Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory_provider.cc

+// 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_provider.h"
+
+#include "base/bind.h"
+#include "base/containers/hash_tables.h"
+#include "base/containers/mru_cache.h"
+#include "base/memory/discardable_memory.h"
+#include "base/memory/singleton.h"
+#include "base/synchronization/lock.h"
+#include "base/sys_info.h"
+
+namespace base {
+
+namespace {
+
+// If this is given a valid value via SetInstanceForTest, this pointer will be
+// returned by GetInstance rather than the usual singleton.
+static base::DiscardableMemoryProvider* s_provider_for_test = NULL;
+
+// This is admittedly pretty magical. It's approximately enough memory for two
+// 2560x1600 images.
+static const size_t kDefaultDiscardableMemoryLimit = 32 * 1024 * 1024;
+static const size_t kDefaultBytesToReclaimUnderModeratePressure =
+    kDefaultDiscardableMemoryLimit / 2;
+
+}  // namespace
+
+DiscardableMemoryProvider::DiscardableMemoryProvider()
+    : allocations_(AllocationMap::NO_AUTO_EVICT),
+      bytes_allocated_(0),
+      discardable_memory_limit_(kDefaultDiscardableMemoryLimit),
+      bytes_to_reclaim_under_moderate_pressure_(
+          kDefaultBytesToReclaimUnderModeratePressure),
+      memory_pressure_listener_(new MemoryPressureListener(
+          base::Bind(&DiscardableMemoryProvider::NotifyMemoryPressure))) {
+}
+
+DiscardableMemoryProvider::~DiscardableMemoryProvider() {

[Avi (use Gerrit), 2013/06/20 20:47:41]

What is the scenario in which this gets called? I'd imagine that a provider like
this would be installed and live forever. (shrug)

+  AutoLock lock(allocations_lock_);
+  AllocationMap::iterator it = allocations_.begin();
+  for (; it != allocations_.end(); ++it)
+    if (it->first->memory_)
+      it->first->Deallocate();
+}
+
+// static
+DiscardableMemoryProvider* DiscardableMemoryProvider::GetInstance() {
+  if (s_provider_for_test)
+    return s_provider_for_test;
+  return Singleton<DiscardableMemoryProvider>::get();
+}
+
+// static
+void DiscardableMemoryProvider::SetInstanceForTest(
+    DiscardableMemoryProvider* provider) {
+  s_provider_for_test = provider;
+}
+
+// static
+void DiscardableMemoryProvider::NotifyMemoryPressure(
+    MemoryPressureListener::MemoryPressureLevel pressureLevel) {
+  switch (pressureLevel) {
+    case MemoryPressureListener::MEMORY_PRESSURE_MODERATE:
+      DiscardableMemoryProvider::GetInstance()->PurgeLRU();
+      break;
+    case MemoryPressureListener::MEMORY_PRESSURE_CRITICAL:
+      DiscardableMemoryProvider::GetInstance()->PurgeAll();
+      break;
+    default:
+      NOTREACHED();
+  }
+}
+
+void DiscardableMemoryProvider::SetDiscardableMemoryLimit(size_t bytes) {
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    discardable_memory_limit_ = bytes;
+  }
+  EnforcePolicy();
+}
+
+size_t DiscardableMemoryProvider::discardable_memory_limit() const {
+  AutoLock lock(
+      const_cast<DiscardableMemoryProvider*>(this)->bytes_allocated_lock_);

[Avi (use Gerrit), 2013/06/20 20:47:41]

Yikes. Do we want to make the lock mutable then?

+  return discardable_memory_limit_;
+}
+
+void DiscardableMemoryProvider::SetBytesToReclaimUnderModeratePressure(
+    size_t bytes) {
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    bytes_to_reclaim_under_moderate_pressure_ = bytes;
+  }
+  EnforcePolicy();
+}
+
+size_t DiscardableMemoryProvider::
+    bytes_to_reclaim_under_moderate_pressure() const {
+  AutoLock lock(
+      const_cast<DiscardableMemoryProvider*>(this)->bytes_allocated_lock_);
+  return bytes_to_reclaim_under_moderate_pressure_;
+}
+
+void DiscardableMemoryProvider::Register(DiscardableMemory* discardable) {
+  DCHECK(allocations_.Peek(discardable) == allocations_.end());
+  {
+    AutoLock lock(allocations_lock_);
+    allocations_.Put(discardable, true);
+  }
+  EnforcePolicy();
+}
+
+void DiscardableMemoryProvider::Unregister(DiscardableMemory* discardable) {
+  {
+    AutoLock lock(allocations_lock_);
+    AllocationMap::iterator it = allocations_.Peek(discardable);
+    if (it != allocations_.end())
+      allocations_.Erase(it);
+  }
+  EnforcePolicy();
+}
+
+void DiscardableMemoryProvider::DidAllocate(size_t bytes) {
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    bytes_allocated_ += bytes;
+  }
+  EnforcePolicy();
+}
+
+void DiscardableMemoryProvider::DidDeallocate(size_t bytes) {
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    DCHECK(bytes <= bytes_allocated_);
+    bytes_allocated_ -= bytes;
+  }
+  EnforcePolicy();
+}
+
+bool DiscardableMemoryProvider::DidAccess(DiscardableMemory* discardable) {
+  AutoLock lock(allocations_lock_);
+  AllocationMap::iterator it = allocations_.Get(discardable);
+  return it != allocations_.end();
+}
+
+void DiscardableMemoryProvider::PurgeAll() {
+  AutoLock lock(allocations_lock_);
+  AllocationMap::iterator it = allocations_.begin();
+  for (; it != allocations_.end(); ++it) {
+    if (it->first->memory_ && !it->first->is_locked()) {
+      it->first->Deallocate();
+      DCHECK(!it->first->memory_);
+    }
+  }
+}
+
+void DiscardableMemoryProvider::PurgeLRU() {
+  size_t limit = 0;
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    if (bytes_to_reclaim_under_moderate_pressure_ == 0)
+      return;
+
+    if (bytes_to_reclaim_under_moderate_pressure_ < discardable_memory_limit_)
+      limit = bytes_allocated_ - bytes_to_reclaim_under_moderate_pressure_;
+  }
+
+  AutoLock lock(allocations_lock_);
+  AllocationMap::reverse_iterator it = allocations_.rbegin();
+  for(; it != allocations_.rend(); ++it) {
+    if (!it->first->memory_ || it->first->is_locked())
+      continue;
+    it->first->Deallocate();
+    DCHECK(!it->first->memory_);
+    AutoLock bytes_lock(bytes_allocated_lock_);
+    if (bytes_allocated_ <= limit)
+      break;
+  }
+}
+
+void DiscardableMemoryProvider::EnforcePolicy() {
+  bool exceeded_bound = false;
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    if (discardable_memory_limit_ == 0)
+      return;
+    exceeded_bound = bytes_allocated_ > discardable_memory_limit_;
+  }
+  if (exceeded_bound)
+    PurgeLRU();
+}
+
+}  // namespace base