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/**
* Copyright 2015 Netflix, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.netflix.hystrix.collapser;
import java.util.Collection;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicBoolean;
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.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
* @param
* @param
*/
public class RequestBatch {
private static final Logger logger = LoggerFactory.getLogger(RequestBatch.class);
private final HystrixCollapserBridge commandCollapser;
private final int maxBatchSize;
private final AtomicBoolean batchStarted = new AtomicBoolean();
private final ConcurrentMap> argumentMap =
new ConcurrentHashMap>();
private final HystrixCollapserProperties properties;
private ReentrantReadWriteLock batchLock = new ReentrantReadWriteLock();
public RequestBatch(HystrixCollapserProperties properties, HystrixCollapserBridge commandCollapser, int maxBatchSize) {
this.properties = properties;
this.commandCollapser = commandCollapser;
this.maxBatchSize = maxBatchSize;
}
/**
* @return Observable if offer accepted, null if batch is full, already started or completed
*/
public Observable 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;
}
if (argumentMap.size() >= maxBatchSize) {
return null;
} else {
CollapsedRequestSubject collapsedRequest =
new CollapsedRequestSubject(arg, this);
final CollapsedRequestSubject existing = (CollapsedRequestSubject) argumentMap.putIfAbsent(arg, collapsedRequest);
/**
* If the argument already exists in the batch, then there are 2 options:
* A) If request caching is ON (the default): only keep 1 argument in the batch and let all responses
* be hooked up to that argument
* B) If request caching is OFF: return an error to all duplicate argument requests
*
* This maintains the invariant that each batch has no duplicate arguments. This prevents the impossible
* logic (in a user-provided mapResponseToRequests for HystrixCollapser and the internals of HystrixObservableCollapser)
* of trying to figure out which argument of a set of duplicates should get attached to a response.
*
* See https://github.com/Netflix/Hystrix/pull/1176 for further discussion.
*/
if (existing != null) {
boolean requestCachingEnabled = properties.requestCacheEnabled().get();
if (requestCachingEnabled) {
return existing.toObservable();
} else {
return Observable.error(new IllegalArgumentException("Duplicate argument in collapser batch : [" + arg + "] This is not supported. Please turn request-caching on for HystrixCollapser:" + commandCollapser.getCollapserKey().name() + " or prevent duplicates from making it into the batch!"));
}
} else {
return collapsedRequest.toObservable();
}
}
} finally {
batchLock.readLock().unlock();
}
} else {
return null;
}
}
/**
* Best-effort attempt to remove an argument from a batch. This may get invoked when a cancellation occurs somewhere downstream.
* This method finds the argument in the batch, and removes it.
*
* @param arg argument to remove from batch
*/
/* package-private */ void remove(RequestArgumentType arg) {
if (batchStarted.get()) {
//nothing we can do
return;
}
if (batchLock.readLock().tryLock()) {
try {
/* double-check now that we have the lock - if the batch is started, deleting is useless */
if (batchStarted.get()) {
return;
}
argumentMap.remove(arg);
} finally {
batchLock.readLock().unlock();
}
}
}
/**
* Collapsed requests are triggered for batch execution and the array of arguments is passed in.
*
* IMPORTANT IMPLEMENTATION DETAILS => The expected contract (responsibilities) of this method implementation is:
*
*
* - Do NOT block => Do the work on a separate worker thread. Do not perform inline otherwise it will block other requests.
* - Set ALL CollapsedRequest response values => Set the response values T on each CollapsedRequest
, 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.
*
*
*/
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'/'remove' threads to finish before executing the batch so 'requests' is complete */
batchLock.writeLock().lock();
try {
// shard batches
Collection>> shards = commandCollapser.shardRequests(argumentMap.values());
// for each shard execute its requests
for (final Collection> shardRequests : shards) {
try {
// create a new command to handle this batch of requests
Observable o = commandCollapser.createObservableCommand(shardRequests);
commandCollapser.mapResponseToRequests(o, shardRequests).doOnError(new Action1() {
/**
* 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;
if (e instanceof Exception) {
ee = (Exception) e;
} else {
ee = new RuntimeException("Throwable caught while executing batch and mapping responses.", e);
}
logger.debug("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 request : argumentMap.values()) {
try {
((CollapsedRequestSubject) 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
Exception e = null;
for (CollapsedRequest request : shardRequests) {
try {
e = ((CollapsedRequestSubject) request).setExceptionIfResponseNotReceived(e,"No response set by " + commandCollapser.getCollapserKey().name() + " 'mapResponseToRequests' implementation.");
} 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 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 request : argumentMap.values()) {
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 (argumentMap.size() > 0) {
logger.warn("Requests still exist in queue but will not be executed due to RequestCollapser shutdown: " + argumentMap.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 request : argumentMap.values()) {
try {
((CollapsedRequestSubject) 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();
}
}
}
public int getSize() {
return argumentMap.size();
}
}