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/*
* Copyright 2015 Ben Manes. All Rights Reserved.
*
* 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.github.benmanes.caffeine.cache;
import java.util.function.Consumer;
/**
* A multiple-producer / single-consumer buffer that rejects new elements if it is full or
* fails spuriously due to contention. Unlike a queue and stack, a buffer does not guarantee an
* ordering of elements in either FIFO or LIFO order.
*
* Beware that it is the responsibility of the caller to ensure that a consumer has exclusive read
* access to the buffer. This implementation does not include fail-fast behavior to guard
* against incorrect consumer usage.
*
* @param the type of elements maintained by this buffer
* @author [email protected] (Ben Manes)
*/
interface Buffer {
int FULL = 1; // if the buffer is full
int FAILED = -1; // if the CAS failed
int SUCCESS = 0; // if added
/** Returns a no-op implementation. */
@SuppressWarnings("unchecked")
static Buffer disabled() {
return (Buffer) DisabledBuffer.INSTANCE;
}
/**
* Inserts the specified element into this buffer if it is possible to do so immediately without
* violating capacity restrictions. The addition is allowed to fail spuriously if multiple
* threads insert concurrently.
*
* @param e the element to add
* @return {@code Buffer.SUCCESS}, {@code Buffer.FAILED}, or {@code Buffer.FULL}
*/
int offer(E e);
/**
* Drains the buffer, sending each element to the consumer for processing. The caller must ensure
* that a consumer has exclusive read access to the buffer.
*
* @param consumer the action to perform on each element
*/
void drainTo(Consumer consumer);
/**
* Returns the number of elements residing in the buffer.
*
* @return the number of elements in this buffer
*/
default long size() {
return writes() - reads();
}
/**
* Returns the number of elements that have been read from the buffer.
*
* @return the number of elements read from this buffer
*/
long reads();
/**
* Returns the number of elements that have been written to the buffer.
*
* @return the number of elements written to this buffer
*/
long writes();
}
enum DisabledBuffer implements Buffer