/*
* 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.flink.runtime.io.disk.iomanager;
import java.io.EOFException;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.LinkedBlockingQueue;
import org.apache.flink.core.memory.MemorySegment;
import org.apache.flink.runtime.memorymanager.AbstractPagedInputView;
/**
* A {@link org.apache.flink.core.memory.DataInputView} that is backed by a
* {@link BlockChannelReader}, making it effectively a data input
* stream. The view reads it data in blocks from the underlying channel. The view can only read data that
* has been written by a {@link ChannelWriterOutputView}, due to block formatting.
*/
public class ChannelReaderInputView extends AbstractPagedInputView {
protected final BlockChannelReader reader; // the block reader that reads memory segments
protected int numRequestsRemaining; // the number of block requests remaining
private final int numSegments; // the number of memory segment the view works with
private final ArrayList<MemorySegment> freeMem; // memory gathered once the work is done
private boolean inLastBlock; // flag indicating whether the view is already in the last block
private boolean closed; // flag indicating whether the reader is closed
// --------------------------------------------------------------------------------------------
/**
* Creates a new channel reader that reads from the given channel until the last block
* (as marked by a {@link ChannelWriterOutputView}) is found.
*
* @param reader The reader that reads the data from disk back into memory.
* @param memory A list of memory segments that the reader uses for reading the data in. If the
* list contains more than one segment, the reader will asynchronously pre-fetch
* blocks ahead.
* @param waitForFirstBlock A flag indicating weather this constructor call should block
* until the first block has returned from the asynchronous I/O reader.
*
* @throws IOException Thrown, if the read requests for the first blocks fail to be
* served by the reader.
*/
public ChannelReaderInputView(BlockChannelReader reader, List<MemorySegment> memory, boolean waitForFirstBlock)
throws IOException
{
this(reader, memory, -1, waitForFirstBlock);
}
/**
* Creates a new channel reader that reads from the given channel, expecting a specified
* number of blocks in the channel.
* <p>
* WARNING: The reader will lock if the number of blocks given here is actually lower than
* the actual number of blocks in the channel.
*
* @param reader The reader that reads the data from disk back into memory.
* @param memory A list of memory segments that the reader uses for reading the data in. If the
* list contains more than one segment, the reader will asynchronously pre-fetch
* blocks ahead.
* @param numBlocks The number of blocks this channel will read. If this value is
* given, the reader avoids issuing pre-fetch requests for blocks
* beyond the channel size.
* @param waitForFirstBlock A flag indicating weather this constructor call should block
* until the first block has returned from the asynchronous I/O reader.
*
* @throws IOException Thrown, if the read requests for the first blocks fail to be
* served by the reader.
*/
public ChannelReaderInputView(BlockChannelReader reader, List<MemorySegment> memory,
int numBlocks, boolean waitForFirstBlock)
throws IOException
{
this(reader, memory, numBlocks, ChannelWriterOutputView.HEADER_LENGTH, waitForFirstBlock);
}
/**
* Non public constructor to allow subclasses to use this input view with different headers.
* <p>
* WARNING: The reader will lock if the number of blocks given here is actually lower than
* the actual number of blocks in the channel.
*
* @param reader The reader that reads the data from disk back into memory.
* @param memory A list of memory segments that the reader uses for reading the data in. If the
* list contains more than one segment, the reader will asynchronously pre-fetch
* blocks ahead.
* @param numBlocks The number of blocks this channel will read. If this value is
* given, the reader avoids issuing pre-fetch requests for blocks
* beyond the channel size.
* @param headerLen The length of the header assumed at the beginning of the block. Note that the
* {@link #nextSegment(org.apache.flink.core.memory.MemorySegment)} method assumes the default header length,
* so any subclass changing the header length should override that methods as well.
* @param waitForFirstBlock A flag indicating weather this constructor call should block
* until the first block has returned from the asynchronous I/O reader.
