Package io.awspring.cloud.sqs.listener.backpressure

Interface BackPressureHandler

All Known Subinterfaces:

BatchAwareBackPressureHandler

All Known Implementing Classes:

CompositeBackPressureHandler, ConcurrencyLimiterBlockingBackPressureHandler, FullBatchBackPressureHandler, SemaphoreBackPressureHandler, ThroughputBackPressureHandler

public interface BackPressureHandler

Abstraction to handle backpressure within a PollingMessageSource. Release methods must be thread-safe so that many messages can be processed asynchronously. Example strategies are semaphore-based, rate limiter-based, a mix of both, or any other.

Since:

3.0

Author:

Tomaz Fernandes, Loïc Rouchon

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static enum	BackPressureHandler.ReleaseReason

Method Summary

Modifier and Type	Method	Description
boolean	drain(Duration timeout)	Attempts to acquire all permits up to the specified timeout.
default void	release(int amount)	Deprecated. This method is deprecated and will not be called by the Spring Cloud AWS SQS listener anymore.
void	release(int amount, BackPressureHandler.ReleaseReason reason)	Releases the specified amount of permits for processed messages.
int	request(int amount)	Requests a number of permits.

Method Details

request

int request(int amount)
     throws InterruptedException

Requests a number of permits. Each obtained permit allows the MessageSource to retrieve one message.

Parameters:

amount - the amount of permits to request.

Returns:

the amount of permits obtained.

Throws:

InterruptedException - if the Thread is interrupted while waiting for permits.

release

void release(int amount,
 BackPressureHandler.ReleaseReason reason)

Releases the specified amount of permits for processed messages. Each message that has been processed should release one permit, whether processing was successful or not.

This method can be called in the following use cases:

• BackPressureHandler.ReleaseReason.LIMITED: all/some permits were not used because another BackPressureHandler has a lower permits limit and the difference in permits needs to be returned.
• BackPressureHandler.ReleaseReason.NONE_FETCHED: none of the permits were actually used because no messages were retrieved from SQS. Permits need to be returned.
• BackPressureHandler.ReleaseReason.PARTIAL_FETCH: some of the permits were used (some messages were retrieved from SQS). The unused ones need to be returned. The amount to be returned might be 0, in which case it means all the permits will be used as the same number of messages were fetched from SQS.
• BackPressureHandler.ReleaseReason.PROCESSED: a message processing finished, successfully or not.

Parameters:

amount - the amount of permits to release.

reason - the reason why the permits were released.

release

@Deprecated
default void release(int amount)

Deprecated.

This method is deprecated and will not be called by the Spring Cloud AWS SQS listener anymore. Implement release(int, ReleaseReason) instead.

Release the specified amount of permits. Each message that has been processed should release one permit, whether processing was successful or not.

Parameters:

amount - the amount of permits to release.

drain

boolean drain(Duration timeout)

Attempts to acquire all permits up to the specified timeout. If successful, means all permits were returned and thus no activity is left in the MessageSource.

Parameters:

timeout - the maximum amount of time to wait for all permits to be released.

Returns:

whether all permits were acquired.