xpcom/io/nsStorageStream.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /*
   8  * The storage stream provides an internal buffer that can be filled by a
   9  * client using a single output stream.  One or more independent input streams
  10  * can be created to read the data out non-destructively.  The implementation
  11  * uses a segmented buffer internally to avoid realloc'ing of large buffers,
  12  * with the attendant performance loss and heap fragmentation.
  13  */
  14
  15 #ifndef _nsStorageStream_h_
  16 #define _nsStorageStream_h_
  17
  18 #include "nsIStorageStream.h"
  19 #include "nsIOutputStream.h"
  20 #include "mozilla/Attributes.h"
  21 #include "mozilla/Mutex.h"
  22
  23 #define NS_STORAGESTREAM_CID                         \
  24   { /* 669a9795-6ff7-4ed4-9150-c34ce2971b63 */       \
  25     0x669a9795, 0x6ff7, 0x4ed4, {                    \
  26       0x91, 0x50, 0xc3, 0x4c, 0xe2, 0x97, 0x1b, 0x63 \
  27     }                                                \
  28   }
  29
  30 #define NS_STORAGESTREAM_CONTRACTID "@mozilla.org/storagestream;1"
  31
  32 class nsSegmentedBuffer;
  33
  34 class nsStorageStream final : public nsIStorageStream, public nsIOutputStream {
  35  public:
  36   nsStorageStream();
  37
  38   NS_DECL_THREADSAFE_ISUPPORTS
  39   NS_DECL_NSISTORAGESTREAM
  40   NS_DECL_NSIOUTPUTSTREAM
  41
  42   friend class nsStorageInputStream;
  43
  44  private:
  45   ~nsStorageStream();
  46
  47   mozilla::Mutex mMutex{"nsStorageStream"};
  48   nsSegmentedBuffer* mSegmentedBuffer MOZ_GUARDED_BY(mMutex) = nullptr;
  49   // All segments, except possibly the last, are of this size.  Must be
  50   // power-of-2
  51   uint32_t mSegmentSize MOZ_GUARDED_BY(mMutex) = 0;
  52   // log2(mSegmentSize)
  53   uint32_t mSegmentSizeLog2 MOZ_GUARDED_BY(mMutex) = 0;
  54   // true, if an un-Close'ed output stream exists
  55   bool mWriteInProgress MOZ_GUARDED_BY(mMutex) = false;
  56   // Last segment # in use, -1 initially
  57   int32_t mLastSegmentNum MOZ_GUARDED_BY(mMutex) = -1;
  58   // Pointer to next byte to be written
  59   char* mWriteCursor MOZ_GUARDED_BY(mMutex) = nullptr;
  60   // Pointer to one byte after end of segment containing the write cursor
  61   char* mSegmentEnd MOZ_GUARDED_BY(mMutex) = nullptr;
  62   // Maximum number of bytes which may be written to the stream
  63   uint32_t mMaxLogicalLength MOZ_GUARDED_BY(mMutex) = 0;
  64   // Number of bytes written to stream
  65   uint32_t mLogicalLength MOZ_GUARDED_BY(mMutex) = 0;
  66   // number of input streams actively reading a segment.
  67   uint32_t mActiveSegmentBorrows MOZ_GUARDED_BY(mMutex) = 0;
  68
  69   nsresult SetLengthLocked(uint32_t aLength) MOZ_REQUIRES(mMutex);
  70   nsresult Seek(int32_t aPosition) MOZ_REQUIRES(mMutex);
  71   uint32_t SegNum(uint32_t aPosition) MOZ_REQUIRES(mMutex) {
  72     return aPosition >> mSegmentSizeLog2;
  73   }
  74   uint32_t SegOffset(uint32_t aPosition) MOZ_REQUIRES(mMutex) {
  75     return aPosition & (mSegmentSize - 1);
  76   }
  77 };
  78
  79 #endif  //  _nsStorageStream_h_