Upstream Chrome on iOS source code [9/11].

ios/chrome/browser/ui/tab_switcher/tab_switcher_cache.mm

+// Copyright 2015 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.
+
+#import "ios/chrome/browser/ui/tab_switcher/tab_switcher_cache.h"
+
+#include <unordered_map>
+
+#import "base/ios/weak_nsobject.h"
+#include "base/logging.h"
+#include "base/mac/scoped_nsobject.h"
+#include "base/strings/stringprintf.h"
+#include "base/synchronization/lock.h"
+#import "ios/chrome/browser/tabs/tab.h"
+#import "ios/chrome/browser/tabs/tab_model.h"
+#import "ios/chrome/browser/ui/uikit_ui_util.h"
+#include "ios/chrome/common/ios_app_bundle_id_prefix.h"
+#include "ios/web/public/navigation_item.h"
+
+namespace {
+// The maximum amount of pixels the cache should hold.
+NSUInteger kCacheMaxPixelCount = 2048 * 1536 * 4;
+// Two floats that are different from less than |kMaxFloatDelta| are considered
+// equals.
+const CGFloat kMaxFloatDelta = 0.01;
+}  // namespace
+
+@interface TabSwitcherCache ()
+// Clears the cache. Called when a low memory warning was received.
+- (void)lowMemoryWarningReceived;
+// Returns a autoreleased resized image of |image|.
++ (UIImage*)resizedImage:(UIImage*)image toSize:(CGSize)size;
+
+@end
+
+@implementation TabSwitcherCache {
+  base::scoped_nsobject<NSCache> _cache;
+  dispatch_queue_t _cacheQueue;
+  // The tab models.
+  TabModel* _mainTabModel;  // weak
+  TabModel* _otrTabModel;   // weak
+
+  // Lock protecting the pending requests map.
+  base::Lock _lock;
+  std::unordered_map<NSUInteger, PendingSnapshotRequest> _pendingRequests;
+}
+
+@synthesize mainTabModel = _mainTabModel;
+
+- (instancetype)init {
+  self = [super init];
+  if (self) {
+    _cache.reset([[NSCache alloc] init]);
+    [_cache setTotalCostLimit:kCacheMaxPixelCount];
+    NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
+    [nc addObserver:self
+           selector:@selector(lowMemoryWarningReceived)
+               name:UIApplicationDidReceiveMemoryWarningNotification
+             object:nil];
+    std::string queueName =
+        base::StringPrintf("%s.chrome.ios.TabSwitcherCacheQueue",
+                           BUILDFLAG(IOS_APP_BUNDLE_ID_PREFIX));
+    _cacheQueue =
+        dispatch_queue_create(queueName.c_str(), DISPATCH_QUEUE_SERIAL);
+  }
+  return self;
+}
+
+- (void)dealloc {
+  NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
+  [nc removeObserver:self
+                name:UIApplicationDidReceiveMemoryWarningNotification
+              object:nil];
+  dispatch_release(_cacheQueue);
+  [_mainTabModel removeObserver:self];
+  [_otrTabModel removeObserver:self];
+  [super dealloc];
+}
+
+- (PendingSnapshotRequest)requestSnapshotForTab:(Tab*)tab
+                                       withSize:(CGSize)size
+                                completionBlock:
+                                    (SnapshotCompletionBlock)completionBlock {
+  DCHECK([NSThread isMainThread]);
+  DCHECK(tab);
+  DCHECK(completionBlock);
+  DCHECK(!CGSizeEqualToSize(size, CGSizeZero));
+  PendingSnapshotRequest currentRequest;
+  UIImage* snapshot = [_cache objectForKey:[self keyForTab:tab]];
+  if (snapshot) {
+    CGFloat tabContentAreaRatio = tab.snapshotContentArea.size.width /
+                                  tab.snapshotContentArea.size.height;
+    CGFloat cachedSnapshotRatio =
+        [snapshot size].width / [snapshot size].height;
+    // Check that the cached snapshot's ratio matches the content area ratio.
+    if (std::abs(tabContentAreaRatio - cachedSnapshotRatio) < kMaxFloatDelta &&
+        [snapshot size].width >= size.width) {
+      // Cache hit.
+      completionBlock(snapshot);
+      return currentRequest;
+    }
+  }
+
+  // Cache miss.
+  currentRequest = [self recordPendingRequestForTab:tab];
+  NSString* key = [self keyForTab:tab];
+  [tab retrieveSnapshot:^(UIImage* snapshot) {
+    PendingSnapshotRequest requestForSession = [self pendingRequestForTab:tab];
+    // Cancel this request if another one has replaced it for this sessionId.
+    if (currentRequest.requestId != requestForSession.requestId)
+      return;
+    dispatch_async(_cacheQueue, ^{
+      DCHECK(![NSThread isMainThread]);
+      UIImage* resizedSnapshot =
+          [TabSwitcherCache resizedImage:snapshot toSize:size];
+      if ([self storeImage:resizedSnapshot forKey:key request:currentRequest]) {
+        dispatch_async(dispatch_get_main_queue(), ^{
+          // Cancel this request if another one has replaced it for this
+          // sessionId.
