nsStorageStream.h - mozsearch

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*

 * The storage stream provides an internal buffer that can be filled by a

 * client using a single output stream.  One or more independent input streams

 * can be created to read the data out non-destructively.  The implementation

 * uses a segmented buffer internally to avoid realloc'ing of large buffers,

 * with the attendant performance loss and heap fragmentation.

*/

#ifndef _nsStorageStream_h_

#define _nsStorageStream_h_

#include "nsIStorageStream.h"

#include "nsIOutputStream.h"

#include "mozilla/Attributes.h"

#include "mozilla/Mutex.h"

#define NS_STORAGESTREAM_CID                         \

  { /* 669a9795-6ff7-4ed4-9150-c34ce2971b63 */       \

    0x669a9795, 0x6ff7, 0x4ed4, {                    \

      0x91, 0x50, 0xc3, 0x4c, 0xe2, 0x97, 0x1b, 0x63 \

    }                                                \

#define NS_STORAGESTREAM_CONTRACTID "@mozilla.org/storagestream;1"

class nsSegmentedBuffer;

class nsStorageStream final : public nsIStorageStream, public nsIOutputStream {

 public:

  nsStorageStream();

  NS_DECL_THREADSAFE_ISUPPORTS

  NS_DECL_NSISTORAGESTREAM

  NS_DECL_NSIOUTPUTSTREAM

  friend class nsStorageInputStream;

 private:

  ~nsStorageStream();

  mozilla::Mutex mMutex{"nsStorageStream"};

  nsSegmentedBuffer* mSegmentedBuffer MOZ_GUARDED_BY(mMutex) = nullptr;

  // All segments, except possibly the last, are of this size.  Must be

  // power-of-2

  uint32_t mSegmentSize MOZ_GUARDED_BY(mMutex) = 0;

  // log2(mSegmentSize)

  uint32_t mSegmentSizeLog2 MOZ_GUARDED_BY(mMutex) = 0;

  // true, if an un-Close'ed output stream exists

  bool mWriteInProgress MOZ_GUARDED_BY(mMutex) = false;

  // Last segment # in use, -1 initially

  int32_t mLastSegmentNum MOZ_GUARDED_BY(mMutex) = -1;

  // Pointer to next byte to be written

  char* mWriteCursor MOZ_GUARDED_BY(mMutex) = nullptr;

  // Pointer to one byte after end of segment containing the write cursor

  char* mSegmentEnd MOZ_GUARDED_BY(mMutex) = nullptr;

  // Maximum number of bytes which may be written to the stream

  uint32_t mMaxLogicalLength MOZ_GUARDED_BY(mMutex) = 0;

  // Number of bytes written to stream

  uint32_t mLogicalLength MOZ_GUARDED_BY(mMutex) = 0;

  // number of input streams actively reading a segment.

  uint32_t mActiveSegmentBorrows MOZ_GUARDED_BY(mMutex) = 0;

  nsresult SetLengthLocked(uint32_t aLength) MOZ_REQUIRES(mMutex);

  nsresult Seek(int32_t aPosition) MOZ_REQUIRES(mMutex);

  uint32_t SegNum(uint32_t aPosition) MOZ_REQUIRES(mMutex) {

    return aPosition >> mSegmentSizeLog2;

  uint32_t SegOffset(uint32_t aPosition) MOZ_REQUIRES(mMutex) {

    return aPosition & (mSegmentSize - 1);

};

#endif  //  _nsStorageStream_h_