net/disk_cache/blockfile/sparse_control.h

   1 // Copyright (c) 2012 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 NET_DISK_CACHE_BLOCKFILE_SPARSE_CONTROL_H_
   6 #define NET_DISK_CACHE_BLOCKFILE_SPARSE_CONTROL_H_
   7
   8 #include <string>
   9 #include <vector>
  10
  11 #include "base/basictypes.h"
  12 #include "base/compiler_specific.h"
  13 #include "net/base/completion_callback.h"
  14 #include "net/disk_cache/blockfile/bitmap.h"
  15 #include "net/disk_cache/blockfile/disk_format.h"
  16
  17 namespace net {
  18 class IOBuffer;
  19 class DrainableIOBuffer;
  20 }
  21
  22 namespace disk_cache {
  23
  24 class Entry;
  25 class EntryImpl;
  26
  27 // This class provides support for the sparse capabilities of the disk cache.
  28 // Basically, sparse IO is directed from EntryImpl to this class, and we split
  29 // the operation into multiple small pieces, sending each one to the
  30 // appropriate entry. An instance of this class is asociated with each entry
  31 // used directly for sparse operations (the entry passed in to the constructor).
  32 class SparseControl {
  33  public:
  34   typedef net::CompletionCallback CompletionCallback;
  35
  36   // The operation to perform.
  37   enum SparseOperation {
  38     kNoOperation,
  39     kReadOperation,
  40     kWriteOperation,
  41     kGetRangeOperation
  42   };
  43
  44   explicit SparseControl(EntryImpl* entry);
  45   ~SparseControl();
  46
  47   // Initializes the object for the current entry. If this entry already stores
  48   // sparse data, or can be used to do it, it updates the relevant information
  49   // on disk and returns net::OK. Otherwise it returns a net error code.
  50   int Init();
  51
  52   // Performs a quick test to see if the entry is sparse or not, without
  53   // generating disk IO (so the answer provided is only a best effort).
  54   bool CouldBeSparse() const;
  55
  56   // Performs an actual sparse read or write operation for this entry. |op| is
  57   // the operation to perform, |offset| is the desired sparse offset, |buf| and
  58   // |buf_len| specify the actual data to use and |callback| is the callback
  59   // to use for asynchronous operations. See the description of the Read /
  60   // WriteSparseData for details about the arguments. The return value is the
  61   // number of bytes read or written, or a net error code.
  62   int StartIO(SparseOperation op, int64 offset, net::IOBuffer* buf,
  63               int buf_len, const CompletionCallback& callback);
  64
  65   // Implements Entry::GetAvailableRange().
  66   int GetAvailableRange(int64 offset, int len, int64* start);
  67
  68   // Cancels the current sparse operation (if any).
  69   void CancelIO();
  70
  71   // Returns OK if the entry can be used for new IO or ERR_IO_PENDING if we are
  72   // busy. If the entry is busy, we'll invoke the callback when we are ready
  73   // again. See disk_cache::Entry::ReadyToUse() for more info.
  74   int ReadyToUse(const CompletionCallback& completion_callback);
  75
  76   // Deletes the children entries of |entry|.
  77   static void DeleteChildren(EntryImpl* entry);
  78
  79  private:
  80   // Creates a new sparse entry or opens an aready created entry from disk.
  81   // These methods just read / write the required info from disk for the current
  82   // entry, and verify that everything is correct. The return value is a net
  83   // error code.
  84   int CreateSparseEntry();
  85   int OpenSparseEntry(int data_len);
  86
  87   // Opens and closes a child entry. A child entry is a regular EntryImpl object
  88   // with a key derived from the key of the resource to store and the range
  89   // stored by that child.
  90   bool OpenChild();
  91   void CloseChild();
  92   std::string GenerateChildKey();
  93
  94   // Deletes the current child and continues the current operation (open).
  95   bool KillChildAndContinue(const std::string& key, bool fatal);
  96
  97   // Continues the current operation (open) without a current child.
  98   bool ContinueWithoutChild(const std::string& key);
  99
 100   // Returns true if the required child is tracked by the parent entry, i.e. it
 101   // was already created.
 102   bool ChildPresent();
 103
 104   // Sets the bit for the current child to the provided |value|. In other words,
 105   // starts or stops tracking this child.
 106   void SetChildBit(bool value);
 107
 108   // Writes to disk the tracking information for this entry.
 109   void WriteSparseData();
 110
 111   // Verify that the range to be accessed for the current child is appropriate.
 112   // Returns false if an error is detected or there is no need to perform the
 113   // current IO operation (for instance if the required range is not stored by
 114   // the child).
 115   bool VerifyRange();
 116
 117   // Updates the contents bitmap for the current range, based on the result of
 118   // the current operation.
 119   void UpdateRange(int result);
 120
 121   // Returns the number of bytes stored at |block_index|, if its allocation-bit
 122   // is off (because it is not completely filled).
 123   int PartialBlockLength(int block_index) const;
 124
 125   // Initializes the sparse info for the current child.
 126   void InitChildData();
 127
 128   // Iterates through all the children needed to complete the current operation.
 129   void DoChildrenIO();
 130
 131   // Performs a single operation with the current child. Returns true when we
 132   // should move on to the next child and false when we should interrupt our
 133   // work.
 134   bool DoChildIO();
 135
 136   // Performs the required work for GetAvailableRange for one child.
 137   int DoGetAvailableRange();
 138
 139   // Performs the required work after a single IO operations finishes.
 140   void DoChildIOCompleted(int result);
 141
 142   // Invoked by the callback of asynchronous operations.
 143   void OnChildIOCompleted(int result);
 144
 145   // Reports to the user that we are done.
 146   void DoUserCallback();
 147   void DoAbortCallbacks();
 148
 149   EntryImpl* entry_;  // The sparse entry.
 150   EntryImpl* child_;  // The current child entry.
 151   SparseOperation operation_;
 152   bool pending_;  // True if any child IO operation returned pending.
 153   bool finished_;
 154   bool init_;
 155   bool range_found_;  // True if GetAvailableRange found something.
 156   bool abort_;  // True if we should abort the current operation ASAP.
 157
 158   SparseHeader sparse_header_;  // Data about the children of entry_.
 159   Bitmap children_map_;  // The actual bitmap of children.
 160   SparseData child_data_;  // Parent and allocation map of child_.
 161   Bitmap child_map_;  // The allocation map as a bitmap.
 162
 163   CompletionCallback user_callback_;
 164   std::vector<CompletionCallback> abort_callbacks_;
 165   int64 offset_;  // Current sparse offset.
 166   scoped_refptr<net::DrainableIOBuffer> user_buf_;
 167   int buf_len_;  // Bytes to read or write.
 168   int child_offset_;  // Offset to use for the current child.
 169   int child_len_;  // Bytes to read or write for this child.
 170   int result_;
 171
 172   DISALLOW_COPY_AND_ASSIGN(SparseControl);
 173 };
 174
 175 }  // namespace disk_cache
 176
 177 #endif  // NET_DISK_CACHE_BLOCKFILE_SPARSE_CONTROL_H_