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abseil-cpp/absl/strings/cord.cc

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// Copyright 2020 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "absl/strings/cord.h"
#include <algorithm>
#include <atomic>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <limits>
#include <ostream>
#include <sstream>
#include <type_traits>
#include <unordered_set>
#include <vector>
#include "absl/base/casts.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/macros.h"
#include "absl/base/port.h"
#include "absl/container/fixed_array.h"
#include "absl/container/inlined_vector.h"
#include "absl/strings/escaping.h"
#include "absl/strings/internal/cord_internal.h"
#include "absl/strings/internal/cord_rep_btree.h"
#include "absl/strings/internal/cord_rep_flat.h"
#include "absl/strings/internal/cordz_statistics.h"
#include "absl/strings/internal/cordz_update_scope.h"
#include "absl/strings/internal/cordz_update_tracker.h"
#include "absl/strings/internal/resize_uninitialized.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"
#include "absl/strings/str_join.h"
#include "absl/strings/string_view.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
using ::absl::cord_internal::CordRep;
using ::absl::cord_internal::CordRepBtree;
using ::absl::cord_internal::CordRepConcat;
using ::absl::cord_internal::CordRepExternal;
using ::absl::cord_internal::CordRepFlat;
using ::absl::cord_internal::CordRepSubstring;
using ::absl::cord_internal::CordzUpdateTracker;
using ::absl::cord_internal::InlineData;
using ::absl::cord_internal::kMaxFlatLength;
using ::absl::cord_internal::kMinFlatLength;
using ::absl::cord_internal::kInlinedVectorSize;
using ::absl::cord_internal::kMaxBytesToCopy;
constexpr uint64_t Fibonacci(unsigned char n, uint64_t a = 0, uint64_t b = 1) {
return n == 0 ? a : Fibonacci(n - 1, b, a + b);
}
static_assert(Fibonacci(63) == 6557470319842,
"Fibonacci values computed incorrectly");
// Minimum length required for a given depth tree -- a tree is considered
// balanced if
// length(t) >= min_length[depth(t)]
// The root node depth is allowed to become twice as large to reduce rebalancing
// for larger strings (see IsRootBalanced).
static constexpr uint64_t min_length[] = {
Fibonacci(2), Fibonacci(3), Fibonacci(4), Fibonacci(5),
Fibonacci(6), Fibonacci(7), Fibonacci(8), Fibonacci(9),
Fibonacci(10), Fibonacci(11), Fibonacci(12), Fibonacci(13),
Fibonacci(14), Fibonacci(15), Fibonacci(16), Fibonacci(17),
Fibonacci(18), Fibonacci(19), Fibonacci(20), Fibonacci(21),
Fibonacci(22), Fibonacci(23), Fibonacci(24), Fibonacci(25),
Fibonacci(26), Fibonacci(27), Fibonacci(28), Fibonacci(29),
Fibonacci(30), Fibonacci(31), Fibonacci(32), Fibonacci(33),
Fibonacci(34), Fibonacci(35), Fibonacci(36), Fibonacci(37),
Fibonacci(38), Fibonacci(39), Fibonacci(40), Fibonacci(41),
Fibonacci(42), Fibonacci(43), Fibonacci(44), Fibonacci(45),
Fibonacci(46), Fibonacci(47),
0xffffffffffffffffull, // Avoid overflow
};
static const int kMinLengthSize = ABSL_ARRAYSIZE(min_length);
static inline bool btree_enabled() {
return cord_internal::cord_btree_enabled.load(
std::memory_order_relaxed);
}
static inline bool IsRootBalanced(CordRep* node) {
if (!node->IsConcat()) {
return true;
} else if (node->concat()->depth() <= 15) {
return true;
} else if (node->concat()->depth() > kMinLengthSize) {
return false;
} else {
// Allow depth to become twice as large as implied by fibonacci rule to
// reduce rebalancing for larger strings.
return (node->length >= min_length[node->concat()->depth() / 2]);
}
}
static CordRep* Rebalance(CordRep* node);
static void DumpNode(CordRep* rep, bool include_data, std::ostream* os,
int indent = 0);
static bool VerifyNode(CordRep* root, CordRep* start_node,
bool full_validation);
static inline CordRep* VerifyTree(CordRep* node) {
// Verification is expensive, so only do it in debug mode.
// Even in debug mode we normally do only light validation.
// If you are debugging Cord itself, you should define the
// macro EXTRA_CORD_VALIDATION, e.g. by adding
// --copt=-DEXTRA_CORD_VALIDATION to the blaze line.
#ifdef EXTRA_CORD_VALIDATION
assert(node == nullptr || VerifyNode(node, node, /*full_validation=*/true));
#else // EXTRA_CORD_VALIDATION
assert(node == nullptr || VerifyNode(node, node, /*full_validation=*/false));
#endif // EXTRA_CORD_VALIDATION
static_cast<void>(&VerifyNode);
return node;
}
// Return the depth of a node
static int Depth(const CordRep* rep) {
if (rep->IsConcat()) {
return rep->concat()->depth();
} else {
return 0;
}
}
static void SetConcatChildren(CordRepConcat* concat, CordRep* left,
CordRep* right) {
concat->left = left;
concat->right = right;
concat->length = left->length + right->length;
concat->set_depth(1 + std::max(Depth(left), Depth(right)));
}
// Create a concatenation of the specified nodes.
// Does not change the refcounts of "left" and "right".
// The returned node has a refcount of 1.
static CordRep* RawConcat(CordRep* left, CordRep* right) {
// Avoid making degenerate concat nodes (one child is empty)
if (left == nullptr) return right;
if (right == nullptr) return left;
if (left->length == 0) {
CordRep::Unref(left);
return right;
}
if (right->length == 0) {
CordRep::Unref(right);
return left;
}
CordRepConcat* rep = new CordRepConcat();
rep->tag = cord_internal::CONCAT;
SetConcatChildren(rep, left, right);
return rep;
}
static CordRep* Concat(CordRep* left, CordRep* right) {
CordRep* rep = RawConcat(left, right);
if (rep != nullptr && !IsRootBalanced(rep)) {
rep = Rebalance(rep);
}
return VerifyTree(rep);
}
// Make a balanced tree out of an array of leaf nodes.
static CordRep* MakeBalancedTree(CordRep** reps, size_t n) {
// Make repeated passes over the array, merging adjacent pairs
// until we are left with just a single node.
while (n > 1) {
size_t dst = 0;
for (size_t src = 0; src < n; src += 2) {
if (src + 1 < n) {
reps[dst] = Concat(reps[src], reps[src + 1]);
} else {
reps[dst] = reps[src];
}
dst++;
}
n = dst;
}
return reps[0];
}
static CordRepFlat* CreateFlat(const char* data, size_t length,
size_t alloc_hint) {
CordRepFlat* flat = CordRepFlat::New(length + alloc_hint);
flat->length = length;
memcpy(flat->Data(), data, length);
return flat;
}
// Creates a new flat or Btree out of the specified array.
// The returned node has a refcount of 1.
static CordRep* NewBtree(const char* data, size_t length, size_t alloc_hint) {
if (length <= kMaxFlatLength) {
return CreateFlat(data, length, alloc_hint);
}
CordRepFlat* flat = CreateFlat(data, kMaxFlatLength, 0);
data += kMaxFlatLength;
length -= kMaxFlatLength;
auto* root = CordRepBtree::Create(flat);
return CordRepBtree::Append(root, {data, length}, alloc_hint);
}
// Create a new tree out of the specified array.
// The returned node has a refcount of 1.
static CordRep* NewTree(const char* data, size_t length, size_t alloc_hint) {
if (length == 0) return nullptr;
if (btree_enabled()) {
return NewBtree(data, length, alloc_hint);
}
absl::FixedArray<CordRep*> reps((length - 1) / kMaxFlatLength + 1);
size_t n = 0;
do {
const size_t len = std::min(length, kMaxFlatLength);
CordRepFlat* rep = CordRepFlat::New(len + alloc_hint);
rep->length = len;
memcpy(rep->Data(), data, len);
reps[n++] = VerifyTree(rep);
data += len;
length -= len;
} while (length != 0);
return MakeBalancedTree(reps.data(), n);
}
namespace cord_internal {
void InitializeCordRepExternal(absl::string_view data, CordRepExternal* rep) {
assert(!data.empty());
rep->length = data.size();
rep->tag = EXTERNAL;
rep->base = data.data();
VerifyTree(rep);
}
} // namespace cord_internal
static CordRep* NewSubstring(CordRep* child, size_t offset, size_t length) {
// Never create empty substring nodes
if (length == 0) {
CordRep::Unref(child);
return nullptr;
} else {
CordRepSubstring* rep = new CordRepSubstring();
assert((offset + length) <= child->length);
rep->length = length;
rep->tag = cord_internal::SUBSTRING;
rep->start = offset;
rep->child = child;
return VerifyTree(rep);
}
}
// Creates a CordRep from the provided string. If the string is large enough,
// and not wasteful, we move the string into an external cord rep, preserving
// the already allocated string contents.
