| // Protocol Buffers - Google's data interchange format |
| // Copyright 2008 Google Inc. All rights reserved. |
| // https://developers.google.com/protocol-buffers/ |
| // |
| // 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 Google 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 com.google.protobuf; |
| |
| import static java.lang.Math.max; |
| import static java.lang.Math.min; |
| |
| import java.io.FileOutputStream; |
| import java.io.IOException; |
| import java.io.OutputStream; |
| import java.lang.ref.SoftReference; |
| import java.nio.ByteBuffer; |
| |
| /** |
| * Utility class to provide efficient writing of {@link ByteBuffer}s to {@link OutputStream}s. |
| */ |
| final class ByteBufferWriter { |
| private ByteBufferWriter() {} |
| |
| /** |
| * Minimum size for a cached buffer. This prevents us from allocating buffers that are too |
| * small to be easily reused. |
| */ |
| // TODO(nathanmittler): tune this property or allow configuration? |
| private static final int MIN_CACHED_BUFFER_SIZE = 1024; |
| |
| /** |
| * Maximum size for a cached buffer. If a larger buffer is required, it will be allocated |
| * but not cached. |
| */ |
| // TODO(nathanmittler): tune this property or allow configuration? |
| private static final int MAX_CACHED_BUFFER_SIZE = 16 * 1024; |
| |
| /** |
| * The fraction of the requested buffer size under which the buffer will be reallocated. |
| */ |
| // TODO(nathanmittler): tune this property or allow configuration? |
| private static final float BUFFER_REALLOCATION_THRESHOLD = 0.5f; |
| |
| /** |
| * Keeping a soft reference to a thread-local buffer. This buffer is used for writing a |
| * {@link ByteBuffer} to an {@link OutputStream} when no zero-copy alternative was available. |
| * Using a "soft" reference since VMs may keep this reference around longer than "weak" |
| * (e.g. HotSpot will maintain soft references until memory pressure warrants collection). |
| */ |
| private static final ThreadLocal<SoftReference<byte[]>> BUFFER = |
| new ThreadLocal<SoftReference<byte[]>>(); |
| |
| /** |
| * For testing purposes only. Clears the cached buffer to force a new allocation on the next |
| * invocation. |
| */ |
| static void clearCachedBuffer() { |
| BUFFER.set(null); |
| } |
| |
| /** |
| * Writes the remaining content of the buffer to the given stream. The buffer {@code position} |
| * will remain unchanged by this method. |
| */ |
| static void write(ByteBuffer buffer, OutputStream output) throws IOException { |
| final int initialPos = buffer.position(); |
| try { |
| if (buffer.hasArray()) { |
| // Optimized write for array-backed buffers. |
| // Note that we're taking the risk that a malicious OutputStream could modify the array. |
| output.write(buffer.array(), buffer.arrayOffset() + buffer.position(), buffer.remaining()); |
| } else if (output instanceof FileOutputStream) { |
| // Use a channel to write out the ByteBuffer. This will automatically empty the buffer. |
| ((FileOutputStream) output).getChannel().write(buffer); |
| } else { |
| // Read all of the data from the buffer to an array. |
| // TODO(nathanmittler): Consider performance improvements for other "known" stream types. |
| final byte[] array = getOrCreateBuffer(buffer.remaining()); |
| while (buffer.hasRemaining()) { |
| int length = min(buffer.remaining(), array.length); |
| buffer.get(array, 0, length); |
| output.write(array, 0, length); |
| } |
| } |
| } finally { |
| // Restore the initial position. |
| buffer.position(initialPos); |
| } |
| } |
| |
| private static byte[] getOrCreateBuffer(int requestedSize) { |
| requestedSize = max(requestedSize, MIN_CACHED_BUFFER_SIZE); |
| |
| byte[] buffer = getBuffer(); |
| // Only allocate if we need to. |
| if (buffer == null || needToReallocate(requestedSize, buffer.length)) { |
| buffer = new byte[requestedSize]; |
| |
| // Only cache the buffer if it's not too big. |
| if (requestedSize <= MAX_CACHED_BUFFER_SIZE) { |
| setBuffer(buffer); |
| } |
| } |
| return buffer; |
| } |
| |
| private static boolean needToReallocate(int requestedSize, int bufferLength) { |
| // First check against just the requested length to avoid the multiply. |
| return bufferLength < requestedSize |
| && bufferLength < requestedSize * BUFFER_REALLOCATION_THRESHOLD; |
| } |
| |
| private static byte[] getBuffer() { |
| SoftReference<byte[]> sr = BUFFER.get(); |
| return sr == null ? null : sr.get(); |
| } |
| |
| private static void setBuffer(byte[] value) { |
| BUFFER.set(new SoftReference<byte[]>(value)); |
| } |
| } |