本文转载：http://www.cnblogs.com/kiddo/archive/2008/09/25/1299089.html
我们说一个数据结构是线程安全指的是同一时间只有一个线程可以改写它。这样即使多个线程来访问它，它也不会产生对线程来说很意外的数据。
C#中的Dictionary不是线程安全的，我在下面这个例子中，把一个Dictionary对象作为了全局的static变量。会有多个线程来访问它。所以我需要包装一下.net自带的Dictionrary.
发生冲突的部分无非是写的地方，所以在离写Dictionary最近的地方加一个锁。其他的外层代码可以自带的Dictionary相同了。
我们看Dictionary的实现接口，
自定义一个线程安全的数据对象类。
public class SafeDictionary<TKey, TValue> : IDictionary<TKey, TValue>
{
private readonly object syncRoot = new object();
private readonly Dictionary<TKey, TValue> d = new Dictionary<TKey, TValue>();
#region IDictionary<TKey,TValue> Members
/// <summary>
/// Adds an element with the provided key and value to the <see cref="T:System.Collections.Generic.IDictionary`2"></see>.
/// </summary>
/// <param name="key">The object to use as the key of the element to add.</param>
/// <param name="value">The object to use as the value of the element to add.</param>
/// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IDictionary`2"></see> is read-only.</exception>
/// <exception cref="T:System.ArgumentException">An element with the same key already exists in the <see cref="T:System.Collections.Generic.IDictionary`2"></see>.</exception>
/// <exception cref="T:System.ArgumentNullException">key is null.</exception>
public void Add(TKey key, TValue value)
{
lock (syncRoot)
{
d.Add(key, value);
}
}
/// <summary>
/// Determines whether the <see cref="T:System.Collections.Generic.IDictionary`2"></see> contains an element with the specified key.
/// </summary>
/// <param name="key">The key to locate in the <see cref="T:System.Collections.Generic.IDictionary`2"></see>.</param>
/// <returns>
/// true if the <see cref="T:System.Collections.Generic.IDictionary`2"></see> contains an element with the key; otherwise, false.
/// </returns>
/// <exception cref="T:System.ArgumentNullException">key is null.</exception>
public bool ContainsKey(TKey key)
{
return d.ContainsKey(key);
}
/// <summary>
/// Gets an <see cref="T:System.Collections.Generic.ICollection`1"></see> containing the keys of the <see cref="T:System.Collections.Generic.IDictionary`2"></see>.
/// </summary>
/// <value></value>
/// <returns>An <see cref="T:System.Collections.Generic.ICollection`1"></see> containing the keys of the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"></see>.</returns>
public ICollection<TKey> Keys
{
get
{
lock (syncRoot)
{
return d.Keys;
}
}
}
/// <summary>
/// Removes the element with the specified key from the <see cref="T:System.Collections.Generic.IDictionary`2"></see>.
/// </summary>
/// <param name="key">The key of the element to remove.</param>
/// <returns>
/// true if the element is successfully removed; otherwise, false. This method also returns false if key was not found in the original <see cref="T:System.Collections.Generic.IDictionary`2"></see>.
/// </returns>
/// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IDictionary`2"></see> is read-only.</exception>
/// <exception cref="T:System.ArgumentNullException">key is null.</exception>
public bool Remove(TKey key)
{
lock (syncRoot)
{
return d.Remove(key);
}
}
/// <summary>
/// Tries the get value.
/// </summary>
/// <param name="key">The key.</param>
/// <param name="value">The value.</param>
/// <returns></returns>
public bool TryGetValue(TKey key, out TValue value)
{
lock (syncRoot)
{
return d.TryGetValue(key, out value);
}
}
/// <summary>
/// Gets an <see cref="T:System.Collections.Generic.ICollection`1"></see> containing the values in the <see cref="T:System.Collections.Generic.IDictionary`2"></see>.
/// </summary>
/// <value></value>
/// <returns>An <see cref="T:System.Collections.Generic.ICollection`1"></see> containing the values in the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"></see>.</returns>
public ICollection<TValue> Values
{
get
{
lock (syncRoot)
{
return d.Values;
}
}
}
/// <summary>
/// Gets or sets the <see cref="TValue"/> with the specified key.
/// </summary>
/// <value></value>
public TValue this[TKey key]
{
get { return d[key]; }
set
{
lock (syncRoot)
{
d[key] = value;
}
}
}
/// <summary>
/// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"></see>.
