我需要一个循环缓冲区（或其他数据结构），我可以在其上执行“ToArray”或类似的调用来获取缓冲区的当前状态并使用，而缓冲区可能会覆盖所持有的值
此用例的原因是返回的数据被传递给工作线程进行处理，其目的是确保在调用之间尽可能少地覆盖数据。圆形数据结构的选择表面上是为了将缓冲区的内存使用量减少到固定值。
我构建了下面的数据结构，直到昨天我的需求已经足够了。相关的调用是TakeSnapshot，TakeAll和TakeWeakArraySnapshot，它们都是同一主题的变体。
当大约1000个参考类型样本可用时，调用非常频繁。
所有调用都会在某些时候导致内存不足异常。 TakeWeakArraySnapshot是一个例外，它在使用数组的过程中基本上恢复为null（我想这与gc句柄很弱的事实有关吗？）
是否有更合适的内存效率数据结构用于此用途或我做错了什么？将gc句柄类型更改为正常帮助。是否有可能创建一个包装引用的输出类型（就像我尝试使用弱引用一样），垃圾收集器可以很容易地回收它？
感谢阅读。
using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Threading;
using System.Runtime.InteropServices;
public class WeakArray<T>
{
private GCHandle[] fArray;
public WeakArray(int length)
{
fArray = new GCHandle[length];
for (int i = 0; i < length; i++)
fArray[i] = GCHandle.Alloc(null, GCHandleType.Weak);
}
~WeakArray()
{
if (fArray == null)
return;
int count = fArray.Length;
for (int i = 0; i < count; i++)
{
GCHandle gcHandle = fArray[i];
if (!gcHandle.IsAllocated)
break;
gcHandle.Free();
}
}
public int Length
{
get
{
return fArray.Length;
}
}
public T this[int index]
{
get
{
return (T) fArray[index].Target;
}
set
{
fArray[index].Target = value;
}
}
}
public class OutputData<TDataType>:IEnumerable<TDataType>,IDisposable
{
private TDataType[] Buffer { get; set; }
private readonly object _lock = new object();
public OutputData(ref TDataType[] buffer,long length)
{
Buffer = buffer;
Length = length;
}
public long Length { get; private set; }
/// <summary>
/// Gets the <see cref="`0"/> at the specified index. Throws IndexOutOfRange for an invalid index
/// or returns the default value of the generic type on an empty queue
/// </summary>
/// <value>
/// The <see cref="`0"/>.
/// </value>
/// <param name="i">The item at that index.</param>
/// <returns></returns>
public TDataType this[int i]
{
get
{
lock (_lock)
{
return Length > 0 ? Buffer[i] : default(TDataType);
}
}
}
public IEnumerator<TDataType> GetEnumerator()
{
for (int i = 0; i < Length; i++)
{
yield return Buffer[i];
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public void Dispose()
{
Array.Clear(Buffer,0,Buffer.Length);
}
public void SetLength(int count)
{
Length = count;
}
}
/// <summary>
/// Implements a CircularBuffer that behaves as a queue
/// </summary>
/// <typeparam name="T"></typeparam>
public class FixedCapacityQueue<T>
{
private T[] _buffer;
private T[] _output;
private OutputData<T> _outputData;
/// <summary>
/// Gets the dropped count. This is the number of samples that have been dropped to
/// maintain the fixed size of the datastructure.
/// </summary>
/// <value>
/// The dropped count.
/// </value>
public int DroppedCount { get; protected set; }
/// <summary>
/// The default number of dropped items required to generate a report
/// </summary>
protected const int DroppedFramesBetweenReports = 1000;
/// <summary>
/// The _start. Index of the first element in buffer.
/// </summary>
private int _start;
/// <summary>
/// The _end. Index after the last element in the buffer.
/// </summary>
private int _end;
/// <summary>
/// The _size. Buffer size.
/// </summary>
private int _numberOfItemsInBuffer;
private readonly object _lock = new object();
/// <summary>
/// Gets or sets the name of the buffer.
/// </summary>
/// <value>
/// The name.
/// </value>
public string Name { get; protected set; }
private readonly T _default = default(T);
/// <summary>
/// Initializes a new instance of the <see cref="FixedCapacityQueue{T}" /> class.
/// </summary>
/// <param name="name">The name of the queue.</param>
/// <param name="bufferSize">Size of the buffer.</param>
public FixedCapacityQueue(string name, int bufferSize)
{
Contract.Requires(bufferSize > 0);
Contract.Requires(!String.IsNullOrEmpty(name));
_buffer = new T[bufferSize];
_output = new T[bufferSize];
_outputData = new OutputData<T>(ref _output, 0);
_start = 0;
_end = _numberOfItemsInBuffer == bufferSize ? 0 : _numberOfItemsInBuffer;
Name = String.Format("FixedCapacityQueue for {0}", name);
}
/// <summary>
/// Initializes a new instance of the <see cref="FixedCapacityQueue{T}" /> class.
