内存中事件溯源算法 - 对吗?它是线程安全的吗?
对于这个问题的轻微推测性质表示歉意。
我正在使用内存中的静态对象编写一个 Cms 来保存系统的当前状态,并使用事件源创建一个事件日志,我可以用它来重建对象状态,并提供回滚等(请参阅http://martinfowler.com/articles/lmax.html 如果你不知道我是什么关于)
public class Cms
{
private static object WriteLock = new object();
public static Cms Read { get; set; }
static Cms Write { get; set; }
static Cms()
{
Read = RebuildFromActionLog();
Write = RebuildFromActionLog();
}
public static void Update(Action action)
{
lock (WriteLock)
{
try
{
action.Apply(Write);
}
catch(Exception ex)
{
Write = RebuildFromActionLog(); //ditch the potentially messed up Write model
throw;
}
LogAction(action); //the action was a keeper, so keep it
Read = Write; //ditch the current read only model - it will continue to be used by any requests that have grabbed it
Write = RebuildFromActionLog(); //get a new model ready for the next write
}
}
...
}
除了潜力如果执行或重建需要很长时间,并且可能会使用大量内存,则大量写入会堆积起来,这是否存在任何错误,特别是与并发相关的错误?
Apologies for the slightly speculative nature of this question.
I am writing a Cms using an in-memory static object to hold the current state of the system, and am using Event Sourcing to create an event log which I can use to rebuild the object state, and to provide roll back etc. (see http://martinfowler.com/articles/lmax.html if you have no idea what I am on about)
public class Cms
{
private static object WriteLock = new object();
public static Cms Read { get; set; }
static Cms Write { get; set; }
static Cms()
{
Read = RebuildFromActionLog();
Write = RebuildFromActionLog();
}
public static void Update(Action action)
{
lock (WriteLock)
{
try
{
action.Apply(Write);
}
catch(Exception ex)
{
Write = RebuildFromActionLog(); //ditch the potentially messed up Write model
throw;
}
LogAction(action); //the action was a keeper, so keep it
Read = Write; //ditch the current read only model - it will continue to be used by any requests that have grabbed it
Write = RebuildFromActionLog(); //get a new model ready for the next write
}
}
...
}
Aside from the potential for lots of writes to stack up if execution or rebuilding takes a long time, and the potential for lots of memory to be used, are there any bugs in this, particularly concurrency related bugs?
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如果有人使用
Read
的公共 getter 或 setter,您可能会遇到问题,因为您在那里没有同步。如果有人在另一个线程在Update
中修改该属性的同时使用该属性,则读取可能会获取过时的值,或者写入所做的更改可能会默默丢失。该财产真的需要公开吗?并且公开可写?
You may have a problem if someone uses the public getter or setter of
Read
, as you have no synchronization there. If someone uses that property at the same time as another thread modifies it inUpdate
the read could fetch a stale value, or a change made by writing could be silently lost.Does that property really need to be public? And publicly writeable?