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ISQSQueuePoller

Interface in AWS.SQS

Queue poller interface. See TSQSQueuePoller for implementation.

Properties​

AttributeNames​

property AttributeNames: TList<string>

List of message attribute names to return along with each message. Valid values: All | Policy | VisibilityTimeout | MaximumMessageSize | MessageRetentionPeriod | ApproximateNumberOfMessages | ApproximateNumberOfMessagesNotVisible | CreatedTimestamp | LastModifiedTimestamp | QueueArn | ApproximateNumberOfMessagesDelayed | DelaySeconds | ReceiveMessageWaitTimeSeconds | RedrivePolicy | FifoQueue | ContentBasedDeduplication | KmsMasterKeyId | KmsDataKeyReusePeriodSeconds | DeduplicationScope | FifoThroughputLimit | RedriveAllowPolicy

IdleTimeout​

property IdleTimeout: TOptional<Integer>

An optional IdleTimeout value for Poll operations specified in milliseconds.

MaxNumberOfMessages​

property MaxNumberOfMessages: TOptional<Integer>

Optional value for specifying maximum number of messages to retrieve in a single Poll batch. Valid values range from 1 to 10. When not specified the default number of messages requested is 1.

MessageAttributeNames​

property MessageAttributeNames: TList<string>

Specifies a list of message attributes by name to be returned along with each message. Specifying All or .* will return all message attributes.

OnBeforeRequest​

property OnBeforeRequest: TSQSQueuePollerBeforeRequestHandler

Optionally specify an OnBeforeRequest to receive a callback before each Poll request is started. The handler method is provided with polling statistics.

var QueueUrl := 'https://...'; var Poller := TSQSQueuePoller.Create(QueueUrl) as ISQSQueuePoller; Poller.OnBeforeRequest := procedure(const APoller: ISQSQueuePoller; const AStats: TSQSQueuePollerStatistics) begin if AStats.RequestCount = 0 then Log(Format('Polling started at %s', [FormatDateTime('c', AStats.PollingStartedAt)])) else Log(Format('Polling iteration %d', [AStats.RequestCount])); Log(Format('Messages received to date %d', [AStats.ReceivedMessageCount])); end; )

SkipDelete​

property SkipDelete: Boolean

Property defining behaviour at end of each polling loop cycle. By default this property is set to false and messages will be automatically deleted at the end of the Poll procedure. When setting this property to true, use DeleteMessage or DeleteMessages to remove messages you have successfully processed.

VisibilityTimeout​

property VisibilityTimeout: TOptional<Integer>

Optionally specify VisibilityTimeout to set the amount of time in seconds you have to process each received message before it is returned to the queue.

WaitTimeSeconds​

property WaitTimeSeconds: TOptional<Integer>

Optionally specify the long poll interval in seconds. Messages are yielded as soon as they are received. The WaitTimeSeconds specifies the maximum period of time to wait on each polling attempt before starting a new poll attempt. The default value is 20 seconds if not specified.

Methods​

ChangeMessageVisibilityTimeout​

procedure ChangeMessageVisibilityTimeout(const AMessage: ISQSMessage; const ATimeout: Integer);

ISQSMessage

Changes the message visibility timeout for a given message.

This should be called within a Poll procedure block.

var QueueUrl := 'https://...'; var Poller = TSQSQueuePoller.Create(QueueUrl) as ISQSQueuePoller; Poller.Poll( procedure(const AMessages: TSQSMessages) begin for var LMessage in AMessages do begin // If you need more time to process the message, // change it's visibility timeout. Poller.ChangeMessageVisibilityTimeout(LMessage, 900); end; end ); )

Parameters

NameDescription
AMessageSpecify the message.
ATimeoutNew timeout value in seconds. Valid values range from 0 to 43200 (12 hours).

DeleteMessage​

procedure DeleteMessage(const AMessage: ISQSMessage);

ISQSMessage

Deletes the specified message.

Use this in conjunction with SkipDelete to control which messages are deleted during processing. This should be called within a Poll procedure block.

var QueueUrl := 'https://...'; var Poller = TSQSQueuePoller.Create(QueueUrl) as ISQSQueuePoller; Poller.SkipDelete := True; Poller.Poll( procedure(const AMessages: TSQSMessages) begin for var LMessage in AMessages do begin // Process the message then delete it when you're done. Poller.DeleteMessage(LMessage); end; end ); )

Parameters

NameDescription
AMessageSpecify the message to delete.

DeleteMessages​

procedure DeleteMessages(const AMessages: TSQSMessages);

Deletes the specified list of messages.

Use this in conjunction with SkipDelete to control which messages are deleted during processing. This should be called within a Poll procedure block.

NOTE: The behaviour of this example is the same as leaving SkipDelete unchanged (false). <code lang="delphi"> var QueueUrl := 'https://...'; var Poller = TSQSQueuePoller.Create(QueueUrl) as ISQSQueuePoller; Poller.SkipDelete := True; Poller.Poll( procedure(const AMessages: TSQSMessages) begin for var LMessage in AMessages do begin // Process the message. end; // Delete the messages. Poller.DeleteMessages(AMessages); end ); )

Parameters

NameDescription
AMessagesSpecify a list of messages to delete.

Poll​

procedure Poll(const AHandler: TSQSQueuePollerHandler);

Polls for messages.

Messages are automatically deleted from the queue at the end of the given Poll procedure. Use SkipDelete property to change this behaviour.

var QueueUrl := 'https://...'; var Poller = TSQSQueuePoller.Create(QueueUrl) as ISQSQueuePoller; Poller.Poll( procedure(const AMessages: TSQSMessages) begin // Do something with AMessages. end ); )

Parameters

NameDescription
AHandlerProvide a handler method for processing messages.

StopPolling​

procedure StopPolling;

Stops the polling gracefully.

This should be called within a Poll procedure block.