我正在寻找实现一种通用方法的好思路,以便在超时情况下执行单行代码(或匿名委托)。
TemperamentalClass tc = new TemperamentalClass();
tc.DoSomething(); // normally runs in 30 sec. Want to error at 1 min
我正在寻找一种解决方案,可以在我的代码与不稳定的代码(无法更改)交互的许多地方优雅地实现。
此外,如果可能的话,我希望能够停止执行导致错误“超时”的代码。
我正在寻找实现一种通用方法的好思路,以便在超时情况下执行单行代码(或匿名委托)。
TemperamentalClass tc = new TemperamentalClass();
tc.DoSomething(); // normally runs in 30 sec. Want to error at 1 min
我正在寻找一种解决方案,可以在我的代码与不稳定的代码(无法更改)交互的许多地方优雅地实现。
此外,如果可能的话,我希望能够停止执行导致错误“超时”的代码。
这里真正棘手的部分是通过将执行器线程从操作传递回到可以中止它的位置来终止长时间运行的任务。我使用一个包装委托来实现这一点,该委托将要终止的线程传递给创建 lambda 表达式的方法中的局部变量。
为了您的享受,我提交此示例。您真正感兴趣的方法是 CallWithTimeout。 通过中止它并捕获 ThreadAbortException,这将取消长时间运行的线程:
用法:
class Program
{
static void Main(string[] args)
{
//try the five second method with a 6 second timeout
CallWithTimeout(FiveSecondMethod, 6000);
//try the five second method with a 4 second timeout
//this will throw a timeout exception
CallWithTimeout(FiveSecondMethod, 4000);
}
static void FiveSecondMethod()
{
Thread.Sleep(5000);
}
执行工作的静态方法:
static void CallWithTimeout(Action action, int timeoutMilliseconds)
{
Thread threadToKill = null;
Action wrappedAction = () =>
{
threadToKill = Thread.CurrentThread;
try
{
action();
}
catch(ThreadAbortException ex){
Thread.ResetAbort();// cancel hard aborting, lets to finish it nicely.
}
};
IAsyncResult result = wrappedAction.BeginInvoke(null, null);
if (result.AsyncWaitHandle.WaitOne(timeoutMilliseconds))
{
wrappedAction.EndInvoke(result);
}
else
{
threadToKill.Abort();
throw new TimeoutException();
}
}
}
我们在生产中大量使用类似以下代码的内容:
var result = WaitFor<Result>.Run(1.Minutes(), () => service.GetSomeFragileResult());
该实现是开源的,即使在并行计算场景中也能高效工作,并作为Lokad共享库的一部分提供。
/// <summary>
/// Helper class for invoking tasks with timeout. Overhead is 0,005 ms.
/// </summary>
/// <typeparam name="TResult">The type of the result.</typeparam>
[Immutable]
public sealed class WaitFor<TResult>
{
readonly TimeSpan _timeout;
/// <summary>
/// Initializes a new instance of the <see cref="WaitFor{T}"/> class,
/// using the specified timeout for all operations.
/// </summary>
/// <param name="timeout">The timeout.</param>
public WaitFor(TimeSpan timeout)
{
_timeout = timeout;
}
/// <summary>
/// Executes the spcified function within the current thread, aborting it
/// if it does not complete within the specified timeout interval.
/// </summary>
/// <param name="function">The function.</param>
/// <returns>result of the function</returns>
/// <remarks>
/// The performance trick is that we do not interrupt the current
/// running thread. Instead, we just create a watcher that will sleep
/// until the originating thread terminates or until the timeout is
/// elapsed.
/// </remarks>
/// <exception cref="ArgumentNullException">if function is null</exception>
/// <exception cref="TimeoutException">if the function does not finish in time </exception>
public TResult Run(Func<TResult> function)
{
if (function == null) throw new ArgumentNullException("function");
var sync = new object();
var isCompleted = false;
WaitCallback watcher = obj =>
{
var watchedThread = obj as Thread;
lock (sync)
{
if (!isCompleted)
{
Monitor.Wait(sync, _timeout);
}
}
// CAUTION: the call to Abort() can be blocking in rare situations
// http://msdn.microsoft.com/en-us/library/ty8d3wta.aspx
// Hence, it should not be called with the 'lock' as it could deadlock
// with the 'finally' block below.
if (!isCompleted)
{
watchedThread.Abort();
}
};
try
{
ThreadPool.QueueUserWorkItem(watcher, Thread.CurrentThread);
return function();
}
catch (ThreadAbortException)
{
// This is our own exception.
Thread.ResetAbort();
throw new TimeoutException(string.Format("The operation has timed out after {0}.", _timeout));
}
finally
{
lock (sync)
{
isCompleted = true;
Monitor.Pulse(sync);
}
}
}
/// <summary>
/// Executes the spcified function within the current thread, aborting it
/// if it does not complete within the specified timeout interval.
/// </summary>
/// <param name="timeout">The timeout.</param>
/// <param name="function">The function.</param>
/// <returns>result of the function</returns>
/// <remarks>
/// The performance trick is that we do not interrupt the current
/// running thread. Instead, we just create a watcher that will sleep
/// until the originating thread terminates or until the timeout is
/// elapsed.
