我正在使用ConcurrentQueue一个共享数据结构，其目的是保存传递给它的最后 N 个对象（一种历史）。
假设我们有一个浏览器，我们想要最近 100 个浏览的 Url。我想要一个队列，当容量已满（历史上的 100 个地址）时，它会在新条目插入（入队）时自动丢弃（出队）最旧的（第一个）条目。
我怎样才能做到这一点System.Collections？
问问题
96881 次
15 回答
125
我会编写一个包装类，在 Enqueue 上检查 Count，然后在计数超过限制时检查 Dequeue。
public class FixedSizedQueue<T>
{
ConcurrentQueue<T> q = new ConcurrentQueue<T>();
private object lockObject = new object();
public int Limit { get; set; }
public void Enqueue(T obj)
{
q.Enqueue(obj);
lock (lockObject)
{
T overflow;
while (q.Count > Limit && q.TryDequeue(out overflow)) ;
}
}
}
于 2011-05-02T02:10:48.820 回答
108
我会选择一个轻微的变体......扩展 ConcurrentQueue 以便能够在 FixedSizeQueue 上使用 Linq 扩展
public class FixedSizedQueue<T> : ConcurrentQueue<T>
{
private readonly object syncObject = new object();
public int Size { get; private set; }
public FixedSizedQueue(int size)
{
Size = size;
}
public new void Enqueue(T obj)
{
base.Enqueue(obj);
lock (syncObject)
{
while (base.Count > Size)
{
T outObj;
base.TryDequeue(out outObj);
}
}
}
}
于 2012-04-24T14:07:45.310 回答
32
对于任何觉得它有用的人，这里有一些基于 Richard Schneider 上面回答的工作代码：
public class FixedSizedQueue<T>
{
readonly ConcurrentQueue<T> queue = new ConcurrentQueue<T>();
public int Size { get; private set; }
public FixedSizedQueue(int size)
{
Size = size;
}
public void Enqueue(T obj)
{
queue.Enqueue(obj);
while (queue.Count > Size)
{
T outObj;
queue.TryDequeue(out outObj);
}
}
}
于 2012-02-21T02:30:33.263 回答
14
对于它的价值，这是一个轻量级的循环缓冲区，其中一些方法标记为安全和不安全使用。
public class CircularBuffer<T> : IEnumerable<T>
{
readonly int size;
readonly object locker;
int count;
int head;
int rear;
T[] values;
public CircularBuffer(int max)
{
this.size = max;
locker = new object();
count = 0;
head = 0;
rear = 0;
values = new T[size];
}
static int Incr(int index, int size)
{
return (index + 1) % size;
}
private void UnsafeEnsureQueueNotEmpty()
{
if (count == 0)
throw new Exception("Empty queue");
}
public int Size { get { return size; } }
public object SyncRoot { get { return locker; } }
#region Count
public int Count { get { return UnsafeCount; } }
public int SafeCount { get { lock (locker) { return UnsafeCount; } } }
public int UnsafeCount { get { return count; } }
#endregion
#region Enqueue
public void Enqueue(T obj)
{
UnsafeEnqueue(obj);
}
public void SafeEnqueue(T obj)
{
lock (locker) { UnsafeEnqueue(obj); }
}
public void UnsafeEnqueue(T obj)
{
values[rear] = obj;
if (Count == Size)
head = Incr(head, Size);
rear = Incr(rear, Size);
count = Math.Min(count + 1, Size);
}
#endregion
#region Dequeue
public T Dequeue()
{
return UnsafeDequeue();
}
public T SafeDequeue()
{
lock (locker) { return UnsafeDequeue(); }
}
public T UnsafeDequeue()
{
UnsafeEnsureQueueNotEmpty();
T res = values[head];
values[head] = default(T);
head = Incr(head, Size);
count--;
return res;
}
#endregion
#region Peek
public T Peek()
{
return UnsafePeek();
}
public T SafePeek()
{
lock (locker) { return UnsafePeek(); }
}
public T UnsafePeek()
{
UnsafeEnsureQueueNotEmpty();
return values[head];
}
#endregion
#region GetEnumerator
public IEnumerator<T> GetEnumerator()
{
return UnsafeGetEnumerator();
}
public IEnumerator<T> SafeGetEnumerator()
{
lock (locker)
{
List<T> res = new List<T>(count);
var enumerator = UnsafeGetEnumerator();
while (enumerator.MoveNext())
res.Add(enumerator.Current);
return res.GetEnumerator();
}
}
public IEnumerator<T> UnsafeGetEnumerator()
{
int index = head;
for (int i = 0; i < count; i++)
{
yield return values[index];
index = Incr(index, size);
}
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
#endregion
}
我喜欢使用Foo()/SafeFoo()/UnsafeFoo()约定：
FooUnsafeFoo默认调用方法。UnsafeFoo方法可以在没有锁的情况下自由修改状态，它们应该只调用其他不安全的方法。SafeFoo方法调用UnsafeFoo锁内的方法。
它有点冗长，但它会产生明显的错误，例如在应该是线程安全的方法中调用锁之外的不安全方法，更加明显。
于 2011-05-07T23:53:48.633 回答
6
我的版本只是普通版本的子类Queue。没什么特别的，但看到每个人都参与其中，而且它仍然与主题标题一致，我不妨把它放在这里。为了以防万一，它还返回出列的那些。
public sealed class SizedQueue<T> : Queue<T>
{
public int FixedCapacity { get; }
public SizedQueue(int fixedCapacity)
{
this.FixedCapacity = fixedCapacity;
}
/// <summary>
/// If the total number of item exceed the capacity, the oldest ones automatically dequeues.
