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diff --git a/net/disk_cache/in_flight_backend_io.h b/net/disk_cache/in_flight_backend_io.h
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+++ b/net/disk_cache/in_flight_backend_io.h
@@ -0,0 +1,200 @@
+// Copyright (c) 2010 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 NET_DISK_CACHE_IN_FLIGHT_BACKEND_IO_H_
+#define NET_DISK_CACHE_IN_FLIGHT_BACKEND_IO_H_
+
+#include <string>
+
+#include "base/message_loop_proxy.h"
+#include "net/base/completion_callback.h"
+#include "net/base/io_buffer.h"
+#include "net/disk_cache/entry_impl.h"
+#include "net/disk_cache/in_flight_io.h"
+
+namespace disk_cache {
+
+class BackendImpl;
+
+// This class represents a single asynchronous disk cache IO operation while it
+// is being bounced between threads.
+class BackendIO : public BackgroundIO {
+ public:
+  BackendIO(InFlightIO* controller, BackendImpl* backend,
+            net::CompletionCallback* callback);
+
+  // Runs the actual operation on the background thread.
+  void ExecuteOperation();
+
+  // Callback implementation.
+  void OnIOComplete(int result);
+
+  // Returns true if this operation is directed to an entry (vs. the backend).
+  bool IsEntryOperation();
+
+  net::CompletionCallback* callback() { return callback_; }
+
+  void ReleaseEntry();
+
+  // The operations we proxy:
+  void Init();
+  void OpenEntry(const std::string& key, Entry** entry);
+  void CreateEntry(const std::string& key, Entry** entry);
+  void DoomEntry(const std::string& key);
+  void DoomAllEntries();
+  void DoomEntriesBetween(const base::Time initial_time,
+                          const base::Time end_time);
+  void DoomEntriesSince(const base::Time initial_time);
+  void OpenNextEntry(void** iter, Entry** next_entry);
+  void OpenPrevEntry(void** iter, Entry** prev_entry);
+  void EndEnumeration(void* iterator);
+  void CloseEntryImpl(EntryImpl* entry);
+  void DoomEntryImpl(EntryImpl* entry);
+  void FlushQueue();  // Dummy operation.
+  void ReadData(EntryImpl* entry, int index, int offset, net::IOBuffer* buf,
+                int buf_len);
+  void WriteData(EntryImpl* entry, int index, int offset, net::IOBuffer* buf,
+                 int buf_len, bool truncate);
+  void ReadSparseData(EntryImpl* entry, int64 offset, net::IOBuffer* buf,
+                      int buf_len);
+  void WriteSparseData(EntryImpl* entry, int64 offset, net::IOBuffer* buf,
+                       int buf_len);
+  void GetAvailableRange(EntryImpl* entry, int64 offset, int len, int64* start);
+  void CancelSparseIO(EntryImpl* entry);
+  void ReadyForSparseIO(EntryImpl* entry);
+
+ private:
+  // There are two types of operations to proxy: regular backend operations are
+  // queued so that we don't have more than one operation going on at the same
+  // time (for instance opening an entry and creating the same entry). On the
+  // other hand, operations targeted to a given entry can be long lived and
+  // support multiple simultaneous users (multiple reads or writes to the same
+  // entry), so they are not queued, just posted to the worker thread as they
+  // come.
+  enum Operation {
+    OP_NONE = 0,
+    OP_INIT,
+    OP_OPEN,
+    OP_CREATE,
+    OP_DOOM,
+    OP_DOOM_ALL,
+    OP_DOOM_BETWEEN,
+    OP_DOOM_SINCE,
+    OP_OPEN_NEXT,
+    OP_OPEN_PREV,
+    OP_END_ENUMERATION,
+    OP_CLOSE_ENTRY,
+    OP_DOOM_ENTRY,
+    OP_FLUSH_QUEUE,
+    OP_MAX_BACKEND,
+    OP_READ,
+    OP_WRITE,
+    OP_READ_SPARSE,
+    OP_WRITE_SPARSE,
+    OP_GET_RANGE,
+    OP_CANCEL_IO,
+    OP_IS_READY
+  };
+
+  ~BackendIO() {}
+
+  void ExecuteBackendOperation();
+  void ExecuteEntryOperation();
+
+  BackendImpl* backend_;
+  net::CompletionCallback* callback_;
+  Operation operation_;
+  net::CompletionCallbackImpl<BackendIO> my_callback_;
+
+  // The arguments of all the operations we proxy:
+  std::string key_;
+  Entry** entry_ptr_;
+  base::Time initial_time_;
+  base::Time end_time_;
+  void** iter_ptr_;
+  void* iter_;
+  EntryImpl* entry_;
+  int index_;
+  int offset_;
+  scoped_refptr<net::IOBuffer> buf_;
+  int buf_len_;
+  bool truncate_;
+  int64 offset64_;
+  int64* start_;
+
+  DISALLOW_COPY_AND_ASSIGN(BackendIO);
+};
+
+// The specialized controller that keeps track of current operations.
