// Copyright 2013 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 "base/memory/discardable_memory_emulated.h"

#include "base/lazy_instance.h"
#include "base/memory/discardable_memory_manager.h"

namespace base {
namespace {

// This is admittedly pretty magical.
const size_t kEmulatedMemoryLimit = 512 * 1024 * 1024;
const size_t kEmulatedSoftMemoryLimit = 32 * 1024 * 1024;
const size_t kEmulatedBytesToKeepUnderModeratePressure = 4 * 1024 * 1024;
const size_t kEmulatedHardMemoryLimitExpirationTimeMs = 1000;

struct SharedState {
  SharedState()
      : manager(kEmulatedMemoryLimit,
                kEmulatedSoftMemoryLimit,
                kEmulatedBytesToKeepUnderModeratePressure,
                TimeDelta::FromMilliseconds(
                    kEmulatedHardMemoryLimitExpirationTimeMs)) {}

  internal::DiscardableMemoryManager manager;
};
LazyInstance<SharedState>::Leaky g_shared_state = LAZY_INSTANCE_INITIALIZER;

}  // namespace

namespace internal {

DiscardableMemoryEmulated::DiscardableMemoryEmulated(size_t bytes)
    : bytes_(bytes),
      is_locked_(false) {
  g_shared_state.Pointer()->manager.Register(this, bytes);
}

DiscardableMemoryEmulated::~DiscardableMemoryEmulated() {
  if (is_locked_)
    Unlock();
  g_shared_state.Pointer()->manager.Unregister(this);
}

// static
void DiscardableMemoryEmulated::RegisterMemoryPressureListeners() {
  g_shared_state.Pointer()->manager.RegisterMemoryPressureListener();
}

// static
void DiscardableMemoryEmulated::UnregisterMemoryPressureListeners() {
  g_shared_state.Pointer()->manager.UnregisterMemoryPressureListener();
}

// static
bool DiscardableMemoryEmulated::ReduceMemoryUsage() {
  return g_shared_state.Pointer()->manager.ReduceMemoryUsage();
}

// static
void DiscardableMemoryEmulated::PurgeForTesting() {
  g_shared_state.Pointer()->manager.PurgeAll();
}

bool DiscardableMemoryEmulated::Initialize() {
  return Lock() != DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;
}

DiscardableMemoryLockStatus DiscardableMemoryEmulated::Lock() {
  DCHECK(!is_locked_);

  bool purged = false;
  if (!g_shared_state.Pointer()->manager.AcquireLock(this, &purged))
    return DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;

  is_locked_ = true;
  return purged ? DISCARDABLE_MEMORY_LOCK_STATUS_PURGED
                : DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS;
}

void DiscardableMemoryEmulated::Unlock() {
  DCHECK(is_locked_);
  g_shared_state.Pointer()->manager.ReleaseLock(this);
  is_locked_ = false;
}

void* DiscardableMemoryEmulated::Memory() const {
  DCHECK(is_locked_);
  DCHECK(memory_);
  return memory_.get();
}

bool DiscardableMemoryEmulated::AllocateAndAcquireLock() {
  if (memory_)
    return true;

  memory_.reset(new uint8[bytes_]);
  return false;
}

void DiscardableMemoryEmulated::Purge() {
  memory_.reset();
}

}  // namespace internal
}  // namespace base