因此,我的要求是让我的函数等待来自另一个类和另一个线程的event Action<T>
的第一个实例,并在我的线程上处理它,允许等待被超时或CancellationToken
中断。
我想创建一个可以重用的泛型函数。我设法创建了几个(我认为)能满足我需要的选项,但这两个选项似乎都比我想象的要复杂。
用法
为了清楚起见,此函数的示例用法如下所示,其中serialDevice
在单独的线程上输出事件:
var eventOccurred = Helper.WaitForSingleEvent<StatusPacket>(
cancellationToken,
statusPacket => OnStatusPacketReceived(statusPacket),
a => serialDevice.StatusPacketReceived += a,
a => serialDevice.StatusPacketReceived -= a,
5000,
() => serialDevice.RequestStatusPacket());
选项1-手动重置
这个选项不错,但是ManualResetEventSlim
的Dispose
处理比它看起来应该的要混乱。我在闭包中访问修改过的/处理过的东西,这让ReSharper很适合,这确实很难遵循,所以我甚至不确定它是否正确。也许我遗漏了一些东西可以解决这个问题,这将是我的偏好,但我不会马上看到它。这是代码。
public static bool WaitForSingleEvent<TEvent>(this CancellationToken token, Action<TEvent> handler, Action<Action<TEvent>> subscribe, Action<Action<TEvent>> unsubscribe, int msTimeout, Action initializer = null)
{
var eventOccurred = false;
var eventResult = default(TEvent);
var o = new object();
var slim = new ManualResetEventSlim();
Action<TEvent> setResult = result =>
{
lock (o) // ensures we get the first event only
{
if (!eventOccurred)
{
eventResult = result;
eventOccurred = true;
// ReSharper disable AccessToModifiedClosure
// ReSharper disable AccessToDisposedClosure
if (slim != null)
{
slim.Set();
}
// ReSharper restore AccessToDisposedClosure
// ReSharper restore AccessToModifiedClosure
}
}
};
subscribe(setResult);
try
{
if (initializer != null)
{
initializer();
}
slim.Wait(msTimeout, token);
}
finally // ensures unsubscription in case of exception
{
unsubscribe(setResult);
lock(o) // ensure we don't access slim
{
slim.Dispose();
slim = null;
}
}
lock (o) // ensures our variables don't get changed in middle of things
{
if (eventOccurred)
{
handler(eventResult);
}
return eventOccurred;
}
}
选项2-不使用WaitHandle
进行轮询
这里的WaitForSingleEvent
函数要干净得多。我能够使用ConcurrentQueue
,因此甚至不需要锁。但我就是不喜欢轮询函数Sleep
,而且我看不出这种方法有什么办法可以绕过它。我想传入一个WaitHandle
而不是Func<bool>
来清理Sleep
,但是一旦我这么做了,我又要清理整个Dispose
的烂摊子。
public static bool WaitForSingleEvent<TEvent>(this CancellationToken token, Action<TEvent> handler, Action<Action<TEvent>> subscribe, Action<Action<TEvent>> unsubscribe, int msTimeout, Action initializer = null)
{
var q = new ConcurrentQueue<TEvent>();
subscribe(q.Enqueue);
try
{
if (initializer != null)
{
initializer();
}
token.Sleep(msTimeout, () => !q.IsEmpty);
}
finally // ensures unsubscription in case of exception
{
unsubscribe(q.Enqueue);
}
TEvent eventResult;
var eventOccurred = q.TryDequeue(out eventResult);
if (eventOccurred)
{
handler(eventResult);
}
return eventOccurred;
}
public static void Sleep(this CancellationToken token, int ms, Func<bool> exitCondition)
{
var start = DateTime.Now;
while ((DateTime.Now - start).TotalMilliseconds < ms && !exitCondition())
{
token.ThrowIfCancellationRequested();
Thread.Sleep(1);
}
}
问题是
我不是特别关心这两个解决方案中的任何一个,我也不是100%确定它们中的任何一个是100%正确的。这些解决方案中有哪一个比另一个更好(习惯用法、效率等),还是有更简单的方法或内置函数来满足我在这里需要做的事情?
更新:目前为止最好的答案
下面是对TaskCompletionSource
解决方案的修改。不需要长时间的闭包、锁或任何东西。看起来很简单。这里有什么错误吗?
public static bool WaitForSingleEvent<TEvent>(this CancellationToken token, Action<TEvent> onEvent, Action<Action<TEvent>> subscribe, Action<Action<TEvent>> unsubscribe, int msTimeout, Action initializer = null)
{
var tcs = new TaskCompletionSource<TEvent>();
Action<TEvent> handler = result => tcs.TrySetResult(result);
var task = tcs.Task;
subscribe(handler);
try
{
if (initializer != null)
{
initializer();
}
task.Wait(msTimeout, token);
}
finally
{
unsubscribe(handler);
// Do not dispose task http://blogs.msdn.com/b/pfxteam/archive/2012/03/25/10287435.aspx
}
if (task.Status == TaskStatus.RanToCompletion)
{
onEvent(task.Result);
return true;
}
return false;
}
更新2:另一个很棒的解决方案
事实证明,BlockingCollection
的工作方式与ConcurrentQueue
类似,但也有接受超时和取消令牌的方法。这个解决方案的一个好处是,它可以很容易地更新为WaitForNEvents
:
public static bool WaitForSingleEvent<TEvent>(this CancellationToken token, Action<TEvent> handler, Action<Action<TEvent>> subscribe, Action<Action<TEvent>> unsubscribe, int msTimeout, Action initializer = null)
{
var q = new BlockingCollection<TEvent>();
Action<TEvent> add = item => q.TryAdd(item);
subscribe(add);
try
{
if (initializer != null)
{
initializer();
}
TEvent eventResult;
if (q.TryTake(out eventResult, msTimeout, token))
{
handler(eventResult);
return true;
}
return false;
}
finally
{
unsubscribe(add);
q.Dispose();
}
}
https://stackoverflow.com/questions/17635440
复制相似问题