internal static TResult Implementation <TResult>(
Func <Context, CancellationToken, TResult> action,
Context context,
CancellationToken cancellationToken,
Func <Context, TimeSpan> timeoutProvider,
TimeoutStrategy timeoutStrategy,
Action <Context, TimeSpan, Task, Exception> onTimeout)
{
cancellationToken.ThrowIfCancellationRequested();
TimeSpan timeout = timeoutProvider(context);
using (CancellationTokenSource timeoutCancellationTokenSource = new CancellationTokenSource())
{
using (CancellationTokenSource combinedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeoutCancellationTokenSource.Token))
{
CancellationToken combinedToken = combinedTokenSource.Token;
Task <TResult> actionTask = null;
try
{
if (timeoutStrategy == TimeoutStrategy.Optimistic)
{
SystemClock.CancelTokenAfter(timeoutCancellationTokenSource, timeout);
return(action(context, combinedToken));
}
// else: timeoutStrategy == TimeoutStrategy.Pessimistic
SystemClock.CancelTokenAfter(timeoutCancellationTokenSource, timeout);
actionTask = Task.Run(() =>
action(context, combinedToken) // cancellation token here allows the user delegate to react to cancellation: possibly clear up; then throw an OperationCanceledException.
, combinedToken); // cancellation token here only allows Task.Run() to not begin the passed delegate at all, if cancellation occurs prior to invoking the delegate.
try
{
actionTask.Wait(timeoutCancellationTokenSource.Token); // cancellation token here cancels the Wait() and causes it to throw, but does not cancel actionTask. We use only timeoutCancellationTokenSource.Token here, not combinedToken. If we allowed the user's cancellation token to cancel the Wait(), in this pessimistic scenario where the user delegate may not observe that cancellation, that would create a no-longer-observed task. That task could in turn later fault before completing, risking an UnobservedTaskException.
}
catch (AggregateException ex) when(ex.InnerExceptions.Count == 1) // Issue #270. Unwrap extra AggregateException caused by the way pessimistic timeout policy for synchronous executions is necessarily constructed.
{
ExceptionDispatchInfo.Capture(ex.InnerException).Throw();
}
return(actionTask.Result);
}
catch (Exception ex)
{
// Note that we cannot rely on testing (operationCanceledException.CancellationToken == combinedToken || operationCanceledException.CancellationToken == timeoutCancellationTokenSource.Token)
// as either of those tokens could have been onward combined with another token by executed code, and so may not be the token expressed on operationCanceledException.CancellationToken.
if (ex is OperationCanceledException && timeoutCancellationTokenSource.IsCancellationRequested)
{
onTimeout(context, timeout, actionTask, ex);
throw new TimeoutRejectedException("The delegate executed through TimeoutPolicy did not complete within the timeout.", ex);
}
throw;
}
}
}
}
internal static async Task <TResult> ImplementationAsync <TResult>(
Func <Context, CancellationToken, Task <TResult> > action,
Context context,
Func <Context, TimeSpan> timeoutProvider,
TimeoutStrategy timeoutStrategy,
Func <Context, TimeSpan, Task, Exception, Task> onTimeoutAsync,
CancellationToken cancellationToken,
bool continueOnCapturedContext)
{
cancellationToken.ThrowIfCancellationRequested();
TimeSpan timeout = timeoutProvider(context);
using (CancellationTokenSource timeoutCancellationTokenSource = new CancellationTokenSource())
{
using (CancellationTokenSource combinedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeoutCancellationTokenSource.Token))
{
Task <TResult> actionTask = null;
CancellationToken combinedToken = combinedTokenSource.Token;
try
{
if (timeoutStrategy == TimeoutStrategy.Optimistic)
{
SystemClock.CancelTokenAfter(timeoutCancellationTokenSource, timeout);
return(await action(context, combinedToken).ConfigureAwait(continueOnCapturedContext));
}
// else: timeoutStrategy == TimeoutStrategy.Pessimistic
Task <TResult> timeoutTask = timeoutCancellationTokenSource.Token.AsTask <TResult>();
SystemClock.CancelTokenAfter(timeoutCancellationTokenSource, timeout);
actionTask = action(context, combinedToken);
return(await(await
#if NET40
TaskEx
#else
Task
#endif
.WhenAny(actionTask, timeoutTask).ConfigureAwait(continueOnCapturedContext)).ConfigureAwait(continueOnCapturedContext));
}
catch (Exception ex)
{
if (timeoutCancellationTokenSource.IsCancellationRequested)
{
await onTimeoutAsync(context, timeout, actionTask, ex).ConfigureAwait(continueOnCapturedContext);
throw new TimeoutRejectedException("The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.", ex);
}
throw;
}
}
}
}
internal static async Task <TResult> ImplementationAsync <TResult>(
Func <Context, CancellationToken, Task <TResult> > action,
Context context,
CancellationToken cancellationToken,
Func <Context, TimeSpan> timeoutProvider,
TimeoutStrategy timeoutStrategy,
Func <Context, TimeSpan, Task, Exception, Task> onTimeoutAsync,
bool continueOnCapturedContext)
{
cancellationToken.ThrowIfCancellationRequested();
TimeSpan timeout = timeoutProvider(context);
using (CancellationTokenSource timeoutCancellationTokenSource = new CancellationTokenSource())
{
using (CancellationTokenSource combinedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeoutCancellationTokenSource.Token))
{
Task <TResult> actionTask = null;
CancellationToken combinedToken = combinedTokenSource.Token;
try
{
if (timeoutStrategy == TimeoutStrategy.Optimistic)
{
SystemClock.CancelTokenAfter(timeoutCancellationTokenSource, timeout);
return(await action(context, combinedToken).ConfigureAwait(continueOnCapturedContext));
}
// else: timeoutStrategy == TimeoutStrategy.Pessimistic
Task <TResult> timeoutTask = timeoutCancellationTokenSource.Token.AsTask <TResult>();
SystemClock.CancelTokenAfter(timeoutCancellationTokenSource, timeout);
actionTask = action(context, combinedToken);
return(await(await Task.WhenAny(actionTask, timeoutTask).ConfigureAwait(continueOnCapturedContext)).ConfigureAwait(continueOnCapturedContext));
}
catch (Exception ex)
{
// Note that we cannot rely on testing (operationCanceledException.CancellationToken == combinedToken || operationCanceledException.CancellationToken == timeoutCancellationTokenSource.Token)
// as either of those tokens could have been onward combined with another token by executed code, and so may not be the token expressed on operationCanceledException.CancellationToken.
if (ex is OperationCanceledException && timeoutCancellationTokenSource.IsCancellationRequested)
{
await onTimeoutAsync(context, timeout, actionTask, ex).ConfigureAwait(continueOnCapturedContext);
throw new TimeoutRejectedException("The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.", ex);
}
throw;
}
}
}
}