private void StartAsynchronousComputation(AsynchronousComputationToStart computationToStart, Request requestToCompleteSynchronously, CancellationToken callerCancellationToken)
{
var cancellationToken = computationToStart.CancellationTokenSource.Token;
try
{
cancellationToken.ThrowIfCancellationRequested();
// DO NOT ACCESS ANY FIELDS OR STATE BEYOND THIS POINT. Since this function
// runs unsynchronized, it's possible that during this function this request
// might be cancelled, and then a whole additional request might start and
// complete inline, and cache the result. By grabbing state before we check
// the cancellation token, we can be assured that we are only operating on
// a state that was complete.
try
{
// We avoid creating a full closure just to pass the token along
// Also, use TaskContinuationOptions.ExecuteSynchronously so that we inline
// the continuation if asynchronousComputeFunction completes synchronously
var task = computationToStart.AsynchronousComputeFunction(cancellationToken);
task.ContinueWith(
(t, s) => CompleteWithTask(t, ((CancellationTokenSource)s).Token),
computationToStart.CancellationTokenSource,
cancellationToken,
TaskContinuationOptions.ExecuteSynchronously,
TaskScheduler.Default);
if (requestToCompleteSynchronously != null && task.IsCompleted)
{
using (TakeLock(CancellationToken.None))
{
task = GetCachedValueAndCacheThisValueIfNoneCached_NoLock(task);
}
// It's safe to synchronously complete this task, since the Task object hasn't been returned
// to the caller of GetValueAsync yet
requestToCompleteSynchronously.CompleteFromTaskSynchronously(task);
}
}
catch (Exception e) when(FatalError.ReportUnlessCanceled(e))
{
throw ExceptionUtilities.Unreachable;
}
}
catch (OperationCanceledException oce) when(CrashIfCanceledWithDifferentToken(oce, cancellationToken))
{
// The underlying computation cancelled with the correct token, but we must ourselves ensure that the caller
// on our stack gets an OperationCanceledException thrown with the right token
callerCancellationToken.ThrowIfCancellationRequested();
// We can only be here if the computation was cancelled, which means all requests for the value
// must have been cancelled. Therefore, the ThrowIfCancellationRequested above must have thrown
// because that token from the requestor was cancelled.
throw ExceptionUtilities.Unreachable;
}
}
private void StartAsynchronousComputation(AsynchronousComputationToStart computationToStart, Request requestToCompleteSynchronously)
{
var cancellationToken = computationToStart.CancellationTokenSource.Token;
try
{
cancellationToken.ThrowIfCancellationRequested();
// DO NOT ACCESS ANY FIELDS OR STATE BEYOND THIS POINT. Since this function
// runs unsynchronized, it's possible that during this function this request
// might be cancelled, and then a whole additional request might start and
// complete inline, and cache the result. By grabbing state before we check
// the cancellation token, we can be assured that we are only operating on
// a state that was complete.
try
{
// We avoid creating a full closure just to pass the token along
// Also, use TaskContinuationOptions.ExecuteSynchronously so that we inline
// the continuation if asynchronousComputeFunction completes synchronously
var task = computationToStart.AsynchronousComputeFunction(cancellationToken);
task.ContinueWith(
(t, s) => CompleteWithTask(t, ((CancellationTokenSource)s).Token),
computationToStart.CancellationTokenSource,
cancellationToken,
TaskContinuationOptions.ExecuteSynchronously,
TaskScheduler.Default);
if (requestToCompleteSynchronously != null && task.IsCompleted)
{
using (TakeLock(CancellationToken.None))
{
task = GetCachedValueAndCacheThisValueIfNoneCached_NoLock(task);
}
requestToCompleteSynchronously.CompleteFromTaskSynchronously(task);
}
}
catch (Exception e) when(FatalError.ReportUnlessCanceled(e))
{
throw ExceptionUtilities.Unreachable;
}
}
catch (OperationCanceledException oce) when(CrashIfCanceledWithDifferentToken(oce, cancellationToken))
{
// As long as it's the right token, this means that our thread was the first thread
// to start an asynchronous computation, but the requestor cancelled as we were starting up
// the computation.
throw ExceptionUtilities.Unreachable;
}
}
private void StartAsynchronousComputation(AsynchronousComputationToStart computationToStart, Request requestToCompleteSynchronously, CancellationToken callerCancellationToken)
{
var cancellationToken = computationToStart.CancellationTokenSource.Token;
try
{
cancellationToken.ThrowIfCancellationRequested();
// DO NOT ACCESS ANY FIELDS OR STATE BEYOND THIS POINT. Since this function
// runs unsynchronized, it's possible that during this function this request
// might be cancelled, and then a whole additional request might start and
// complete inline, and cache the result. By grabbing state before we check
// the cancellation token, we can be assured that we are only operating on
// a state that was complete.
try
{
var task = computationToStart.AsynchronousComputeFunction(cancellationToken);
// As an optimization, if the task is already completed, mark the
// request as being completed as well.
//
// Note: we want to do this before we do the .ContinueWith below. That way,
// when the async call to CompleteWithTask runs, it sees that we've already
// completed and can bail immediately. If we were to do this after we
// kicked off the async work, then we'd have the chance that both would
// run concurrently and we'd have a higher change of hitting the race condition
// of calling AsyncMethodBuilder.SetResult simultaneously (and thus having
// the InvalidOperationException that we have to ignore).
if (requestToCompleteSynchronously != null && task.IsCompleted)
{
using (TakeLock(CancellationToken.None))
{
task = GetCachedValueAndCacheThisValueIfNoneCached_NoLock(task);
}
// It's safe to synchronously complete this task, since the Task object hasn't been returned
// to the caller of GetValueAsync yet
requestToCompleteSynchronously.CompleteFromTaskSynchronously(task);
}
// We avoid creating a full closure just to pass the token along
// Also, use TaskContinuationOptions.ExecuteSynchronously so that we inline
// the continuation if asynchronousComputeFunction completes synchronously
task.ContinueWith(
(t, s) => CompleteWithTask(t, ((CancellationTokenSource)s).Token),
computationToStart.CancellationTokenSource,
cancellationToken,
TaskContinuationOptions.ExecuteSynchronously,
TaskScheduler.Default);
}
catch (Exception e) when(FatalError.ReportUnlessCanceled(e))
{
throw ExceptionUtilities.Unreachable;
}
}
catch (OperationCanceledException oce) when(CrashIfCanceledWithDifferentToken(oce, cancellationToken))
{
// The underlying computation cancelled with the correct token, but we must ourselves ensure that the caller
// on our stack gets an OperationCanceledException thrown with the right token
callerCancellationToken.ThrowIfCancellationRequested();
// We can only be here if the computation was cancelled, which means all requests for the value
// must have been cancelled. Therefore, the ThrowIfCancellationRequested above must have thrown
// because that token from the requester was cancelled.
throw ExceptionUtilities.Unreachable;
}
}
