Upstream //ios/chrome/browser/snapshots

ios/chrome/browser/snapshots/snapshot_cache.h

+// Copyright 2012 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.
+
+#ifndef IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_H_
+#define IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_H_
+
+#import <UIKit/UIKit.h>
+
+#include "base/mac/objc_property_releaser.h"
+#include "base/mac/scoped_nsobject.h"
+#include "base/time/time.h"
+
+typedef void (^GreyBlock)(UIImage*);
+
+// A singleton providing an in-memory and on-disk cache of tab snapshots.
+// A snapshot is a full-screen image of the contents of the page at the current
+// scroll offset and zoom level, used to stand in for the UIWebView if it has
+// been purged from memory or when quickly switching tabs.
+// Persists to disk on a background thread each time a snapshot changes.
+@interface SnapshotCache : NSObject {
+ @private
+  // Dictionary to hold color snapshots in memory. n.b. Color snapshots are not
+  // kept in memory on tablets.
+  base::scoped_nsobject<NSMutableDictionary> imageDictionary_;
+  // Temporary dictionary to hold grey snapshots for tablet side swipe. This
+  // will be nil before -createGreyCache is called and after -removeGreyCache
+  // is called.
+  base::scoped_nsobject<NSMutableDictionary> greyImageDictionary_;
+  NSSet* pinnedIDs_;
+
+  // Session ID of most recent pending grey snapshot request.
+  base::scoped_nsobject<NSString> mostRecentGreySessionId_;
+  // Block used by pending request for a grey snapshot.
+  base::scoped_nsprotocol<GreyBlock> mostRecentGreyBlock_;
+
+  // Session ID and correspoinding UIImage for the snapshot that will likely
+  // be requested to be saved to disk when the application is backgrounded.
+  base::scoped_nsobject<NSString> backgroundingImageSessionId_;
+  base::scoped_nsobject<UIImage> backgroundingColorImage_;
+
+  base::mac::ObjCPropertyReleaser propertyReleaser_SnapshotCache_;
+}
+
+// Track session IDs to not release on low memory and to reload on
+// |UIApplicationDidBecomeActiveNotification|.
+@property(nonatomic, retain) NSSet* pinnedIDs;
+
++ (SnapshotCache*)sharedInstance;
+
+// The scale that should be used for snapshots.
++ (CGFloat)snapshotScaleForDevice;
+
+// Retrieve a cached snapshot for the |sessionID| and return it via the callback
+// if it exists. The callback is guaranteed to be called synchronously if the
+// image is in memory. It will be called asynchronously if the image is on disk
+// or with nil if the image is not present at all.
+- (void)retrieveImageForSessionID:(NSString*)sessionID
+                         callback:(void (^)(UIImage*))callback;
+
+// Request the session's grey snapshot. If the image is already loaded in
+// memory, this will immediately call back on |callback|.
+- (void)retrieveGreyImageForSessionID:(NSString*)sessionID
+                             callback:(void (^)(UIImage*))callback;
+
+- (void)setImage:(UIImage*)img withSessionID:(NSString*)sessionID;
+- (void)removeImageWithSessionID:(NSString*)sessionID;
+// Purge the cache of snapshots that are older than |date|. The snapshots for
+// the sessions given in |liveSessionIds| will be kept. This will be done
+// asynchronously on a background thread.
+- (void)purgeCacheOlderThan:(const base::Time&)date
+                    keeping:(NSSet*)liveSessionIds;
+// Hint that the snapshot for |sessionID| will likely be saved to disk when the
+// application is backgrounded.  The snapshot is then saved in memory, so it
+// does not need to be read off disk.
+- (void)willBeSavedGreyWhenBackgrounding:(NSString*)sessionID;
+
+// Create temporary cache of grey images for tablet side swipe.
+- (void)createGreyCache:(NSArray*)sessionIDs;
+// Release all images in grey cache.
+- (void)removeGreyCache;
+// Request the session's grey snapshot. If the image is already loaded this will
+// immediately call back on |callback|. Otherwise, only use |callback| for the
+// most recent caller. The callback is not guaranteed to be called.
+- (void)greyImageForSessionID:(NSString*)sessionID
+                     callback:(void (^)(UIImage*))callback;
+
+// Write a grey copy of the snapshot for |sessionID| to disk, but if and only if
+// a color version of the snapshot already exists in memory or on disk.
+- (void)saveGreyInBackgroundForSessionID:(NSString*)sessionID;
+@end
+
+#endif  // IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_H_