*
* @throws IOException
*/
ChannelReaderInputView(BlockChannelReader reader, List<MemorySegment> memory,
int numBlocks, int headerLen, boolean waitForFirstBlock)
throws IOException
{
super(headerLen);
if (reader == null || memory == null) {
throw new NullPointerException();
}
if (memory.isEmpty()) {
throw new IllegalArgumentException("Empty list of memory segments given.");
}
if (numBlocks < 1 && numBlocks != -1) {
throw new IllegalArgumentException("The number of blocks must be a positive number, or -1, if unknown.");
}
this.reader = reader;
this.numRequestsRemaining = numBlocks;
this.numSegments = memory.size();
this.freeMem = new ArrayList<MemorySegment>(this.numSegments);
for (int i = 0; i < memory.size(); i++) {
sendReadRequest(memory.get(i));
}
if (waitForFirstBlock) {
advance();
}
}
public void waitForFirstBlock() throws IOException
{
if (getCurrentSegment() == null) {
advance();
}
}
public boolean isClosed() {
return this.closed;
}
/**
* Closes this InputView, closing the underlying reader and returning all memory segments.
*
* @return A list containing all memory segments originally supplied to this view.
* @throws IOException Thrown, if the underlying reader could not be properly closed.
*/
public List<MemorySegment> close() throws IOException
{
if (this.closed) {
throw new IllegalStateException("Already closed.");
}
this.closed = true;
// re-collect all memory segments
ArrayList<MemorySegment> list = this.freeMem;
final MemorySegment current = getCurrentSegment();
if (current != null) {
list.add(current);
}
clear();
// close the writer and gather all segments
final LinkedBlockingQueue<MemorySegment> queue = this.reader.getReturnQueue();
this.reader.close();
while (list.size() < this.numSegments) {
final MemorySegment m = queue.poll();
if (m == null) {
// we get null if the queue is empty. that should not be the case if the reader was properly closed.
throw new RuntimeException("Bug in ChannelReaderInputView: MemorySegments lost.");
}
list.add(m);
}
return list;
}
// --------------------------------------------------------------------------------------------
// Utilities
// --------------------------------------------------------------------------------------------
/**
* Gets the next segment from the asynchronous block reader. If more requests are to be issued, the method
* first sends a new request with the current memory segment. If no more requests are pending, the method
* adds the segment to the readers return queue, which thereby effectively collects all memory segments.
* Secondly, the method fetches the next non-consumed segment
* returned by the reader. If no further segments are available, this method thrown an {@link EOFException}.
*
* @param current The memory segment used for the next request.
* @return The memory segment to read from next.
*
* @throws EOFException Thrown, if no further segments are available.
* @throws IOException Thrown, if an I/O error occurred while reading
* @see AbstractPagedInputView#nextSegment(org.apache.flink.core.memory.MemorySegment)
*/
@Override
protected MemorySegment nextSegment(MemorySegment current) throws IOException {
// check if we are at our end
if (this.inLastBlock) {
throw new EOFException();
}
// send a request first. if we have only a single segment, this same segment will be the one obtained in
// the next lines
if (current != null) {
sendReadRequest(current);
}
// get the next segment
final MemorySegment seg = this.reader.getNextReturnedSegment();
// check the header
if (seg.getShort(0) != ChannelWriterOutputView.HEADER_MAGIC_NUMBER) {
throw new IOException("The current block does not belong to a ChannelWriterOutputView / " +
"ChannelReaderInputView: Wrong magic number.");
}
if ( (seg.getShort(ChannelWriterOutputView.HEADER_FLAGS_OFFSET) & ChannelWriterOutputView.FLAG_LAST_BLOCK) != 0) {
// last block
this.numRequestsRemaining = 0;
this.inLastBlock = true;
}
return seg;
}
@Override
protected int getLimitForSegment(MemorySegment segment) {
return segment.getInt(ChannelWriterOutputView.HEAD_BLOCK_LENGTH_OFFSET);
}
/**
* Sends a new read requests, if further requests remain. Otherwise, this method adds the segment
* directly to the readers return queue.
*
* @param seg The segment to use for the read request.
* @throws IOException Thrown, if the reader is in error.
*/
protected void sendReadRequest(MemorySegment seg) throws IOException {
if (this.numRequestsRemaining != 0) {
this.reader.readBlock(seg);
if (this.numRequestsRemaining != -1) {
this.numRequestsRemaining--;
}
} else {
// directly add it to the end of the return queue
this.freeMem.add(seg);
}
}
}