third_party/blink/renderer/platform/bindings/parkable_string_manager.cc

// Copyright 2018 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/bindings/parkable_string_manager.h"

#include <utility>

#include "base/bind.h"
#include "base/macros.h"
#include "base/metrics/histogram_functions.h"
#include "base/metrics/histogram_macros.h"
#include "base/single_thread_task_runner.h"
#include "base/trace_event/memory_allocator_dump.h"
#include "base/trace_event/process_memory_dump.h"
#include "base/trace_event/trace_event.h"
#include "third_party/blink/public/platform/platform.h"
#include "third_party/blink/renderer/platform/bindings/parkable_string.h"
#include "third_party/blink/renderer/platform/instrumentation/memory_pressure_listener.h"
#include "third_party/blink/renderer/platform/scheduler/public/thread.h"
#include "third_party/blink/renderer/platform/scheduler/public/thread_scheduler.h"
#include "third_party/blink/renderer/platform/wtf/text/wtf_string.h"
#include "third_party/blink/renderer/platform/wtf/vector.h"
#include "third_party/blink/renderer/platform/wtf/wtf.h"

namespace blink {

struct ParkableStringManager::Statistics {
  size_t original_size;
  size_t uncompressed_size;
  size_t compressed_original_size;
  size_t compressed_size;
  size_t metadata_size;
  size_t overhead_size;
  size_t total_size;
  int64_t savings_size;
};

namespace {

class OnPurgeMemoryListener : public GarbageCollected<OnPurgeMemoryListener>,
                              public MemoryPressureListener {
  USING_GARBAGE_COLLECTED_MIXIN(OnPurgeMemoryListener);

  void OnPurgeMemory() override {
    ParkableStringManager::Instance().PurgeMemory();
  }
};

}  // namespace

struct ParkableStringManager::ParkableStringImplHash {
  STATIC_ONLY(ParkableStringImplHash);

  static unsigned GetHash(ParkableStringImpl* key) { return key->GetHash(); }

  static inline bool Equal(const ParkableStringImpl* a,
                           const ParkableStringImpl* b) {
    return a->Equal(*b);
  }

  static constexpr bool safe_to_compare_to_empty_or_deleted = false;
};

struct ParkableStringManager::ParkableStringImplTranslator {
  STATIC_ONLY(ParkableStringImplTranslator);

  static unsigned GetHash(const scoped_refptr<StringImpl>& string) {
    return string->GetHash();
  }

  static bool Equal(const ParkableStringImpl* parkable,
                    const scoped_refptr<StringImpl>& string) {
    return parkable->Equal(string);
  }

  static void Translate(ParkableStringImpl*& new_parkable,
                        scoped_refptr<StringImpl>&& string,
                        unsigned hash) {
    new_parkable = new ParkableStringImpl(
        std::move(string), ParkableStringImpl::ParkableState::kParkable);
    DCHECK_EQ(hash, new_parkable->GetHash());
  }
};

// static
ParkableStringManagerDumpProvider*
ParkableStringManagerDumpProvider::Instance() {
  static ParkableStringManagerDumpProvider instance;
  return &instance;
}

bool ParkableStringManagerDumpProvider::OnMemoryDump(
    const base::trace_event::MemoryDumpArgs& args,
    base::trace_event::ProcessMemoryDump* pmd) {
  return ParkableStringManager::Instance().OnMemoryDump(pmd);
}

ParkableStringManagerDumpProvider::~ParkableStringManagerDumpProvider() =
    default;
ParkableStringManagerDumpProvider::ParkableStringManagerDumpProvider() =
    default;

ParkableStringManager& ParkableStringManager::Instance() {
  DCHECK(IsMainThread());
  DEFINE_STATIC_LOCAL(ParkableStringManager, instance, ());
  return instance;
}

ParkableStringManager::~ParkableStringManager() = default;

void ParkableStringManager::SetRendererBackgrounded(bool backgrounded) {
  DCHECK(IsMainThread());
  backgrounded_ = backgrounded;
}

bool ParkableStringManager::IsRendererBackgrounded() const {
  DCHECK(IsMainThread());
  return backgrounded_;
}

bool ParkableStringManager::OnMemoryDump(
    base::trace_event::ProcessMemoryDump* pmd) {
  DCHECK(IsMainThread());
  base::trace_event::MemoryAllocatorDump* dump =
      pmd->CreateAllocatorDump("parkable_strings");

