| /* |
| * Copyright (C) 2011, Google Inc. |
| * and other copyright owners as documented in the project's IP log. |
| * |
| * This program and the accompanying materials are made available |
| * under the terms of the Eclipse Distribution License v1.0 which |
| * accompanies this distribution, is reproduced below, and is |
| * available at http://www.eclipse.org/org/documents/edl-v10.php |
| * |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or |
| * without modification, are permitted provided that the following |
| * conditions are met: |
| * |
| * - Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * |
| * - Redistributions in binary form must reproduce the above |
| * copyright notice, this list of conditions and the following |
| * disclaimer in the documentation and/or other materials provided |
| * with the distribution. |
| * |
| * - Neither the name of the Eclipse Foundation, Inc. nor the |
| * names of its contributors may be used to endorse or promote |
| * products derived from this software without specific prior |
| * written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND |
| * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, |
| * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
| * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR |
| * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
| * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER |
| * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, |
| * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF |
| * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| package org.eclipse.jgit.internal.storage.dfs; |
| |
| import java.io.IOException; |
| import java.nio.channels.ReadableByteChannel; |
| |
| /** Readable random access byte channel from a file. */ |
| public interface ReadableChannel extends ReadableByteChannel { |
| /** |
| * Get the current position of the channel. |
| * |
| * @return r current offset. |
| * @throws IOException |
| * the channel's current position cannot be obtained. |
| */ |
| public long position() throws IOException; |
| |
| /** |
| * Seek the current position of the channel to a new offset. |
| * |
| * @param newPosition |
| * position to move the channel to. The next read will start from |
| * here. This should be a multiple of the {@link #blockSize()}. |
| * @throws IOException |
| * the position cannot be updated. This may be because the |
| * channel only supports block aligned IO and the current |
| * position is not block aligned. |
| */ |
| public void position(long newPosition) throws IOException; |
| |
| /** |
| * Get the total size of the channel. |
| * <p> |
| * Prior to reading from a channel the size might not yet be known. |
| * Implementors may return -1 until after the first read method call. Once a |
| * read has been completed, the underlying file size should be available. |
| * |
| * @return r total size of the channel; -1 if not yet available. |
| * @throws IOException |
| * the size cannot be determined. |
| */ |
| public long size() throws IOException; |
| |
| /** |
| * Get the recommended alignment for reads. |
| * <p> |
| * Starting a read at multiples of the blockSize is more efficient than |
| * starting a read at any other position. If 0 or -1 the channel does not |
| * have any specific block size recommendation. |
| * <p> |
| * Channels should not recommend large block sizes. Sizes up to 1-4 MiB may |
| * be reasonable, but sizes above that may be horribly inefficient. The |
| * {@link DfsBlockCache} favors the alignment suggested by the channel |
| * rather than the configured size under the assumption that reads are very |
| * expensive and the channel knows what size is best to access it with. |
| * |
| * @return recommended alignment size for randomly positioned reads. Does |
| * not need to be a power of 2. |
| */ |
| public int blockSize(); |
| |
| /** |
| * Recommend the channel maintain a read-ahead buffer. |
| * <p> |
| * A read-ahead buffer of approximately {@code bufferSize} in bytes may be |
| * allocated and used by the channel to smooth out latency for read. |
| * <p> |
| * Callers can continue to read in smaller than {@code bufferSize} chunks. |
| * With read-ahead buffering enabled read latency may fluctuate in a pattern |
| * of one slower read followed by {@code (bufferSize / readSize) - 1} fast |
| * reads satisfied by the read-ahead buffer. When summed up overall time to |
| * read the same contiguous range should be lower than if read-ahead was not |
| * enabled, as the implementation can combine reads to increase throughput. |
| * <p> |
| * To avoid unnecessary IO callers should only enable read-ahead if the |
| * majority of the channel will be accessed in order. |
| * <p> |
| * Implementations may chose to read-ahead using asynchronous APIs or |
| * background threads, or may simply aggregate reads using a buffer. |
| * <p> |
| * This read ahead stays in effect until the channel is closed or the buffer |
| * size is set to 0. |
| * |
| * @param bufferSize |
| * requested size of the read ahead buffer, in bytes. |
| * @throws IOException |
| * if the read ahead cannot be adjusted. |
| */ |
| public void setReadAheadBytes(int bufferSize) throws IOException; |
| } |