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

PollForActivityTask

Used by workers to get an ActivityTask from the specified activity taskList. This initiates a long poll, where the service holds the HTTP connection open and responds as soon as a task becomes available. The maximum time the service holds on to the request before responding is 60 seconds. If no task is available within 60 seconds, the poll returns an empty result. An empty result, in this context, means that an ActivityTask is returned, but that the value of taskToken is an empty string. If a task is returned, the worker should use its type to identify and process it correctly.

Important

Workers should set their client side socket timeout to at least 70 seconds (10 seconds higher than the maximum time service may hold the poll request).

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

{
   "domain": "string",
   "identity": "string",
   "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 that contains the task lists being polled.

Type: String

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

Required: Yes

identity

Identity of the worker making the request, recorded in the ActivityTaskStarted 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

taskList

Specifies the task list to poll for activity 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

{
   "activityId": "string",
   "activityType": { 
      "name": "string",
      "version": "string"
   },
   "input": "string",
   "startedEventId": number,
   "taskToken": "string",
   "workflowExecution": { 
      "runId": "string",
      "workflowId": "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.

activityId

The unique ID of the task.

Type: String

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

activityType

The type of this activity task.

Type: ActivityType object

input

The inputs provided when the activity task was scheduled. The form of the input is user defined and should be meaningful to the activity implementation.

Type: String

Length Constraints: Maximum length of 32768.

startedEventId

The ID of the ActivityTaskStarted 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 that started this activity task.

Type: WorkflowExecution 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

PollForActivityTask Example

Sample Request

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: Mon, 16 Jan 2012 03:53:52 GMT
X-Amz-Target: SimpleWorkflowService.PollForActivityTask
Content-Encoding: amz-1.0
X-Amzn-Authorization: AWS3 AWSAccessKeyId=AKIAIOSFODNN7EXAMPLE,Algorithm=HmacSHA256,SignedHeaders=Host;X-Amz-Date;X-Amz-Target;Content-Encoding,Signature=dv0H1RPYucoIcRckspWO0f8xG120MWZRKmj3O5/A4rY=
Referer: http://swf.us-east-1.amazonaws.com/explorer/index.html
Content-Length: 108
Pragma: no-cache
Cache-Control: no-cache

{"domain": "867530901",
"taskList":
{"name": "mainTaskList"},
"identity": "VerifyCreditCardWorker01"}

Sample Response

HTTP/1.1 200 OK
Content-Length: 837
Content-Type: application/json
x-amzn-RequestId: b48fb6b5-3ff5-11e1-a23a-99d60383ae71

{"activityId": "verification-27",
"activityType":
{"name": "activityVerify",
"version": "1.0"},
"input": "5634-0056-4367-0923,12/12,437",
"startedEventId": 11,
"taskToken": "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",
"workflowExecution":
{"runId": "cfa2bd33-31b0-4b75-b131-255bb0d97b3f",
"workflowId": "20110927-T-1"}
}

See Also

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