  Statistics stats = ComputeStatistics();

  dump->AddScalar("size", "bytes", stats.total_size);
  dump->AddScalar("original_size", "bytes", stats.original_size);
  dump->AddScalar("uncompressed_size", "bytes", stats.uncompressed_size);
  dump->AddScalar("compressed_size", "bytes", stats.compressed_size);
  dump->AddScalar("metadata_size", "bytes", stats.metadata_size);
  dump->AddScalar("overhead_size", "bytes", stats.overhead_size);
  // Has to be uint64_t.
  dump->AddScalar("savings_size", "bytes",
                  stats.savings_size > 0 ? stats.savings_size : 0);

  pmd->AddSuballocation(dump->guid(),
                        WTF::Partitions::kAllocatedObjectPoolName);
  return true;
}

// static
bool ParkableStringManager::ShouldPark(const StringImpl& string) {
  // Don't attempt to park strings smaller than this size.
  static constexpr unsigned int kSizeThreshold = 10000;
  // TODO(lizeb): Consider parking non-main thread strings.
  return string.length() > kSizeThreshold && IsMainThread();
}

scoped_refptr<ParkableStringImpl> ParkableStringManager::Add(
    scoped_refptr<StringImpl>&& string) {
  DCHECK(IsMainThread());

  ScheduleAgingTaskIfNeeded();

  scoped_refptr<StringImpl> string_ptr(string);
  // Hit in either the unparked or parked strings.
  auto it = unparked_strings_
                .Find<ParkableStringImplTranslator, scoped_refptr<StringImpl>>(
                    string_ptr);
  if (it != unparked_strings_.end())
    return *it;

  // This is an "expensive hit", as we unparked then discarded the unparked
  // representation of a string.
  //
  // If this is problematic, we can unpark the string for "free" (since the
  // incoming) string is unparked and has the same content, or change the
  // interface. Note that at the same time the hit means that we avoided an
  // expensive compression task.
  it = parked_strings_
           .Find<ParkableStringImplTranslator, scoped_refptr<StringImpl>>(
               string_ptr);
  if (it != parked_strings_.end())
    return *it;

  // No hit, new unparked string.
  auto add_result =
      unparked_strings_.AddWithTranslator<ParkableStringImplTranslator,
                                          scoped_refptr<StringImpl>>(
          std::move(string_ptr));
  DCHECK(add_result.is_new_entry);

  // Lazy registration because registering too early can cause crashes on Linux,
  // see crbug.com/930117, and registering without any strings is pointless
  // anyway.
  if (!did_register_memory_pressure_listener_) {
    // No need to ever unregister, as the only ParkableStringManager instance
    // lives forever.
    MemoryPressureListenerRegistry::Instance().RegisterClient(
        MakeGarbageCollected<OnPurgeMemoryListener>());
    did_register_memory_pressure_listener_ = true;
  }

  if (!has_posted_unparking_time_accounting_task_) {
    scoped_refptr<base::SingleThreadTaskRunner> task_runner =
        Thread::Current()->GetTaskRunner();
    DCHECK(task_runner);
    task_runner->PostDelayedTask(
        FROM_HERE,
        base::BindOnce(&ParkableStringManager::RecordStatisticsAfter5Minutes,
                       base::Unretained(this)),
        base::TimeDelta::FromMinutes(5));
    has_posted_unparking_time_accounting_task_ = true;
  }

  return base::AdoptRef(*add_result.stored_value);
}

void ParkableStringManager::Remove(ParkableStringImpl* string) {
  DCHECK(IsMainThread());
  DCHECK(string->may_be_parked());
  if (string->is_parked()) {
    auto it = parked_strings_.find(string);
    DCHECK(it != parked_strings_.end());
    parked_strings_.erase(it);
  } else {
    auto it = unparked_strings_.find(string);
    DCHECK(it != unparked_strings_.end());
    unparked_strings_.erase(it);
  }
}

