package com.netflix.hystrix.collapser;
import java.util.Collection;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import rx.Observable;
import rx.functions.Action0;
import rx.functions.Action1;
import com.netflix.hystrix.HystrixCollapser;
import com.netflix.hystrix.HystrixCollapser.CollapsedRequest;
import com.netflix.hystrix.HystrixCollapserProperties;
/**
* A batch of requests collapsed together by a RequestCollapser instance. When full or time has expired it will execute and stop accepting further submissions.
*
* @param <BatchReturnType>
* @param <ResponseType>
* @param <RequestArgumentType>
*/
public class RequestBatch<BatchReturnType, ResponseType, RequestArgumentType> {
private static final Logger logger = LoggerFactory.getLogger(HystrixCollapser.class);
private final HystrixCollapserBridge<BatchReturnType, ResponseType, RequestArgumentType> commandCollapser;
final ConcurrentLinkedQueue<CollapsedRequest<ResponseType, RequestArgumentType>> requests = new ConcurrentLinkedQueue<CollapsedRequest<ResponseType, RequestArgumentType>>();
// use AtomicInteger to count so we can use ConcurrentLinkedQueue instead of LinkedBlockingQueue
private final AtomicInteger count = new AtomicInteger(0);
private final int maxBatchSize;
private final AtomicBoolean batchStarted = new AtomicBoolean();
private ReentrantReadWriteLock batchLock = new ReentrantReadWriteLock();
public RequestBatch(HystrixCollapserProperties properties, HystrixCollapserBridge<BatchReturnType, ResponseType, RequestArgumentType> commandCollapser, int maxBatchSize) {
this.commandCollapser = commandCollapser;
this.maxBatchSize = maxBatchSize;
}
/**
* @return Observable if offer accepted, null if batch is full, already started or completed
*/
public Observable<ResponseType> offer(RequestArgumentType arg) {
/* short-cut - if the batch is started we reject the offer */
if (batchStarted.get()) {
return null;
}
/*
* The 'read' just means non-exclusive even though we are writing.
*/
if (batchLock.readLock().tryLock()) {
try {
/* double-check now that we have the lock - if the batch is started we reject the offer */
if (batchStarted.get()) {
return null;
}
int s = count.incrementAndGet();
if (s > maxBatchSize) {
return null;
} else {
CollapsedRequestObservableFunction<ResponseType, RequestArgumentType> f = new CollapsedRequestObservableFunction<ResponseType, RequestArgumentType>(arg);
requests.add(f);
return Observable.create(f);
}
} finally {
batchLock.readLock().unlock();
}
} else {
return null;
}
}
/**
* Collapsed requests are triggered for batch execution and the array of arguments is passed in.
* <p>
* IMPORTANT IMPLEMENTATION DETAILS => The expected contract (responsibilities) of this method implementation is:
* <p>
* <ul>
* <li>Do NOT block => Do the work on a separate worker thread. Do not perform inline otherwise it will block other requests.</li>
* <li>Set ALL CollapsedRequest response values => Set the response values T on each CollapsedRequest<T, R>, even if the response is NULL otherwise the user thread waiting on the response will
* think a response was never received and will either block indefinitely or will timeout while waiting.</li>
* </ul>
*
* @param args
*/
public void executeBatchIfNotAlreadyStarted() {
/*
* - check that we only execute once since there's multiple paths to do so (timer, waiting thread or max batch size hit)
* - close the gate so 'offer' can no longer be invoked and we turn those threads away so they create a new batch
*/
if (batchStarted.compareAndSet(false, true)) {
/* wait for 'offer' threads to finish before executing the batch so 'requests' is complete */
batchLock.writeLock().lock();
try {
// shard batches
Collection<Collection<CollapsedRequest<ResponseType, RequestArgumentType>>> shards = commandCollapser.shardRequests(requests);
// for each shard execute its requests
for (final Collection<CollapsedRequest<ResponseType, RequestArgumentType>> shardRequests : shards) {
try {
// create a new command to handle this batch of requests
Observable<BatchReturnType> o = commandCollapser.createObservableCommand(shardRequests);
commandCollapser.mapResponseToRequests(o, shardRequests).doOnError(new Action1<Throwable>() {
/**
* This handles failed completions
*/
@Override
public void call(Throwable e) {
// handle Throwable in case anything is thrown so we don't block Observers waiting for onError/onCompleted
Exception ee = null;