// Requires the provided string length to be larger than `kMaxInline`.
static CordRep* CordRepFromString(std::string&& src) {
assert(src.length() > cord_internal::kMaxInline);
if (
// String is short: copy data to avoid external block overhead.
src.size() <= kMaxBytesToCopy ||
// String is wasteful: copy data to avoid pinning too much unused memory.
src.size() < src.capacity() / 2
) {
return NewTree(src.data(), src.size(), 0);
}
struct StringReleaser {
void operator()(absl::string_view /* data */) {}
std::string data;
};
const absl::string_view original_data = src;
auto* rep =
static_cast<::absl::cord_internal::CordRepExternalImpl<StringReleaser>*>(
absl::cord_internal::NewExternalRep(original_data,
StringReleaser{std::move(src)}));
// Moving src may have invalidated its data pointer, so adjust it.
rep->base = rep->template get<0>().data.data();
return rep;
}
// --------------------------------------------------------------------
// Cord::InlineRep functions
constexpr unsigned char Cord::InlineRep::kMaxInline;
inline void Cord::InlineRep::set_data(const char* data, size_t n,
bool nullify_tail) {
static_assert(kMaxInline == 15, "set_data is hard-coded for a length of 15");
cord_internal::SmallMemmove(data_.as_chars(), data, n, nullify_tail);
set_inline_size(n);
}
inline char* Cord::InlineRep::set_data(size_t n) {
assert(n <= kMaxInline);
ResetToEmpty();
set_inline_size(n);
return data_.as_chars();
}
inline void Cord::InlineRep::reduce_size(size_t n) {
size_t tag = inline_size();
assert(tag <= kMaxInline);
assert(tag >= n);
tag -= n;
memset(data_.as_chars() + tag, 0, n);
set_inline_size(static_cast<char>(tag));
}
inline void Cord::InlineRep::remove_prefix(size_t n) {
cord_internal::SmallMemmove(data_.as_chars(), data_.as_chars() + n,
inline_size() - n);
reduce_size(n);
}
// Returns `rep` converted into a CordRepBtree.
// Directly returns `rep` if `rep` is already a CordRepBtree.
static CordRepBtree* ForceBtree(CordRep* rep) {
return rep->IsBtree() ? rep->btree() : CordRepBtree::Create(rep);
}
void Cord::InlineRep::AppendTreeToInlined(CordRep* tree,
MethodIdentifier method) {
assert(!is_tree());
if (!data_.is_empty()) {
CordRepFlat* flat = MakeFlatWithExtraCapacity(0);
if (btree_enabled()) {
tree = CordRepBtree::Append(CordRepBtree::Create(flat), tree);
} else {
tree = Concat(flat, tree);
}
}
EmplaceTree(tree, method);
}
void Cord::InlineRep::AppendTreeToTree(CordRep* tree, MethodIdentifier method) {
assert(is_tree());
const CordzUpdateScope scope(data_.cordz_info(), method);
if (btree_enabled()) {
tree = CordRepBtree::Append(ForceBtree(data_.as_tree()), tree);
} else {
tree = Concat(data_.as_tree(), tree);
}
SetTree(tree, scope);
}
void Cord::InlineRep::AppendTree(CordRep* tree, MethodIdentifier method) {
if (tree == nullptr) return;
if (data_.is_tree()) {
AppendTreeToTree(tree, method);
} else {
AppendTreeToInlined(tree, method);
}
}
void Cord::InlineRep::PrependTreeToInlined(CordRep* tree,
MethodIdentifier method) {
assert(!is_tree());
if (!data_.is_empty()) {
CordRepFlat* flat = MakeFlatWithExtraCapacity(0);
if (btree_enabled()) {
tree = CordRepBtree::Prepend(CordRepBtree::Create(flat), tree);
} else {
tree = Concat(tree, flat);
}
}
EmplaceTree(tree, method);
}
void Cord::InlineRep::PrependTreeToTree(CordRep* tree,
MethodIdentifier method) {
assert(is_tree());
const CordzUpdateScope scope(data_.cordz_info(), method);
if (btree_enabled()) {
tree = CordRepBtree::Prepend(ForceBtree(data_.as_tree()), tree);
} else {
tree = Concat(tree, data_.as_tree());
}
SetTree(tree, scope);
}
void Cord::InlineRep::PrependTree(CordRep* tree, MethodIdentifier method) {
assert(tree != nullptr);
if (data_.is_tree()) {
PrependTreeToTree(tree, method);
} else {
PrependTreeToInlined(tree, method);
}
}
// Searches for a non-full flat node at the rightmost leaf of the tree. If a
// suitable leaf is found, the function will update the length field for all
// nodes to account for the size increase. The append region address will be
// written to region and the actual size increase will be written to size.
static inline bool PrepareAppendRegion(CordRep* root, char** region,
size_t* size, size_t max_length) {
if (root->IsBtree() && root->refcount.IsOne()) {
Span<char> span = root->btree()->GetAppendBuffer(max_length);
if (!span.empty()) {
*region = span.data();
*size = span.size();
return true;
}
}
// Search down the right-hand path for a non-full FLAT node.
CordRep* dst = root;
while (dst->IsConcat() && dst->refcount.IsOne()) {
dst = dst->concat()->right;
}
if (!dst->IsFlat() || !dst->refcount.IsOne()) {
*region = nullptr;
*size = 0;
return false;
}
const size_t in_use = dst->length;
const size_t capacity = dst->flat()->Capacity();
if (in_use == capacity) {
*region = nullptr;
*size = 0;
return false;
}
size_t size_increase = std::min(capacity - in_use, max_length);
// We need to update the length fields for all nodes, including the leaf node.
for (CordRep* rep = root; rep != dst; rep = rep->concat()->right) {
rep->length += size_increase;
}
dst->length += size_increase;
*region = dst->flat()->Data() + in_use;
*size = size_increase;
return true;
}
template <bool has_length>
void Cord::InlineRep::GetAppendRegion(char** region, size_t* size,
size_t length) {
auto constexpr method = CordzUpdateTracker::kGetAppendRegion;
CordRep* root = tree();
size_t sz = root ? root->length : inline_size();
if (root == nullptr) {
size_t available = kMaxInline - sz;
if (available >= (has_length ? length : 1)) {
*region = data_.as_chars() + sz;
*size = has_length ? length : available;
set_inline_size(has_length ? sz + length : kMaxInline);
return;
}
}
size_t extra = has_length ? length : (std::max)(sz, kMinFlatLength);
CordRep* rep = root ? root : MakeFlatWithExtraCapacity(extra);
CordzUpdateScope scope(root ? data_.cordz_info() : nullptr, method);
if (PrepareAppendRegion(rep, region, size, length)) {
CommitTree(root, rep, scope, method);
return;
}
// Allocate new node.
CordRepFlat* new_node = CordRepFlat::New(extra);
new_node->length = std::min(new_node->Capacity(), length);
*region = new_node->Data();
*size = new_node->length;
if (btree_enabled()) {
rep = CordRepBtree::Append(ForceBtree(rep), new_node);
} else {
rep = Concat(rep, new_node);
}
CommitTree(root, rep, scope, method);
}
// Computes the memory side of the provided edge which must be a valid data edge
// for a btrtee, i.e., a FLAT, EXTERNAL or SUBSTRING of a FLAT or EXTERNAL node.
static bool RepMemoryUsageDataEdge(const CordRep* rep,
size_t* total_mem_usage) {
size_t maybe_sub_size = 0;
if (ABSL_PREDICT_FALSE(rep->IsSubstring())) {
maybe_sub_size = sizeof(cord_internal::CordRepSubstring);
rep = rep->substring()->child;
}
if (rep->IsFlat()) {
*total_mem_usage += maybe_sub_size + rep->flat()->AllocatedSize();
return true;
}
if (rep->IsExternal()) {
// We don't know anything about the embedded / bound data, but we can safely
// assume it is 'at least' a word / pointer to data. In the future we may
// choose to use the 'data' byte as a tag to identify the types of some
// well-known externals, such as a std::string instance.
