001/* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, 013 * software distributed under the License is distributed on an 014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 015 * KIND, either express or implied. See the License for the 016 * specific language governing permissions and limitations 017 * under the License. 018 */ 019package org.apache.reef.io.checkpoint; 020 021import java.io.IOException; 022import java.nio.channels.ReadableByteChannel; 023import java.nio.channels.WritableByteChannel; 024 025/** 026 * The CheckpointService provides a simple API to store and retrieve the state of a task. 027 * <p> 028 * Checkpoints are assumed to be atomic, single-writer, write-once, multiple-readers, ready-many type of objects. 029 * 030 * To ensure this, any implementation of this interface must. 031 * 1) Return a CheckpointID to a client only 032 * upon the successful {@link #commit(CheckpointWriteChannel) commit} of the checkpoint. 033 * 2) Prevent any checkpoint from being re-opened for writes. 034 * <p> 035 * Non-functional properties such as durability, availability, compression, garbage collection, and 036 * quotas are left to the implementation. 037 * <p> 038 * This API is envisioned as the basic building block for a checkpoint service, on top of which richer 039 * interfaces can be layered (e.g., frameworks providing object-serialization, checkpoint metadata and 040 * provenance, etc.) 041 */ 042public interface CheckpointService { 043 044 /** 045 * Creates a checkpoint and provides a channel to write to it. 046 * The name/location of the checkpoint are unknown to the user as of this time, in fact, 047 * the CheckpointID is not released to the user until {@link #commit(CheckpointWriteChannel) commit} is called. 048 * This makes enforcing atomicity of writes easy. 049 * 050 * @return a CheckpointWriteChannel that can be used to write to the checkpoint 051 * @throws IOException 052 * @throws InterruptedException 053 */ 054 CheckpointWriteChannel create() throws IOException, InterruptedException; 055 056 /** 057 * Closes an existing checkpoint for writes and returns the CheckpointID that can be later 058 * used to get the read-only access to this checkpoint. 059 * 060 * Implementation is supposed to return the CheckpointID to the caller only on the 061 * successful completion of checkpoint to guarantee atomicity of the checkpoint. 062 * 063 * @param channel the CheckpointWriteChannel to commit 064 * @return a CheckpointID 065 * @throws IOException 066 * @throws InterruptedException 067 */ 068 CheckpointID commit(CheckpointWriteChannel channel) throws IOException, InterruptedException; 069 070 /** 071 * Aborts the current checkpoint. Garbage collection choices are 072 * left to the implementation. The CheckpointID is neither generated nor released to the 073 * client so the checkpoint is not accessible. 074 * 075 * @param channel the CheckpointWriteChannel to abort 076 * @throws IOException 077 * @throws InterruptedException 078 */ 079 void abort(CheckpointWriteChannel channel) throws IOException, InterruptedException; 080 081 /** 082 * Returns a reading channel to a checkpoint identified by the CheckpointID. 083 * 084 * @param checkpointId CheckpointID for the checkpoint to be opened 085 * @return a CheckpointReadChannel 086 * @throws IOException 087 * @throws InterruptedException 088 */ 089 CheckpointReadChannel open(CheckpointID checkpointId) throws IOException, InterruptedException; 090 091 /** 092 * Discards an existing checkpoint identified by its CheckpointID. 093 * 094 * @param checkpointId CheckpointID for the checkpoint to be deleted 095 * @return a boolean confirming success of the deletion 096 * @throws IOException 097 * @throws InterruptedException 098 */ 099 boolean delete(CheckpointID checkpointId) throws IOException, InterruptedException; 100 101 /** 102 * A channel to write to a checkpoint. 103 */ 104 interface CheckpointWriteChannel extends WritableByteChannel { 105 } 106 107 /** 108 * A channel to read from a checkpoint. 109 */ 110 interface CheckpointReadChannel extends ReadableByteChannel { 111 } 112}