. |
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// The 'empty value' is an inlined data value of zero length. |
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bool is_empty() const { return tag() == 0; } |
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// Returns true if the current instance holds a tree value. |
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bool is_tree() const { return (tag() & 1) != 0; } |
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// Returns true if the current instance holds a cordz_info value. |
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// Requires the current instance to hold a tree value. |
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bool is_profiled() const { |
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assert(is_tree()); |
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return as_tree_.cordz_info != kNullCordzInfo; |
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} |
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// Returns true if either of the provided instances hold a cordz_info value. |
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// This method is more efficient than the equivalent `data1.is_profiled() || |
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// data2.is_profiled()`. Requires both arguments to hold a tree. |
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static bool is_either_profiled(const InlineData& data1, |
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const InlineData& data2) { |
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assert(data1.is_tree() && data2.is_tree()); |
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return (data1.as_tree_.cordz_info | data2.as_tree_.cordz_info) != |
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kNullCordzInfo; |
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} |
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// Returns the cordz_info sampling instance for this instance, or nullptr |
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// if the current instance is not sampled and does not have CordzInfo data. |
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// Requires the current instance to hold a tree value. |
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CordzInfo* cordz_info() const { |
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assert(is_tree()); |
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intptr_t info = static_cast<intptr_t>( |
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absl::big_endian::ToHost64(static_cast<uint64_t>(as_tree_.cordz_info))); |
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assert(info & 1); |
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return reinterpret_cast<CordzInfo*>(info - 1); |
|
} |
|
|
|
// Sets the current cordz_info sampling instance for this instance, or nullptr |
|
// if the current instance is not sampled and does not have CordzInfo data. |
|
// Requires the current instance to hold a tree value. |
|
void set_cordz_info(CordzInfo* cordz_info) { |
|
assert(is_tree()); |
|
uintptr_t info = reinterpret_cast<uintptr_t>(cordz_info) | 1; |
|
as_tree_.cordz_info = |
|
static_cast<cordz_info_t>(absl::big_endian::FromHost64(info)); |
|
} |
|
|
|
// Resets the current cordz_info to null / empty. |
|
void clear_cordz_info() { |
|
assert(is_tree()); |
|
as_tree_.cordz_info = kNullCordzInfo; |
|
} |
|
|
|
// Returns a read only pointer to the character data inside this instance. |
|
// Requires the current instance to hold inline data. |
|
const char* as_chars() const { |
|
assert(!is_tree()); |
|
return as_chars_; |
|
} |
|
|
|
// Returns a mutable pointer to the character data inside this instance. |
|
// Should be used for 'write only' operations setting an inlined value. |
|
// Applications can set the value of inlined data either before or after |
|
// setting the inlined size, i.e., both of the below are valid: |
|
// |
|
// // Set inlined data and inline size |
|
// memcpy(data_.as_chars(), data, size); |
|
// data_.set_inline_size(size); |
|
// |
|
// // Set inlined size and inline data |
|
// data_.set_inline_size(size); |
|
// memcpy(data_.as_chars(), data, size); |
|
// |
|
// It's an error to read from the returned pointer without a preceding write |
|
// if the current instance does not hold inline data, i.e.: is_tree() == true. |
|
char* as_chars() { return as_chars_; } |
|
|
|
// Returns the tree value of this value. |
