// 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
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// 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.IOException;
import java.io.OutputStream;
import java.lang.ref.SoftReference;
import java.lang.reflect.Field;
import java.nio.ByteBuffer;
import java.nio.channels.WritableByteChannel;
/**
* 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[]>>();
/**
* This is a hack for GAE, where {@code FileOutputStream} is unavailable.
*/
private static final Class<?> FILE_OUTPUT_STREAM_CLASS = safeGetClass("java.io.FileOutputStream");
private static final long CHANNEL_FIELD_OFFSET = getChannelFieldOffset(FILE_OUTPUT_STREAM_CLASS);
/**
* 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 (!writeToChannel(buffer, output)){
// 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));
}
private static boolean writeToChannel(ByteBuffer buffer, OutputStream output) throws IOException {
if (CHANNEL_FIELD_OFFSET >= 0 && FILE_OUTPUT_STREAM_CLASS.isInstance(output)) {
// Use a channel to write out the ByteBuffer. This will automatically empty the buffer.
WritableByteChannel channel = null;
try {
channel = (WritableByteChannel) UnsafeUtil.getObject(output, CHANNEL_FIELD_OFFSET);
} catch (ClassCastException e) {
// Absorb.
}
if (channel != null) {
channel.write(buffer);
return true;
}
}
return false;
}
private static Class<?> safeGetClass(String className) {
try {
return Class.forName(className);
} catch (ClassNotFoundException e) {
return null;
}
}
private static long getChannelFieldOffset(Class<?> clazz) {
try {
if (clazz != null && UnsafeUtil.hasUnsafeArrayOperations()) {
Field field = clazz.getDeclaredField("channel");
return UnsafeUtil.objectFieldOffset(field);
}
} catch (Throwable e) {
// Absorb
}
return -1;
}
}