*total_mem_usage += maybe_sub_size +
sizeof(cord_internal::CordRepExternalImpl<intptr_t>) +
rep->length;
return true;
}
return false;
}
// If the rep is a leaf, this will increment the value at total_mem_usage and
// will return true.
static bool RepMemoryUsageLeaf(const CordRep* rep, size_t* total_mem_usage) {
if (rep->IsFlat()) {
*total_mem_usage += rep->flat()->AllocatedSize();
return true;
}
if (rep->IsExternal()) {
// We don't know anything about the embedded / bound data, but we can safely
// assume it is 'at least' a word / pointer to data. In the future we may
// choose to use the 'data' byte as a tag to identify the types of some
// well-known externals, such as a std::string instance.
*total_mem_usage +=
sizeof(cord_internal::CordRepExternalImpl<intptr_t>) + rep->length;
return true;
}
return false;
}
void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) {
assert(&src != this);
assert(is_tree() || src.is_tree());
auto constexpr method = CordzUpdateTracker::kAssignCord;
if (ABSL_PREDICT_TRUE(!is_tree())) {
EmplaceTree(CordRep::Ref(src.as_tree()), src.data_, method);
return;
}
CordRep* tree = as_tree();
if (CordRep* src_tree = src.tree()) {
// Leave any existing `cordz_info` in place, and let MaybeTrackCord()
// decide if this cord should be (or remains to be) sampled or not.
data_.set_tree(CordRep::Ref(src_tree));
CordzInfo::MaybeTrackCord(data_, src.data_, method);
} else {
CordzInfo::MaybeUntrackCord(data_.cordz_info());
data_ = src.data_;
}
CordRep::Unref(tree);
}
void Cord::InlineRep::UnrefTree() {
if (is_tree()) {
CordzInfo::MaybeUntrackCord(data_.cordz_info());
CordRep::Unref(tree());
}
}
// --------------------------------------------------------------------
// Constructors and destructors
Cord::Cord(absl::string_view src, MethodIdentifier method)
: contents_(InlineData::kDefaultInit) {
const size_t n = src.size();
if (n <= InlineRep::kMaxInline) {
contents_.set_data(src.data(), n, true);
} else {
CordRep* rep = NewTree(src.data(), n, 0);
contents_.EmplaceTree(rep, method);
}
}
template <typename T, Cord::EnableIfString<T>>
Cord::Cord(T&& src) : contents_(InlineData::kDefaultInit) {
if (src.size() <= InlineRep::kMaxInline) {
contents_.set_data(src.data(), src.size(), true);
} else {
CordRep* rep = CordRepFromString(std::forward<T>(src));
contents_.EmplaceTree(rep, CordzUpdateTracker::kConstructorString);
}
}
template Cord::Cord(std::string&& src);
// The destruction code is separate so that the compiler can determine
// that it does not need to call the destructor on a moved-from Cord.
void Cord::DestroyCordSlow() {
assert(contents_.is_tree());
CordzInfo::MaybeUntrackCord(contents_.cordz_info());
CordRep::Unref(VerifyTree(contents_.as_tree()));
}
// --------------------------------------------------------------------
// Mutators
void Cord::Clear() {
if (CordRep* tree = contents_.clear()) {
CordRep::Unref(tree);
}
}
Cord& Cord::AssignLargeString(std::string&& src) {
auto constexpr method = CordzUpdateTracker::kAssignString;
assert(src.size() > kMaxBytesToCopy);
CordRep* rep = CordRepFromString(std::move(src));
if (CordRep* tree = contents_.tree()) {
CordzUpdateScope scope(contents_.cordz_info(), method);
contents_.SetTree(rep, scope);
CordRep::Unref(tree);
} else {
contents_.EmplaceTree(rep, method);
}
return *this;
}
Cord& Cord::operator=(absl::string_view src) {
auto constexpr method = CordzUpdateTracker::kAssignString;
const char* data = src.data();
size_t length = src.size();
CordRep* tree = contents_.tree();
if (length <= InlineRep::kMaxInline) {
// Embed into this->contents_, which is somewhat subtle:
// - MaybeUntrackCord must be called before Unref(tree).
// - MaybeUntrackCord must be called before set_data() clobbers cordz_info.
// - set_data() must be called before Unref(tree) as it may reference tree.
if (tree != nullptr) CordzInfo::MaybeUntrackCord(contents_.cordz_info());
contents_.set_data(data, length, true);
if (tree != nullptr) CordRep::Unref(tree);
return *this;
}
if (tree != nullptr) {
CordzUpdateScope scope(contents_.cordz_info(), method);
if (tree->IsFlat() && tree->flat()->Capacity() >= length &&
tree->refcount.IsOne()) {
// Copy in place if the existing FLAT node is reusable.
memmove(tree->flat()->Data(), data, length);
tree->length = length;
VerifyTree(tree);
return *this;
}
contents_.SetTree(NewTree(data, length, 0), scope);
CordRep::Unref(tree);
} else {
contents_.EmplaceTree(NewTree(data, length, 0), method);
}
return *this;
}
// TODO(sanjay): Move to Cord::InlineRep section of file. For now,
// we keep it here to make diffs easier.
void Cord::InlineRep::AppendArray(absl::string_view src,
MethodIdentifier method) {
if (src.empty()) return; // memcpy(_, nullptr, 0) is undefined.
size_t appended = 0;
CordRep* rep = tree();
const CordRep* const root = rep;
CordzUpdateScope scope(root ? cordz_info() : nullptr, method);
if (root != nullptr) {
char* region;
if (PrepareAppendRegion(rep, &region, &appended, src.size())) {
memcpy(region, src.data(), appended);
}
} else {
// Try to fit in the inline buffer if possible.
size_t inline_length = inline_size();
if (src.size() <= kMaxInline - inline_length) {
// Append new data to embedded array
memcpy(data_.as_chars() + inline_length, src.data(), src.size());
set_inline_size(inline_length + src.size());
return;
}
// Allocate flat to be a perfect fit on first append exceeding inlined size.
// Subsequent growth will use amortized growth until we reach maximum flat
// size.
rep = CordRepFlat::New(inline_length + src.size());
appended = std::min(src.size(), rep->flat()->Capacity() - inline_length);
memcpy(rep->flat()->Data(), data_.as_chars(), inline_length);
memcpy(rep->flat()->Data() + inline_length, src.data(), appended);
rep->length = inline_length + appended;
}
src.remove_prefix(appended);
if (src.empty()) {
CommitTree(root, rep, scope, method);
return;
}
if (btree_enabled()) {
// TODO(b/192061034): keep legacy 10% growth rate: consider other rates.
rep = ForceBtree(rep);
const size_t min_growth = std::max<size_t>(rep->length / 10, src.size());
rep = CordRepBtree::Append(rep->btree(), src, min_growth - src.size());
} else {
// Use new block(s) for any remaining bytes that were not handled above.
// Alloc extra memory only if the right child of the root of the new tree
// is going to be a FLAT node, which will permit further inplace appends.
size_t length = src.size();
if (src.size() < kMaxFlatLength) {
// The new length is either
// - old size + 10%
// - old_size + src.size()
// This will cause a reasonable conservative step-up in size that is
// still large enough to avoid excessive amounts of small fragments
// being added.
length = std::max<size_t>(rep->length / 10, src.size());
}
rep = Concat(rep, NewTree(src.data(), src.size(), length - src.size()));
}
CommitTree(root, rep, scope, method);
}
inline CordRep* Cord::TakeRep() const& {
return CordRep::Ref(contents_.tree());
}
inline CordRep* Cord::TakeRep() && {
CordRep* rep = contents_.tree();
contents_.clear();
return rep;
}
template <typename C>
inline void Cord::AppendImpl(C&& src) {
auto constexpr method = CordzUpdateTracker::kAppendCord;
if (empty()) {
// Since destination is empty, we can avoid allocating a node,
if (src.contents_.is_tree()) {
// by taking the tree directly
CordRep* rep = std::forward<C>(src).TakeRep();
contents_.EmplaceTree(rep, method);
} else {
// or copying over inline data
contents_.data_ = src.contents_.data_;
}
return;
}
// For short cords, it is faster to copy data if there is room in dst.
const size_t src_size = src.contents_.size();
if (src_size <= kMaxBytesToCopy) {
CordRep* src_tree = src.contents_.tree();
if (src_tree == nullptr) {
// src has embedded data.
contents_.AppendArray({src.contents_.data(), src_size}, method);
return;
}
if (src_tree->IsFlat()) {
// src tree just has one flat node.
contents_.AppendArray({src_tree->flat()->Data(), src_size}, method);
return;
}
if (&src == this) {
// ChunkIterator below assumes that src is not modified during traversal.
