public async Task <TaskAgentMessage> GetNextMessageAsync(CancellationToken token)
{
Trace.Entering();
ArgUtil.NotNull(_session, nameof(_session));
ArgUtil.NotNull(_settings, nameof(_settings));
bool encounteringError = false;
int continuousError = 0;
string errorMessage = string.Empty;
Stopwatch heartbeat = new Stopwatch();
heartbeat.Restart();
while (true)
{
token.ThrowIfCancellationRequested();
TaskAgentMessage message = null;
try
{
message = await _agentServer.GetAgentMessageAsync(_settings.PoolId,
_session.SessionId,
_lastMessageId,
token);
// Decrypt the message body if the session is using encryption
message = DecryptMessage(message);
if (message != null)
{
_lastMessageId = message.MessageId;
}
if (encounteringError) //print the message once only if there was an error
{
_term.WriteLine(StringUtil.Loc("QueueConnected", DateTime.UtcNow));
encounteringError = false;
continuousError = 0;
}
}
catch (OperationCanceledException) when(token.IsCancellationRequested)
{
Trace.Info("Get next message has been cancelled.");
throw;
}
catch (TaskAgentAccessTokenExpiredException)
{
Trace.Info("Agent OAuth token has been revoked. Unable to pull message.");
throw;
}
catch (Exception ex)
{
Trace.Error("Catch exception during get next message.");
Trace.Error(ex);
// don't retry if SkipSessionRecover = true, DT service will delete agent session to stop agent from taking more jobs.
if (ex is TaskAgentSessionExpiredException && !_settings.SkipSessionRecover && await CreateSessionAsync(token))
{
Trace.Info($"{nameof(TaskAgentSessionExpiredException)} received, recovered by recreate session.");
}
else if (!IsGetNextMessageExceptionRetriable(ex))
{
throw;
}
else
{
continuousError++;
//retry after a random backoff to avoid service throttling
//in case of there is a service error happened and all agents get kicked off of the long poll and all agent try to reconnect back at the same time.
if (continuousError <= 5)
{
// random backoff [15, 30]
_getNextMessageRetryInterval = BackoffTimerHelper.GetRandomBackoff(TimeSpan.FromSeconds(15), TimeSpan.FromSeconds(30), _getNextMessageRetryInterval);
}
else
{
// more aggressive backoff [30, 60]
_getNextMessageRetryInterval = BackoffTimerHelper.GetRandomBackoff(TimeSpan.FromSeconds(30), TimeSpan.FromSeconds(60), _getNextMessageRetryInterval);
}
if (!encounteringError)
{
//print error only on the first consecutive error
_term.WriteError(StringUtil.Loc("QueueConError", DateTime.UtcNow, ex.Message));
encounteringError = true;
}
// re-create VssConnection before next retry
await _agentServer.RefreshConnectionAsync(AgentConnectionType.MessageQueue, TimeSpan.FromSeconds(60));
Trace.Info("Sleeping for {0} seconds before retrying.", _getNextMessageRetryInterval.TotalSeconds);
await HostContext.Delay(_getNextMessageRetryInterval, token);
}
}
if (message == null)
{
if (heartbeat.Elapsed > TimeSpan.FromMinutes(30))
{
Trace.Info($"No message retrieved from session '{_session.SessionId}' within last 30 minutes.");
heartbeat.Restart();
}
else
{
Trace.Verbose($"No message retrieved from session '{_session.SessionId}'.");
}
continue;
}
Trace.Info($"Message '{message.MessageId}' received from session '{_session.SessionId}'.");
return(message);
}
}