/*
* Copyright (C) 2012 The Guava Authors
*
* Licensed 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 com.google.common.util.concurrent;
import com.google.common.collect.Lists;
import junit.framework.TestCase;
import java.util.Arrays;
import java.util.List;
import java.util.Random;
import java.util.concurrent.TimeUnit;
/**
* Tests for RateLimiter.
*
* @author Dimitris Andreou
*/
public class RateLimiterTest extends TestCase {
/**
* The ticker gathers events and presents them as strings.
* R0.6 means a delay of 0.6 seconds caused by the (R)ateLimiter
* U1.0 means the (U)ser caused the ticker to sleep for a second.
*/
private final FakeTicker ticker = new FakeTicker();
public void testSimple() {
RateLimiter limiter = RateLimiter.create(ticker, 5.0);
limiter.acquire(); // R0.00, since it's the first request
limiter.acquire(); // R0.20
limiter.acquire(); // R0.20
assertEvents("R0.00", "R0.20", "R0.20");
}
public void testSimpleRateUpdate() {
RateLimiter limiter = RateLimiter.create(5.0, 5, TimeUnit.SECONDS);
assertEquals(5.0, limiter.getRate());
limiter.setRate(10.0);
assertEquals(10.0, limiter.getRate());
try {
limiter.setRate(0.0);
fail();
} catch (IllegalArgumentException ok) {}
try {
limiter.setRate(-10.0);
fail();
} catch (IllegalArgumentException ok) {}
}
public void testSimpleWithWait() {
RateLimiter limiter = RateLimiter.create(ticker, 5.0);
limiter.acquire(); // R0.00
ticker.sleepMillis(200); // U0.20, we are ready for the next request...
limiter.acquire(); // R0.00, ...which is granted immediately
limiter.acquire(); // R0.20
assertEvents("R0.00", "U0.20", "R0.00", "R0.20");
}
public void testOneSecondBurst() {
RateLimiter limiter = RateLimiter.create(ticker, 5.0);
ticker.sleepMillis(1000); // max capacity reached
ticker.sleepMillis(1000); // this makes no difference
limiter.acquire(1); // R0.00, since it's the first request
limiter.acquire(1); // R0.00, from capacity
limiter.acquire(3); // R0.00, from capacity
limiter.acquire(1); // R0.00, concluding a burst of 5 permits
limiter.acquire(); // R0.20, capacity exhausted
assertEvents("U1.00", "U1.00",
"R0.00", "R0.00", "R0.00", "R0.00", // first request and burst
"R0.20");
}
public void testWarmUp() {
RateLimiter limiter = RateLimiter.create(ticker, 2.0, 4000, TimeUnit.MILLISECONDS);
for (int i = 0; i < 8; i++) {
limiter.acquire(); // #1
}
ticker.sleepMillis(500); // #2: to repay for the last acquire
ticker.sleepMillis(4000); // #3: becomes cold again
for (int i = 0; i < 8; i++) {
limiter.acquire(); // // #4
}
ticker.sleepMillis(500); // #5: to repay for the last acquire
ticker.sleepMillis(2000); // #6: didn't get cold! It would take another 2 seconds to go cold
for (int i = 0; i < 8; i++) {
limiter.acquire(); // #7
}
assertEvents(
"R0.00, R1.38, R1.13, R0.88, R0.63, R0.50, R0.50, R0.50", // #1
"U0.50", // #2
"U4.00", // #3
"R0.00, R1.38, R1.13, R0.88, R0.63, R0.50, R0.50, R0.50", // #4
"U0.50", // #5
"U2.00", // #6
"R0.00, R0.50, R0.50, R0.50, R0.50, R0.50, R0.50, R0.50"); // #7
}
public void testWarmUpAndUpdate() {
RateLimiter limiter = RateLimiter.create(ticker, 2.0, 4000, TimeUnit.MILLISECONDS);
for (int i = 0; i < 8; i++) {
limiter.acquire(); // // #1
}
ticker.sleepMillis(4500); // #2: back to cold state (warmup period + repay last acquire)
for (int i = 0; i < 3; i++) { // only three steps, we're somewhere in the warmup period
limiter.acquire(); // #3
}
limiter.setRate(4.0); // double the rate!