void ParkableStringManager::OnParked(ParkableStringImpl* newly_parked_string) {
  DCHECK(IsMainThread());
  DCHECK(newly_parked_string->may_be_parked());
  DCHECK(newly_parked_string->is_parked());
  auto it = unparked_strings_.find(newly_parked_string);
  DCHECK(it != unparked_strings_.end());
  DCHECK_EQ(*it, newly_parked_string);
  unparked_strings_.erase(it);
  parked_strings_.insert(newly_parked_string);
}

void ParkableStringManager::OnUnparked(ParkableStringImpl* was_parked_string) {
  DCHECK(IsMainThread());
  DCHECK(was_parked_string->may_be_parked());
  DCHECK(!was_parked_string->is_parked());
  auto it = parked_strings_.find(was_parked_string);
  DCHECK(it != parked_strings_.end());
  DCHECK_EQ(*it, was_parked_string);
  parked_strings_.erase(it);
  unparked_strings_.insert(was_parked_string);
  ScheduleAgingTaskIfNeeded();
}

void ParkableStringManager::RecordUnparkingTime(
    base::TimeDelta unparking_time) {
  total_unparking_time_ += unparking_time;
}

void ParkableStringManager::ParkAll(ParkableStringImpl::ParkingMode mode) {
  DCHECK(IsMainThread());

  size_t total_size = 0;
  for (ParkableStringImpl* str : parked_strings_)
    total_size += str->CharactersSizeInBytes();

  // Parking may be synchronous, need to copy values first.
  // In case of synchronous parking, |ParkableStringImpl::Park()| calls
  // |OnParked()|, which moves the string from |unparked_strings_|
  // to |parked_strings_|, hence the need to copy values first.
  //
  // Efficiency: In practice, either we are parking strings for the first time,
  // and |unparked_strings_| can contain a few 10s of strings (and we will
  // trigger expensive compression), or this is a subsequent one, and
  // |unparked_strings_| will have few entries.
  WTF::Vector<ParkableStringImpl*> unparked = GetUnparkedStrings();

  for (ParkableStringImpl* str : unparked) {
    str->Park(mode);
    total_size += str->CharactersSizeInBytes();
  }
}

size_t ParkableStringManager::Size() const {
  return parked_strings_.size() + unparked_strings_.size();
}

void ParkableStringManager::RecordStatisticsAfter5Minutes() const {
  base::UmaHistogramTimes("Memory.ParkableString.MainThreadTime.5min",
                          total_unparking_time_);
  if (base::ThreadTicks::IsSupported()) {
    base::UmaHistogramTimes("Memory.ParkableString.ParkingThreadTime.5min",
                            total_parking_thread_time_);
  }
  Statistics stats = ComputeStatistics();
  base::UmaHistogramCounts100000("Memory.ParkableString.TotalSizeKb.5min",
                                 stats.original_size / 1000);
  base::UmaHistogramCounts100000("Memory.ParkableString.CompressedSizeKb.5min",
                                 stats.compressed_size / 1000);
  size_t savings = stats.compressed_original_size - stats.compressed_size;
  base::UmaHistogramCounts100000("Memory.ParkableString.SavingsKb.5min",
                                 savings / 1000);

  if (stats.compressed_original_size != 0) {
    size_t ratio_percentage =
        (100 * stats.compressed_size) / stats.compressed_original_size;
    base::UmaHistogramPercentage("Memory.ParkableString.CompressionRatio.5min",
                                 ratio_percentage);
  }
}

void ParkableStringManager::AgeStringsAndPark() {
  TRACE_EVENT0("blink", "ParkableStringManager::AgeStringsAndPark");
  has_pending_aging_task_ = false;

  WTF::Vector<ParkableStringImpl*> unparked = GetUnparkedStrings();
  bool can_make_progress = false;
  for (ParkableStringImpl* str : unparked) {
    if (str->MaybeAgeOrParkString() ==
        ParkableStringImpl::AgeOrParkResult::kSuccessOrTransientFailure)
      can_make_progress = true;
  }