/// </summary>
/// <returns>The dequeued value, if any.</returns>
public new T Enqueue(T item)
{
base.Enqueue(item);
if (base.Count > FixedCapacity)
{
return base.Dequeue();
}
return default;
}
}
于 2018-04-19T15:34:16.407 回答
5
这是我对固定大小队列的看法
它使用常规队列，以避免在Count属性上使用时的同步开销ConcurrentQueue。它还实现IReadOnlyCollection了可以使用 LINQ 方法。其余的与此处的其他答案非常相似。
[Serializable]
[DebuggerDisplay("Count = {" + nameof(Count) + "}, Limit = {" + nameof(Limit) + "}")]
public class FixedSizedQueue<T> : IReadOnlyCollection<T>
{
private readonly Queue<T> _queue = new Queue<T>();
private readonly object _lock = new object();
public int Count { get { lock (_lock) { return _queue.Count; } } }
public int Limit { get; }
public FixedSizedQueue(int limit)
{
if (limit < 1)
throw new ArgumentOutOfRangeException(nameof(limit));
Limit = limit;
}
public FixedSizedQueue(IEnumerable<T> collection)
{
if (collection is null || !collection.Any())
throw new ArgumentException("Can not initialize the Queue with a null or empty collection", nameof(collection));
_queue = new Queue<T>(collection);
Limit = _queue.Count;
}
public void Enqueue(T obj)
{
lock (_lock)
{
_queue.Enqueue(obj);
while (_queue.Count > Limit)
_queue.Dequeue();
}
}
public void Clear()
{
lock (_lock)
_queue.Clear();
}
public IEnumerator<T> GetEnumerator()
{
lock (_lock)
return new List<T>(_queue).GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
于 2018-12-28T05:28:30.343 回答
4
只是因为还没有人说..您可以使用 aLinkedList<T>并添加线程安全性：
public class Buffer<T> : LinkedList<T>
{
private int capacity;
public Buffer(int capacity)
{
this.capacity = capacity;
}
public void Enqueue(T item)
{
// todo: add synchronization mechanism
if (Count == capacity) RemoveLast();
AddFirst(item);
}
public T Dequeue()
{
// todo: add synchronization mechanism
var last = Last.Value;
RemoveLast();
return last;
}
}
需要注意的一点是，在此示例中，默认枚举顺序将是 LIFO。但如有必要，可以覆盖它。
于 2020-05-30T20:29:05.107 回答
3
只是为了好玩，我相信这是另一个实现，它解决了大多数评论者的担忧。特别是，线程安全是在没有锁定的情况下实现的，并且实现被包装类隐藏。
public class FixedSizeQueue<T> : IReadOnlyCollection<T>
{
private ConcurrentQueue<T> _queue = new ConcurrentQueue<T>();
private int _count;
public int Limit { get; private set; }
public FixedSizeQueue(int limit)
{
this.Limit = limit;
}
public void Enqueue(T obj)
{
_queue.Enqueue(obj);
Interlocked.Increment(ref _count);
// Calculate the number of items to be removed by this thread in a thread safe manner
int currentCount;
int finalCount;
do
{
currentCount = _count;
finalCount = Math.Min(currentCount, this.Limit);
} while (currentCount !=
Interlocked.CompareExchange(ref _count, finalCount, currentCount));
T overflow;
while (currentCount > finalCount && _queue.TryDequeue(out overflow))
currentCount--;
}
public int Count
{
get { return _count; }
}
public IEnumerator<T> GetEnumerator()
{
return _queue.GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return _queue.GetEnumerator();
}
}
于 2015-08-25T20:56:45.543 回答
2
让我们再添加一个答案。为什么这比其他人更重要？
1）简单。试图保证大小是好的，但会导致不必要的复杂性，这可能会表现出自己的问题。
2) 实现 IReadOnlyCollection，这意味着你可以在它上面使用 Linq 并将它传递给各种期望 IEnumerable 的东西。
3) 无锁定。上面的许多解决方案都使用了锁，这在无锁集合上是不正确的。
4) 实现与 ConcurrentQueue 相同的一组方法、属性和接口，包括 IProducerConsumerCollection，如果您想将集合与 BlockingCollection 一起使用，这很重要。
如果 TryDequeue 失败，此实现可能最终会产生比预期更多的条目，但这种发生的频率似乎不值得专门的代码，因为这将不可避免地影响性能并导致其自身的意外问题。
如果您绝对想保证大小，实现 Prune() 或类似方法似乎是最好的主意。您可以在其他方法（包括 TryDequeue）中使用 ReaderWriterLockSlim 读锁，并且仅在修剪时使用写锁。
