package org.apache.lucene.store;
/*
* 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.
*/
import org.apache.lucene.util.ThreadInterruptedException;
/** Abstract base class to rate limit IO. Typically implementations are
* shared across multiple IndexInputs or IndexOutputs (for example
* those involved all merging). Those IndexInputs and
* IndexOutputs would call {@link #pause} whenever they
* want to read bytes or write bytes. */
public abstract class RateLimiter {
/**
* Sets an updated mb per second rate limit.
*/
public abstract void setMbPerSec(double mbPerSec);
/**
* The current mb per second rate limit.
*/
public abstract double getMbPerSec();
/** Pauses, if necessary, to keep the instantaneous IO
* rate at or below the target.
* <p>
* Note: the implementation is thread-safe
* </p>
* @return the pause time in nano seconds
* */
public abstract long pause(long bytes);
/**
* Simple class to rate limit IO.
*/
public static class SimpleRateLimiter extends RateLimiter {
private volatile double mbPerSec;
private volatile double nsPerByte;
private volatile long lastNS;
// TODO: we could also allow eg a sub class to dynamically
// determine the allowed rate, eg if an app wants to
// change the allowed rate over time or something
/** mbPerSec is the MB/sec max IO rate */
public SimpleRateLimiter(double mbPerSec) {
setMbPerSec(mbPerSec);
}
/**
* Sets an updated mb per second rate limit.
*/
@Override
public void setMbPerSec(double mbPerSec) {
this.mbPerSec = mbPerSec;
nsPerByte = 1000000000. / (1024*1024*mbPerSec);
}
/**
* The current mb per second rate limit.
*/
@Override
public double getMbPerSec() {
return this.mbPerSec;
}
/** Pauses, if necessary, to keep the instantaneous IO
* rate at or below the target. NOTE: multiple threads
* may safely use this, however the implementation is
* not perfectly thread safe but likely in practice this
* is harmless (just means in some rare cases the rate
* might exceed the target). It's best to call this
* with a biggish count, not one byte at a time.
* @return the pause time in nano seconds
* */
@Override
public long pause(long bytes) {
if (bytes == 1) {
return 0;
}
// TODO: this is purely instantaneous rate; maybe we
// should also offer decayed recent history one?
final long targetNS = lastNS = lastNS + ((long) (bytes * nsPerByte));
final long startNS;
long curNS = startNS = System.nanoTime();
if (lastNS < curNS) {
lastNS = curNS;
}
// While loop because Thread.sleep doesn't always sleep
// enough:
while(true) {
final long pauseNS = targetNS - curNS;
if (pauseNS > 0) {
try {
Thread.sleep((int) (pauseNS/1000000), (int) (pauseNS % 1000000));
} catch (InterruptedException ie) {
throw new ThreadInterruptedException(ie);
}
curNS = System.nanoTime();
continue;
}
break;
}
return curNS - startNS;
}
}
}