  // Some strings will never be parkable because there are lasting external
  // references to them. Don't endlessely reschedule the aging task if we are
  // not making progress (that is, no new string was either aged or parked).
  //
  // This ensures that the tasks will stop getting scheduled, assuming that
  // the renderer is otherwise idle. Note that we cannot use "idle" tasks as
  // we need to age and park strings after the renderer becomes idle, meaning
  // that this has to run when the idle tasks are not. As a consequence, it
  // is important to make sure that this will not reschedule tasks forever.
  bool reschedule = !unparked_strings_.IsEmpty() && can_make_progress;
  if (reschedule)
    ScheduleAgingTaskIfNeeded();
}

void ParkableStringManager::ScheduleAgingTaskIfNeeded() {
  if (has_pending_aging_task_)
    return;

  scoped_refptr<base::SingleThreadTaskRunner> task_runner =
      Thread::Current()->GetTaskRunner();
  task_runner->PostDelayedTask(
      FROM_HERE,
      base::BindOnce(&ParkableStringManager::AgeStringsAndPark,
                     base::Unretained(this)),
      base::TimeDelta::FromSeconds(kAgingIntervalInSeconds));
  has_pending_aging_task_ = true;
}

void ParkableStringManager::PurgeMemory() {
  DCHECK(IsMainThread());

  ParkAll(ParkableStringImpl::ParkingMode::kAlways);
  // Critical memory pressure: drop compressed data for strings that we cannot
  // park now.
  //
  // After |ParkAll()| has been called, parkable strings have either been parked
  // synchronously (and no longer in |unparked_strings_|), or being parked and
  // purging is a no-op.
  if (!IsRendererBackgrounded()) {
    for (ParkableStringImpl* str : unparked_strings_)
      str->PurgeMemory();
  }
}

Vector<ParkableStringImpl*> ParkableStringManager::GetUnparkedStrings() const {
  WTF::Vector<ParkableStringImpl*> unparked;
  unparked.ReserveCapacity(unparked_strings_.size());
  for (ParkableStringImpl* str : unparked_strings_)
    unparked.push_back(str);

  return unparked;
}

ParkableStringManager::Statistics ParkableStringManager::ComputeStatistics()
    const {
  ParkableStringManager::Statistics stats = {};

  for (ParkableStringImpl* str : unparked_strings_) {
    size_t size = str->CharactersSizeInBytes();
    stats.original_size += size;
    stats.uncompressed_size += size;
    stats.metadata_size += sizeof(ParkableStringImpl);

    if (str->has_compressed_data())
      stats.overhead_size += str->compressed_size();
  }

  for (ParkableStringImpl* str : parked_strings_) {
    size_t size = str->CharactersSizeInBytes();
    stats.compressed_original_size += size;
    stats.original_size += size;
    stats.compressed_size += str->compressed_size();
    stats.metadata_size += sizeof(ParkableStringImpl);
  }

  stats.total_size = stats.uncompressed_size + stats.compressed_size +
                     stats.metadata_size + stats.overhead_size;
  size_t memory_footprint = stats.compressed_size + stats.uncompressed_size +
                            stats.metadata_size + stats.overhead_size;
  stats.savings_size =
      stats.original_size - static_cast<int64_t>(memory_footprint);

  return stats;
}

void ParkableStringManager::ResetForTesting() {
  backgrounded_ = false;
  has_pending_aging_task_ = false;
  has_posted_unparking_time_accounting_task_ = false;
  did_register_memory_pressure_listener_ = false;
  total_unparking_time_ = base::TimeDelta();
  total_parking_thread_time_ = base::TimeDelta();
  unparked_strings_.clear();
  parked_strings_.clear();
}

ParkableStringManager::ParkableStringManager()
    : backgrounded_(false),
      has_pending_aging_task_(false),
      has_posted_unparking_time_accounting_task_(false),
      did_register_memory_pressure_listener_(false),
      total_unparking_time_(),
      total_parking_thread_time_(),
      unparked_strings_(),
      parked_strings_() {}

}  // namespace blink