class ConcurrentFixedSizeQueue<T> : IProducerConsumerCollection<T>, IReadOnlyCollection<T>, ICollection {
readonly ConcurrentQueue<T> m_concurrentQueue;
readonly int m_maxSize;
public int Count => m_concurrentQueue.Count;
public bool IsEmpty => m_concurrentQueue.IsEmpty;
public ConcurrentFixedSizeQueue (int maxSize) : this(Array.Empty<T>(), maxSize) { }
public ConcurrentFixedSizeQueue (IEnumerable<T> initialCollection, int maxSize) {
if (initialCollection == null) {
throw new ArgumentNullException(nameof(initialCollection));
}
m_concurrentQueue = new ConcurrentQueue<T>(initialCollection);
m_maxSize = maxSize;
}
public void Enqueue (T item) {
m_concurrentQueue.Enqueue(item);
if (m_concurrentQueue.Count > m_maxSize) {
T result;
m_concurrentQueue.TryDequeue(out result);
}
}
public void TryPeek (out T result) => m_concurrentQueue.TryPeek(out result);
public bool TryDequeue (out T result) => m_concurrentQueue.TryDequeue(out result);
public void CopyTo (T[] array, int index) => m_concurrentQueue.CopyTo(array, index);
public T[] ToArray () => m_concurrentQueue.ToArray();
public IEnumerator<T> GetEnumerator () => m_concurrentQueue.GetEnumerator();
IEnumerator IEnumerable.GetEnumerator () => GetEnumerator();
// Explicit ICollection implementations.
void ICollection.CopyTo (Array array, int index) => ((ICollection)m_concurrentQueue).CopyTo(array, index);
object ICollection.SyncRoot => ((ICollection) m_concurrentQueue).SyncRoot;
bool ICollection.IsSynchronized => ((ICollection) m_concurrentQueue).IsSynchronized;
// Explicit IProducerConsumerCollection<T> implementations.
bool IProducerConsumerCollection<T>.TryAdd (T item) => ((IProducerConsumerCollection<T>) m_concurrentQueue).TryAdd(item);
bool IProducerConsumerCollection<T>.TryTake (out T item) => ((IProducerConsumerCollection<T>) m_concurrentQueue).TryTake(out item);
public override int GetHashCode () => m_concurrentQueue.GetHashCode();
public override bool Equals (object obj) => m_concurrentQueue.Equals(obj);
public override string ToString () => m_concurrentQueue.ToString();
}
于 2018-04-13T16:48:32.967 回答
1
为了您的编码乐趣，我向您提交 ' ConcurrentDeck'
public class ConcurrentDeck<T>
{
private readonly int _size;
private readonly T[] _buffer;
private int _position = 0;
public ConcurrentDeck(int size)
{
_size = size;
_buffer = new T[size];
}
public void Push(T item)
{
lock (this)
{
_buffer[_position] = item;
_position++;
if (_position == _size) _position = 0;
}
}
public T[] ReadDeck()
{
lock (this)
{
return _buffer.Skip(_position).Union(_buffer.Take(_position)).ToArray();
}
}
}
示例用法：
void Main()
{
var deck = new ConcurrentDeck<Tuple<string,DateTime>>(25);
var handle = new ManualResetEventSlim();
var task1 = Task.Factory.StartNew(()=>{
var timer = new System.Timers.Timer();
timer.Elapsed += (s,a) => {deck.Push(new Tuple<string,DateTime>("task1",DateTime.Now));};
timer.Interval = System.TimeSpan.FromSeconds(1).TotalMilliseconds;
timer.Enabled = true;
handle.Wait();
});
var task2 = Task.Factory.StartNew(()=>{
var timer = new System.Timers.Timer();
timer.Elapsed += (s,a) => {deck.Push(new Tuple<string,DateTime>("task2",DateTime.Now));};
timer.Interval = System.TimeSpan.FromSeconds(.5).TotalMilliseconds;
timer.Enabled = true;
handle.Wait();
});
var task3 = Task.Factory.StartNew(()=>{
var timer = new System.Timers.Timer();