/// </remarks>
/// <exception cref="ArgumentNullException">if function is null</exception>
/// <exception cref="TimeoutException">if the function does not finish in time </exception>
public static TResult Run(TimeSpan timeout, Func<TResult> function)
{
return new WaitFor<TResult>(timeout).Run(function);
}
}
这段代码仍然存在漏洞,您可以尝试使用此小型测试程序:
static void Main(string[] args) {
// Use a sb instead of Console.WriteLine() that is modifying how synchronous object are working
var sb = new StringBuilder();
for (var j = 1; j < 10; j++) // do the experiment 10 times to have chances to see the ThreadAbortException
for (var ii = 8; ii < 15; ii++) {
int i = ii;
try {
Debug.WriteLine(i);
try {
WaitFor<int>.Run(TimeSpan.FromMilliseconds(10), () => {
Thread.Sleep(i);
sb.Append("Processed " + i + "\r\n");
return i;
});
}
catch (TimeoutException) {
sb.Append("Time out for " + i + "\r\n");
}
Thread.Sleep(10); // Here to wait until we get the abort procedure
}
catch (ThreadAbortException) {
Thread.ResetAbort();
sb.Append(" *** ThreadAbortException on " + i + " *** \r\n");
}
}
Console.WriteLine(sb.ToString());
}
}
存在竞态条件。很明显,在调用方法WaitFor<int>.Run()
之后可能会引发ThreadAbortException异常。我没有找到可靠的解决方法,但是使用相同的测试,我无法重现任何问题,而TheSoftwareJedi的答案被接受。
TimeSpan.FromMinutes(1)
可以减少混淆?或者也可以移除 [Immutable]
。 - Hugh Jeffner你可以使用委托(BeginInvoke,使用回调设置标志-原始代码等待该标志或超时)来完成一些操作,但问题是很难关闭正在运行的代码。例如,杀死(或暂停)线程是危险的...所以我认为没有一种简单的方法可以做到这一点,使其更加稳定。
我会发布这个内容,但请注意它并不理想-它不能停止长时间运行的任务,并且在失败时无法正确清理。
static void Main()
{
DoWork(OK, 5000);
DoWork(Nasty, 5000);
}
static void OK()
{
Thread.Sleep(1000);
}
static void Nasty()
{
Thread.Sleep(10000);
}
static void DoWork(Action action, int timeout)
{
ManualResetEvent evt = new ManualResetEvent(false);
AsyncCallback cb = delegate {evt.Set();};
IAsyncResult result = action.BeginInvoke(cb, null);
if (evt.WaitOne(timeout))
{
action.EndInvoke(result);
}
else
{
throw new TimeoutException();
}
}
static T DoWork<T>(Func<T> func, int timeout)
{
ManualResetEvent evt = new ManualResetEvent(false);
AsyncCallback cb = delegate { evt.Set(); };
IAsyncResult result = func.BeginInvoke(cb, null);
if (evt.WaitOne(timeout))
{
return func.EndInvoke(result);
}
else
{
throw new TimeoutException();
}
}
对Pop Catalin的优秀回答进行了一些小改动:
已添加重载以支持通知工作线程取消执行:
public static T Invoke<T> (Func<CancelEventArgs, T> function, TimeSpan timeout) {
if (timeout.TotalMilliseconds <= 0)
throw new ArgumentOutOfRangeException ("timeout");
CancelEventArgs args = new CancelEventArgs (false);
IAsyncResult functionResult = function.BeginInvoke (args, null, null);
WaitHandle waitHandle = functionResult.AsyncWaitHandle;
if (!waitHandle.WaitOne (timeout)) {
args.Cancel = true; // flag to worker that it should cancel!
/* •————————————————————————————————————————————————————————————————————————•
| IMPORTANT: Always call EndInvoke to complete your asynchronous call. |
| http://msdn.microsoft.com/en-us/library/2e08f6yc(VS.80).aspx |
| (even though we arn't interested in the result) |
•————————————————————————————————————————————————————————————————————————• */
ThreadPool.UnsafeRegisterWaitForSingleObject (waitHandle,
(state, timedOut) => function.EndInvoke (functionResult),
null, -1, true);
throw new TimeoutException ();
}
else
return function.EndInvoke (functionResult);
}
public static T Invoke<T> (Func<T> function, TimeSpan timeout) {
return Invoke (args => function (), timeout); // ignore CancelEventArgs
}
public static void Invoke (Action<CancelEventArgs> action, TimeSpan timeout) {
Invoke<int> (args => { // pass a function that returns 0 & ignore result
action (args);
return 0;
}, timeout);
}
public static void TryInvoke (Action action, TimeSpan timeout) {
Invoke (args => action (), timeout); // ignore CancelEventArgs
}
我会这样做:
public static class Runner
{
public static void Run(Action action, TimeSpan timeout)
{
IAsyncResult ar = action.BeginInvoke(null, null);
if (ar.AsyncWaitHandle.WaitOne(timeout))
action.EndInvoke(ar); // This is necesary so that any exceptions thrown by action delegate is rethrown on completion
else
throw new TimeoutException("Action failed to complete using the given timeout!");
}
}
我刚刚完成了这个,可能需要改进,但可以满足你的需求。它是一个简单的控制台应用程序,但演示了所需的原则。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace TemporalThingy
{
class Program
{
static void Main(string[] args)
{
Action action = () => Thread.Sleep(10000);
DoSomething(action, 5000);
Console.ReadKey();
}
static void DoSomething(Action action, int timeout)
{
EventWaitHandle waitHandle = new EventWaitHandle(false, EventResetMode.ManualReset);
AsyncCallback callback = ar => waitHandle.Set();
action.BeginInvoke(callback, null);
if (!waitHandle.WaitOne(timeout))
throw new Exception("Failed to complete in the timeout specified.");
}
}
}
public static void CallWithTimeout(Action act, int millisecondsTimeout)
{
var thread = new Thread(new ThreadStart(act));
thread.Start();
if (!thread.Join(millisecondsTimeout))
throw new Exception("Timed out");
}