I'm trying to define a flow for a single-threaded handler. Messages come in great number and the handler is slow (it's inefficient to process them one by one). So I want to make the handler consume all messages available in the channel at once (or wait until a few messages accumulate) with Java DSL. If there are no messages in the channel and the handler has processed a previous group it should wait for a certain period of time (timeout "a") for a few messages to accumulate in the channel. But if messages keep coming, the handler MUST consume them after a certain period of time from the previous execution (timeout "b"). Therefore time intervals between handler executions should be no more than "b" (unless no messages arrive in the channel).
There is no reason to make multiple instances of that sort of handler: it generates data for interfaces. The code below describes some basic configuration. My problem is that I'm not able to come up with debouncing (the timeout "b") and releasing the group once the handler execution is completed.
@Configuration
public class SomeConfig {
private AtomicBoolean someHandlerBusy = new AtomicBoolean(false);
@Bean
StandardIntegrationFlow someFlow() {
return IntegrationFlows
.from("someChannel")
.aggregate(aggregatorSpec -> aggregatorSpec
//The only rule to release a group:
//wait 500ms after last message and have a free someHandler
.groupTimeout(500)
.sendPartialResultOnExpiry(true) //if 500ms expired - send group
.expireGroupsUponCompletion(true) //group should be filled again
.correlationStrategy(message -> true) //one group key, all messages in oe group
.releaseStrategy(message -> false) //never release messages, only with timeout
//Send messages one by one. This is not part of this task.
//I just want to know how to do that. Like splitter.
//.outputProcessor(MessageGroup::getMessages)
)
.handle("someHandler")
.get();
}
}
I have the solution with plain Java (kotlin) code: https://pastebin.com/mti3Y5tD
UPDATE
The configuration below does not erase group. The group is growing and growing and it falls wit error at the end.
Error:
*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message transform method call failed at JPLISAgent.c line: 844
Configuration:
@Configuration
public class InterfaceHandlerConfigJava {
@Bean
MessageChannel interfaceAggregatorFlowChannel() {
return MessageChannels.publishSubscribe("interfaceAggregatorFlowChannel").get();
}
@EventListener(ApplicationReadyEvent.class)
public void initTriggerPacket(ApplicationReadyEvent event) {
MessageChannel channel = event.getApplicationContext().getBean("interfaceAggregatorFlowChannel", MessageChannel.class);
channel.send(MessageBuilder.withPayload(new InterfaceHandler.HandlerReadyMessage()).build());
}
@Bean
StandardIntegrationFlow someFlow(
InterfaceHandler interfaceHandler
) {
long lastMessageTimeout = 10L;
return IntegrationFlows
.from("interfaceAggregatorFlowChannel")
.aggregate(aggregatorSpec -> aggregatorSpec
.groupTimeout(messageGroup -> {
if (haveInstance(messageGroup, InterfaceHandler.HandlerReadyMessage.class)) {
System.out.println("case HandlerReadyMessage");
if (haveInstance(messageGroup, DbChangeStreamConfiguration.InitFromDbMessage.class)) {
System.out.println("case InitFromDbMessage");
return 0L;
} else if (messageGroup.size() > 1) {
long groupCreationTimeout =
messageGroup.getTimestamp() + 500L - System.currentTimeMillis();
long timeout = Math.min(groupCreationTimeout, lastMessageTimeout);
System.out.println("case messageGroup.size() > 1, timeout: " + timeout);
return timeout;
}
}
System.out.println("case Handler NOT ReadyMessage");
return null;
})
.sendPartialResultOnExpiry(true)
.expireGroupsUponCompletion(true)
.expireGroupsUponTimeout(true)
.correlationStrategy(message -> true)
.releaseStrategy(message -> false)
)
.handle(interfaceHandler, "handle")
.channel("interfaceAggregatorFlowChannel")
.get();
}
private boolean haveInstance(MessageGroup messageGroup, Class clazz) {
for (Message<?> message : messageGroup.getMessages()) {
if (clazz.isInstance(message.getPayload())) {
return true;
}
}
return false;
}
}
I want to highlight: this flow is in the cycle. There is IN and no OUT. Messages go to the IN but handler emits HandlerReadyMessage at the end. Maybe there should be some thread breaker channel?
FINAL VARIANT
As aggregator and handler should not blocks each other and should not try to make a stackoverflow exception they should run in different threads. In the configuration above this achieved with queue channels. Looks that publish-subscribe channels are not running subscribers in different threads (at least for one subscriber).
@Configuration
public class InterfaceHandlerConfigJava {
// acts as thread breaker too
@Bean
MessageChannel interfaceAggregatorFlowChannel() {
return MessageChannels.queue("interfaceAggregatorFlowChannel").get();
}
@Bean
MessageChannel threadBreaker() {
return MessageChannels.queue("threadBreaker").get();
}
@EventListener(ApplicationReadyEvent.class)
public void initTriggerPacket(ApplicationReadyEvent event) {
MessageChannel channel = event.getApplicationContext().getBean("interfaceAggregatorFlowChannel", MessageChannel.class);
channel.send(MessageBuilder.withPayload(new InterfaceHandler.HandlerReadyMessage()).build());
}
@Bean
StandardIntegrationFlow someFlow(
InterfaceHandler interfaceHandler
) {
long lastMessageTimeout = 10L;
return IntegrationFlows
.from("interfaceAggregatorFlowChannel")
.aggregate(aggregatorSpec -> aggregatorSpec
.groupTimeout(messageGroup -> {
if (haveInstance(messageGroup, InterfaceHandler.HandlerReadyMessage.class)) {
System.out.println("case HandlerReadyMessage");
if (haveInstance(messageGroup, DbChangeStreamConfiguration.InitFromDbMessage.class)) {
System.out.println("case InitFromDbMessage");
return 0L;
} else if (messageGroup.size() > 1) {
long groupCreationTimeout =
messageGroup.getTimestamp() + 500L - System.currentTimeMillis();
long timeout = Math.min(groupCreationTimeout, lastMessageTimeout);
System.out.println("case messageGroup.size() > 1, timeout: " + timeout);
return timeout;
}
}
System.out.println("case Handler NOT ReadyMessage");
return null;
})
.sendPartialResultOnExpiry(true)
.expireGroupsUponCompletion(true)
.expireGroupsUponTimeout(true)
.correlationStrategy(message -> true)
.releaseStrategy(message -> false)
.poller(pollerFactory -> pollerFactory.fixedRate(1))
)
.channel("threadBreaker")
.handle(interfaceHandler, "handle", spec -> spec.poller(meta -> meta.fixedRate(1)))
.channel("interfaceAggregatorFlowChannel")
.get();
}
private boolean haveInstance(MessageGroup messageGroup, Class clazz) {
for (Message<?> message : messageGroup.getMessages()) {
if (clazz.isInstance(message.getPayload())) {
return true;
}
}
return false;
}
}