+class InFlightBackendIO : public InFlightIO {
+ public:
+  InFlightBackendIO(BackendImpl* backend,
+                    base::MessageLoopProxy* background_thread)
+      : backend_(backend), background_thread_(background_thread) {}
+  ~InFlightBackendIO() {}
+
+  // The operations we proxy:
+  void Init(net::CompletionCallback* callback);
+  void OpenEntry(const std::string& key, Entry** entry,
+                 net::CompletionCallback* callback);
+  void CreateEntry(const std::string& key, Entry** entry,
+                   net::CompletionCallback* callback);
+  void DoomEntry(const std::string& key, net::CompletionCallback* callback);
+  void DoomAllEntries(net::CompletionCallback* callback);
+  void DoomEntriesBetween(const base::Time initial_time,
+                          const base::Time end_time,
+                          net::CompletionCallback* callback);
+  void DoomEntriesSince(const base::Time initial_time,
+                        net::CompletionCallback* callback);
+  void OpenNextEntry(void** iter, Entry** next_entry,
+                     net::CompletionCallback* callback);
+  void OpenPrevEntry(void** iter, Entry** prev_entry,
+                     net::CompletionCallback* callback);
+  void EndEnumeration(void* iterator);
+  void CloseEntryImpl(EntryImpl* entry);
+  void DoomEntryImpl(EntryImpl* entry);
+  void FlushQueue(net::CompletionCallback* callback);
+  void ReadData(EntryImpl* entry, int index, int offset, net::IOBuffer* buf,
+                int buf_len, net::CompletionCallback* callback);
+  void WriteData(EntryImpl* entry, int index, int offset, net::IOBuffer* buf,
+                 int buf_len, bool truncate, net::CompletionCallback* callback);
+  void ReadSparseData(EntryImpl* entry, int64 offset, net::IOBuffer* buf,
+                      int buf_len, net::CompletionCallback* callback);
+  void WriteSparseData(EntryImpl* entry, int64 offset, net::IOBuffer* buf,
+                       int buf_len, net::CompletionCallback* callback);
+  void GetAvailableRange(EntryImpl* entry, int64 offset, int len, int64* start,
+                         net::CompletionCallback* callback);
+  void CancelSparseIO(EntryImpl* entry);
+  void ReadyForSparseIO(EntryImpl* entry, net::CompletionCallback* callback);
+
+  // Blocks until all operations are cancelled or completed.
+  void WaitForPendingIO();
+
+  scoped_refptr<base::MessageLoopProxy> background_thread() {
+    return background_thread_;
+  }
+
+  // Returns true if the current thread is the background thread.
+  bool BackgroundIsCurrentThread() {
+    return background_thread_->BelongsToCurrentThread();
+  }
+
+ protected:
+  virtual void OnOperationComplete(BackgroundIO* operation, bool cancel);
+
+ private:
+  typedef std::list<scoped_refptr<BackendIO> > OperationList;
+  void QueueOperation(BackendIO* operation);
+  void PostOperation(BackendIO* operation);
+
+  BackendImpl* backend_;
+  scoped_refptr<base::MessageLoopProxy> background_thread_;
+  OperationList pending_ops_;  // The list of operations to be posted.
+
+  DISALLOW_COPY_AND_ASSIGN(InFlightBackendIO);
+};
+
+}  // namespace disk_cache
+
+#endif  // NET_DISK_CACHE_IN_FLIGHT_BACKEND_IO_H_