线程安全的ArrayList和HashTable

在.net 2.0中,ArrayList和HashTable都有一个封装了同步功能的新实现.

它们可以通过ArrayList.Synchronized方法或者HashTable.Synchronized方法来获得.

下面是方法的具体实现:

 

代码
[HostProtection(SecurityAction.LinkDemand, Synchronization=true)]
public static ArrayList Synchronized(ArrayList list)
{
if (list == null)
{
throw new ArgumentNullException("list");
}
return new SyncArrayList(list);
}

[HostProtection(SecurityAction.LinkDemand, Synchronization
=true)]
public static IList Synchronized(IList list)
{
if (list == null)
{
throw new ArgumentNullException("list");
}
return new SyncIList(list);
}


[HostProtection(SecurityAction.LinkDemand, Synchronization
=true)]
public static Hashtable Synchronized(Hashtable table)
{
if (table == null)
{
throw new ArgumentNullException("table");
}
return new SyncHashtable(table);
}


里面的SyncHashtable之流便是同步的HashTable了,

再看看它的实现

 

代码
[Serializable]
private class SyncHashtable : Hashtable
{
// Fields
protected Hashtable _table;

// Methods
internal SyncHashtable(Hashtable table) : base(false)
{
this._table = table;
}

internal SyncHashtable(SerializationInfo info, StreamingContext context) : base(info, context)
{
this._table = (Hashtable) info.GetValue("ParentTable", typeof(Hashtable));
if (this._table == null)
{
throw new SerializationException(Environment.GetResourceString("Serialization_InsufficientState"));
}
}

public override void Add(object key, object value)
{
lock (this._table.SyncRoot)
{
this._table.Add(key, value);
}
}

public override void Clear()
{
lock (this._table.SyncRoot)
{
this._table.Clear();
}
}

public override object Clone()
{
lock (this._table.SyncRoot)
{
return Hashtable.Synchronized((Hashtable) this._table.Clone());
}
}

public override bool Contains(object key)
{
return this._table.Contains(key);
}

public override bool ContainsKey(object key)
{
return this._table.ContainsKey(key);
}

public override bool ContainsValue(object key)
{
lock (this._table.SyncRoot)
{
return this._table.ContainsValue(key);
}
}

public override void CopyTo(Array array, int arrayIndex)
{
lock (this._table.SyncRoot)
{
this._table.CopyTo(array, arrayIndex);
}
}

public override IDictionaryEnumerator GetEnumerator()
{
return this._table.GetEnumerator();
}

public override void GetObjectData(SerializationInfo info, StreamingContext context)
{
if (info == null)
{
throw new ArgumentNullException("info");
}
info.AddValue(
"ParentTable", this._table, typeof(Hashtable));
}

public override void OnDeserialization(object sender)
{
}

public override void Remove(object key)
{
lock (this._table.SyncRoot)
{
this._table.Remove(key);
}
}

internal override KeyValuePairs[] ToKeyValuePairsArray()
{
return this._table.ToKeyValuePairsArray();
}

// Properties
public override int Count
{
get
{
return this._table.Count;
}
}

public override bool IsFixedSize
{
get
{
return this._table.IsFixedSize;
}
}

public override bool IsReadOnly
{
get
{
return this._table.IsReadOnly;
}
}

public override bool IsSynchronized
{
get
{
return true;
}
}

public override object this[object key]
{
get
{
return this._table[key];
}
set
{
lock (this._table.SyncRoot)
{
this._table[key] = value;
}
}
}

public override ICollection Keys
{
get
{
lock (this._table.SyncRoot)
{
return this._table.Keys;
}
}
}

public override object SyncRoot
{
get
{
return this._table.SyncRoot;
}
}

public override ICollection Values
{
get
{
lock (this._table.SyncRoot)
{
return this._table.Values;
}
}
}
}

这下明白了吧,就是给ArrayList和HashTable的访问方法加了个lock,

不过,这可比我们自己手写还是要靠谱的多..(注意:在进行轶代时,并不是线程安全的。如果要求绝对的线程安全,可以自行lock对象的SyncRoot)

不过有些场景可是不能lock太过的,比如读写比很高的场景(很少写,而读很多)

不过不用担心,并发环境下的缓存容器性能优化(上):不可变的哈希表

老赵的这篇文章已经有了很好的解决办法了.

 

 

 

posted @ 2009-12-13 15:03 lsjwzh 阅读(...) 评论(...) 编辑 收藏