Append(Cord(src));
return;
}
// TODO(mec): Should we only do this if "dst" has space?
for (absl::string_view chunk : src.Chunks()) {
Append(chunk);
}
return;
}
// Guaranteed to be a tree (kMaxBytesToCopy > kInlinedSize)
CordRep* rep = std::forward<C>(src).TakeRep();
contents_.AppendTree(rep, CordzUpdateTracker::kAppendCord);
}
void Cord::Append(const Cord& src) {
AppendImpl(src);
}
void Cord::Append(Cord&& src) {
AppendImpl(std::move(src));
}
template <typename T, Cord::EnableIfString<T>>
void Cord::Append(T&& src) {
if (src.size() <= kMaxBytesToCopy) {
Append(absl::string_view(src));
} else {
CordRep* rep = CordRepFromString(std::forward<T>(src));
contents_.AppendTree(rep, CordzUpdateTracker::kAppendString);
}
}
template void Cord::Append(std::string&& src);
void Cord::Prepend(const Cord& src) {
CordRep* src_tree = src.contents_.tree();
if (src_tree != nullptr) {
CordRep::Ref(src_tree);
contents_.PrependTree(src_tree, CordzUpdateTracker::kPrependCord);
return;
}
// `src` cord is inlined.
absl::string_view src_contents(src.contents_.data(), src.contents_.size());
return Prepend(src_contents);
}
void Cord::Prepend(absl::string_view src) {
if (src.empty()) return; // memcpy(_, nullptr, 0) is undefined.
if (!contents_.is_tree()) {
size_t cur_size = contents_.inline_size();
if (cur_size + src.size() <= InlineRep::kMaxInline) {
// Use embedded storage.
char data[InlineRep::kMaxInline + 1] = {0};
memcpy(data, src.data(), src.size());
memcpy(data + src.size(), contents_.data(), cur_size);
memcpy(contents_.data_.as_chars(), data, InlineRep::kMaxInline + 1);
contents_.set_inline_size(cur_size + src.size());
return;
}
}
CordRep* rep = NewTree(src.data(), src.size(), 0);
contents_.PrependTree(rep, CordzUpdateTracker::kPrependString);
}
template <typename T, Cord::EnableIfString<T>>
inline void Cord::Prepend(T&& src) {
if (src.size() <= kMaxBytesToCopy) {
Prepend(absl::string_view(src));
} else {
CordRep* rep = CordRepFromString(std::forward<T>(src));
contents_.PrependTree(rep, CordzUpdateTracker::kPrependString);
}
}
template void Cord::Prepend(std::string&& src);
static CordRep* RemovePrefixFrom(CordRep* node, size_t n) {
if (n >= node->length) return nullptr;
if (n == 0) return CordRep::Ref(node);
absl::InlinedVector<CordRep*, kInlinedVectorSize> rhs_stack;
while (node->IsConcat()) {
assert(n <= node->length);
if (n < node->concat()->left->length) {
// Push right to stack, descend left.
rhs_stack.push_back(node->concat()->right);
node = node->concat()->left;
} else {
// Drop left, descend right.
n -= node->concat()->left->length;
node = node->concat()->right;
}
}
assert(n <= node->length);
if (n == 0) {
CordRep::Ref(node);
} else {
size_t start = n;
size_t len = node->length - n;
if (node->IsSubstring()) {
// Consider in-place update of node, similar to in RemoveSuffixFrom().
start += node->substring()->start;
node = node->substring()->child;
}
node = NewSubstring(CordRep::Ref(node), start, len);
}
while (!rhs_stack.empty()) {
node = Concat(node, CordRep::Ref(rhs_stack.back()));
rhs_stack.pop_back();
}
return node;
}
// RemoveSuffixFrom() is very similar to RemovePrefixFrom(), with the
// exception that removing a suffix has an optimization where a node may be
// edited in place iff that node and all its ancestors have a refcount of 1.
static CordRep* RemoveSuffixFrom(CordRep* node, size_t n) {
if (n >= node->length) return nullptr;
if (n == 0) return CordRep::Ref(node);
absl::InlinedVector<CordRep*, kInlinedVectorSize> lhs_stack;
bool inplace_ok = node->refcount.IsOne();
while (node->IsConcat()) {
assert(n <= node->length);
if (n < node->concat()->right->length) {
// Push left to stack, descend right.
lhs_stack.push_back(node->concat()->left);
node = node->concat()->right;
} else {
// Drop right, descend left.
n -= node->concat()->right->length;
node = node->concat()->left;
}
inplace_ok = inplace_ok && node->refcount.IsOne();
}
assert(n <= node->length);
if (n == 0) {
CordRep::Ref(node);
} else if (inplace_ok && !node->IsExternal()) {
// Consider making a new buffer if the current node capacity is much
// larger than the new length.
CordRep::Ref(node);
node->length -= n;
} else {
size_t start = 0;
size_t len = node->length - n;
if (node->IsSubstring()) {
start = node->substring()->start;
node = node->substring()->child;
}
node = NewSubstring(CordRep::Ref(node), start, len);
}
while (!lhs_stack.empty()) {
node = Concat(CordRep::Ref(lhs_stack.back()), node);
lhs_stack.pop_back();
}
return node;
}
void Cord::RemovePrefix(size_t n) {
ABSL_INTERNAL_CHECK(n <= size(),
absl::StrCat("Requested prefix size ", n,
" exceeds Cord's size ", size()));
CordRep* tree = contents_.tree();
if (tree == nullptr) {
contents_.remove_prefix(n);
} else {
auto constexpr method = CordzUpdateTracker::kRemovePrefix;
CordzUpdateScope scope(contents_.cordz_info(), method);
if (tree->IsBtree()) {
CordRep* old = tree;
tree = tree->btree()->SubTree(n, tree->length - n);
CordRep::Unref(old);
} else {
CordRep* newrep = RemovePrefixFrom(tree, n);
CordRep::Unref(tree);
tree = VerifyTree(newrep);
}
contents_.SetTreeOrEmpty(tree, scope);
}
}
void Cord::RemoveSuffix(size_t n) {
ABSL_INTERNAL_CHECK(n <= size(),
absl::StrCat("Requested suffix size ", n,
" exceeds Cord's size ", size()));
CordRep* tree = contents_.tree();
if (tree == nullptr) {
contents_.reduce_size(n);
} else {
auto constexpr method = CordzUpdateTracker::kRemoveSuffix;
CordzUpdateScope scope(contents_.cordz_info(), method);
if (tree->IsBtree()) {
CordRep* old = tree;
tree = tree->btree()->SubTree(0, tree->length - n);
CordRep::Unref(old);
} else {
CordRep* newrep = RemoveSuffixFrom(tree, n);
CordRep::Unref(tree);
tree = VerifyTree(newrep);
}
contents_.SetTreeOrEmpty(tree, scope);
}
}
// Work item for NewSubRange().
struct SubRange {
SubRange(CordRep* a_node, size_t a_pos, size_t a_n)
: node(a_node), pos(a_pos), n(a_n) {}
CordRep* node; // nullptr means concat last 2 results.