/// </summary>
/// <param name="name">The nameof the buffer.</param>
/// <param name="bufferSize">Size of the buffer.</param>
/// <param name="data">The data to be added to the queue.</param>
/// <exception cref="System.ArgumentException"></exception>
public FixedCapacityQueue(string name, int bufferSize, ICollection<T> data)
: this(name, bufferSize)
{
Contract.Requires(data != null);
Contract.Requires(bufferSize > 0);
Contract.Requires(data.Count < bufferSize);
foreach (var dataItem in data)
{
Enqueue(dataItem);
}
}
/// <summary>
/// Gets a value indicating whether the queue [is empty].
/// </summary>
/// <value>
/// <c>true</c> if [is empty]; otherwise, <c>false</c>.
/// </value>
public bool IsEmpty
{
get
{
lock (_lock)
{
return _numberOfItemsInBuffer == 0;
}
}
}
/// <summary>
/// Gets a value indicating whether the queue [is full].
/// </summary>
/// <value>
/// <c>true</c> if [is full]; otherwise, <c>false</c>.
/// </value>
public bool IsFull
{
get
{
lock (_lock)
{
return Count == Size;
}
}
}
/// <summary>
/// Gets the number of items currently present in the queue.
/// </summary>
/// <value>
/// The count.
/// </value>
public int Count
{
get
{
lock (_lock)
{
return _numberOfItemsInBuffer;
}
}
}
/// <summary>
/// Gets the declared size of the queue.
/// </summary>
/// <value>
/// The size.
/// </value>
public int Size
{
get
{
lock (_lock)
{
return _buffer.Length;
}
}
}
/// <summary>
/// Dequeues an item from the queue. The expected behaviour is that if a Dequeue operation is
/// requested whilst a queue is empty, the default type of the generic queue is returned.
/// </summary>
/// <returns></returns>
public T Dequeue()
{
lock (_lock)
{
if (IsEmpty) return _default;
var item = _buffer[_start];
_buffer[_start] = _default;
Increment(ref _start);
--_numberOfItemsInBuffer;
return item;
}
}
/// <summary>
/// Enqueues the specified item to the queue.
/// </summary>
/// <param name="toAdd">To add.</param>
public void Enqueue(T toAdd)
{
lock (_lock)
{
if (IsFull)
{
_buffer[_end] = toAdd;
Increment(ref _end);
_start = _end;
DroppedCount++;
//report drops
if (DroppedCount >= DroppedFramesBetweenReports)
{
//EventAndErrorPump.Instance.WriteOnce(1000, ReportLevelEnum.Warning,
// String.Format("{0} FixedQueue Dropped Items: {1} ", Name, DroppedCount));
DroppedCount = 0;
}
}
else
{
_buffer[_end] = toAdd;
Increment(ref _end);
++_numberOfItemsInBuffer;
}
}
}
/// <summary>
/// Increments the provided index variable by one, wrapping
/// around if necessary.
/// </summary>
/// <param name="index"></param>
private void Increment(ref int index)
{
if (++index == Size)
{
index = 0;
}
}
/// <summary>
/// Decrements the provided index variable by one, wrapping
/// around if necessary.
/// </summary>
/// <param name="index"></param>
private void Decrement(ref int index)
{
if (index == 0)
{
index = Size;
}
index--;
}
public void Enqueue(IEnumerable<T> toAdd)
{
lock (_lock)
{
foreach (var dataItem in toAdd)
{
Enqueue(dataItem);
}
}
}
public IEnumerator<T> GetEnumerator()
{
var segments = new ArraySegment<T>[2] {ArrayOne(), ArrayTwo()};
foreach (ArraySegment<T> segment in segments)
{
for (int i = 0; i < segment.Count; i++)
{
yield return segment.Array[segment.Offset + i];
}
}
}
/// <summary>
/// Gets the at the specified index. Throws IndexOutOfRange for an invalid index
/// or returns the default value of the generic type on an empty queue. The head/earliest item index can also be
/// null in the event of a dequeue. If the front of the queue is required,please use the front function instead
/// </summary>
/// <param name="i">The item at that index.</param>
/// <returns></returns>
/// <exception cref="System.IndexOutOfRangeException"></exception>
public T this[int index]
{
get
{
lock (_lock)
{
if (IsEmpty)
{
return _default;
}
if (index >= _numberOfItemsInBuffer)
{
throw new IndexOutOfRangeException(string.Format("Cannot access index {0}. Buffer size is {1}",
index, _numberOfItemsInBuffer));
}
int actualIndex = InternalIndex(index);
return _buffer[actualIndex];
}
}
}
/// <summary>
/// Converts the index in the argument to an index in <code>_buffer</code>
/// </summary>
/// <returns>
/// The transformed index.
/// </returns>
/// <param name='index'>
/// External index.
/// </param>
private int InternalIndex(int index)
{
return _start + (index < (Size - _start) ? index : index - Size);
}
/// <summary>
/// Clears this instance.
/// </summary>
public void Clear()
{
lock (_lock)
{
_numberOfItemsInBuffer = 0;
_start = 0;
_end = 0;
}
}
/// <summary>
/// Takes a snapshot of the queue and returns it. If used in isolation .i.e not in a buffer implementation
/// it will return all the elements of the queue and leave the queue empty.
