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Amazon Simple Workflow Service
API Reference (API Version 2012-01-25)

PollForDecisionTask

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.

Important

Deciders should set their client side socket timeout to at least 70 seconds (10 seconds higher than the timeout).

Important

Because the number of workflow history events for a single workflow execution might be very large, the result returned might be split up across a number of pages. To retrieve subsequent pages, make additional calls to PollForDecisionTask using the nextPageToken returned by the initial call. Note that you do not call GetWorkflowExecutionHistory with this nextPageToken. Instead, call PollForDecisionTask again.

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.

Request Syntax

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{ "domain": "string", "identity": "string", "maximumPageSize": number, "nextPageToken": "string", "reverseOrder": boolean, "taskList": { "name": "string" } }

Request Parameters

For information about the parameters that are common to all actions, see Common Parameters.

The request accepts the following data in JSON format.

domain

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

Type: String

Length Constraints: Minimum length of 1. Maximum length of 256.

Required: Yes

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.

Type: String

Length Constraints: Maximum length of 256.

Required: No

maximumPageSize

The maximum number of results that are returned per call. nextPageToken can be used to obtain futher pages of results. The default is 1000, which is the maximum allowed page size. You can, however, specify a page size smaller than the maximum.

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

Type: Integer

Valid Range: Minimum value of 0. Maximum value of 1000.

Required: No

nextPageToken

If a NextPageToken was returned by a previous call, there are more results available. To retrieve the next page of results, make the call again using the returned token in nextPageToken. Keep all other arguments unchanged.

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

Note

The nextPageToken returned by this action cannot be used with GetWorkflowExecutionHistory to get the next page. You must call PollForDecisionTask again (with the nextPageToken) to retrieve the next page of history records. Calling PollForDecisionTask with a nextPageToken doesn't return a new decision task.

Type: String

Length Constraints: Maximum length of 2048.

Required: No

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.

Type: Boolean

Required: No

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 contain the literal string arn.

