AsyncStreamingOutputPlus.java
/*
* 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.cassandra.net;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.FileChannel;
import com.google.common.annotations.VisibleForTesting;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import io.netty.channel.Channel;
import io.netty.channel.ChannelPromise;
import io.netty.channel.DefaultFileRegion;
import io.netty.channel.FileRegion;
import io.netty.channel.WriteBufferWaterMark;
import io.netty.handler.ssl.SslHandler;
import org.apache.cassandra.io.compress.BufferType;
import org.apache.cassandra.io.util.DataOutputStreamPlus;
import org.apache.cassandra.net.SharedDefaultFileRegion.SharedFileChannel;
import org.apache.cassandra.streaming.StreamingDataOutputPlus;
import org.apache.cassandra.utils.memory.BufferPool;
import org.apache.cassandra.utils.memory.BufferPools;
import static java.lang.Math.min;
/**
* A {@link DataOutputStreamPlus} that writes ASYNCHRONOUSLY to a Netty Channel.
*
* The close() and flush() methods synchronously wait for pending writes, and will propagate any exceptions
* encountered in writing them to the wire.
*
* The correctness of this class depends on the ChannelPromise we create against a Channel always being completed,
* which appears to be a guarantee provided by Netty so long as the event loop is running.
*/
public class AsyncStreamingOutputPlus extends AsyncChannelOutputPlus implements StreamingDataOutputPlus
{
private static final Logger logger = LoggerFactory.getLogger(AsyncStreamingOutputPlus.class);
private final BufferPool bufferPool = BufferPools.forNetworking();
final int defaultLowWaterMark;
final int defaultHighWaterMark;
public AsyncStreamingOutputPlus(Channel channel)
{
super(channel);
WriteBufferWaterMark waterMark = channel.config().getWriteBufferWaterMark();
this.defaultLowWaterMark = waterMark.low();
this.defaultHighWaterMark = waterMark.high();
allocateBuffer();
}
private void allocateBuffer()
{
// this buffer is only used for small quantities of data
buffer = bufferPool.getAtLeast(8 << 10, BufferType.OFF_HEAP);
}
@Override
protected void doFlush(int count) throws IOException
{
if (!channel.isOpen())
throw new ClosedChannelException();
// flush the current backing write buffer only if there's any pending data
ByteBuffer flush = buffer;
if (flush.position() == 0)
return;
flush.flip();
int byteCount = flush.limit();
ChannelPromise promise = beginFlush(byteCount, 0, Integer.MAX_VALUE);
channel.writeAndFlush(GlobalBufferPoolAllocator.wrap(flush), promise);
allocateBuffer();
}
public long position()
{
return flushed() + buffer.position();
}
/**
* Provide a lambda that can request a buffer of suitable size, then fill the buffer and have
* that buffer written and flushed to the underlying channel, without having to handle buffer
* allocation, lifetime or cleanup, including in case of exceptions.
* <p>
* Any exception thrown by the Write will be propagated to the caller, after any buffer is cleaned up.
*/
public int writeToChannel(Write write, RateLimiter limiter) throws IOException
{
doFlush(0);
class Holder
{
ChannelPromise promise;
ByteBuffer buffer;
}
Holder holder = new Holder();
try
{
write.write(size -> {
if (holder.buffer != null)
throw new IllegalStateException("Can only allocate one ByteBuffer");
limiter.acquire(size);
holder.promise = beginFlush(size, defaultLowWaterMark, defaultHighWaterMark);
holder.buffer = bufferPool.get(size, BufferType.OFF_HEAP);
return holder.buffer;
});
}
catch (Throwable t)
{
// we don't currently support cancelling the flush, but at this point we are recoverable if we want
if (holder.buffer != null)
bufferPool.put(holder.buffer);
if (holder.promise != null)
holder.promise.tryFailure(t);
throw t;
}
ByteBuffer buffer = holder.buffer;
bufferPool.putUnusedPortion(buffer);
int length = buffer.limit();
channel.writeAndFlush(GlobalBufferPoolAllocator.wrap(buffer), holder.promise);
return length;
}
/**
* Writes all data in file channel to stream: <br>
* * For zero-copy-streaming, 1MiB at a time, with at most 2MiB in flight at once. <br>
* * For streaming with SSL, 64KiB at a time, with at most 32+64KiB (default low water mark + batch size) in flight. <br>
* <p>
* This method takes ownership of the provided {@link FileChannel}.
