storage/browser/blob/blob_data_handle.h

   1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef STORAGE_BROWSER_BLOB_BLOB_DATA_HANDLE_H_
   6 #define STORAGE_BROWSER_BLOB_BLOB_DATA_HANDLE_H_
   7
   8 #include <string>
   9
  10 #include "base/memory/ref_counted.h"
  11 #include "base/memory/weak_ptr.h"
  12 #include "base/supports_user_data.h"
  13 #include "storage/browser/storage_browser_export.h"
  14
  15 namespace base {
  16 class SequencedTaskRunner;
  17 }
  18
  19 namespace storage {
  20
  21 class BlobDataSnapshot;
  22 class BlobStorageContext;
  23
  24 // BlobDataHandle ensures that the underlying blob (keyed by the uuid) remains
  25 // in the BlobStorageContext's collection while this object is alive. Anything
  26 // that needs to keep a blob alive needs to store this handle.
  27 // When the blob data itself is needed, clients must call the CreateSnapshot()
  28 // method on the IO thread to create a snapshot of the blob data.  This snapshot
  29 // is not intended to be persisted, and serves to ensure that the backing
  30 // resources remain around for the duration of reading the blob.  This snapshot
  31 // can be read on any thread, but it must be destructed on the IO thread.
  32 // This object has delete semantics and may be deleted on any thread.
  33 class STORAGE_EXPORT BlobDataHandle
  34     : public base::SupportsUserData::Data {
  35  public:
  36   BlobDataHandle(const BlobDataHandle& other);  // May be copied on any thread.
  37   ~BlobDataHandle() override;                   // May be deleted on any thread.
  38
  39   // A BlobDataSnapshot is used to read the data from the blob.  This object is
  40   // intended to be transient and should not be stored for any extended period
  41   // of time.
  42   // This call and the destruction of the returned snapshot must be called
  43   // on the IO thread.
  44   scoped_ptr<BlobDataSnapshot> CreateSnapshot() const;
  45
  46   const std::string& uuid() const;  // May be accessed on any thread.
  47
  48  private:
  49   // Internal class whose destructor is guarenteed to be called on the IO
  50   // thread.
  51   class BlobDataHandleShared
  52       : public base::RefCountedThreadSafe<BlobDataHandleShared> {
  53    public:
  54     BlobDataHandleShared(const std::string& uuid,
  55                          BlobStorageContext* context,
  56                          base::SequencedTaskRunner* task_runner);
  57
  58     scoped_ptr<BlobDataSnapshot> CreateSnapshot() const;
  59     const std::string& uuid() const;
  60
  61    private:
  62     friend class base::DeleteHelper<BlobDataHandleShared>;
  63     friend class base::RefCountedThreadSafe<BlobDataHandleShared>;
  64     friend class BlobDataHandle;
  65
  66     virtual ~BlobDataHandleShared();
  67
  68     const std::string uuid_;
  69     base::WeakPtr<BlobStorageContext> context_;
  70
  71     DISALLOW_COPY_AND_ASSIGN(BlobDataHandleShared);
  72   };
  73
  74   friend class BlobStorageContext;
  75   BlobDataHandle(const std::string& uuid,
  76                  BlobStorageContext* context,
  77                  base::SequencedTaskRunner* task_runner);
  78
  79   scoped_refptr<base::SequencedTaskRunner> io_task_runner_;
  80   scoped_refptr<BlobDataHandleShared> shared_;
  81 };
  82
  83 }  // namespace storage
  84
  85 #endif  // STORAGE_BROWSER_BLOB_BLOB_DATA_HANDLE_H_