public AzureDiscoveryFetcher()
{
_discovery = new AzureDiscovery(
CloudConfiguration.SubscriptionId,
CloudConfiguration.GetManagementCertificate());
}
public Task<DeploymentReference> Discover(CancellationToken cancellationToken)
{
var client = HttpClientFactory.Create(_subscriptionId, _certificate);
var completionSource = new TaskCompletionSource<DeploymentReference>();
Task<DeploymentReference> previousTask;
var discovery = new AzureDiscovery(_subscriptionId, _certificate, _observer);
// If we have already succeeded, just pass on the result from the last time (shortcut)
lock (_currentDeploymentDiscoveryLock)
{
if (_currentDeployment != null)
{
completionSource.TrySetResult(_currentDeployment);
return completionSource.Task;
}
previousTask = _currentDeploymentDiscoveryTask;
_currentDeploymentDiscoveryTask = completionSource.Task;
}
// If this is the first time this is called, create a new query and return
if (previousTask == null)
{
discovery.DoDiscoverDeploymentAsync(client, _deploymentPrivateId, completionSource, cancellationToken);
completionSource.Task.ContinueRaiseSystemEventOnFault(_observer, AzureDiscovery.EventForFailedOperation);
return completionSource.Task;
}
// We have already called but have not got the result yet.
// In case there is already a task running (this is likely in our scenarios) wait for the result.
// Retry once in case it will fail, or, more importantly, if it has already failed (the last time).
previousTask.ContinueWith(task =>
{
try
{
if (task.IsFaulted || (task.IsCanceled && !cancellationToken.IsCancellationRequested))
{
discovery.DoDiscoverDeploymentAsync(client, _deploymentPrivateId, completionSource, cancellationToken);
completionSource.Task.ContinueRaiseSystemEventOnFault(_observer, AzureDiscovery.EventForFailedOperation);
return;
}
if (task.IsCanceled)
{
completionSource.TrySetCanceled();
return;
}
completionSource.TrySetResult(task.Result);
}
catch (Exception exception)
{
// this should never happen, so forward but do not try to handle/retry here.
completionSource.TrySetException(exception);
}
}, TaskContinuationOptions.ExecuteSynchronously);
// NOTE: _currentDeployment may not be available yet in other continuations. This is ok.
completionSource.Task.ContinueWith(t =>
{
lock (_currentDeploymentDiscoveryLock)
{
_currentDeployment = t.Result;
}
}, TaskContinuationOptions.OnlyOnRanToCompletion);
return completionSource.Task;
}