+          PendingSnapshotRequest requestForSession =
+              [self pendingRequestForTab:tab];
+          if (currentRequest.requestId != requestForSession.requestId)
+            return;
+          completionBlock(resizedSnapshot);
+          [self removePendingSnapshotRequest:currentRequest];
+        });
+      }
+    });
+  }];
+  return currentRequest;
+}
+
+- (void)updateSnapshotForTab:(Tab*)tab
+                   withImage:(UIImage*)image
+                        size:(CGSize)size {
+  DCHECK([NSThread isMainThread]);
+  DCHECK(tab);
+  DCHECK(image);
+  PendingSnapshotRequest currentRequest = [self recordPendingRequestForTab:tab];
+  NSString* key = [self keyForTab:tab];
+
+  dispatch_async(_cacheQueue, ^{
+    DCHECK(![NSThread isMainThread]);
+    UIImage* resizedSnapshot =
+        [TabSwitcherCache resizedImage:image toSize:size];
+    [self storeImage:resizedSnapshot forKey:key request:currentRequest];
+    [self removePendingSnapshotRequest:currentRequest];
+  });
+}
+
+- (void)cancelPendingSnapshotRequest:(PendingSnapshotRequest)pendingRequest {
+  [self removePendingSnapshotRequest:pendingRequest];
+}
+
+#pragma mark - Private
+
+- (NSString*)keyForTab:(Tab*)tab {
+  DCHECK([NSThread isMainThread]);
+  return [tab currentSessionID];
+}
+
+- (PendingSnapshotRequest)recordPendingRequestForTab:(Tab*)tab {
+  PendingSnapshotRequest pendingRequest;
+  pendingRequest.requestId = [[NSDate date] timeIntervalSince1970];
+  pendingRequest.sessionId = [[self keyForTab:tab] hash];
+  base::AutoLock guard(_lock);
+  _pendingRequests[pendingRequest.sessionId] = pendingRequest;
+  return pendingRequest;
+}
+
+- (PendingSnapshotRequest)pendingRequestForTab:(Tab*)tab {
+  DCHECK([NSThread isMainThread]);
+  PendingSnapshotRequest pendingRequest;
+  if (![tab webStateImpl])
+    return pendingRequest;
+  NSUInteger sessionId = [[self keyForTab:tab] hash];
+  base::AutoLock guard(_lock);
+  auto it = _pendingRequests.find(sessionId);
+  if (it != _pendingRequests.end())
+    pendingRequest = it->second;
+  return pendingRequest;
+}
+
+- (void)removePendingSnapshotRequest:(PendingSnapshotRequest)pendingRequest {
+  base::AutoLock guard(_lock);
+  auto itRequest = _pendingRequests.find(pendingRequest.sessionId);
+  if (itRequest != _pendingRequests.end() &&
+      pendingRequest.requestId == itRequest->second.requestId) {
+    _pendingRequests.erase(itRequest);
+  }
+}
+
+- (void)removePendingSnapshotRequestForTab:(Tab*)tab {
+  base::AutoLock guard(_lock);
+  auto itRequest = _pendingRequests.find([[self keyForTab:tab] hash]);
+  if (itRequest != _pendingRequests.end())
+    _pendingRequests.erase(itRequest);
+}
+
+- (BOOL)storeImage:(UIImage*)image
+            forKey:(NSString*)key
+           request:(PendingSnapshotRequest)request {
+  DCHECK(request.requestId != 0);
+  if (!image)
+    return NO;
+
+  {
+    base::AutoLock guard(_lock);
+    auto it = _pendingRequests.find(request.sessionId);
+    if (it == _pendingRequests.end())
+      return NO;
+
+    // Only write the image in cache if the request is still valid.
+    if (request.requestId != it->second.requestId)
+      return NO;
+  }
+
+  const CGFloat screenScale = [[UIScreen mainScreen] scale];
+  const NSUInteger cost =
+      image.size.width * screenScale * image.size.height * screenScale;
+  [_cache setObject:image forKey:key cost:cost];
+  return YES;
+}
+
++ (UIImage*)resizedImage:(UIImage*)image toSize:(CGSize)size {
+  DCHECK(image.scale == 1);
+  CGFloat screenScale = [[UIScreen mainScreen] scale];
+  CGSize pixelSize = size;
+  pixelSize.width *= screenScale;
+  pixelSize.height *= screenScale;
+  UIImage* resizedSnapshot =
+      ResizeImage(image, pixelSize, ProjectionMode::kAspectFillNoClipping, YES);
+  // Creates a new image with the correct |scale| attribute.
+  return [[[UIImage alloc] initWithCGImage:resizedSnapshot.CGImage
+                                     scale:screenScale
+                               orientation:UIImageOrientationUp] autorelease];
+}
+
+- (void)lowMemoryWarningReceived {
+  [_cache removeAllObjects];
+}
+
+- (void)setMainTabModel:(TabModel*)mainTabModel
+            otrTabModel:(TabModel*)otrTabModel {
+  if (mainTabModel != _mainTabModel)
+    [self replaceOldTabModel:&_mainTabModel withTabModel:mainTabModel];
+  if (otrTabModel != _otrTabModel)
+    [self replaceOldTabModel:&_otrTabModel withTabModel:otrTabModel];
+}
+
+- (void)replaceOldTabModel:(TabModel**)oldTabModel
+              withTabModel:(TabModel*)newTabModel {
+  [*oldTabModel removeObserver:self];
+  *oldTabModel = newTabModel;
+  [newTabModel addObserver:self];
+}
+
+#pragma mark - TabModelObserver
+
+- (void)tabModel:(TabModel*)model
+    didRemoveTab:(Tab*)tab
+         atIndex:(NSUInteger)index {
+  [self removePendingSnapshotRequestForTab:tab];
+  [_cache removeObjectForKey:[self keyForTab:tab]];
+}
+
+- (void)tabModel:(TabModel*)model
+    didChangeTabSnapshot:(Tab*)tab
+               withImage:image {
+  [self removePendingSnapshotRequestForTab:tab];
+  [_cache removeObjectForKey:[self keyForTab:tab]];
+}
+
+@end