size_t pos;
size_t n;
};
static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) {
absl::InlinedVector<CordRep*, kInlinedVectorSize> results;
absl::InlinedVector<SubRange, kInlinedVectorSize> todo;
todo.push_back(SubRange(node, pos, n));
do {
const SubRange& sr = todo.back();
node = sr.node;
pos = sr.pos;
n = sr.n;
todo.pop_back();
if (node == nullptr) {
assert(results.size() >= 2);
CordRep* right = results.back();
results.pop_back();
CordRep* left = results.back();
results.pop_back();
results.push_back(Concat(left, right));
} else if (pos == 0 && n == node->length) {
results.push_back(CordRep::Ref(node));
} else if (!node->IsConcat()) {
if (node->IsSubstring()) {
pos += node->substring()->start;
node = node->substring()->child;
}
results.push_back(NewSubstring(CordRep::Ref(node), pos, n));
} else if (pos + n <= node->concat()->left->length) {
todo.push_back(SubRange(node->concat()->left, pos, n));
} else if (pos >= node->concat()->left->length) {
pos -= node->concat()->left->length;
todo.push_back(SubRange(node->concat()->right, pos, n));
} else {
size_t left_n = node->concat()->left->length - pos;
todo.push_back(SubRange(nullptr, 0, 0)); // Concat()
todo.push_back(SubRange(node->concat()->right, 0, n - left_n));
todo.push_back(SubRange(node->concat()->left, pos, left_n));
}
} while (!todo.empty());
assert(results.size() == 1);
return results[0];
}
Cord Cord::Subcord(size_t pos, size_t new_size) const {
Cord sub_cord;
size_t length = size();
if (pos > length) pos = length;
if (new_size > length - pos) new_size = length - pos;
if (new_size == 0) return sub_cord;
CordRep* tree = contents_.tree();
if (tree == nullptr) {
// sub_cord is newly constructed, no need to re-zero-out the tail of
// contents_ memory.
sub_cord.contents_.set_data(contents_.data() + pos, new_size, false);
return sub_cord;
}
if (new_size <= InlineRep::kMaxInline) {
char* dest = sub_cord.contents_.data_.as_chars();
Cord::ChunkIterator it = chunk_begin();
it.AdvanceBytes(pos);
size_t remaining_size = new_size;
while (remaining_size > it->size()) {
cord_internal::SmallMemmove(dest, it->data(), it->size());
remaining_size -= it->size();
dest += it->size();
++it;
}
cord_internal::SmallMemmove(dest, it->data(), remaining_size);
sub_cord.contents_.set_inline_size(new_size);
return sub_cord;
}
if (tree->IsBtree()) {
tree = tree->btree()->SubTree(pos, new_size);
} else {
tree = NewSubRange(tree, pos, new_size);
}
sub_cord.contents_.EmplaceTree(tree, contents_.data_,
CordzUpdateTracker::kSubCord);
return sub_cord;
}
// --------------------------------------------------------------------
// Balancing
class CordForest {
public:
explicit CordForest(size_t length)
: root_length_(length), trees_(kMinLengthSize, nullptr) {}
void Build(CordRep* cord_root) {
std::vector<CordRep*> pending = {cord_root};
while (!pending.empty()) {
CordRep* node = pending.back();
pending.pop_back();
CheckNode(node);
if (ABSL_PREDICT_FALSE(!node->IsConcat())) {
AddNode(node);
continue;
}
CordRepConcat* concat_node = node->concat();
if (concat_node->depth() >= kMinLengthSize ||
concat_node->length < min_length[concat_node->depth()]) {
pending.push_back(concat_node->right);
pending.push_back(concat_node->left);
if (concat_node->refcount.IsOne()) {
concat_node->left = concat_freelist_;
concat_freelist_ = concat_node;
} else {
CordRep::Ref(concat_node->right);
CordRep::Ref(concat_node->left);
CordRep::Unref(concat_node);
}
} else {
AddNode(node);
}
}
}
CordRep* ConcatNodes() {
CordRep* sum = nullptr;
for (auto* node : trees_) {
if (node == nullptr) continue;
sum = PrependNode(node, sum);
root_length_ -= node->length;
if (root_length_ == 0) break;
}
ABSL_INTERNAL_CHECK(sum != nullptr, "Failed to locate sum node");
return VerifyTree(sum);
}
private:
CordRep* AppendNode(CordRep* node, CordRep* sum) {
return (sum == nullptr) ? node : MakeConcat(sum, node);
}
CordRep* PrependNode(CordRep* node, CordRep* sum) {
return (sum == nullptr) ? node : MakeConcat(node, sum);
}
void AddNode(CordRep* node) {
CordRep* sum = nullptr;
// Collect together everything with which we will merge with node
int i = 0;
for (; node->length > min_length[i + 1]; ++i) {
auto& tree_at_i = trees_[i];
if (tree_at_i == nullptr) continue;
sum = PrependNode(tree_at_i, sum);
tree_at_i = nullptr;
}
sum = AppendNode(node, sum);
// Insert sum into appropriate place in the forest
for (; sum->length >= min_length[i]; ++i) {
auto& tree_at_i = trees_[i];
if (tree_at_i == nullptr) continue;
sum = MakeConcat(tree_at_i, sum);
tree_at_i = nullptr;
}
// min_length[0] == 1, which means sum->length >= min_length[0]
assert(i > 0);
trees_[i - 1] = sum;
}
// Make concat node trying to resue existing CordRepConcat nodes we
// already collected in the concat_freelist_.
CordRep* MakeConcat(CordRep* left, CordRep* right) {
if (concat_freelist_ == nullptr) return RawConcat(left, right);
CordRepConcat* rep = concat_freelist_;
if (concat_freelist_->left == nullptr) {
concat_freelist_ = nullptr;
} else {
concat_freelist_ = concat_freelist_->left->concat();
}
SetConcatChildren(rep, left, right);
return rep;
}
static void CheckNode(CordRep* node) {
ABSL_INTERNAL_CHECK(node->length != 0u, "");
if (node->IsConcat()) {
ABSL_INTERNAL_CHECK(node->concat()->left != nullptr, "");
ABSL_INTERNAL_CHECK(node->concat()->right != nullptr, "");
ABSL_INTERNAL_CHECK(node->length == (node->concat()->left->length +
node->concat()->right->length),
"");
}
}
size_t root_length_;
// use an inlined vector instead of a flat array to get bounds checking
absl::InlinedVector<CordRep*, kInlinedVectorSize> trees_;
// List of concat nodes we can re-use for Cord balancing.
CordRepConcat* concat_freelist_ = nullptr;
};
static CordRep* Rebalance(CordRep* node) {
VerifyTree(node);
assert(node->IsConcat());
if (node->length == 0) {
return nullptr;
}
CordForest forest(node->length);
forest.Build(node);
return forest.ConcatNodes();
}
// --------------------------------------------------------------------
// Comparators
namespace {
int ClampResult(int memcmp_res) {
return static_cast<int>(memcmp_res > 0) - static_cast<int>(memcmp_res < 0);
}
int CompareChunks(absl::string_view* lhs, absl::string_view* rhs,
size_t* size_to_compare) {
size_t compared_size = std::min(lhs->size(), rhs->size());
assert(*size_to_compare >= compared_size);
*size_to_compare -= compared_size;
int memcmp_res = ::memcmp(lhs->data(), rhs->data(), compared_size);
if (memcmp_res != 0) return memcmp_res;
lhs->remove_prefix(compared_size);
rhs->remove_prefix(compared_size);
return 0;
}
// This overload set computes comparison results from memcmp result. This
// interface is used inside GenericCompare below. Differet implementations
// are specialized for int and bool. For int we clamp result to {-1, 0, 1}
// set. For bool we just interested in "value == 0".
template <typename ResultType>
ResultType ComputeCompareResult(int memcmp_res) {
return ClampResult(memcmp_res);
}
template <>
bool ComputeCompareResult<bool>(int memcmp_res) {
return memcmp_res == 0;
}
} // namespace
// Helper routine. Locates the first flat or external chunk of the Cord without
// initializing the iterator, and returns a string_view referencing the data.
inline absl::string_view Cord::InlineRep::FindFlatStartPiece() const {
if (!is_tree()) {
return absl::string_view(data_.as_chars(), data_.inline_size());
}
CordRep* node = tree();
if (node->IsFlat()) {
return absl::string_view(node->flat()->Data(), node->length);
}
if (node->IsExternal()) {
return absl::string_view(node->external()->base, node->length);
}
if (node->IsBtree()) {
CordRepBtree* tree = node->btree();
int height = tree->height();
while (--height >= 0) {
tree = tree->Edge(CordRepBtree::kFront)->btree();
}
return tree->Data(tree->begin());
}
// Walk down the left branches until we hit a non-CONCAT node.
while (node->IsConcat()) {
node = node->concat()->left;
}
// Get the child node if we encounter a SUBSTRING.
size_t offset = 0;
size_t length = node->length;
assert(length != 0);
if (node->IsSubstring()) {
offset = node->substring()->start;
node = node->substring()->child;
}
if (node->IsFlat()) {
return absl::string_view(node->flat()->Data() + offset, length);
}
assert(node->IsExternal() && "Expect FLAT or EXTERNAL node here");
return absl::string_view(node->external()->base + offset, length);
}
inline int Cord::CompareSlowPath(absl::string_view rhs, size_t compared_size,
size_t size_to_compare) const {
auto advance = [](Cord::ChunkIterator* it, absl::string_view* chunk) {
if (!chunk->empty()) return true;
++*it;
if (it->bytes_remaining_ == 0) return false;
*chunk = **it;
return true;
};
Cord::ChunkIterator lhs_it = chunk_begin();
// compared_size is inside first chunk.
