/*
* 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.beam.sdk.io.range;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.annotations.VisibleForTesting;
import org.apache.beam.sdk.io.BoundedSource.BoundedReader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A {@link RangeTracker} for non-negative positions of type {@code long}.
*/
public class OffsetRangeTracker implements RangeTracker<Long> {
private static final Logger LOG = LoggerFactory.getLogger(OffsetRangeTracker.class);
private long startOffset;
private long stopOffset;
private long lastRecordStart = -1L;
private long offsetOfLastSplitPoint = -1L;
private long splitPointsSeen = 0L;
private boolean done = false;
/**
* Offset corresponding to infinity. This can only be used as the upper-bound of a range, and
* indicates reading all of the records until the end without specifying exactly what the end is.
*
* <p>Infinite ranges cannot be split because it is impossible to estimate progress within them.
*/
public static final long OFFSET_INFINITY = Long.MAX_VALUE;
/**
* Creates an {@code OffsetRangeTracker} for the specified range.
*/
public OffsetRangeTracker(long startOffset, long stopOffset) {
this.startOffset = startOffset;
this.stopOffset = stopOffset;
}
public synchronized boolean isStarted() {
// done => started: handles the case when the reader was empty.
return (offsetOfLastSplitPoint != -1) || done;
}
public synchronized boolean isDone() {
return done;
}
@Override
public synchronized Long getStartPosition() {
return startOffset;
}
@Override
public synchronized Long getStopPosition() {
return stopOffset;
}
@Override
public boolean tryReturnRecordAt(boolean isAtSplitPoint, Long recordStart) {
return tryReturnRecordAt(isAtSplitPoint, recordStart.longValue());
}
public synchronized boolean tryReturnRecordAt(boolean isAtSplitPoint, long recordStart) {
if (!isStarted() && !isAtSplitPoint) {
throw new IllegalStateException(
String.format("The first record [starting at %d] must be at a split point", recordStart));
}
if (recordStart < startOffset) {
throw new IllegalStateException(
String.format(
"Trying to return record [starting at %d] which is before the start offset [%d]",
recordStart,
startOffset));
}
if (recordStart < lastRecordStart) {
throw new IllegalStateException(
String.format(
"Trying to return record [starting at %d] "
+ "which is before the last-returned record [starting at %d]",
recordStart,
lastRecordStart));
}
if (lastRecordStart == -1) {
startOffset = recordStart;
}
lastRecordStart = recordStart;
if (isAtSplitPoint) {
if (recordStart == offsetOfLastSplitPoint) {
throw new IllegalStateException(
String.format(
"Record at a split point has same offset as the previous split point: "
+ "previous split point at %d, current record starts at %d",
offsetOfLastSplitPoint, recordStart));
}
if (recordStart >= stopOffset) {
done = true;
return false;
}
offsetOfLastSplitPoint = recordStart;
++splitPointsSeen;
}
return true;
}
@Override
public boolean trySplitAtPosition(Long splitOffset) {
return trySplitAtPosition(splitOffset.longValue());
}
public synchronized boolean trySplitAtPosition(long splitOffset) {
if (stopOffset == OFFSET_INFINITY) {
LOG.debug("Refusing to split {} at {}: stop position unspecified", this, splitOffset);
return false;
}
if (!isStarted()) {
LOG.debug("Refusing to split {} at {}: unstarted", this, splitOffset);
return false;
}
// Note: technically it is correct to split at any position after the last returned
// split point, not just the last returned record.
// TODO: Investigate whether in practice this is useful or, rather, confusing.
if (splitOffset <= lastRecordStart) {
LOG.debug(
"Refusing to split {} at {}: already past proposed split position", this, splitOffset);
return false;
}
if (splitOffset < startOffset || splitOffset >= stopOffset) {
LOG.debug(
"Refusing to split {} at {}: proposed split position out of range", this, splitOffset);
return false;
}
LOG.debug("Agreeing to split {} at {}", this, splitOffset);
this.stopOffset = splitOffset;
return true;
}
/**
* Returns a position {@code P} such that the range {@code [start, P)} represents approximately
* the given fraction of the range {@code [start, end)}. Assumes that the density of records
* in the range is approximately uniform.