if (e instanceof Exception) {
ee = (Exception) e;
} else {
ee = new RuntimeException("Throwable caught while executing batch and mapping responses.", e);
}
logger.error("Exception mapping responses to requests.", e);
// if a failure occurs we want to pass that exception to all of the Futures that we've returned
for (CollapsedRequest<ResponseType, RequestArgumentType> request : requests) {
try {
((CollapsedRequestObservableFunction<ResponseType, RequestArgumentType>) request).setExceptionIfResponseNotReceived(ee);
} catch (IllegalStateException e2) {
// if we have partial responses set in mapResponseToRequests
// then we may get IllegalStateException as we loop over them
// so we'll log but continue to the rest
logger.error("Partial success of 'mapResponseToRequests' resulted in IllegalStateException while setting Exception. Continuing ... ", e2);
}
}
}
}).doOnCompleted(new Action0() {
/**
* This handles successful completions
*/
@Override
public void call() {
// check that all requests had setResponse or setException invoked in case 'mapResponseToRequests' was implemented poorly
IllegalStateException ie = new IllegalStateException("No response set by " + commandCollapser.getCollapserKey().name() + " 'mapResponseToRequests' implementation.");
for (CollapsedRequest<ResponseType, RequestArgumentType> request : shardRequests) {
try {
((CollapsedRequestObservableFunction<ResponseType, RequestArgumentType>) request).setExceptionIfResponseNotReceived(ie);
} catch (IllegalStateException e2) {
logger.debug("Partial success of 'mapResponseToRequests' resulted in IllegalStateException while setting 'No response set' Exception. Continuing ... ", e2);
}
}
}
}).subscribe();
} catch (Exception e) {
logger.error("Exception while creating and queueing command with batch.", e);
// if a failure occurs we want to pass that exception to all of the Futures that we've returned
for (CollapsedRequest<ResponseType, RequestArgumentType> request : shardRequests) {
try {
request.setException(e);
} catch (IllegalStateException e2) {
logger.debug("Failed trying to setException on CollapsedRequest", e2);
}
}
}
}
} catch (Exception e) {
logger.error("Exception while sharding requests.", e);
// same error handling as we do around the shards, but this is a wider net in case the shardRequest method fails
for (CollapsedRequest<ResponseType, RequestArgumentType> request : requests) {
try {
request.setException(e);
} catch (IllegalStateException e2) {
logger.debug("Failed trying to setException on CollapsedRequest", e2);
}
}
} finally {
batchLock.writeLock().unlock();
}
}
}
public void shutdown() {
// take the 'batchStarted' state so offers and execution will not be triggered elsewhere
if (batchStarted.compareAndSet(false, true)) {
// get the write lock so offers are synced with this (we don't really need to unlock as this is a one-shot deal to shutdown)
batchLock.writeLock().lock();
try {
// if we win the 'start' and once we have the lock we can now shut it down otherwise another thread will finish executing this batch
if (requests.size() > 0) {
logger.warn("Requests still exist in queue but will not be executed due to RequestCollapser shutdown: " + requests.size(), new IllegalStateException());
/*
* In the event that there is a concurrency bug or thread scheduling prevents the timer from ticking we need to handle this so the Future.get() calls do not block.
*
* I haven't been able to reproduce this use case on-demand but when stressing a machine saw this occur briefly right after the JVM paused (logs stopped scrolling).
*
* This safety-net just prevents the CollapsedRequestFutureImpl.get() from waiting on the CountDownLatch until its max timeout.
*/
for (CollapsedRequest<ResponseType, RequestArgumentType> request : requests) {
try {
((CollapsedRequestObservableFunction<ResponseType, RequestArgumentType>) request).setExceptionIfResponseNotReceived(new IllegalStateException("Requests not executed before shutdown."));
} catch (Exception e) {
logger.debug("Failed to setException on CollapsedRequestFutureImpl instances.", e);
}
/**
* https://github.com/Netflix/Hystrix/issues/78 Include more info when collapsed requests remain in queue
*/
logger.warn("Request still in queue but not be executed due to RequestCollapser shutdown. Argument => " + request.getArgument() + " Request Object => " + request, new IllegalStateException());
}
}
} finally {
batchLock.writeLock().unlock();
}
}
}
}