absl::string_view lhs_chunk =
(lhs_it.bytes_remaining_ != 0) ? *lhs_it : absl::string_view();
assert(compared_size <= lhs_chunk.size());
assert(compared_size <= rhs.size());
lhs_chunk.remove_prefix(compared_size);
rhs.remove_prefix(compared_size);
size_to_compare -= compared_size; // skip already compared size.
while (advance(&lhs_it, &lhs_chunk) && !rhs.empty()) {
int comparison_result = CompareChunks(&lhs_chunk, &rhs, &size_to_compare);
if (comparison_result != 0) return comparison_result;
if (size_to_compare == 0) return 0;
}
return static_cast<int>(rhs.empty()) - static_cast<int>(lhs_chunk.empty());
}
inline int Cord::CompareSlowPath(const Cord& rhs, size_t compared_size,
size_t size_to_compare) const {
auto advance = [](Cord::ChunkIterator* it, absl::string_view* chunk) {
if (!chunk->empty()) return true;
++*it;
if (it->bytes_remaining_ == 0) return false;
*chunk = **it;
return true;
};
Cord::ChunkIterator lhs_it = chunk_begin();
Cord::ChunkIterator rhs_it = rhs.chunk_begin();
// compared_size is inside both first chunks.
absl::string_view lhs_chunk =
(lhs_it.bytes_remaining_ != 0) ? *lhs_it : absl::string_view();
absl::string_view rhs_chunk =
(rhs_it.bytes_remaining_ != 0) ? *rhs_it : absl::string_view();
assert(compared_size <= lhs_chunk.size());
assert(compared_size <= rhs_chunk.size());
lhs_chunk.remove_prefix(compared_size);
rhs_chunk.remove_prefix(compared_size);
size_to_compare -= compared_size; // skip already compared size.
while (advance(&lhs_it, &lhs_chunk) && advance(&rhs_it, &rhs_chunk)) {
int memcmp_res = CompareChunks(&lhs_chunk, &rhs_chunk, &size_to_compare);
if (memcmp_res != 0) return memcmp_res;
if (size_to_compare == 0) return 0;
}
return static_cast<int>(rhs_chunk.empty()) -
static_cast<int>(lhs_chunk.empty());
}
inline absl::string_view Cord::GetFirstChunk(const Cord& c) {
return c.contents_.FindFlatStartPiece();
}
inline absl::string_view Cord::GetFirstChunk(absl::string_view sv) {
return sv;
}
// Compares up to 'size_to_compare' bytes of 'lhs' with 'rhs'. It is assumed
// that 'size_to_compare' is greater that size of smallest of first chunks.
template <typename ResultType, typename RHS>
ResultType GenericCompare(const Cord& lhs, const RHS& rhs,
size_t size_to_compare) {
absl::string_view lhs_chunk = Cord::GetFirstChunk(lhs);
absl::string_view rhs_chunk = Cord::GetFirstChunk(rhs);
size_t compared_size = std::min(lhs_chunk.size(), rhs_chunk.size());
assert(size_to_compare >= compared_size);
int memcmp_res = ::memcmp(lhs_chunk.data(), rhs_chunk.data(), compared_size);
if (compared_size == size_to_compare || memcmp_res != 0) {
return ComputeCompareResult<ResultType>(memcmp_res);
}
return ComputeCompareResult<ResultType>(
lhs.CompareSlowPath(rhs, compared_size, size_to_compare));
}
bool Cord::EqualsImpl(absl::string_view rhs, size_t size_to_compare) const {
return GenericCompare<bool>(*this, rhs, size_to_compare);
}
bool Cord::EqualsImpl(const Cord& rhs, size_t size_to_compare) const {
return GenericCompare<bool>(*this, rhs, size_to_compare);
}
template <typename RHS>
inline int SharedCompareImpl(const Cord& lhs, const RHS& rhs) {
size_t lhs_size = lhs.size();
size_t rhs_size = rhs.size();
if (lhs_size == rhs_size) {
return GenericCompare<int>(lhs, rhs, lhs_size);
}
if (lhs_size < rhs_size) {
auto data_comp_res = GenericCompare<int>(lhs, rhs, lhs_size);
return data_comp_res == 0 ? -1 : data_comp_res;
}
auto data_comp_res = GenericCompare<int>(lhs, rhs, rhs_size);
return data_comp_res == 0 ? +1 : data_comp_res;
}
int Cord::Compare(absl::string_view rhs) const {
return SharedCompareImpl(*this, rhs);
}
int Cord::CompareImpl(const Cord& rhs) const {
return SharedCompareImpl(*this, rhs);
}
bool Cord::EndsWith(absl::string_view rhs) const {
size_t my_size = size();
size_t rhs_size = rhs.size();
if (my_size < rhs_size) return false;
Cord tmp(*this);
tmp.RemovePrefix(my_size - rhs_size);
return tmp.EqualsImpl(rhs, rhs_size);
}
bool Cord::EndsWith(const Cord& rhs) const {
size_t my_size = size();
size_t rhs_size = rhs.size();
if (my_size < rhs_size) return false;
Cord tmp(*this);
tmp.RemovePrefix(my_size - rhs_size);
return tmp.EqualsImpl(rhs, rhs_size);
}
// --------------------------------------------------------------------
// Misc.
Cord::operator std::string() const {
std::string s;
absl::CopyCordToString(*this, &s);
return s;
}
void CopyCordToString(const Cord& src, std::string* dst) {
if (!src.contents_.is_tree()) {
src.contents_.CopyTo(dst);
} else {
absl::strings_internal::STLStringResizeUninitialized(dst, src.size());
src.CopyToArraySlowPath(&(*dst)[0]);
}
}
void Cord::CopyToArraySlowPath(char* dst) const {
assert(contents_.is_tree());
absl::string_view fragment;
if (GetFlatAux(contents_.tree(), &fragment)) {
memcpy(dst, fragment.data(), fragment.size());
return;
}
for (absl::string_view chunk : Chunks()) {
memcpy(dst, chunk.data(), chunk.size());
dst += chunk.size();
}
}
Cord::ChunkIterator& Cord::ChunkIterator::AdvanceStack() {
auto& stack_of_right_children = stack_of_right_children_;
if (stack_of_right_children.empty()) {
assert(!current_chunk_.empty()); // Called on invalid iterator.
// We have reached the end of the Cord.
return *this;
}
// Process the next node on the stack.
CordRep* node = stack_of_right_children.back();
stack_of_right_children.pop_back();
// Walk down the left branches until we hit a non-CONCAT node. Save the
// right children to the stack for subsequent traversal.
while (node->IsConcat()) {
stack_of_right_children.push_back(node->concat()->right);
node = node->concat()->left;
}
// Get the child node if we encounter a SUBSTRING.
size_t offset = 0;
size_t length = node->length;
if (node->IsSubstring()) {
offset = node->substring()->start;
node = node->substring()->child;
}
assert(node->IsExternal() || node->IsFlat());
assert(length != 0);
const char* data =
node->IsExternal() ? node->external()->base : node->flat()->Data();
current_chunk_ = absl::string_view(data + offset, length);
current_leaf_ = node;
return *this;
}
Cord Cord::ChunkIterator::AdvanceAndReadBytes(size_t n) {
ABSL_HARDENING_ASSERT(bytes_remaining_ >= n &&
"Attempted to iterate past `end()`");
Cord subcord;
auto constexpr method = CordzUpdateTracker::kCordReader;
if (n <= InlineRep::kMaxInline) {
// Range to read fits in inline data. Flatten it.
char* data = subcord.contents_.set_data(n);
while (n > current_chunk_.size()) {
memcpy(data, current_chunk_.data(), current_chunk_.size());
data += current_chunk_.size();
n -= current_chunk_.size();
++*this;
}
memcpy(data, current_chunk_.data(), n);
if (n < current_chunk_.size()) {
RemoveChunkPrefix(n);
} else if (n > 0) {
++*this;
}
return subcord;
}
if (btree_reader_) {
size_t chunk_size = current_chunk_.size();
if (n <= chunk_size && n <= kMaxBytesToCopy) {
subcord = Cord(current_chunk_.substr(0, n), method);
if (n < chunk_size) {
current_chunk_.remove_prefix(n);
} else {
current_chunk_ = btree_reader_.Next();
}
} else {
CordRep* rep;
current_chunk_ = btree_reader_.Read(n, chunk_size, rep);
subcord.contents_.EmplaceTree(rep, method);
}
bytes_remaining_ -= n;
return subcord;
}
auto& stack_of_right_children = stack_of_right_children_;
if (n < current_chunk_.size()) {
// Range to read is a proper subrange of the current chunk.