/// </summary>
/// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"></see>.</param>
/// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"></see> is read-only.</exception>
public void Add(KeyValuePair<TKey, TValue> item)
{
lock (syncRoot)
{
((ICollection<KeyValuePair<TKey, TValue>>)d).Add(item);
}
}
/// <summary>
/// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"></see>.
/// </summary>
/// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"></see> is read-only. </exception>
public void Clear()
{
lock (syncRoot)
{
d.Clear();
}
}
/// <summary>
/// Determines whether the <see cref="T:System.Collections.Generic.ICollection`1"></see> contains a specific value.
/// </summary>
/// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"></see>.</param>
/// <returns>
/// true if item is found in the <see cref="T:System.Collections.Generic.ICollection`1"></see>; otherwise, false.
/// </returns>
public bool Contains(KeyValuePair<TKey, TValue> item)
{
return ((ICollection<KeyValuePair<TKey, TValue>>)d).Contains(item);
}
/// <summary>
/// Copies the elements of the <see cref="T:System.Collections.Generic.ICollection`1"></see> to an <see cref="T:System.Array"></see>, starting at a particular <see cref="T:System.Array"></see> index.
/// </summary>
/// <param name="array">The one-dimensional <see cref="T:System.Array"></see> that is the destination of the elements copied from <see cref="T:System.Collections.Generic.ICollection`1"></see>. The <see cref="T:System.Array"></see> must have zero-based indexing.</param>
/// <param name="arrayIndex">The zero-based index in array at which copying begins.</param>
/// <exception cref="T:System.ArgumentOutOfRangeException">arrayIndex is less than 0.</exception>
/// <exception cref="T:System.ArgumentNullException">array is null.</exception>
/// <exception cref="T:System.ArgumentException">array is multidimensional.-or-arrayIndex is equal to or greater than the length of array.-or-The number of elements in the source <see cref="T:System.Collections.Generic.ICollection`1"></see> is greater than the available space from arrayIndex to the end of the destination array.-or-Type T cannot be cast automatically to the type of the destination array.</exception>
public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
{
lock (syncRoot)
{
((ICollection<KeyValuePair<TKey, TValue>>)d).CopyTo(array, arrayIndex);
}
}
/// <summary>
/// Gets the number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"></see>.
/// </summary>
/// <value></value>
/// <returns>The number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"></see>.</returns>
public int Count
{
get { return d.Count; }
}
/// <summary>
/// Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"></see> is read-only.
/// </summary>
/// <value></value>
/// <returns>true if the <see cref="T:System.Collections.Generic.ICollection`1"></see> is read-only; otherwise, false.</returns>
public bool IsReadOnly
{
get { return false; }
}
/// <summary>
/// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"></see>.
/// </summary>
/// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"></see>.</param>
/// <returns>
/// true if item was successfully removed from the <see cref="T:System.Collections.Generic.ICollection`1"></see>; otherwise, false. This method also returns false if item is not found in the original <see cref="T:System.Collections.Generic.ICollection`1"></see>.
/// </returns>
/// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"></see> is read-only.</exception>
public bool Remove(KeyValuePair<TKey, TValue> item)
{
lock (syncRoot)
{
return ((ICollection<KeyValuePair<TKey, TValue>>)d).Remove(item);
}
}
/// <summary>
/// Returns an enumerator that iterates through the collection.
/// </summary>
/// <returns>
/// A <see cref="T:System.Collections.Generic.IEnumerator`1"></see> that can be used to iterate through the collection.
/// </returns>
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
{
return ((ICollection<KeyValuePair<TKey, TValue>>)d).GetEnumerator();
}
/// <summary>
/// Returns an enumerator that iterates through a collection.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.IEnumerator"></see> object that can be used to iterate through the collection.
/// </returns>
IEnumerator IEnumerable.GetEnumerator()
{
return ((IEnumerable)d).GetEnumerator();
}
#endregion
}
微软4.0框架已经有了这个线程安全的Dictionary。
ConcurrentDictionary<TKey, TValue> 类
详细可以查看：http://msdn.microsoft.com/zh-cn/library/dd287191(v=vs.110).aspx
ConcurrentDictionary<TKey, TValue> 类
详细可以查看：http://msdn.microsoft.com/zh-cn/library/dd287191(v=vs.110).aspx
4.0中新增的线程安全集合类：
| 线程安全集合类 | 非线程安全集合类 |
ConcurrentQueue<T> |
Queue<T> |
ConcurrentStack<T> |
Stack<T> |
ConcurrentBag<T> |
List<T> |
ConcurrentDictionary<TKey,TValue> |
Dictionary<TKey,TValue> |