org.apache.flume.Channel Maven / Gradle / Ivy
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.flume;
import org.apache.flume.annotations.InterfaceAudience;
import org.apache.flume.annotations.InterfaceStability;
import org.apache.flume.lifecycle.LifecycleAware;
/**
*
* A channel connects a {@link Source} to a {@link Sink}. The source
* acts as producer while the sink acts as a consumer of events. The channel
* itself is the buffer between the two.
*
*
* A channel exposes a {@link Transaction} interface that can be used by
* its clients to ensure atomic {@linkplain #put(Event) put} and
* {@linkplain #take() take} semantics.
* This is necessary to guarantee single hop reliability between agents.
* For instance, a source will successfully produce an {@linkplain Event event}
* if and only if that event can be committed to the source's associated
* channel. Similarly, a sink will consume an event if and
* only if its respective endpoint can accept the event. The
* extent of transaction support varies for different channel implementations
* ranging from strong to best-effort semantics.
*
*
* Channels are associated with unique {@linkplain NamedComponent names} that
* can be used for separating configuration and working namespaces.
*
*
* Channels must be thread safe, protecting any internal invariants as no
* guarantees are given as to when and by how many sources/sinks they may
* be simultaneously accessed by.
*
*
* @see org.apache.flume.Source
* @see org.apache.flume.Sink
* @see org.apache.flume.Transaction
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public interface Channel extends LifecycleAware, NamedComponent {
/**
* Puts the given event into the channel.
* Note: This method must be invoked within an active
* {@link Transaction} boundary. Failure to do so can lead to unpredictable
* results.
* @param event the event to transport.
* @throws ChannelException in case this operation fails.
* @see org.apache.flume.Transaction#begin()
*/
public void put(Event event) throws ChannelException;
/**
* Returns the next event from the channel if available. If the channel
* does not have any events available, this method must return {@code null}.
*
* Note: This method must be invoked within an active
* {@link Transaction} boundary. Failure to do so can lead to unpredictable
* results.
* @return the next available event or {@code null} if no events are
* available.
* @throws ChannelException in case this operation fails.
* @see org.apache.flume.Transaction#begin()
*/
public Event take() throws ChannelException;
/**
* @return the transaction instance associated with this channel.
*/
public Transaction getTransaction();
}