我试图有效地确定哪种方法比较好:
目前,我有一个单一实例暴露以延迟加载方式加载的实体。我列出了三种方法,每种方法都有一些优点。第一种方法完全依靠双重锁定模式来确保线程安全。第二种方法不使用锁定,但在比赛的情况下它有双重加载的潜力。第三种方法确实使用了我非常喜欢的解决方案。 (System.Lazy)。
出于某种原因,我觉得第二种方法(System.Thread.InterLocked)有问题,但我不能指出它。是否有理由相互支持一种方法?我在之前的一篇文章中提到过,我觉得第三种选择是从现在开始的方式。
我将代码剥离到准系统,以便能够解释设计。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace TPLDemo
{
public class SomeEntity
{
}
public class MultiThreadedManager
{
private static readonly System.Lazy<MultiThreadedManager> instance = new Lazy<MultiThreadedManager>(() => { return new MultiThreadedManager(); });
private readonly object _syncRoot = new object();
private List<SomeEntity> _inMemoryEntities = null;
private List<SomeEntity> _inMemoryEntitiesUsingLockFreeApproach = null;
private System.Lazy<List<SomeEntity>> _inMemoryUsingLazy = new Lazy<List<SomeEntity>>(() => { return MultiThreadedManager.Instance.LoadFromSomewhere(); });
public static MultiThreadedManager Instance
{
get { return instance.Value; }
}
public IEnumerable<SomeEntity> LazyEntities
{
get
{
return _inMemoryUsingLazy.Value;
}
}
public IEnumerable<SomeEntity> LocklessEntities
{
get
{
if (_inMemoryEntitiesUsingLockFreeApproach == null)
{
do
{
// Is it possible multiple threads hit this at the same time?
} while (System.Threading.Interlocked.CompareExchange<List<SomeEntity>>(ref _inMemoryEntitiesUsingLockFreeApproach, this.LoadFromSomewhere(), null) != null);
}
return _inMemoryEntitiesUsingLockFreeApproach;
}
}
/// <summary>
/// This is thread safe but it involved some locking.
/// </summary>
public IEnumerable<SomeEntity> Entities
{
get
{
if (_inMemoryEntities == null)
{
lock (_syncRoot)
{
if (_inMemoryEntities == null)
{
List<SomeEntity> list = this.LoadFromSomewhere();
_inMemoryEntities = list;
}
}
}
return _inMemoryEntities;
}
}
private List<SomeEntity> LoadFromSomewhere()
{
return new List<SomeEntity>();
}
public void ReloadEntities()
{
// This is sufficient becasue any subsequent call will reload them safely.
_inMemoryEntities = null;
// This is sufficient becasue any subsequent call will reload them safely.
_inMemoryEntitiesUsingLockFreeApproach = null;
// This is necessary becasue _inMemoryUsingLazy.Value is readonly.
_inMemoryUsingLazy = new Lazy<List<SomeEntity>>(() => { return MultiThreadedManager.Instance.LoadFromSomewhere(); });
}
}
}
为什么在你的第一篇文章中没有回答(使用'System.Lazy',这就是它的好处)? –