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Made HystrixCollapser.toObservable lazy by wrapping all work in an Observable.defer #1277

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Jul 11, 2016
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Made HystrixCollapser.toObservable lazy by wrapping all work in an Observable.defer #1277

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74 changes: 39 additions & 35 deletions hystrix-core/src/main/java/com/netflix/hystrix/HystrixCollapser.java
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@
import rx.Subscription;
import rx.functions.Action0;
import rx.functions.Action1;
import rx.functions.Func0;
import rx.schedulers.Schedulers;
import rx.subjects.ReplaySubject;

Expand Down Expand Up @@ -379,42 +380,45 @@ public Observable<ResponseType> toObservable() {
*/
public Observable<ResponseType> toObservable(Scheduler observeOn) {

final boolean isRequestCacheEnabled = getProperties().requestCacheEnabled().get();
final String cacheKey = getCacheKey();

/* try from cache first */
if (isRequestCacheEnabled) {
HystrixCachedObservable<ResponseType> fromCache = requestCache.get(cacheKey);
if (fromCache != null) {
metrics.markResponseFromCache();
return fromCache.toObservable();
}
}

final HystrixCollapser<BatchReturnType, ResponseType, RequestArgumentType> _self = this;

RequestCollapser<BatchReturnType, ResponseType, RequestArgumentType> requestCollapser = collapserFactory.getRequestCollapser(collapserInstanceWrapper);
Observable<ResponseType> response = requestCollapser.submitRequest(getRequestArgument());

if (isRequestCacheEnabled && cacheKey != null) {
/*
* A race can occur here with multiple threads queuing but only one will be cached.
* This means we can have some duplication of requests in a thread-race but we're okay
* with having some inefficiency in duplicate requests in the same batch
* and then subsequent requests will retrieve a previously cached Observable.
*
* If this is an issue we can make a lazy-future that gets set in the cache
* then only the winning 'put' will be invoked to actually call 'submitRequest'
*/
HystrixCachedObservable<ResponseType> toCache = HystrixCachedObservable.from(response);
HystrixCachedObservable<ResponseType> fromCache = requestCache.putIfAbsent(cacheKey, toCache);
if (fromCache == null) {
return toCache.toObservable();
} else {
return fromCache.toObservable();
return Observable.defer(new Func0<Observable<ResponseType>>() {
@Override
public Observable<ResponseType> call() {
final boolean isRequestCacheEnabled = getProperties().requestCacheEnabled().get();
final String cacheKey = getCacheKey();

/* try from cache first */
if (isRequestCacheEnabled) {
HystrixCachedObservable<ResponseType> fromCache = requestCache.get(cacheKey);
if (fromCache != null) {
metrics.markResponseFromCache();
return fromCache.toObservable();
}
}

RequestCollapser<BatchReturnType, ResponseType, RequestArgumentType> requestCollapser = collapserFactory.getRequestCollapser(collapserInstanceWrapper);
Observable<ResponseType> response = requestCollapser.submitRequest(getRequestArgument());

if (isRequestCacheEnabled && cacheKey != null) {
/*
* A race can occur here with multiple threads queuing but only one will be cached.
* This means we can have some duplication of requests in a thread-race but we're okay
* with having some inefficiency in duplicate requests in the same batch
* and then subsequent requests will retrieve a previously cached Observable.
*
* If this is an issue we can make a lazy-future that gets set in the cache
* then only the winning 'put' will be invoked to actually call 'submitRequest'
*/
HystrixCachedObservable<ResponseType> toCache = HystrixCachedObservable.from(response);
HystrixCachedObservable<ResponseType> fromCache = requestCache.putIfAbsent(cacheKey, toCache);
if (fromCache == null) {
return toCache.toObservable();
} else {
return fromCache.toObservable();
}
}
return response;
}
}
return response;
});
}

/**
Expand Down