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// Copyright 2021 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_analysis.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <unordered_set>
#include "absl/base/config.h"
#include "absl/base/nullability.h"
#include "absl/strings/internal/cord_data_edge.h"
#include "absl/strings/internal/cord_internal.h"
#include "absl/strings/internal/cord_rep_btree.h"
#include "absl/strings/internal/cord_rep_crc.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace cord_internal {
namespace {
// Accounting mode for analyzing memory usage.
enum class Mode { kFairShare, kTotal, kTotalMorePrecise };
// CordRepRef holds a `const CordRep*` reference in rep, and depending on mode,
// holds a 'fraction' representing a cumulative inverse refcount weight.
template <Mode mode>
struct CordRepRef {
// Instantiates a CordRepRef instance.
explicit CordRepRef(const CordRep* absl_nonnull r) : rep(r) {}
// Creates a child reference holding the provided child.
// Overloaded to add cumulative reference count for kFairShare.
CordRepRef Child(const CordRep* absl_nonnull child) const {
return CordRepRef(child);
}
const CordRep* absl_nonnull rep;
};
// RawUsage holds the computed total number of bytes.
template <Mode mode>
struct RawUsage {
size_t total = 0;
// Add 'size' to total, ignoring the CordRepRef argument.
void Add(size_t size, CordRepRef<mode>) { total += size; }
};
// Overloaded representation of RawUsage that tracks the set of objects
// counted, and avoids double-counting objects referenced more than once
// by the same Cord.
template <>
struct RawUsage<Mode::kTotalMorePrecise> {
size_t total = 0;
// TODO(b/289250880): Replace this with a flat_hash_set.
std::unordered_set<const CordRep* absl_nonnull> counted;
void Add(size_t size, CordRepRef<Mode::kTotalMorePrecise> repref) {
if (counted.insert(repref.rep).second) {
total += size;
}
}
};
// Returns n / refcount avoiding a div for the common refcount == 1.
template <typename refcount_t>
double MaybeDiv(double d, refcount_t refcount) {
return refcount == 1 ? d : d / refcount;
}
// Overloaded 'kFairShare' specialization for CordRepRef. This class holds a
// `fraction` value which represents a cumulative inverse refcount weight.
// For example, a top node with a reference count of 2 will have a fraction
// value of 1/2 = 0.5, representing the 'fair share' of memory it references.
// A node below such a node with a reference count of 5 then has a fraction of
// 0.5 / 5 = 0.1 representing the fair share of memory below that node, etc.
template <>
struct CordRepRef<Mode::kFairShare> {
// Creates a CordRepRef with the provided rep and top (parent) fraction.
explicit CordRepRef(const CordRep* absl_nonnull r, double frac = 1.0)
: rep(r), fraction(MaybeDiv(frac, r->refcount.Get())) {}
// Returns a CordRepRef with a fraction of `this->fraction / child.refcount`
CordRepRef Child(const CordRep* absl_nonnull child) const {
return CordRepRef(child, fraction);
}
const CordRep* absl_nonnull rep;
double fraction;
};
// Overloaded 'kFairShare' specialization for RawUsage
template <>
struct RawUsage<Mode::kFairShare> {
double total = 0;
// Adds `size` multiplied by `rep.fraction` to the total size.
void Add(size_t size, CordRepRef<Mode::kFairShare> rep) {
total += static_cast<double>(size) * rep.fraction;
}
};
// Computes the estimated memory size of the provided data edge.
// External reps are assumed 'heap allocated at their exact size'.
template <Mode mode>
void AnalyzeDataEdge(CordRepRef<mode> rep, RawUsage<mode>& raw_usage) {
assert(IsDataEdge(rep.rep));
// Consume all substrings
if (rep.rep->tag == SUBSTRING) {
raw_usage.Add(sizeof(CordRepSubstring), rep);
rep = rep.Child(rep.rep->substring()->child);
}
// Consume FLAT / EXTERNAL
const size_t size =
rep.rep->tag >= FLAT
? rep.rep->flat()->AllocatedSize()
: rep.rep->length + sizeof(CordRepExternalImpl<intptr_t>);
raw_usage.Add(size, rep);
}
// Computes the memory size of the provided Btree tree.
template <Mode mode>
void AnalyzeBtree(CordRepRef<mode> rep, RawUsage<mode>& raw_usage) {
raw_usage.Add(sizeof(CordRepBtree), rep);
const CordRepBtree* tree = rep.rep->btree();
if (tree->height() > 0) {
for (CordRep* edge : tree->Edges()) {
AnalyzeBtree(rep.Child(edge), raw_usage);
}
} else {
for (CordRep* edge : tree->Edges()) {
AnalyzeDataEdge(rep.Child(edge), raw_usage);
}
}
}
template <Mode mode>
size_t GetEstimatedUsage(const CordRep* absl_nonnull rep) {
// Zero initialized memory usage totals.
RawUsage<mode> raw_usage;
// Capture top level node and refcount into a CordRepRef.
CordRepRef<mode> repref(rep);
// Consume the top level CRC node if present.
if (repref.rep->tag == CRC) {
raw_usage.Add(sizeof(CordRepCrc), repref);
if (repref.rep->crc()->child == nullptr) {
return static_cast<size_t>(raw_usage.total);
}
repref = repref.Child(repref.rep->crc()->child);
}
if (IsDataEdge(repref.rep)) {
AnalyzeDataEdge(repref, raw_usage);
} else if (repref.rep->tag == BTREE) {
AnalyzeBtree(repref, raw_usage);
} else {
assert(false);
}
return static_cast<size_t>(raw_usage.total);
}
} // namespace
size_t GetEstimatedMemoryUsage(const CordRep* absl_nonnull rep) {
return GetEstimatedUsage<Mode::kTotal>(rep);
}
size_t GetEstimatedFairShareMemoryUsage(const CordRep* absl_nonnull rep) {
return GetEstimatedUsage<Mode::kFairShare>(rep);
}
size_t GetMorePreciseMemoryUsage(const CordRep* absl_nonnull rep) {
return GetEstimatedUsage<Mode::kTotalMorePrecise>(rep);
}
} // namespace cord_internal
ABSL_NAMESPACE_END
} // namespace absl
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