咨詢區

• Sebastian

在 .NET 框架中并沒有線程安全的 ConcurrentHashSet 類，我想模仿 ConcurrentDictionary 來實現一個，目前寫了一下樁代碼。

public?class?ConcurrentHashSet<TElement>?:?ISet<TElement> {private?readonly?ConcurrentDictionary<TElement,?object>?_internal;public?ConcurrentHashSet(IEnumerable<TElement>?elements?=?null){_internal?=?new?ConcurrentDictionary<TElement,?object>();if?(elements?!=?null)UnionWith(elements);}public?void?UnionWith(IEnumerable<TElement>?other){if?(other?==?null)?throw?new?ArgumentNullException("other");foreach?(var?otherElement?in?other)Add(otherElement);}public?bool?Add(TElement?item){return?_internal.TryAdd(item,?null);}//?I?am?not?sure?here?if?that?fullfills?contract?correctlyvoid?ICollection<TElement>.Add(TElement?item){Add(item);}public?bool?Contains(TElement?item){return?_internal.ContainsKey(item);}public?bool?Remove(TElement?item){object?ignore;return?_internal.TryRemove(item,?out?ignore);}public?int?Count{get?{?return?_internal.Count;?}}public?IEnumerator<TElement>?GetEnumerator(){return?_internal.Keys.GetEnumerator();} }

我不確定這代碼能否在 foreach 中還能保證原子性，請問是否有更好的實現？

回答區

• Ben Mosher

我最近遇到了類似的場景，不過我更關注的更高性能的 Add,Contains,Remove 方法，下面是我的實現。

using?System.Collections.Generic; using?System.Threading;namespace?BlahBlah.Utilities {public?class?ConcurrentHashSet<T>?:?IDisposable{private?readonly?ReaderWriterLockSlim?_lock?=?new?ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);private?readonly?HashSet<T>?_hashSet?=?new?HashSet<T>();#region?Implementation?of?ICollection<T>?...ishpublic?bool?Add(T?item){try{_lock.EnterWriteLock();return?_hashSet.Add(item);}finally{if?(_lock.IsWriteLockHeld)?_lock.ExitWriteLock();}}public?void?Clear(){try{_lock.EnterWriteLock();_hashSet.Clear();}finally{if?(_lock.IsWriteLockHeld)?_lock.ExitWriteLock();}}public?bool?Contains(T?item){try{_lock.EnterReadLock();return?_hashSet.Contains(item);}finally{if?(_lock.IsReadLockHeld)?_lock.ExitReadLock();}}public?bool?Remove(T?item){try{_lock.EnterWriteLock();return?_hashSet.Remove(item);}finally{if?(_lock.IsWriteLockHeld)?_lock.ExitWriteLock();}}public?int?Count{get{try{_lock.EnterReadLock();return?_hashSet.Count;}finally{if?(_lock.IsReadLockHeld)?_lock.ExitReadLock();}}}#endregion#region?Disposepublic?void?Dispose(){if?(_lock?!=?null)?_lock.Dispose();}#endregion} }

點評區

實現一個 ConcurrentSet<T> 其實蠻有必要的，你在 github 或者其他第三方網站上會找到很多類似的 ConcurrentSet<T> 的實現，比如：https://pastebin.com/8REHRFFL

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