assert(current_leaf_ != nullptr);
CordRep* subnode = CordRep::Ref(current_leaf_);
const char* data = subnode->IsExternal() ? subnode->external()->base
: subnode->flat()->Data();
subnode = NewSubstring(subnode, current_chunk_.data() - data, n);
subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
RemoveChunkPrefix(n);
return subcord;
}
// Range to read begins with a proper subrange of the current chunk.
assert(!current_chunk_.empty());
assert(current_leaf_ != nullptr);
CordRep* subnode = CordRep::Ref(current_leaf_);
if (current_chunk_.size() < subnode->length) {
const char* data = subnode->IsExternal() ? subnode->external()->base
: subnode->flat()->Data();
subnode = NewSubstring(subnode, current_chunk_.data() - data,
current_chunk_.size());
}
n -= current_chunk_.size();
bytes_remaining_ -= current_chunk_.size();
// Process the next node(s) on the stack, reading whole subtrees depending on
// their length and how many bytes we are advancing.
CordRep* node = nullptr;
while (!stack_of_right_children.empty()) {
node = stack_of_right_children.back();
stack_of_right_children.pop_back();
if (node->length > n) break;
// TODO(qrczak): This might unnecessarily recreate existing concat nodes.
// Avoiding that would need pretty complicated logic (instead of
// current_leaf, keep current_subtree_ which points to the highest node
// such that the current leaf can be found on the path of left children
// starting from current_subtree_; delay creating subnode while node is
// below current_subtree_; find the proper node along the path of left
// children starting from current_subtree_ if this loop exits while staying
// below current_subtree_; etc.; alternatively, push parents instead of
// right children on the stack).
subnode = Concat(subnode, CordRep::Ref(node));
n -= node->length;
bytes_remaining_ -= node->length;
node = nullptr;
}
if (node == nullptr) {
// We have reached the end of the Cord.
assert(bytes_remaining_ == 0);
subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
return subcord;
}
// Walk down the appropriate branches until we hit a non-CONCAT node. Save the
// right children to the stack for subsequent traversal.
while (node->IsConcat()) {
if (node->concat()->left->length > n) {
// Push right, descend left.
stack_of_right_children.push_back(node->concat()->right);
node = node->concat()->left;
} else {
// Read left, descend right.
subnode = Concat(subnode, CordRep::Ref(node->concat()->left));
n -= node->concat()->left->length;
bytes_remaining_ -= node->concat()->left->length;
node = node->concat()->right;
}
}
// Get the child node if we encounter a SUBSTRING.
size_t offset = 0;
size_t length = node->length;
if (node->IsSubstring()) {
offset = node->substring()->start;
node = node->substring()->child;
}
// Range to read ends with a proper (possibly empty) subrange of the current
// chunk.
assert(node->IsExternal() || node->IsFlat());
assert(length > n);
if (n > 0) {
subnode = Concat(subnode, NewSubstring(CordRep::Ref(node), offset, n));
}
const char* data =
node->IsExternal() ? node->external()->base : node->flat()->Data();
current_chunk_ = absl::string_view(data + offset + n, length - n);
current_leaf_ = node;
bytes_remaining_ -= n;
subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
return subcord;
}
void Cord::ChunkIterator::AdvanceBytesSlowPath(size_t n) {
assert(bytes_remaining_ >= n && "Attempted to iterate past `end()`");
assert(n >= current_chunk_.size()); // This should only be called when
// iterating to a new node.
n -= current_chunk_.size();
bytes_remaining_ -= current_chunk_.size();
if (stack_of_right_children_.empty()) {
// We have reached the end of the Cord.
assert(bytes_remaining_ == 0);
return;
}
// Process the next node(s) on the stack, skipping whole subtrees depending on
// their length and how many bytes we are advancing.
CordRep* node = nullptr;
auto& stack_of_right_children = stack_of_right_children_;
while (!stack_of_right_children.empty()) {
node = stack_of_right_children.back();
stack_of_right_children.pop_back();
if (node->length > n) break;
n -= node->length;
bytes_remaining_ -= node->length;
node = nullptr;
}
if (node == nullptr) {
// We have reached the end of the Cord.
assert(bytes_remaining_ == 0);
return;
}
// Walk down the appropriate branches until we hit a non-CONCAT node. Save the
// right children to the stack for subsequent traversal.
while (node->IsConcat()) {
if (node->concat()->left->length > n) {
// Push right, descend left.
stack_of_right_children.push_back(node->concat()->right);
node = node->concat()->left;
} else {
// Skip left, descend right.
n -= node->concat()->left->length;
bytes_remaining_ -= node->concat()->left->length;
node = node->concat()->right;
}
}
// Get the child node if we encounter a SUBSTRING.
size_t offset = 0;
size_t length = node->length;
if (node->IsSubstring()) {
offset = node->substring()->start;
node = node->substring()->child;
}
assert(node->IsExternal() || node->IsFlat());
assert(length > n);
const char* data =
node->IsExternal() ? node->external()->base : node->flat()->Data();
current_chunk_ = absl::string_view(data + offset + n, length - n);
current_leaf_ = node;
bytes_remaining_ -= n;
}
char Cord::operator[](size_t i) const {
ABSL_HARDENING_ASSERT(i < size());
size_t offset = i;
const CordRep* rep = contents_.tree();
if (rep == nullptr) {
return contents_.data()[i];
}
while (true) {
assert(rep != nullptr);
assert(offset < rep->length);
if (rep->IsFlat()) {
// Get the "i"th character directly from the flat array.
return rep->flat()->Data()[offset];
} else if (rep->IsBtree()) {
return rep->btree()->GetCharacter(offset);
} else if (rep->IsExternal()) {
// Get the "i"th character from the external array.
return rep->external()->base[offset];
} else if (rep->IsConcat()) {
// Recursively branch to the side of the concatenation that the "i"th
// character is on.
size_t left_length = rep->concat()->left->length;
if (offset < left_length) {
rep = rep->concat()->left;
} else {
offset -= left_length;
rep = rep->concat()->right;
}
} else {
// This must be a substring a node, so bypass it to get to the child.
assert(rep->IsSubstring());
offset += rep->substring()->start;
rep = rep->substring()->child;
}
}
}
absl::string_view Cord::FlattenSlowPath() {
assert(contents_.is_tree());
size_t total_size = size();
CordRep* new_rep;
char* new_buffer;
// Try to put the contents into a new flat rep. If they won't fit in the
// biggest possible flat node, use an external rep instead.
if (total_size <= kMaxFlatLength) {
new_rep = CordRepFlat::New(total_size);
new_rep->length = total_size;
new_buffer = new_rep->flat()->Data();
CopyToArraySlowPath(new_buffer);
} else {
new_buffer = std::allocator<char>().allocate(total_size);
CopyToArraySlowPath(new_buffer);
new_rep = absl::cord_internal::NewExternalRep(
absl::string_view(new_buffer, total_size), [](absl::string_view s) {
std::allocator<char>().deallocate(const_cast<char*>(s.data()),
s.size());
});
}
CordzUpdateScope scope(contents_.cordz_info(), CordzUpdateTracker::kFlatten);
CordRep::Unref(contents_.as_tree());
contents_.SetTree(new_rep, scope);
return absl::string_view(new_buffer, total_size);
}
/* static */ bool Cord::GetFlatAux(CordRep* rep, absl::string_view* fragment) {
assert(rep != nullptr);
if (rep->IsFlat()) {
*fragment = absl::string_view(rep->flat()->Data(), rep->length);
return true;
} else if (rep->IsExternal()) {
*fragment = absl::string_view(rep->external()->base, rep->length);
return true;
} else if (rep->IsBtree()) {
return rep->btree()->IsFlat(fragment);
} else if (rep->IsSubstring()) {
CordRep* child = rep->substring()->child;
if (child->IsFlat()) {
*fragment = absl::string_view(
child->flat()->Data() + rep->substring()->start, rep->length);
return true;
} else if (child->IsExternal()) {
*fragment = absl::string_view(
child->external()->base + rep->substring()->start, rep->length);
return true;
} else if (child->IsBtree()) {
return child->btree()->IsFlat(rep->substring()->start, rep->length,
fragment);
}
}
return false;
}
/* static */ void Cord::ForEachChunkAux(
absl::cord_internal::CordRep* rep,
absl::FunctionRef<void(absl::string_view)> callback) {
if (rep->IsBtree()) {
ChunkIterator it(rep), end;
while (it != end) {
callback(*it);
++it;
}
return;
}
assert(rep != nullptr);
int stack_pos = 0;
constexpr int stack_max = 128;
// Stack of right branches for tree traversal
absl::cord_internal::CordRep* stack[stack_max];
absl::cord_internal::CordRep* current_node = rep;
while (true) {
if (current_node->IsConcat()) {
if (stack_pos == stack_max) {
// There's no more room on our stack array to add another right branch,
// and the idea is to avoid allocations, so call this function
// recursively to navigate this subtree further. (This is not something
// we expect to happen in practice).