timer.Elapsed += (s,a) => {deck.Push(new Tuple<string,DateTime>("task3",DateTime.Now));};
timer.Interval = System.TimeSpan.FromSeconds(.25).TotalMilliseconds;
timer.Enabled = true;
handle.Wait();
});
System.Threading.Thread.Sleep(TimeSpan.FromSeconds(10));
handle.Set();
var outputtime = DateTime.Now;
deck.ReadDeck().Select(d => new {Message = d.Item1, MilliDiff = (outputtime - d.Item2).TotalMilliseconds}).Dump(true);
}
于 2015-06-24T20:18:40.170 回答
1
好吧，这取决于使用情况，我注意到在多线程环境中使用时，上述某些解决方案可能会超出大小。无论如何，我的用例是显示最后 5 个事件，并且有多个线程将事件写入队列，另一个线程从中读取并将其显示在 Winform 控件中。所以这是我的解决方案。
编辑：由于我们已经在我们的实现中使用了锁定，我们并不真的需要 ConcurrentQueue 它可能会提高性能。
class FixedSizedConcurrentQueue<T>
{
readonly Queue<T> queue = new Queue<T>();
readonly object syncObject = new object();
public int MaxSize { get; private set; }
public FixedSizedConcurrentQueue(int maxSize)
{
MaxSize = maxSize;
}
public void Enqueue(T obj)
{
lock (syncObject)
{
queue.Enqueue(obj);
while (queue.Count > MaxSize)
{
queue.Dequeue();
}
}
}
public T[] ToArray()
{
T[] result = null;
lock (syncObject)
{
result = queue.ToArray();
}
return result;
}
public void Clear()
{
lock (syncObject)
{
queue.Clear();
}
}
}
syncObject编辑：我们在上面的例子中并不真正需要，我们可以使用queue对象，因为我们没有在任何函数中重新初始化queue并且它被标记为readonly无论如何。
于 2018-08-29T00:36:14.670 回答
1
接受的答案将产生可避免的副作用。
下面的链接是我在下面编写示例时使用的参考。
虽然 Microsoft 的文档有点误导，因为它们确实使用了锁，但它们锁定了分段类。段类本身使用互锁。
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
namespace Lib.Core
{
// Sources:
// https://docs.microsoft.com/en-us/dotnet/standard/collections/thread-safe/
// https://docs.microsoft.com/en-us/dotnet/api/system.threading.interlocked?view=netcore-3.1
// https://github.com/dotnet/runtime/blob/master/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueue.cs
// https://github.com/dotnet/runtime/blob/master/src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueueSegment.cs
/// <summary>
/// Concurrent safe circular buffer that will used a fixed capacity specified and resuse slots as it goes.
/// </summary>
/// <typeparam name="TObject">The object that you want to go into the slots.</typeparam>
public class ConcurrentCircularBuffer<TObject>
{
private readonly ConcurrentQueue<TObject> _queue;
public int Capacity { get; private set; }
public ConcurrentCircularBuffer(int capacity)
{
if(capacity <= 0)
{
throw new ArgumentException($"The capacity specified '{capacity}' is not valid.", nameof(capacity));
}
// Setup the queue to the initial capacity using List's underlying implementation.
_queue = new ConcurrentQueue<TObject>(new List<TObject>(capacity));
Capacity = capacity;
}
public void Enqueue(TObject @object)
{
// Enforce the capacity first so the head can be used instead of the entire segment (slow).
while (_queue.Count + 1 > Capacity)
{
if (!_queue.TryDequeue(out _))
{
// Handle error condition however you want to ie throw, return validation object, etc.
var ex = new Exception("Concurrent Dequeue operation failed.");
ex.Data.Add("EnqueueObject", @object);
throw ex;
}
}
// Place the item into the queue
_queue.Enqueue(@object);
}
public TObject Dequeue()
{
if(_queue.TryDequeue(out var result))
{
return result;
}
return default;
}
}
}
于 2020-04-29T02:01:44.640 回答
0
这是另一个实现，它尽可能多地使用底层 ConcurrentQueue，同时提供通过 ConcurrentQueue 提供的相同接口。
/// <summary>
/// This is a FIFO concurrent queue that will remove the oldest added items when a given limit is reached.