Type: TaskList object

Required: Yes

Response Syntax

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{ "events": [ { "activityTaskCanceledEventAttributes": { "details": "string", "latestCancelRequestedEventId": number, "scheduledEventId": number, "startedEventId": number }, "activityTaskCancelRequestedEventAttributes": { "activityId": "string", "decisionTaskCompletedEventId": number }, "activityTaskCompletedEventAttributes": { "result": "string", "scheduledEventId": number, "startedEventId": number }, "activityTaskFailedEventAttributes": { "details": "string", "reason": "string", "scheduledEventId": number, "startedEventId": number }, "activityTaskScheduledEventAttributes": { "activityId": "string", "activityType": { "name": "string", "version": "string" }, "control": "string", "decisionTaskCompletedEventId": number, "heartbeatTimeout": "string", "input": "string", "scheduleToCloseTimeout": "string", "scheduleToStartTimeout": "string", "startToCloseTimeout": "string", "taskList": { "name": "string" }, "taskPriority": "string" }, "activityTaskStartedEventAttributes": { "identity": "string", "scheduledEventId": number }, "activityTaskTimedOutEventAttributes": { "details": "string", "scheduledEventId": number, "startedEventId": number, "timeoutType": "string" }, "cancelTimerFailedEventAttributes": { "cause": "string", "decisionTaskCompletedEventId": number, "timerId": "string" }, "cancelWorkflowExecutionFailedEventAttributes": { "cause": "string", "decisionTaskCompletedEventId": number }, "childWorkflowExecutionCanceledEventAttributes": { "details": "string", "initiatedEventId": number, "startedEventId": number, "workflowExecution": { "runId": "string", "workflowId": "string" }, "workflowType": { "name": "string", "version": "string" } }, "childWorkflowExecutionCompletedEventAttributes": { "initiatedEventId": number, "result": "string", "startedEventId": number, "workflowExecution": { "runId": "string", "workflowId": "string" }, "workflowType": { "name": "string", "version": "string" } }, "childWorkflowExecutionFailedEventAttributes": { "details": "string", "initiatedEventId": number, "reason": "string", "startedEventId": number, "workflowExecution": { "runId": "string", "workflowId": "string" }, "workflowType": { "name": "string", "version": "string" } }, "childWorkflowExecutionStartedEventAttributes": { "initiatedEventId": number, "workflowExecution": { "runId": "string", "workflowId": "string" }, "workflowType": { "name": "string", "version": "string" } }, "childWorkflowExecutionTerminatedEventAttributes": { "initiatedEventId": number, "startedEventId": number, "workflowExecution": { "runId": "string", "workflowId": "string" }, "workflowType": { "name": "string", "version": "string" } }, "childWorkflowExecutionTimedOutEventAttributes": { "initiatedEventId": number, "startedEventId": number, "timeoutType": "string", "workflowExecution": { "runId": "string", "workflowId": "string" }, "workflowType": { "name": "string", "version": "string" } }, "completeWorkflowExecutionFailedEventAttributes": { "cause": "string", "decisionTaskCompletedEventId": number }, "continueAsNewWorkflowExecutionFailedEventAttributes": { "cause": "string", "decisionTaskCompletedEventId": number }, "decisionTaskCompletedEventAttributes": { "executionContext": "string", "scheduledEventId": number, "startedEventId": number }, "decisionTaskScheduledEventAttributes": { "startToCloseTimeout": "string", "taskList": { "name": "string" }, "taskPriority": "string" }, "decisionTaskStartedEventAttributes": { "identity": "string", "scheduledEventId": number }, "decisionTaskTimedOutEventAttributes": { "scheduledEventId": number, "startedEventId": number, "timeoutType": "string" }, "eventId": number, "eventTimestamp": number, "eventType": "string", "externalWorkflowExecutionCancelRequestedEventAttributes": { "initiatedEventId": number, "workflowExecution": { "runId": "string", "workflowId": "string" } }, "externalWorkflowExecutionSignaledEventAttributes": { "initiatedEventId": number, "workflowExecution": { "runId": "string", "workflowId": "string" } }, "failWorkflowExecutionFailedEventAttributes": { "cause": "string", "decisionTaskCompletedEventId": number }, "lambdaFunctionCompletedEventAttributes": { "result": "string", "scheduledEventId": number, "startedEventId": number }, "lambdaFunctionFailedEventAttributes": { "details": "string", "reason": "string", "scheduledEventId": number, "startedEventId": number }, "lambdaFunctionScheduledEventAttributes": { "control": "string", "decisionTaskCompletedEventId": number, "id": "string", "input": "string", "name": "string", "startToCloseTimeout": "string" }, "lambdaFunctionStartedEventAttributes": { "scheduledEventId": number }, "lambdaFunctionTimedOutEventAttributes": { "scheduledEventId": number, "startedEventId": number, "timeoutType": "string" }, "markerRecordedEventAttributes": { "decisionTaskCompletedEventId": number, "details": "string", "markerName": "string" }, "recordMarkerFailedEventAttributes": { "cause": "string", "decisionTaskCompletedEventId": number, "markerName": "string" }, "requestCancelActivityTaskFailedEventAttributes": { "activityId": "string", "cause": "string", "decisionTaskCompletedEventId": number }, "requestCancelExternalWorkflowExecutionFailedEventAttributes": { "cause": "string", "control": "string", "decisionTaskCompletedEventId": number, "initiatedEventId": number, "runId": "string", "workflowId": "string" }, "requestCancelExternalWorkflowExecutionInitiatedEventAttributes": { "control": "string", "decisionTaskCompletedEventId": number, "runId": "string", "workflowId": "string" }, "scheduleActivityTaskFailedEventAttributes": { "activityId": "string", "activityType": { "name": "string", "version": "string" }, "cause": "string", "decisionTaskCompletedEventId": number }, "scheduleLambdaFunctionFailedEventAttributes": { "cause": "string", "decisionTaskCompletedEventId": number, "id": "string", "name": "string" }, "signalExternalWorkflowExecutionFailedEventAttributes": { "cause": "string", "control": "string", "decisionTaskCompletedEventId": number, "initiatedEventId": number, "runId": "string", "workflowId": "string" }, "signalExternalWorkflowExecutionInitiatedEventAttributes": { "control": "string", "decisionTaskCompletedEventId": number, "input": "string", "runId": "string", "signalName": "string", "workflowId": "string" }, "startChildWorkflowExecutionFailedEventAttributes": { "cause": "string", "control": "string", "decisionTaskCompletedEventId": number, "initiatedEventId": number, "workflowId": "string", "workflowType": { "name": "string", "version": "string" } }, "startChildWorkflowExecutionInitiatedEventAttributes": { "childPolicy": "string", "control": "string", "decisionTaskCompletedEventId": number, "executionStartToCloseTimeout": "string", "input": "string", "lambdaRole": "string", "tagList": [ "string" ], "taskList": { "name": "string" }, "taskPriority": "string", "taskStartToCloseTimeout": "string", "workflowId": "string", "workflowType": { "name": "string", "version": "string" } }, "startLambdaFunctionFailedEventAttributes": { "cause": "string", "message": "string", "scheduledEventId": number }, "startTimerFailedEventAttributes": { "cause": "string", "decisionTaskCompletedEventId": number, "timerId": "string" }, "timerCanceledEventAttributes": { "decisionTaskCompletedEventId": number, "startedEventId": number, "timerId": "string" }, "timerFiredEventAttributes": { "startedEventId": number, "timerId": "string" }, "timerStartedEventAttributes": { "control": "string", "decisionTaskCompletedEventId": number, "startToFireTimeout": "string", "timerId": "string" }, "workflowExecutionCanceledEventAttributes": { "decisionTaskCompletedEventId": number, "details": "string" }, "workflowExecutionCancelRequestedEventAttributes": { "cause": "string", "externalInitiatedEventId": number, "externalWorkflowExecution": { "runId": "string", "workflowId": "string" } }, "workflowExecutionCompletedEventAttributes": { "decisionTaskCompletedEventId": number, "result": "string" }, "workflowExecutionContinuedAsNewEventAttributes": { "childPolicy": "string", "decisionTaskCompletedEventId": number, "executionStartToCloseTimeout": "string", "input": "string", "lambdaRole": "string", "newExecutionRunId": "string", "tagList": [ "string" ], "taskList": { "name": "string" }, "taskPriority": "string", "taskStartToCloseTimeout": "string", "workflowType": { "name": "string", "version": "string" } }, "workflowExecutionFailedEventAttributes": { "decisionTaskCompletedEventId": number, "details": "string", "reason": "string" }, "workflowExecutionSignaledEventAttributes": { "externalInitiatedEventId": number, "externalWorkflowExecution": { "runId": "string", "workflowId": "string" }, "input": "string", "signalName": "string" }, "workflowExecutionStartedEventAttributes": { "childPolicy": "string", "continuedExecutionRunId": "string", "executionStartToCloseTimeout": "string", "input": "string", "lambdaRole": "string", "parentInitiatedEventId": number, "parentWorkflowExecution": { "runId": "string", "workflowId": "string" }, "tagList": [ "string" ], "taskList": { "name": "string" }, "taskPriority": "string", "taskStartToCloseTimeout": "string", "workflowType": { "name": "string", "version": "string" } }, "workflowExecutionTerminatedEventAttributes": { "cause": "string", "childPolicy": "string", "details": "string", "reason": "string" }, "workflowExecutionTimedOutEventAttributes": { "childPolicy": "string", "timeoutType": "string" } } ], "nextPageToken": "string", "previousStartedEventId": number, "startedEventId": number, "taskToken": "string", "workflowExecution": { "runId": "string", "workflowId": "string" }, "workflowType": { "name": "string", "version": "string" } }