ForEachChunkAux(current_node, callback);
// Pop the next right branch and iterate.
current_node = stack[--stack_pos];
continue;
} else {
// Save the right branch for later traversal and continue down the left
// branch.
stack[stack_pos++] = current_node->concat()->right;
current_node = current_node->concat()->left;
continue;
}
}
// This is a leaf node, so invoke our callback.
absl::string_view chunk;
bool success = GetFlatAux(current_node, &chunk);
assert(success);
if (success) {
callback(chunk);
}
if (stack_pos == 0) {
// end of traversal
return;
}
current_node = stack[--stack_pos];
}
}
static void DumpNode(CordRep* rep, bool include_data, std::ostream* os,
int indent) {
const int kIndentStep = 1;
absl::InlinedVector<CordRep*, kInlinedVectorSize> stack;
absl::InlinedVector<int, kInlinedVectorSize> indents;
for (;;) {
*os << std::setw(3) << rep->refcount.Get();
*os << " " << std::setw(7) << rep->length;
*os << " [";
if (include_data) *os << static_cast<void*>(rep);
*os << "]";
*os << " " << (IsRootBalanced(rep) ? 'b' : 'u');
*os << " " << std::setw(indent) << "";
if (rep->IsConcat()) {
*os << "CONCAT depth=" << Depth(rep) << "\n";
indent += kIndentStep;
indents.push_back(indent);
stack.push_back(rep->concat()->right);
rep = rep->concat()->left;
} else if (rep->IsSubstring()) {
*os << "SUBSTRING @ " << rep->substring()->start << "\n";
indent += kIndentStep;
rep = rep->substring()->child;
} else { // Leaf or ring
if (rep->IsExternal()) {
*os << "EXTERNAL [";
if (include_data)
*os << absl::CEscape(std::string(rep->external()->base, rep->length));
*os << "]\n";
} else if (rep->IsFlat()) {
*os << "FLAT cap=" << rep->flat()->Capacity() << " [";
if (include_data)
*os << absl::CEscape(std::string(rep->flat()->Data(), rep->length));
*os << "]\n";
} else {
CordRepBtree::Dump(rep, /*label=*/ "", include_data, *os);
}
if (stack.empty()) break;
rep = stack.back();
stack.pop_back();
indent = indents.back();
indents.pop_back();
}
}
ABSL_INTERNAL_CHECK(indents.empty(), "");
}
static std::string ReportError(CordRep* root, CordRep* node) {
std::ostringstream buf;
buf << "Error at node " << node << " in:";
DumpNode(root, true, &buf);
return buf.str();
}
static bool VerifyNode(CordRep* root, CordRep* start_node,
bool full_validation) {
absl::InlinedVector<CordRep*, 2> worklist;
worklist.push_back(start_node);
do {
CordRep* node = worklist.back();
worklist.pop_back();
ABSL_INTERNAL_CHECK(node != nullptr, ReportError(root, node));
if (node != root) {
ABSL_INTERNAL_CHECK(node->length != 0, ReportError(root, node));
}
if (node->IsConcat()) {
ABSL_INTERNAL_CHECK(node->concat()->left != nullptr,
ReportError(root, node));
ABSL_INTERNAL_CHECK(node->concat()->right != nullptr,
ReportError(root, node));
ABSL_INTERNAL_CHECK((node->length == node->concat()->left->length +
node->concat()->right->length),
ReportError(root, node));
if (full_validation) {
worklist.push_back(node->concat()->right);
worklist.push_back(node->concat()->left);
}
} else if (node->IsFlat()) {
ABSL_INTERNAL_CHECK(node->length <= node->flat()->Capacity(),
ReportError(root, node));
} else if (node->IsExternal()) {
ABSL_INTERNAL_CHECK(node->external()->base != nullptr,
ReportError(root, node));
} else if (node->IsSubstring()) {
ABSL_INTERNAL_CHECK(
node->substring()->start < node->substring()->child->length,
ReportError(root, node));
ABSL_INTERNAL_CHECK(node->substring()->start + node->length <=
node->substring()->child->length,
ReportError(root, node));
}
} while (!worklist.empty());
return true;
}
// Traverses the tree and computes the total memory allocated.
/* static */ size_t Cord::MemoryUsageAux(const CordRep* rep) {
size_t total_mem_usage = 0;
// Allow a quick exit for the common case that the root is a leaf.
if (RepMemoryUsageLeaf(rep, &total_mem_usage)) {
return total_mem_usage;
}
// Iterate over the tree. cur_node is never a leaf node and leaf nodes will
// never be appended to tree_stack. This reduces overhead from manipulating
// tree_stack.
absl::InlinedVector<const CordRep*, kInlinedVectorSize> tree_stack;
const CordRep* cur_node = rep;
while (true) {
const CordRep* next_node = nullptr;
if (cur_node->IsConcat()) {
total_mem_usage += sizeof(CordRepConcat);
const CordRep* left = cur_node->concat()->left;
if (!RepMemoryUsageLeaf(left, &total_mem_usage)) {
next_node = left;
}
const CordRep* right = cur_node->concat()->right;
if (!RepMemoryUsageLeaf(right, &total_mem_usage)) {
if (next_node) {
tree_stack.push_back(next_node);
}
next_node = right;
}
} else if (cur_node->IsBtree()) {
total_mem_usage += sizeof(CordRepBtree);
const CordRepBtree* node = cur_node->btree();
if (node->height() == 0) {
for (const CordRep* edge : node->Edges()) {
RepMemoryUsageDataEdge(edge, &total_mem_usage);
}
} else {
for (const CordRep* edge : node->Edges()) {
tree_stack.push_back(edge);
}
}
} else {
// Since cur_node is not a leaf or a concat node it must be a substring.
assert(cur_node->IsSubstring());
total_mem_usage += sizeof(CordRepSubstring);
next_node = cur_node->substring()->child;
if (RepMemoryUsageLeaf(next_node, &total_mem_usage)) {
next_node = nullptr;
}
}
if (!next_node) {
if (tree_stack.empty()) {
return total_mem_usage;
}
next_node = tree_stack.back();
tree_stack.pop_back();
}
cur_node = next_node;
}
}
std::ostream& operator<<(std::ostream& out, const Cord& cord) {
for (absl::string_view chunk : cord.Chunks()) {
out.write(chunk.data(), chunk.size());
}
return out;
}
namespace strings_internal {
size_t CordTestAccess::FlatOverhead() { return cord_internal::kFlatOverhead; }
size_t CordTestAccess::MaxFlatLength() { return cord_internal::kMaxFlatLength; }
size_t CordTestAccess::FlatTagToLength(uint8_t tag) {
return cord_internal::TagToLength(tag);
}
uint8_t CordTestAccess::LengthToTag(size_t s) {
ABSL_INTERNAL_CHECK(s <= kMaxFlatLength, absl::StrCat("Invalid length ", s));
return cord_internal::AllocatedSizeToTag(s + cord_internal::kFlatOverhead);
}
size_t CordTestAccess::SizeofCordRepConcat() { return sizeof(CordRepConcat); }
size_t CordTestAccess::SizeofCordRepExternal() {
return sizeof(CordRepExternal);
}
size_t CordTestAccess::SizeofCordRepSubstring() {
return sizeof(CordRepSubstring);
}
} // namespace strings_internal
ABSL_NAMESPACE_END
} // namespace absl