提问人:Ultratrunks 提问时间:10/7/2011 更新时间:10/7/2011 访问量:1209
在线程之间传递对象会导致异常,因为其他线程拥有它
Passing objects between threads causes exception because a different thread owns it
问:
我以前遇到过这种问题,通过从自定义类引发的事件更新 GUI 元素,但我能够通过以下方式解决它:
MyTextBlock.Dispatcher.BeginInvoke(DispatcherPriority.Normal,
(Action)(() => { LoggingTextBlock.Text += Message += "\r\n"; }));
我认为这个问题是UI线程独有的,但显然它适用于所有线程。不幸的是,我的自定义类没有 .Dispatcher() 例程调用,就像 UIElements 一样。那么,您应该如何将对象传递给其他线程并让它们能够使用它们呢?
例如,我有一个基侦听器类,其主要工作基本上是查找一些数据,引发事件并传递该数据。以下是我想传递的数据类的一部分:
// Just the class for carrying the job data.
public class JobData
{
// NOTE: I don't no have trouble accessing these properties from a
// different thread
public string SomeProperty1 { get; set; }
public string SomeProperty2 { get; set; }
public string SomeProperty3 { get; set; }
// ...
// more properties
// ...
// This a .NET object of type System.Printing.PrintSystemJobInfo. This
// is the guy that gives me trouble. Later on, I can't access members
// of Job without getting the "The calling thread cannot access this
// object because a different thread owns it" error.
PrintSystemJobInfo m_Job = null;
public PrintSystemJobInfo Job
{
get
{
if (m_Job == null)
{ throw new ArgumentNullException(); }
return m_Job;
}
set { m_Job = value; }
}
}
下面是类的一个段,它在线程中运行,收集数据并触发事件以将该数据传递给任何侦听者。
// Thread who monitors looking for data to package into JobData and send
// to any listeners.
public class JobMonitor
{
public delegate void NewJobEvent(JobData jobStuff);
public event NewJobEvent NewJob;
// Call this when you have some job data and need to notify listeners
private void OnNewJob(object newJobData)
{
JobData newJobData = (JobData)newJobData;
if (NewJob != null)
{
NewJob(newJobData);
}
}
private void WorkerRoutine()
{
while(true)
{
// Wait for data
// ...
// ...
// when data is found
JobData myJobData = new JobData();
myJobData.SomeProperty1 = "some data";
myJobData.SomeProperty2 = "some data";
int jobID = GetCurrentJobID();
string printerName = GetCurrentPrinterName();
// .NET class System.Printing.PrintQueue
PrintQueue printQueue = new PrintQueue(new PrintServer(), printerName);
PrintSystemJobInfo jobInfo = null;
jobInfo = printQueue.GetJob(jobID);
// This is the guy in my JobData class that I'll have trouble accessing
// later on.
myJobData.Job = jobInfo;
// Time to fire off the event
OnNewJob(myJobData);
}
}
}
下面是实例化 JobMonitor 类并捕获其事件的类的段。它在访问 JobMonitor 的某个属性时遇到问题。
// This class signs up to recieve and process events from the JobMonitor class.
public class JobProcessor
{
// this is the method that handles the incoming job events. This is where
// i have trouble.
private void NewJobEventHandler(JobData newJob)
{
string temp = newJob.SomeProperty1; // this works fine
bool bTemp = newJob.Job.IsPaused; // this throws an exception "The
// calling read cannot access this
// object because a different thread
// owns it"
}
private JobMonitor m_monitor = null;
public JobProcessor()
{
m_monitor = new JobMonitor();
//attaches a method to handle incoming job events.
m_monitor.NewJob += new JobMonitor.NewJobEvent(NewJobEventHandler);
m_monitor.Start();
}
}
因此,JobProcessor.NewJobEventHandler() 方法是我收到异常的地方:“调用线程无法访问此对象,因为其他线程拥有它”。我需要能够访问此属性以及下面的属性和方法。我需要做些什么才能访问我需要的内容?
答:
2赞
davisoa
10/7/2011
#1
我会研究 System.Threading 提供的 SyncronizationContext。此类具有一个静态属性,该属性将提供您正在寻找的 Dispatcher 样式调用。Current
其他可能性
如果要在与创建 JobData 类的线程不同的线程上处理事件,则可能需要将 的实际检索移动到事件处理程序。PrintSystemJobInfo
另一种选择是用您创建的新类(没有线程亲和性)抽象出 System 类。
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0赞
Ultratrunks
10/11/2011
好吧,我等了一会儿,看看是否有其他建议可能会出现。“SyncronizationContext”方法对我来说没有结果。我对这个概念有点迷茫,所以我可能做错了。幸运的是,检索 PrintSystemJobInfo 对象很容易,并且有足够的信息让我的目标线程自行获取此对象。理想情况下,我不必这样做,我的目标线程也不需要知道如何获取此信息。哦,好吧,从长远来看,这对我来说并不是一个很大的妥协。
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