pagespeed/kernel/base/circular_buffer.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */


#ifndef PAGESPEED_KERNEL_UTIL_CIRCULAR_BUFFER_H_
#define PAGESPEED_KERNEL_UTIL_CIRCULAR_BUFFER_H_

#include "pagespeed/kernel/base/basictypes.h"
#include "pagespeed/kernel/base/string.h"
#include "pagespeed/kernel/base/string_util.h"

namespace net_instaweb {

class MessageHandler;

// CircularBuffer which can be instantiated using malloc or with a
// pre-allocated buffer.
class CircularBuffer {
 public:
  // Instantiate buffer with malloc.
  static CircularBuffer* Create(const int capacity);
  // Instantiate buffer with pre-allocated block.
  // parent = true if this is invoked in root process (ie, this call should
  // initialize the fields of the segment).
  // block is a pointer to a pre-allocated segment.
  // block_size is the size of the block, it must be equal to Sizeof(capacity).
  // capacity is the size of the data buffer (the maximum amount of data
  // which we can buffer at one time).
  static CircularBuffer* Init(bool parent, void* block,
                              const int block_size,
                              const int capacity);
  // Return the size in bytes of the memory block to allocate to hold a buffer
  // with size equal to capacity.
  // capacity is the size of data buffer.
  static int Sizeof(const int capacity) {
    // buffer[1] is double counted, so -1 here.
    int total = sizeof(CircularBuffer) + capacity - 1;
    return total;
  }
  // Reset offset of data segment and wrapped flag.
  // The old content is not cleared but shouldn't be print out again.
  void Clear();
  // Write message to buffer.
  bool Write(const StringPiece& message);
  // Return data content as string.
  GoogleString ToString(MessageHandler* handler);

 private:
  // Can't construct -- must call Create() or Init() from a pre-allocated
  // block of correct size.
  CircularBuffer();
  ~CircularBuffer();
  // Return the part from offset to the end of buffer.
  StringPiece FirstChunk();
  // Return the part from the beginning to the offset of buffer.
  StringPiece SecondChunk();

  // Capacity of buffer.
  int capacity_;
  // Flag of having wrapped message.
  bool wrapped_;
  // Position to write in buffer.
  int offset_;
  // Buffer.
  char buffer_[1];

  DISALLOW_COPY_AND_ASSIGN(CircularBuffer);
};

}  // namespace net_instaweb

#endif  // PAGESPEED_KERNEL_UTIL_CIRCULAR_BUFFER_H_