|
// Requires the current instance to hold a tree value. |
|
CordRep* as_tree() const { |
|
assert(is_tree()); |
|
return as_tree_.rep; |
|
} |
|
|
|
// Initialize this instance to holding the tree value `rep`, |
|
// initializing the cordz_info to null, i.e.: 'not profiled'. |
|
void make_tree(CordRep* rep) { |
|
as_tree_.rep = rep; |
|
as_tree_.cordz_info = kNullCordzInfo; |
|
} |
|
|
|
// Set the tree value of this instance to 'rep`. |
|
// Requires the current instance to already hold a tree value. |
|
// Does not affect the value of cordz_info. |
|
void set_tree(CordRep* rep) { |
|
assert(is_tree()); |
|
as_tree_.rep = rep; |
|
} |
|
|
|
// Returns the size of the inlined character data inside this instance. |
|
// Requires the current instance to hold inline data. |
|
size_t inline_size() const { |
|
assert(!is_tree()); |
|
return static_cast<size_t>(tag()) >> 1; |
|
} |
|
|
|
// Sets the size of the inlined character data inside this instance. |
|
// Requires `size` to be <= kMaxInline. |
|
// See the documentation on 'as_chars()' for more information and examples. |
|
void set_inline_size(size_t size) { |
|
ABSL_ASSERT(size <= kMaxInline); |
|
tag() = static_cast<char>(size << 1); |
|
} |
|
|
|
// Compares 'this' inlined data with rhs. The comparison is a straightforward |
|
// lexicographic comparison. `Compare()` returns values as follows: |
|
// |
|
// -1 'this' InlineData instance is smaller |
|
// 0 the InlineData instances are equal |
|
// 1 'this' InlineData instance larger |
|
int Compare(const InlineData& rhs) const { |
|
uint64_t x, y; |
|
memcpy(&x, as_chars(), sizeof(x)); |
|
memcpy(&y, rhs.as_chars(), sizeof(y)); |
|
if (x == y) { |
|
memcpy(&x, as_chars() + 7, sizeof(x)); |
|
memcpy(&y, rhs.as_chars() + 7, sizeof(y)); |
|
if (x == y) { |
|
if (inline_size() == rhs.inline_size()) return 0; |
|
return inline_size() < rhs.inline_size() ? -1 : 1; |
|
} |
|
} |
|
x = absl::big_endian::FromHost64(x); |
|
y = absl::big_endian::FromHost64(y); |
|
return x < y ? -1 : 1; |
|
} |
|
|
|
private: |
|
// See cordz_info_t for forced alignment and size of `cordz_info` details. |
|
struct AsTree { |
|
explicit constexpr AsTree(absl::cord_internal::CordRep* tree) |
|
: rep(tree), cordz_info(kNullCordzInfo) {} |
|
// This union uses up extra space so that whether rep is 32 or 64 bits, |
|
// cordz_info will still start at the eighth byte, and the last |
|
// byte of cordz_info will still be the last byte of InlineData. |
|
union { |
|
absl::cord_internal::CordRep* rep; |
|
cordz_info_t unused_aligner; |
|
}; |
|
cordz_info_t cordz_info; |
|
}; |
|
|
|
char& tag() { return reinterpret_cast<char*>(this)[kMaxInline]; } |
|
char tag() const { return reinterpret_cast<const char*>(this)[kMaxInline]; } |
|
|
|
// If the data has length <= kMaxInline, we store it in `as_chars_`, and |
|
// store the size in the last char of `as_chars_` shifted left + 1. |
|
// Else we store it in a tree and store a pointer to that tree in |
|
// `as_tree_.rep` and store a tag in `tagged_size`. |
|
union { |
|
char as_chars_[kMaxInline + 1]; |
|
AsTree as_tree_; |
|
}; |
|
}; |
|
|
|
static_assert(sizeof(InlineData) == kMaxInline + 1, ""); |
|
|
|
inline CordRepSubstring* CordRep::substring() { |
|
assert(IsSubstring()); |
|
return static_cast<CordRepSubstring*>(this); |
|
} |
|
|
|
inline const CordRepSubstring* CordRep::substring() const { |
|
assert(IsSubstring()); |
|
return static_cast<const CordRepSubstring*>(this); |
|
} |
|
|
|
inline CordRepExternal* CordRep::external() { |
|
assert(IsExternal()); |
|
return static_cast<CordRepExternal*>(this); |
|
} |
|
|
|
inline const CordRepExternal* CordRep::external() const { |
|
assert(IsExternal()); |
|
return static_cast<const CordRepExternal*>(this); |
|
} |
|
|
|
inline CordRep* CordRep::Ref(CordRep* rep) { |
|
// ABSL_ASSUME is a workaround for |
|
// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585 |
|
ABSL_ASSUME(rep != nullptr); |
|
rep->refcount.Increment(); |
|
return rep; |
|
} |
|
|
|
inline void CordRep::Unref(CordRep* rep) { |
|
assert(rep != nullptr); |
|
// Expect refcount to be 0. Avoiding the cost of an atomic decrement should |
|
// typically outweigh the cost of an extra branch checking for ref == 1. |
|
if (ABSL_PREDICT_FALSE(!rep->refcount.DecrementExpectHighRefcount())) { |
|
Destroy(rep); |
|
} |
|
} |
|
|
|
} // namespace cord_internal |
|
|
|
ABSL_NAMESPACE_END |
|
} // namespace absl |
|
#endif // ABSL_STRINGS_INTERNAL_CORD_INTERNAL_H_
|
|
|