*/
public synchronized long getPositionForFractionConsumed(double fraction) {
if (stopOffset == OFFSET_INFINITY) {
throw new IllegalArgumentException(
"getPositionForFractionConsumed is not applicable to an unbounded range: " + this);
}
return (long) Math.floor(startOffset + fraction * (stopOffset - startOffset));
}
@Override
public synchronized double getFractionConsumed() {
if (!isStarted()) {
return 0.0;
} else if (isDone()) {
return 1.0;
} else if (stopOffset == OFFSET_INFINITY) {
return 0.0;
} else if (lastRecordStart >= stopOffset) {
return 1.0;
} else {
// E.g., when reading [3, 6) and lastRecordStart is 4, that means we consumed 3 of 3,4,5
// which is (4 - 3) / (6 - 3) = 33%.
// Also, clamp to at most 1.0 because the last consumed position can extend past the
// stop position.
return Math.min(1.0, 1.0 * (lastRecordStart - startOffset) / (stopOffset - startOffset));
}
}
/**
* Returns the total number of split points that have been processed.
*
* <p>A split point at a particular offset has been seen if there has been a corresponding call
* to {@link #tryReturnRecordAt(boolean, long)} with {@code isAtSplitPoint} true. It has been
* processed if there has been a <em>subsequent</em> call to
* {@link #tryReturnRecordAt(boolean, long)} with {@code isAtSplitPoint} true and at a larger
* offset.
*
* <p>Note that for correctness when implementing {@link BoundedReader#getSplitPointsConsumed()},
* if a reader finishes before {@link #tryReturnRecordAt(boolean, long)} returns false,
* the reader should add an additional call to {@link #markDone()}. This will indicate that
* processing for the last seen split point has been finished.
*
* @see org.apache.beam.sdk.io.OffsetBasedSource for a {@link BoundedReader}
* implemented using {@link OffsetRangeTracker}.
*/
public synchronized long getSplitPointsProcessed() {
if (!isStarted()) {
return 0;
} else if (isDone()) {
return splitPointsSeen;
} else {
// There is a current split point, and it has not finished processing.
checkState(
splitPointsSeen > 0,
"A started rangeTracker should have seen > 0 split points (is %s)",
splitPointsSeen);
return splitPointsSeen - 1;
}
}
/**
* Marks this range tracker as being done. Specifically, this will mark the current split point,
* if one exists, as being finished.
*
* <p>Always returns false, so that it can be used in an implementation of
* {@link BoundedReader#start()} or {@link BoundedReader#advance()} as follows:
*
* <pre> {@code
* public boolean start() {
* return startImpl() && rangeTracker.tryReturnRecordAt(isAtSplitPoint, position)
* || rangeTracker.markDone();
* }} </pre>
*/
public synchronized boolean markDone() {
done = true;
return false;
}
@Override
public synchronized String toString() {
String stopString = (stopOffset == OFFSET_INFINITY) ? "infinity" : String.valueOf(stopOffset);
if (lastRecordStart >= 0) {
return String.format(
"<at [starting at %d] of offset range [%d, %s)>",
lastRecordStart,
startOffset,
stopString);
} else {
return String.format("<unstarted in offset range [%d, %s)>", startOffset, stopString);
}
}
/**
* Returns a copy of this tracker for testing purposes (to simplify testing methods with
* side effects).
*/
@VisibleForTesting
OffsetRangeTracker copy() {
OffsetRangeTracker res = new OffsetRangeTracker(startOffset, stopOffset);
res.offsetOfLastSplitPoint = this.offsetOfLastSplitPoint;
res.lastRecordStart = this.lastRecordStart;
res.done = this.done;
res.splitPointsSeen = this.splitPointsSeen;
return res;
}
}