pollForDecisionTask method

Future<DecisionTask> pollForDecisionTask({ required String domain, required TaskList taskList, String? identity, int? maximumPageSize, String? nextPageToken, bool? reverseOrder, })

Used by deciders to get a DecisionTask from the specified decision taskList. A decision task may be returned for any open workflow execution that is using the specified task list. The task includes a paginated view of the history of the workflow execution. The decider should use the workflow type and the history to determine how to properly handle the task.

This action initiates a long poll, where the service holds the HTTP connection open and responds as soon a task becomes available. If no decision task is available in the specified task list before the timeout of 60 seconds expires, an empty result is returned. An empty result, in this context, means that a DecisionTask is returned, but that the value of taskToken is an empty string. Access Control

You can use IAM policies to control this action's access to Amazon SWF resources as follows:

• Use a Resource element with the domain name to limit the action to only specified domains.
• Use an Action element to allow or deny permission to call this action.
• Constrain the taskList.name parameter by using a Condition element with the swf:taskList.name key to allow the action to access only certain task lists.

If the caller doesn't have sufficient permissions to invoke the action, or the parameter values fall outside the specified constraints, the action fails. The associated event attribute's cause parameter is set to OPERATION_NOT_PERMITTED. For details and example IAM policies, see Using IAM to Manage Access to Amazon SWF Workflows in the Amazon SWF Developer Guide.

May throw UnknownResourceFault. May throw OperationNotPermittedFault. May throw LimitExceededFault.

Parameter domain : The name of the domain containing the task lists to poll.

Parameter taskList : Specifies the task list to poll for decision tasks.

The specified string must not start or end with whitespace. It must not contain a : (colon), / (slash), | (vertical bar), or any control characters (\u0000-\u001f | \u007f-\u009f). Also, it must not be the literal string arn.

Parameter identity : Identity of the decider making the request, which is recorded in the DecisionTaskStarted event in the workflow history. This enables diagnostic tracing when problems arise. The form of this identity is user defined.

Parameter maximumPageSize : The maximum number of results that are returned per call. Use nextPageToken to obtain further pages of results.

This is an upper limit only; the actual number of results returned per call may be fewer than the specified maximum.

Parameter nextPageToken : If NextPageToken is returned there are more results available. The value of NextPageToken is a unique pagination token for each page. Make the call again using the returned token to retrieve the next page. Keep all other arguments unchanged. Each pagination token expires after 60 seconds. Using an expired pagination token will return a 400 error: "Specified token has exceeded its maximum lifetime".

The configured maximumPageSize determines how many results can be returned in a single call.

Parameter reverseOrder : When set to true, returns the events in reverse order. By default the results are returned in ascending order of the eventTimestamp of the events.

Implementation

Future<DecisionTask> pollForDecisionTask({
  required String domain,
  required TaskList taskList,
  String? identity,
  int? maximumPageSize,
  String? nextPageToken,
  bool? reverseOrder,
}) async {
  ArgumentError.checkNotNull(domain, 'domain');
  _s.validateStringLength(
    'domain',
    domain,
    1,
    256,
    isRequired: true,
  );
  ArgumentError.checkNotNull(taskList, 'taskList');
  _s.validateStringLength(
    'identity',
    identity,
    0,
    256,
  );
  _s.validateNumRange(
    'maximumPageSize',
    maximumPageSize,
    0,
    1000,
  );
  _s.validateStringLength(
    'nextPageToken',
    nextPageToken,
    0,
    2048,
  );
  final headers = <String, String>{
    'Content-Type': 'application/x-amz-json-1.0',
    'X-Amz-Target': 'SimpleWorkflowService.PollForDecisionTask'
  };
  final jsonResponse = await _protocol.send(
    method: 'POST',
    requestUri: '/',
    exceptionFnMap: _exceptionFns,
    // TODO queryParams
    headers: headers,
    payload: {
      'domain': domain,
      'taskList': taskList,
      if (identity != null) 'identity': identity,
      if (maximumPageSize != null) 'maximumPageSize': maximumPageSize,
      if (nextPageToken != null) 'nextPageToken': nextPageToken,
      if (reverseOrder != null) 'reverseOrder': reverseOrder,
    },
  );

  return DecisionTask.fromJson(jsonResponse.body);
}