[BlobAsync] Disk support for blob storage

storage/browser/blob/shareable_blob_data_item.h

 // 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.
 
 #ifndef STORAGE_BROWSER_BLOB_SHAREABLE_BLOB_DATA_ITEM_H_
 #define STORAGE_BROWSER_BLOB_SHAREABLE_BLOB_DATA_ITEM_H_
 
 #include <string>
 
 #include "base/containers/hash_tables.h"
 #include "base/hash.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "storage/browser/storage_browser_export.h"
 #include "storage/common/data_element.h"
 
 namespace storage {
 class BlobDataItem;
 class InternalBlobData;
 
 // This class allows blob items to be shared between blobs, and is only used by
 // BlobStorageContext. This class contains both the blob data item and the uuids
 // of all the blobs using this item.
 // The data in this class (the item) is immutable, but the item itself can be
 // swapped out with an item with the same data but a different backing (think
 // RAM vs file backed).
-class ShareableBlobDataItem : public base::RefCounted<ShareableBlobDataItem> {
+class STORAGE_EXPORT ShareableBlobDataItem
+    : public base::RefCountedThreadSafe<ShareableBlobDataItem> {
  public:
-  ShareableBlobDataItem(const std::string& blob_uuid,
-                        const scoped_refptr<BlobDataItem>& item);
+  ShareableBlobDataItem(scoped_refptr<BlobDataItem> item);
 
-  const scoped_refptr<BlobDataItem>& item();
+  const scoped_refptr<BlobDataItem>& item() const;
 
-  base::hash_set<std::string>& referencing_blobs() {
+  // This is a unique auto-incrementing id assigned to this item on
+  // construction. It is used to keep track of this item in an LRU data
+  // structure for eviction to disk.
+  uint64_t item_id() const { return item_id_; }
+
+  const base::hash_set<std::string>& referencing_blobs() const {
     return referencing_blobs_;
   }
 
  private:
-  friend class base::RefCounted<ShareableBlobDataItem>;
+  friend class base::RefCountedThreadSafe<ShareableBlobDataItem>;
   friend class InternalBlobData;
+  friend class BlobMemoryController;
+  friend class BlobStorageContext;
+  friend STORAGE_EXPORT void PrintTo(const ShareableBlobDataItem& x,
+                                     ::std::ostream* os);
+
   ~ShareableBlobDataItem();
 
+  // This is a unique identifier for this ShareableBlobDataItem.
+  uint64_t item_id_;
   scoped_refptr<BlobDataItem> item_;
 
   base::hash_set<std::string> referencing_blobs_;
 
   DISALLOW_COPY_AND_ASSIGN(ShareableBlobDataItem);
 };
 
+STORAGE_EXPORT bool operator==(const ShareableBlobDataItem& a,
+                               const ShareableBlobDataItem& b);
+STORAGE_EXPORT bool operator!=(const ShareableBlobDataItem& a,
+                               const ShareableBlobDataItem& b);
+
 }  // namespace storage
 #endif  // STORAGE_BROWSER_BLOB_SHAREABLE_BLOB_DATA_ITEM_H_