/**
* Copyright 2014 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 rx.internal.operators;
import java.util.concurrent.atomic.
AtomicLong;
import rx.*;
import rx.
Observable.
Operator;
import rx.plugins.
RxJavaHooks;
/**
* An {@code Observable} that emits the first {@code num} items emitted by the source {@code Observable}.
* <p>
* <img width="640" height="305" src="https://raw.githubusercontent.com/wiki/ReactiveX/RxJava/images/rx-operators/take.png" alt="" />
* <p>
* You can choose to pay attention only to the first {@code num} items emitted by an {@code Observable} by using
* the {@code take} operator. This operator returns an {@code Observable} that will invoke a subscriber's
* {@link Subscriber#onNext onNext} function a maximum of {@code num} times before invoking
* {@link Subscriber#onCompleted onCompleted}.
* @param <T> the value type
*/
public final class
OperatorTake<T> implements
Operator<T, T> {
final int
limit;
public
OperatorTake(int
limit) {
if (
limit < 0) {
throw new
IllegalArgumentException("limit >= 0 required but it was " +
limit);
}
this.
limit =
limit;
}
@
Override
public
Subscriber<? super T>
call(final
Subscriber<? super T>
child) {
final
Subscriber<T>
parent = new
Subscriber<T>() {
int
count;
boolean
completed;
@
Override
public void
onCompleted() {
if (!
completed) {
completed = true;
child.
onCompleted();
}
}
@
Override
public void
onError(
Throwable e) {
if (!
completed) {
completed = true;
try {
child.
onError(
e);
} finally {
unsubscribe();
}
} else {
RxJavaHooks.
onError(
e);
}
}
@
Override
public void
onNext(T
i) {
if (!
isUnsubscribed() &&
count++ <
limit) {
boolean
stop =
count ==
limit;
child.
onNext(
i);
if (
stop && !
completed) {
completed = true;
try {
child.
onCompleted();
} finally {
unsubscribe();
}
}
}
}
/**
* We want to adjust the requested values based on the `take` count.
*/
@
Override
public void
setProducer(final
Producer producer) {
child.
setProducer(new
Producer() {
// keeps track of requests up to maximum of `limit`
final
AtomicLong requested = new
AtomicLong(0);
@
Override
public void
request(long
n) {
if (
n > 0 && !
completed) {
// because requests may happen concurrently use a CAS loop to
// ensure we only request as much as needed, no more no less
while (true) {
long
r =
requested.
get();
long
c =
Math.
min(
n,
limit -
r);
if (
c == 0) {
break;
} else if (
requested.
compareAndSet(
r,
r +
c)) {
producer.
request(
c);
break;
}
}
}
}
});
}
};
if (
limit == 0) {
child.
onCompleted();
parent.
unsubscribe();
}
/*
* We decouple the parent and child subscription so there can be multiple take() in a chain such as for
* the groupBy Observer use case where you may take(1) on groups and take(20) on the children.
*
* Thus, we only unsubscribe UPWARDS to the parent and an onComplete DOWNSTREAM.
*
* However, if we receive an unsubscribe from the child we still want to propagate it upwards so we
* register 'parent' with 'child'
*/
child.
add(
parent);
return
parent;
}
}