/// </summary>
/// <typeparam name="TValue"></typeparam>
public class FixedSizedConcurrentQueue<TValue> : IProducerConsumerCollection<TValue>, IReadOnlyCollection<TValue>
{
private readonly ConcurrentQueue<TValue> _queue;
private readonly object _syncObject = new object();
public int LimitSize { get; }
public FixedSizedConcurrentQueue(int limit)
{
_queue = new ConcurrentQueue<TValue>();
LimitSize = limit;
}
public FixedSizedConcurrentQueue(int limit, System.Collections.Generic.IEnumerable<TValue> collection)
{
_queue = new ConcurrentQueue<TValue>(collection);
LimitSize = limit;
}
public int Count => _queue.Count;
bool ICollection.IsSynchronized => ((ICollection) _queue).IsSynchronized;
object ICollection.SyncRoot => ((ICollection)_queue).SyncRoot;
public bool IsEmpty => _queue.IsEmpty;
// Not supported until .NET Standard 2.1
//public void Clear() => _queue.Clear();
public void CopyTo(TValue[] array, int index) => _queue.CopyTo(array, index);
void ICollection.CopyTo(Array array, int index) => ((ICollection)_queue).CopyTo(array, index);
public void Enqueue(TValue obj)
{
_queue.Enqueue(obj);
lock( _syncObject )
{
while( _queue.Count > LimitSize ) {
_queue.TryDequeue(out _);
}
}
}
public IEnumerator<TValue> GetEnumerator() => _queue.GetEnumerator();
IEnumerator IEnumerable.GetEnumerator() => ((IEnumerable<TValue>)this).GetEnumerator();
public TValue[] ToArray() => _queue.ToArray();
public bool TryAdd(TValue item)
{
Enqueue(item);
return true;
}
bool IProducerConsumerCollection<TValue>.TryTake(out TValue item) => TryDequeue(out item);
public bool TryDequeue(out TValue result) => _queue.TryDequeue(out result);
public bool TryPeek(out TValue result) => _queue.TryPeek(out result);
}
于 2020-04-29T14:57:42.137 回答
-1
这是我的队列版本：
public class FixedSizedQueue<T> {
private object LOCK = new object();
ConcurrentQueue<T> queue;
public int MaxSize { get; set; }
public FixedSizedQueue(int maxSize, IEnumerable<T> items = null) {
this.MaxSize = maxSize;
if (items == null) {
queue = new ConcurrentQueue<T>();
}
else {
queue = new ConcurrentQueue<T>(items);
EnsureLimitConstraint();
}
}
public void Enqueue(T obj) {
queue.Enqueue(obj);
EnsureLimitConstraint();
}
private void EnsureLimitConstraint() {
if (queue.Count > MaxSize) {
lock (LOCK) {
T overflow;
while (queue.Count > MaxSize) {
queue.TryDequeue(out overflow);
}
}
}
}
/// <summary>
/// returns the current snapshot of the queue
/// </summary>
/// <returns></returns>
public T[] GetSnapshot() {
return queue.ToArray();
}
}
我发现有一个基于 IEnumerable 构建的构造函数很有用，而且我发现有一个 GetSnapshot 在调用时拥有一个项目的多线程安全列表（在这种情况下为数组）很有用，它不会上升如果底层集合发生更改，则会出错。
双重计数检查是为了防止在某些情况下锁定。
于 2015-12-03T08:58:58.470 回答
-1
using System.Collections.Concurrent;
public class FixedSizeQueue<T>
{
ConcurrentQueue<T> _queue = new ConcurrentQueue<T>();
private void Enque(T obj)
{
T temp;
if (_queue.Count > 99)
{
// Remove one of the oldest added items.
_queue.TryDequeue(out temp);
}
_queue.Enqueue(obj);
}
private bool Dequeue(out T obj)
{
return _queue.TryDequeue(out obj);
}
private void Clear()
{
T obj;
// It does not fall into an infinite loop, and clears the contents of the present time.
int cnt = _queue.Count;
for (; cnt > 0; cnt--)
{
_queue.TryDequeue(out obj);
}
}
}
于 2020-11-25T04:44:49.157 回答