Response Elements

If the action is successful, the service sends back an HTTP 200 response.

The following data is returned in JSON format by the service.

events

A paginated list of history events of the workflow execution. The decider uses this during the processing of the decision task.

Type: Array of HistoryEvent objects

nextPageToken

If a NextPageToken was returned by a previous call, there are more results available. To retrieve the next page of results, make the call again using the returned token in nextPageToken. Keep all other arguments unchanged.

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

Type: String

Length Constraints: Maximum length of 2048.

previousStartedEventId

The ID of the DecisionTaskStarted event of the previous decision task of this workflow execution that was processed by the decider. This can be used to determine the events in the history new since the last decision task received by the decider.

Type: Long

startedEventId

The ID of the DecisionTaskStarted event recorded in the history.

Type: Long

taskToken

The opaque string used as a handle on the task. This token is used by workers to communicate progress and response information back to the system about the task.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 1024.

workflowExecution

The workflow execution for which this decision task was created.

Type: WorkflowExecution object

workflowType

The type of the workflow execution for which this decision task was created.

Type: WorkflowType object

Errors

For information about the errors that are common to all actions, see Common Errors.

LimitExceededFault

Returned by any operation if a system imposed limitation has been reached. To address this fault you should either clean up unused resources or increase the limit by contacting AWS.

HTTP Status Code: 400

OperationNotPermittedFault

Returned when the caller doesn't have sufficient permissions to invoke the action.

HTTP Status Code: 400

UnknownResourceFault

Returned when the named resource cannot be found with in the scope of this operation (region or domain). This could happen if the named resource was never created or is no longer available for this operation.

HTTP Status Code: 400

Example

PollForDecisionTask Example

Sample Request

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POST / HTTP/1.1 Host: swf.us-east-1.amazonaws.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.25) Gecko/20111212 Firefox/3.6.25 ( .NET CLR 3.5.30729; .NET4.0E) Accept: application/json, text/javascript, */* Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Connection: keep-alive Content-Type: application/x-amz-json-1.0 X-Requested-With: XMLHttpRequest X-Amz-Date: Sun, 15 Jan 2012 02:09:54 GMT X-Amz-Target: SimpleWorkflowService.PollForDecisionTask Content-Encoding: amz-1.0 X-Amzn-Authorization: AWS3 AWSAccessKeyId=AKIAIOSFODNN7EXAMPLE,Algorithm=HmacSHA256,SignedHeaders=Host;X-Amz-Date;X-Amz-Target;Content-Encoding,Signature=R3CJ2HMLSVpc2p6eafeztZCZWcgza+h61gSUuWx15gw= Referer: http://swf.us-east-1.amazonaws.com/explorer/index.html Content-Length: 171 Pragma: no-cache Cache-Control: no-cache { "maximumPageSize": 50, "domain": "867530901", "taskList": { "name": "specialTaskList" }, "reverseOrder": true, "identity": "Decider01" }

Sample Response

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HTTP/1.1 200 OK Content-Length: 1639 Content-Type: application/json x-amzn-RequestId: 03db54cf-3f1e-11e1-b118-3bfa5e8e7fc3 { "previousStartedEventId": 0, "workflowExecution": { "workflowId": "20110927-T-1", "runId": "06b8f87a-24b3-40b6-9ceb-9676f28e9493" }, "startedEventId": 3, "workflowType": { "version": "1.0", "name": "customerOrderWorkflow" }, "events": [ { "eventId": 3, "decisionTaskStartedEventAttributes": { "scheduledEventId": 2, "identity": "Decider01" }, "eventTimestamp": 1326593394.566, "eventType": "DecisionTaskStarted" }, { "eventId": 2, "eventType": "DecisionTaskScheduled", "decisionTaskScheduledEventAttributes": { "startToCloseTimeout": "600", "taskList": { "name": "specialTaskList" }, "taskPriority": "100" }, "eventTimestamp": 1326592619.474 }, { "eventId": 1, "eventType": "WorkflowExecutionStarted", "workflowExecutionStartedEventAttributes": { "taskList": { "name": "specialTaskList" }, "parentInitiatedEventId": 0, "taskStartToCloseTimeout": "600", "childPolicy": "TERMINATE", "executionStartToCloseTimeout": "3600", "input": "arbitrary-string-that-is-meaningful-to-the-workflow", "workflowType": { "version": "1.0", "name": "customerOrderWorkflow" }, "tagList": [ "music purchase", "digital", "ricoh-the-dog" ] }, "eventTimestamp": 1326592619.474 } ], "taskToken": "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" }

See Also

For more information about using this API in one of the language-specific AWS SDKs, see the following: