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/**
* Copyright 2016 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;
import rx.exceptions.MissingBackpressureException;
/**
* Generic strategy and default implementations to deal with backpressure buffer overflows.
*
* @since 1.3
*/
public final class BackpressureOverflow {
private BackpressureOverflow() {
throw new IllegalStateException("No instances!");
}
/**
* Signal a MissingBackressureException due to lack of requests.
*/
public static final BackpressureOverflow.Strategy ON_OVERFLOW_ERROR = Error.INSTANCE;
/**
* By default, signal a MissingBackressureException due to lack of requests.
*/
public static final BackpressureOverflow.Strategy ON_OVERFLOW_DEFAULT = ON_OVERFLOW_ERROR;
/**
* Drop the oldest value in the buffer.
*/
public static final BackpressureOverflow.Strategy ON_OVERFLOW_DROP_OLDEST = DropOldest.INSTANCE;
/**
* Drop the latest value.
*/
public static final BackpressureOverflow.Strategy ON_OVERFLOW_DROP_LATEST = DropLatest.INSTANCE;
/**
* Represents a callback called when a value is about to be dropped
* due to lack of downstream requests.
*/
public interface Strategy {
/**
* Whether the Backpressure manager should attempt to drop the oldest item, or simply
* drop the item currently causing backpressure.
*
* @return true to request drop of the oldest item, false to drop the newest.
* @throws MissingBackpressureException if the strategy should signal MissingBackpressureException
*/
boolean mayAttemptDrop() throws MissingBackpressureException;
}
/**
* Drop oldest items from the buffer making room for newer ones.
*/
static final class DropOldest implements BackpressureOverflow.Strategy {
static final DropOldest INSTANCE = new DropOldest();
private DropOldest() { }
@Override
public boolean mayAttemptDrop() {
return true;
}
}
/**
* Drop most recent items, but not {@code onError} nor unsubscribe from source
* (as {code OperatorOnBackpressureDrop}).
*/
static final class DropLatest implements BackpressureOverflow.Strategy {
static final DropLatest INSTANCE = new DropLatest();
private DropLatest() { }
@Override
public boolean mayAttemptDrop() {
return false;
}
}
/**
* {@code onError} a MissingBackpressureException and unsubscribe from source.
*/
static final class Error implements BackpressureOverflow.Strategy {
static final Error INSTANCE = new Error();
private Error() { }
@Override
public boolean mayAttemptDrop() throws MissingBackpressureException {
throw new MissingBackpressureException("Overflowed buffer");
}
}
}