Disk cache: First pass to add support for sparse entries....

net/disk_cache/sparse_control.h

+// Copyright (c) 2009 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_SPARSE_CONTROL_H_
+#define NET_DISK_CACHE_SPARSE_CONTROL_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "net/base/completion_callback.h"
+#include "net/disk_cache/bitmap.h"
+#include "net/disk_cache/disk_format.h"
+
+namespace net {
+class IOBuffer;
+class ReusedIOBuffer;
+}
+
+namespace disk_cache {
+
+class Entry;
+class EntryImpl;
+
+// This class provides support for the sparse capabilities of the disk cache.
+// Basically, sparse IO is directed from EntryImpl to this class, and we split
+// the operation into multiple small pieces, sending each one to the
+// appropriate entry. An instance of this class is asociated with each entry
+// used directly for sparse operations (the entry passed in to the constructor).
+class SparseControl {
+ public:
+  // The operation to perform.
+  enum SparseOperation {
+    kNoOperation,
+    kReadOperation,
+    kWriteOperation
+  };
+
+  explicit SparseControl(EntryImpl* entry)
+      : entry_(entry), child_(NULL), operation_(kNoOperation), init_(false),
+        child_map_(child_data_.bitmap, kNumSparseBits, kNumSparseBits / 32),
+        ALLOW_THIS_IN_INITIALIZER_LIST(
+            child_callback_(this, &SparseControl::OnChildIOCompleted)),
+        user_callback_(NULL) {}
+  ~SparseControl();
+
+  // Initializes the object for the current entry. If this entry already stores
+  // sparse data, or can be used to do it, it updates the relevant information
+  // on disk and returns net::OK. Otherwise it returns a net error code.
+  int Init();
+
+  // Performs an actual sparse read or write operation for this entry. |op| is
+  // the operation to perform, |offset| is the desired sparse offset, |buf| and
+  // |buf_len| specify the actual data to use and |callback| is the callback
+  // to use for asynchronous operations. See the description of the Read /
+  // WriteSparseData for details about the arguments. The return value is the
+  // number of bytes read or written, or a net error code.
+  int StartIO(SparseOperation op, int64 offset, net::IOBuffer* buf,
+              int buf_len, net::CompletionCallback* callback);
+
+  // Implements Entry::GetAvailableRange().
+  int GetAvailableRange(int64 offset, int len, int64* start);
+
+ private:
+  // Creates a new sparse entry or opens an aready created entry from disk.
+  // These methods just read / write the required info from disk for the current
+  // entry, and verify that everything is correct. The return value is a net
+  // error code.
+  int CreateSparseEntry();
+  int OpenSparseEntry(int data_len);
+
+  // Opens and closes a child entry. A child entry is a regular EntryImpl object
+  // with a key derived from the key of the resource to store and the range
+  // stored by that child.
+  bool OpenChild();
+  void CloseChild();
+  std::string GenerateChildKey();
+
+  // Returns true if the required child is tracked by the parent entry, i.e. it
+  // was already created.
+  bool ChildPresent();
+
+  // Starts tracking this child. A new child entry was created so we must set
+  // the corresponding bit on the bitmap of children.
+  void SetChildBit();
+
+  // Writes to disk the tracking information for this entry.
+  void WriteSparseData();
+
+  // Verify that the range to be accessed for the current child is appropriate.
+  // Returns false if an error is detected or there is no need to perform the
+  // current IO operation (for instance if the required range is not stored by
+  // the child).
+  bool VerifyRange();
+
+  // Updates the contents bitmap for the current range, based on the result of
+  // the current operation.
+  void UpdateRange(int result);
+
+  // Initializes the sparse info for the current child.
+  void InitChildData();
+
+  // Iterates through all the children needed to complete the current operation.
+  void DoChildrenIO();
+
+  // Performs a single operation with the current child. Returns true when we
+  // should move on to the next child and false when we should interrupt our
+  // work.
+  bool DoChildIO();
+
+  // Performs the required work after a single IO operations finishes.
+  void DoChildIOCompleted(int result);
+
+  // Invoked by the callback of asynchronous operations.
+  void OnChildIOCompleted(int result);
+
+  // Reports to the user that we are done.
+  void DoUserCallback();
+
+  EntryImpl* entry_;  // The sparse entry.
+  Entry* child_;  // The current child entry.
+  SparseOperation operation_;
+  bool pending_;  // True if any child IO operation returned pending.
+  bool finished_;
+  bool init_;
+
+  SparseHeader sparse_header_;  // Data about the children of entry_.
+  Bitmap children_map_;  // The actual bitmap of children.
+  SparseData child_data_;  // Parent and allocation map of child_.
+  Bitmap child_map_;  // The allocation map as a bitmap.
+
+  net::CompletionCallbackImpl<SparseControl> child_callback_;
+  net::CompletionCallback* user_callback_;
+  int64 offset_;  // Current sparse offset.
+  scoped_refptr<net::ReusedIOBuffer> user_buf_;
+  int buf_len_;  // Bytes to read or write.
+  int child_offset_;  // Offset to use for the current child.
+  int child_len_;  // Bytes to read or write for this child.
+  int result_;
+
+  DISALLOW_COPY_AND_ASSIGN(SparseControl);
+};
+
+}  // namespace disk_cache
+
+#endif  // NET_DISK_CACHE_SPARSE_CONTROL_H_