/// In a buffer implementation , since the buffer could be accepting data at the point of this call; it is a stale
/// snapshot of the queue when the call is made.
/// </summary>
/// <returns></returns>
[Obsolete("Use TakeAllData() instead")]
public T[] TakeSnapshot()
{
lock (_lock)
{
return TakeSnapshot(Count);
}
}
/// <summary>
/// Takes all data available in the queue.
/// </summary>
/// <returns></returns>
public OutputData<T> TakeAll()
{
var count = Count;
if (count <= 0) return null;
lock (_lock)
{
CopyInto(count, _output);
_outputData.SetLength(count);
return _outputData;
}
}
/// <summary>
/// Takes a snapshot of the queue using the count to limit the output to return. In the event that the specified
/// count is larger than the current size of the queue, it will throw an exception. A zero count value will immediately return
/// In a buffer implementation , since the buffer could be accepting data at the point of this call; it is a stale
/// snapshot of the queue when the call is made.
/// </summary>
/// <returns></returns>
[Obsolete("Use TakeAllData(int count) instead")]
public T[] TakeSnapshot(int count)
{
if (count == 0) return null;
lock (_lock)
{
if (count > _numberOfItemsInBuffer)
{
count = _numberOfItemsInBuffer;
//throw new ArgumentOutOfRangeException(String.Format("Queue size is {0}", Size));
}
var output = new T[count];
CopyInto(count, output);
return output;
}
}
private void CopyInto(int count, T[] output)
{
var lastIndex = (_start + count) - 1;
if (lastIndex >= Size)
{
Array.Copy(_buffer, _start, output, 0, Size - _start);
Array.Copy(_buffer, 0, output, Size - _start, (lastIndex%Size) + 1);
}
else
{
Array.Copy(_buffer, _start, output, 0, count);
}
_start = (_start + count)%Size;
_numberOfItemsInBuffer = _numberOfItemsInBuffer - count;
}
public T[] PeekSnapshot()
{
lock (_lock)
{
var count = Count;
var output = new T[count];
for (var i = 0; i < count; i++)
{
output[i] = this[i];
}
return output;
}
}
public T[] PeekSnapshot(int count)
{
if (count == 0) return null;
lock (_lock)
{
if (count > Size)
{
throw new ArgumentOutOfRangeException(String.Format("Queue size is {0}", Size));
}
var output = new T[count];
for (var i = 0; i < count; i++)
{
output[i] = this[i];
}
return output;
}
}
/// <summary>
/// Gets the front of the queue. The earliest item added to the queue.
/// Use this in lieu of checking this[0] as that could be null whilst items still
/// exist in the queue
/// </summary>
/// <value>
/// The front.
/// </value>
public T Front()
{
lock (_lock)
{
return IsEmpty ? _default : _buffer[_start];
}
}
/// <summary>
/// Gets the utilisation of the datastructure i.e % of the datastructure currently in use
/// </summary>
/// <value>
/// The utilisation.
/// </value>
public float Utilisation
{
get
{
lock (_lock)
{
return CalculateUtilisation();
}
}
}
private float CalculateUtilisation()
{
var util = 0f;
if (Size > 0)
{
util = (Count/(float) Size)*100;
}
return util;
}
/// <summary>
/// Returns the latest item in the queue.
/// </summary>
/// <returns></returns>
public T Back()
{
lock (_lock)
{
return Count > 0 ? _buffer[_end - 1] : _default;
;
}
}
public WeakArray<T> TakeWeakArraySnapshot()
{
lock (_lock)
{
var count = Count;
var arr = new WeakArray<T>(count);
for (var i = 0; i < count; i++)
{
arr[i] = Dequeue();
}
return arr;
}
}
/// <summary>
/// Gets the internal array. Use with EXTREME CAUTION! This is not a thread safe operation
/// and should ONLY be used in situations where any modification to the queue is not possible.
/// Modification operations include Enqueing or Dequeing
/// </summary>
/// <returns></returns>
public T[] GetInternalArray()
{
return _buffer;
}
// doing ArrayOne and ArrayTwo methods returning ArraySegment<T> as seen here:
// http://www.boost.org/doc/libs/1_37_0/libs/circular_buffer/doc/circular_buffer.html#classboost_1_1circular__buffer_1957cccdcb0c4ef7d80a34a990065818d
// http://www.boost.org/doc/libs/1_37_0/libs/circular_buffer/doc/circular_buffer.html#classboost_1_1circular__buffer_1f5081a54afbc2dfc1a7fb20329df7d5b
// should help a lot with the code.
#region Array items easy access.
// The array is composed by at most two non-contiguous segments,
// the next two methods allow easy access to those.
private ArraySegment<T> ArrayOne()
{
if (_start < _end)
{
return new ArraySegment<T>(_buffer, _start, _end - _start);
}
else
{
return new ArraySegment<T>(_buffer, _start, _buffer.Length - _start);
}
}
private ArraySegment<T> ArrayTwo()
{
if (_start < _end)
{
return new ArraySegment<T>(_buffer, _end, 0);
}
else
{
return new ArraySegment<T>(_buffer, 0, _end);
}
}
#endregion
}
答案 0 :(得分：1)