* <p>
* WARNING: this method blocks only for permission to write to the netty channel; it exits before
* the {@link FileRegion}(zero-copy) or {@link ByteBuffer}(ssl) is flushed to the network.
*/
public long writeFileToChannel(FileChannel file, RateLimiter limiter) throws IOException
{
if (channel.pipeline().get(SslHandler.class) != null)
// each batch is loaded into ByteBuffer, 64KiB is more BufferPool friendly.
return writeFileToChannel(file, limiter, 1 << 16);
else
// write files in 1MiB chunks, since there may be blocking work performed to fetch it from disk,
// the data is never brought in process and is gated by the wire anyway
return writeFileToChannelZeroCopy(file, limiter, 1 << 20, 1 << 20, 2 << 20);
}
@VisibleForTesting
long writeFileToChannel(FileChannel fc, RateLimiter limiter, int batchSize) throws IOException
{
final long length = fc.size();
long bytesTransferred = 0;
try
{
while (bytesTransferred < length)
{
int toWrite = (int) min(batchSize, length - bytesTransferred);
final long position = bytesTransferred;
writeToChannel(bufferSupplier -> {
ByteBuffer outBuffer = bufferSupplier.get(toWrite);
long read = fc.read(outBuffer, position);
if (read != toWrite)
throw new IOException(String.format("could not read required number of bytes from " +
"file to be streamed: read %d bytes, wanted %d bytes",
read, toWrite));
outBuffer.flip();
}, limiter);
if (logger.isTraceEnabled())
logger.trace("Writing {} bytes at position {} of {}", toWrite, bytesTransferred, length);
bytesTransferred += toWrite;
}
}
finally
{
// we don't need to wait until byte buffer is flushed by netty
fc.close();
}
return bytesTransferred;
}
@VisibleForTesting
long writeFileToChannelZeroCopy(FileChannel file, RateLimiter limiter, int batchSize, int lowWaterMark, int highWaterMark) throws IOException
{
if (!limiter.isRateLimited())
return writeFileToChannelZeroCopyUnthrottled(file);
else
return writeFileToChannelZeroCopyThrottled(file, limiter, batchSize, lowWaterMark, highWaterMark);
}
private long writeFileToChannelZeroCopyUnthrottled(FileChannel file) throws IOException
{
final long length = file.size();
if (logger.isTraceEnabled())
logger.trace("Writing {} bytes", length);
ChannelPromise promise = beginFlush(length, 0, length);
final DefaultFileRegion defaultFileRegion = new DefaultFileRegion(file, 0, length);
channel.writeAndFlush(defaultFileRegion, promise);
return length;
}
private long writeFileToChannelZeroCopyThrottled(FileChannel file, RateLimiter limiter, int batchSize, int lowWaterMark, int highWaterMark) throws IOException
{
final long length = file.size();
long bytesTransferred = 0;
final SharedFileChannel sharedFile = SharedDefaultFileRegion.share(file);
try
{
int toWrite;
while (bytesTransferred < length)
{
toWrite = (int) min(batchSize, length - bytesTransferred);
limiter.acquire(toWrite);
ChannelPromise promise = beginFlush(toWrite, lowWaterMark, highWaterMark);
SharedDefaultFileRegion fileRegion = new SharedDefaultFileRegion(sharedFile, bytesTransferred, toWrite);
channel.writeAndFlush(fileRegion, promise);
if (logger.isTraceEnabled())
logger.trace("Writing {} bytes at position {} of {}", toWrite, bytesTransferred, length);
bytesTransferred += toWrite;
}
return bytesTransferred;
}
finally
{
sharedFile.release();
}
}
/**
* Discard any buffered data, and the buffers that contain it.
* May be invoked instead of {@link #close()} if we terminate exceptionally.
*/
public void discard()
{
if (buffer != null)
{
bufferPool.put(buffer);
buffer = null;
}
}
}