[BlobStorage] BlobMemoryController & tests

storage/browser/blob/shareable_blob_data_item.h

Index: storage/browser/blob/shareable_blob_data_item.h
diff --git a/storage/browser/blob/shareable_blob_data_item.h b/storage/browser/blob/shareable_blob_data_item.h
index 4c2f9c1833262d18dfa82b622abdfef8585b9541..7549bb9b402cab2335242982fd9065c8140beeb1 100644
--- a/storage/browser/blob/shareable_blob_data_item.h
+++ b/storage/browser/blob/shareable_blob_data_item.h
@@ -11,40 +11,86 @@
 #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.
+// This class allows blob items to be shared between blobs.  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> {
+// We need to be RefCountedThreadSafe as references of this item are passed to a
+// file thread to save old memory items to disk.

[michaeln, 2016/09/27 00:09:30]

I understand the file created/deletion has to happen on a background thread, but
I think these data structures should remain non-thread-safe refcounted. There's
a containment hierarchy here.

ShareableBlobDataItem
  BlobDataItem
    BlobDataItem::Handle

Making the root of the hierarchy a thread-safe-refcount forces all of them to
have thread-safe-refcounts. The leaf in that tree is an abstract class that
consumers of the blob system define. I don't think we should impose the
thread-safe requirement upon them.

Can this interactions with the background thread to create/delete files be
massaged to not require this class (or its containees) to have a
thread-safe-refcount? We can't delete BlobDataItem::Handle's on other threads
and the easiest way to ensure that is to make all of these structures
single-threaded only.

[dmurph, 2016/09/29 00:44:23]

Done. Thanks for the discussion, I'm glad we could keep things single-threaded.

[michaeln, 2016/10/04 00:11:54]

woot!

+class STORAGE_EXPORT ShareableBlobDataItem
+    : public base::RefCountedThreadSafe<ShareableBlobDataItem> {
  public:
-  ShareableBlobDataItem(const std::string& blob_uuid,
-                        const scoped_refptr<BlobDataItem>& item);
+  enum State {
+    // We're an item that needs quota (either disk or memory).
+    QUOTA_NEEDED,
+    // We have requested quota from the BlobMemoryController.
+    QUOTA_REQUESTED,
+    // Space has been allocated for this item in the BlobMemoryController, but
+    // it may not yet be populated.
+    QUOTA_GRANTED,
+    // We're a populated item that needed quota.
+    POPULATED_WITH_QUOTA,
+    // We're a populated item that didn't need quota.
+    POPULATED_WITHOUT_QUOTA
+  };
 
-  const scoped_refptr<BlobDataItem>& item();
+  ShareableBlobDataItem(const std::string& target_uuid,
+                        scoped_refptr<BlobDataItem> item,
+                        State state);
 
-  base::hash_set<std::string>& referencing_blobs() {
+  const scoped_refptr<BlobDataItem>& item() const { return item_; }
+
+  scoped_refptr<BlobDataItem>* item_mutable() { return &item_; }
+
+  // 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_;
   }
 
+  base::hash_set<std::string>* referencing_blobs_mutable() {
+    return &referencing_blobs_;
+  }
+
+  State state() const { return state_; }
+
+  void set_state(State state) { state_ = state; }
+
+  bool IsPopulated() const {
+    return state_ == POPULATED_WITH_QUOTA || state_ == POPULATED_WITHOUT_QUOTA;
+  }
+
  private:
-  friend class base::RefCounted<ShareableBlobDataItem>;
-  friend class InternalBlobData;
+  friend class base::RefCountedThreadSafe<ShareableBlobDataItem>;
+  friend STORAGE_EXPORT void PrintTo(const ShareableBlobDataItem& x,
+                                     ::std::ostream* os);
+
   ~ShareableBlobDataItem();
 
+  // This is a unique identifier for this ShareableBlobDataItem.
+  const uint64_t item_id_;
+  State state_;
   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_