我们知道,在.net的一些集合类型中,譬如Hashtable和ArrayList,都有Synchronized静态方法和SyncRoot实例方法,他们之间有联系吗?我怎么才能用好他们呢?
我们以Hashtable为例,看看他们的基本用法:
Hashtable ht = Hashtable.Synchronized(new Hashtable());
lock (ht.SyncRoot)
{
//一些操作
}
lock (ht.SyncRoot)
{
//一些操作
}
1,Synchronized表示返回一个线程安全的Hashtable,什么样的hashtable才是一个线程安全的呢?下边我们就从.NET的源码开始理解。
public static Hashtable Synchronized(Hashtable table)
从源码不难看出,Synchronized方法返回的其实是一个SynchHashtable类型的实例。在前边我们说过,Synchronized表示返回一个线程安全的Hashtable,从这个解释不难看出,SynchHashtable应该是继承自Hashtable。下边我们验证一下。看看SynchHashtable类型的源码:
{
if (table == null)
{
throw new ArgumentNullException("table");
}
return new SyncHashtable(table);
}
[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