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// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "content/browser/renderer_host/navigation_transitions/navigation_entry_screenshot_manager.h"
#include "base/memory/ptr_util.h"
#include "base/system/sys_info.h"
#include "content/browser/renderer_host/navigation_transitions/navigation_entry_screenshot.h"
#include "content/browser/renderer_host/navigation_transitions/navigation_entry_screenshot_cache.h"
#include "ui/display/screen.h"
namespace content {
namespace {
// TODO(https://crbug.com/1414164): Consult with Clank team to see if we have
// any metrics for this.
#if BUILDFLAG(IS_ANDROID)
constexpr static size_t kMaxNumThumbnails = 20U;
#else
constexpr static size_t kMaxNumThumbnails = 0U;
#endif
// TODO(https://crbug.com/1414164): Optimise the memory budget. This is fine for
// MVP, but we need to consult the Clank team for a more propriate budget size.
static size_t GetMemoryBudget() {
// Assume 4 bytes per pixel. This value estimates the max number of bytes of
// the physical screen's bitmap.
const static size_t kDisplaySizeInBytes = 4 * display::Screen::GetScreen()
->GetPrimaryDisplay()
.GetSizeInPixel()
.Area64();
size_t physical_memory_budget = 0U;
#if BUILDFLAG(IS_ANDROID)
if (base::SysInfo::IsLowEndDevice()) {
// 64MB.
physical_memory_budget = 64 * 1024 * 1024;
} else {
// For 8GB of RAM, this is ~ 215MB.
physical_memory_budget = base::SysInfo::AmountOfPhysicalMemory() / 40;
}
#endif
// We should at least be able to cache one thumbnail.
physical_memory_budget =
std::max(kDisplaySizeInBytes, physical_memory_budget);
return std::min(kDisplaySizeInBytes * kMaxNumThumbnails,
physical_memory_budget);
}
} // namespace
NavigationEntryScreenshotManager::NavigationEntryScreenshotManager()
: // `NO_AUTO_EVICT` since we want to manually limit the global cache size
// by the number of bytes of the thumbnails, rather than the number of
// entries in the cache.
managed_caches_(base::LRUCacheSet<int>::NO_AUTO_EVICT) {
CHECK(AreBackForwardTransitionsEnabled());
max_cache_size_in_bytes_ = GetMemoryBudget();
listener_ = std::make_unique<base::MemoryPressureListener>(
FROM_HERE,
base::BindRepeating(&NavigationEntryScreenshotManager::OnMemoryPressure,
base::Unretained(this)));
}
NavigationEntryScreenshotManager::~NavigationEntryScreenshotManager() = default;
void NavigationEntryScreenshotManager::OnScreenshotCached(
NavigationEntryScreenshotCacheEvictor* cache,
size_t size) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
if (managed_caches_.Get(cache) == managed_caches_.end()) {
Register(cache);
}
// We shouldn't be able to capture anything greater than the budget.
CHECK_LE(size, max_cache_size_in_bytes_);
current_cache_size_in_bytes_ += size;
EvictIfOutOfMemoryBudget();
}
void NavigationEntryScreenshotManager::OnScreenshotRemoved(
NavigationEntryScreenshotCacheEvictor* cache,
size_t size) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
CHECK(!IsEmpty());
auto it = managed_caches_.Get(cache);
CHECK(it != managed_caches_.end());
CHECK_GE(current_cache_size_in_bytes_, size);
current_cache_size_in_bytes_ -= size;
if (cache->IsEmpty()) {
Unregister(cache);
}
}
void NavigationEntryScreenshotManager::OnCacheBecameVisible(
NavigationEntryScreenshotCacheEvictor* cache) {
// Access the cache in the set to mark it as recently used.
auto it = managed_caches_.Get(cache);
CHECK(it != managed_caches_.end());
}
bool NavigationEntryScreenshotManager::IsEmpty() const {
CHECK(managed_caches_.empty() == (current_cache_size_in_bytes_ == 0U));
return managed_caches_.empty();
}
void NavigationEntryScreenshotManager::Register(
NavigationEntryScreenshotCacheEvictor* cache) {
CHECK(managed_caches_.Peek(cache) == managed_caches_.end());
managed_caches_.Put(std::move(cache));
}
void NavigationEntryScreenshotManager::Unregister(
NavigationEntryScreenshotCacheEvictor* cache) {
auto it = managed_caches_.Peek(cache);
CHECK(it != managed_caches_.end());
managed_caches_.Erase(it);
}
// The current implementation iterates through the tabs in the LRU order and
// evict screenshots from each tab, until either the global size satisfies the
// budget, or the cache of the current tab is empty.
//
// One alternative is to always evict the navigation entries in LRU order,
// regardless of which tab the entry is from. The pro of this alternative is to
// have all the eviction logic inside the global manager.
//
// TODO(https://crbug.com/1420998): We need some metrics to understand if the
// currently implementation affects the cache hit rate. (I.e., would the
// alternative be a better approach?)
void NavigationEntryScreenshotManager::EvictIfOutOfMemoryBudget() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
CHECK(!IsEmpty());
// Start with the least recently used.
auto it = managed_caches_.rbegin();
while (current_cache_size_in_bytes_ > max_cache_size_in_bytes_) {
CHECK(it != managed_caches_.rend());
auto* cache = *it;
cache->EvictScreenshotsUntilUnderBudgetOrEmpty();
CHECK(cache->IsEmpty() ||
current_cache_size_in_bytes_ <= max_cache_size_in_bytes_);
if (cache->IsEmpty()) {
// No need to unregister this cache -
// `EvictScreenshotsUntilUnderBudgetOrEmpty` takes care of that.
CHECK(managed_caches_.Peek(cache) == managed_caches_.end());
it = managed_caches_.rbegin();
}
}
}
void NavigationEntryScreenshotManager::OnMemoryPressure(
base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
if (memory_pressure_level !=
base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL) {
return;
}
// Using a while loop because `Purge` erases the iterator.
auto it = managed_caches_.begin();
while (it != managed_caches_.end()) {
auto* cache = *it;
cache->Purge();
CHECK(cache->IsEmpty());
it = managed_caches_.begin();
}
CHECK(IsEmpty());
}
} // namespace content
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