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// Copyright 2020 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "third_party/blink/renderer/platform/disk_data_allocator.h"
#include <algorithm>
#include <utility>
#include "base/logging.h"
#include "base/threading/thread_restrictions.h"
#include "third_party/blink/renderer/platform/wtf/std_lib_extras.h"
#include "third_party/blink/renderer/platform/wtf/wtf.h"
namespace blink {
DiskDataAllocator::DiskDataAllocator()
: free_chunks_size_(0), file_tail_(0), may_write_(false) {}
DiskDataAllocator::~DiskDataAllocator() = default;
bool DiskDataAllocator::may_write() {
MutexLocker locker(mutex_);
return may_write_;
}
void DiskDataAllocator::set_may_write_for_testing(bool may_write) {
MutexLocker locker(mutex_);
may_write_ = may_write;
}
DiskDataAllocator::Metadata DiskDataAllocator::FindChunk(size_t size) {
// Try to reuse some space. Policy:
// 1. Exact fit
// 2. Worst fit
Metadata chosen_chunk{-1, 0};
size_t worst_fit_size = 0;
for (const auto& chunk : free_chunks_) {
size_t chunk_size = chunk.second;
if (size == chunk_size) {
chosen_chunk = {chunk.first, chunk.second};
break;
} else if (chunk_size > size && chunk_size > worst_fit_size) {
chosen_chunk = {chunk.first, chunk.second};
worst_fit_size = chunk.second;
}
}
if (chosen_chunk.start_offset() != -1) {
free_chunks_size_ -= size;
free_chunks_.erase(chosen_chunk.start_offset());
if (chosen_chunk.size() > size) {
std::pair<int64_t, size_t> remainder_chunk = {
chosen_chunk.start_offset() + size, chosen_chunk.size() - size};
auto result = free_chunks_.insert(remainder_chunk);
DCHECK(result.second);
chosen_chunk.size_ = size;
}
} else {
chosen_chunk = {file_tail_, size};
file_tail_ += size;
}
return chosen_chunk;
}
void DiskDataAllocator::ReleaseChunk(const Metadata& metadata) {
Metadata chunk = metadata;
DCHECK(free_chunks_.find(chunk.start_offset()) == free_chunks_.end());
auto lower_bound = free_chunks_.lower_bound(chunk.start_offset());
DCHECK(free_chunks_.upper_bound(chunk.start_offset()) ==
free_chunks_.lower_bound(chunk.start_offset()));
if (lower_bound != free_chunks_.begin()) {
// There is a chunk left.
auto left = --lower_bound;
// Can merge with the left chunk.
int64_t left_chunk_end = left->first + left->second;
DCHECK_LE(left_chunk_end, chunk.start_offset());
if (left_chunk_end == chunk.start_offset()) {
chunk = {left->first, left->second + chunk.size()};
free_chunks_size_ -= left->second;
free_chunks_.erase(left);
}
}
auto right = free_chunks_.upper_bound(chunk.start_offset());
if (right != free_chunks_.end()) {
DCHECK_NE(right->first, chunk.start_offset());
int64_t chunk_end = chunk.start_offset() + chunk.size();
DCHECK_LE(chunk_end, right->first);
if (right->first == chunk_end) {
chunk = {chunk.start_offset(), chunk.size() + right->second};
free_chunks_size_ -= right->second;
free_chunks_.erase(right);
}
}
auto result = free_chunks_.insert({chunk.start_offset(), chunk.size()});
DCHECK(result.second);
free_chunks_size_ += chunk.size();
}
std::unique_ptr<DiskDataAllocator::Metadata> DiskDataAllocator::Write(
const void* data,
size_t size) {
Metadata chosen_chunk = {0, 0};
{
MutexLocker locker(mutex_);
if (!may_write_)
return nullptr;
chosen_chunk = FindChunk(size);
} // Don't hold the lock during the actual Write().
int size_int = static_cast<int>(size);
const char* data_char = reinterpret_cast<const char*>(data);
int written = DoWrite(chosen_chunk.start_offset(), data_char, size_int);
MutexLocker locker(mutex_);
if (size_int != written) {
// Assume that the error is not transient. This can happen if the disk is
// full for instance, in which case it is likely better not to try writing
// later.
may_write_ = false;
return nullptr;
}
#if DCHECK_IS_ON()
allocated_chunks_.insert({chosen_chunk.start_offset(), chosen_chunk.size()});
#endif
return std::unique_ptr<Metadata>(
new Metadata(chosen_chunk.start_offset(), chosen_chunk.size()));
}
void DiskDataAllocator::Read(const Metadata& metadata, void* data) {
DCHECK(IsMainThread());
// Doesn't need locking as files support concurrent access, and we don't
// update metadata.
char* data_char = reinterpret_cast<char*>(data);
DoRead(metadata.start_offset(), data_char, metadata.size());
#if DCHECK_IS_ON()
{
MutexLocker locker(mutex_);
auto it = allocated_chunks_.find(metadata.start_offset());
DCHECK(it != allocated_chunks_.end());
DCHECK_EQ(metadata.size(), it->second);
}
#endif
}
void DiskDataAllocator::Discard(std::unique_ptr<Metadata> metadata) {
MutexLocker locker(mutex_);
DCHECK(may_write_ || file_.IsValid());
#if DCHECK_IS_ON()
auto it = allocated_chunks_.find(metadata->start_offset());
DCHECK(it != allocated_chunks_.end());
DCHECK_EQ(metadata->size(), it->second);
allocated_chunks_.erase(it);
#endif
ReleaseChunk(*metadata);
}
int DiskDataAllocator::DoWrite(int64_t offset, const char* data, int size) {
int rv = file_.Write(offset, data, size);
// No PCHECK(), since a file writing error is recoverable.
if (rv != size) {
LOG(ERROR) << "DISK: Cannot write to disk. written = " << rv << " "
<< base::File::ErrorToString(base::File::GetLastFileError());
}
return rv;
}
void DiskDataAllocator::DoRead(int64_t offset, char* data, int size) {
// This happens on the main thread, which is typically not allowed. This is
// fine as this is expected to happen rarely, and only be slow with memory
// pressure, in which case writing to/reading from disk is better than
// swapping out random parts of the memory. See crbug.com/1029320 for details.
base::ScopedAllowBlocking allow_blocking;
int rv = file_.Read(offset, data, size);
// Can only crash, since we cannot continue without the data.
PCHECK(rv == size) << "Likely file corruption.";
}
void DiskDataAllocator::ProvideTemporaryFile(base::File file) {
MutexLocker locker(mutex_);
DCHECK(IsMainThread());
DCHECK(!file_.IsValid());
DCHECK(!may_write_);
file_ = std::move(file);
may_write_ = file_.IsValid();
}
// static
DiskDataAllocator& DiskDataAllocator::Instance() {
DEFINE_STATIC_LOCAL(DiskDataAllocator, instance, ());
return instance;
}
// static
void DiskDataAllocator::Bind(
mojo::PendingReceiver<mojom::blink::DiskAllocator> receiver) {
DCHECK(!Instance().receiver_.is_bound());
Instance().receiver_.Bind(std::move(receiver));
}
} // namespace blink
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