limiter.acquire(); // #4, we repay the debt of the last acquire (imposed by the old rate)
for (int i = 0; i < 4; i++) {
limiter.acquire(); // #5
}
ticker.sleepMillis(4250); // #6, back to cold state (warmup period + repay last acquire)
for (int i = 0; i < 11; i++) {
limiter.acquire(); // #7, showing off the warmup starting from totally cold
}
// make sure the areas (times) remain the same, while permits are different
assertEvents(
"R0.00, R1.38, R1.13, R0.88, R0.63, R0.50, R0.50, R0.50", // #1
"U4.50", // #2
"R0.00, R1.38, R1.13", // #3, after that the rate changes
"R0.88", // #4, this is what the throttling would be with the old rate
"R0.34, R0.28, R0.25, R0.25", // #5
"U4.25", // #6
"R0.00, R0.72, R0.66, R0.59, R0.53, R0.47, R0.41", // #7
"R0.34, R0.28, R0.25, R0.25"); // #7 (cont.), note, this matches #5
}
public void testBursty() {
RateLimiter limiter = RateLimiter.createBursty(ticker, 1.0, 10);
ticker.sleepMillis(10000); // reach full capacity
limiter.acquire(11); // all these are served in a burst (10 + 1 by borrowing from the future)
limiter.acquire(1); // out of capacity, we have to wait
limiter.acquire(1); // and wait
ticker.sleepMillis(3000); // fill up 3 permits
limiter.acquire(5); // we had 3 ready, thus we borrow 2 permits
limiter.acquire(1); // this acquire() will also repay for the previous acquire()
assertEvents(
"U10.00",
"R0.00", // 10 permits grabbed
"R1.00", "R1.00", // 1 and 1
"U3.00", "R0.00", // 5 grabbed
"R3.00" // 1 grabbed
);
}
public void testBurstyAndUpdate() {
RateLimiter rateLimiter = RateLimiter.create(ticker, 1.0);
rateLimiter.acquire(1); // no wait
rateLimiter.acquire(1); // R1.00, to repay previous
rateLimiter.setRate(2.0); // update the rate!
rateLimiter.acquire(1); // R1.00, to repay previous (the previous was under the old rate!)
rateLimiter.acquire(2); // R0.50, to repay previous (now the rate takes effect)
rateLimiter.acquire(4); // R1.00, to repay previous
rateLimiter.acquire(1); // R2.00, to repay previous
assertEvents("R0.00", "R1.00", "R1.00", "R0.50", "R1.00", "R2.00");
}
public void testTimeWrapping() {
ticker.instant = Long.MAX_VALUE - TimeUnit.SECONDS.toNanos(1); // 1 second before max value
RateLimiter limiter = RateLimiter.create(ticker, 1.0);
for (int i = 0; i < 4; i++) {
limiter.acquire();
}
// Without protection from overflow, the last wait value would have been huge,
// because "now" would have wrapped into a value near MIN_VALUE, and the limiter would think
// that the next request should be admitted far into the future
assertEvents("R0.00", "R1.00", "R1.00", "R1.00");
}
public void testTryGate() {
RateLimiter limiter = RateLimiter.create(ticker, 5.0);
assertTrue(limiter.tryAcquire(0, TimeUnit.SECONDS));
assertFalse(limiter.tryAcquire(0, TimeUnit.SECONDS));
assertFalse(limiter.tryAcquire(0, TimeUnit.SECONDS));
ticker.sleepMillis(100);
assertFalse(limiter.tryAcquire(0, TimeUnit.SECONDS));
}
public void testSimpleWeights() {
RateLimiter rateLimiter = RateLimiter.create(ticker, 1.0);
rateLimiter.acquire(1); // no wait
rateLimiter.acquire(1); // R1.00, to repay previous
rateLimiter.acquire(2); // R1.00, to repay previous
rateLimiter.acquire(4); // R2.00, to repay previous
rateLimiter.acquire(8); // R4.00, to repay previous
rateLimiter.acquire(1); // R8.00, to repay previous
assertEvents("R0.00", "R1.00", "R1.00", "R2.00", "R4.00", "R8.00");
}
public void testInfinity_Bursty() {
RateLimiter limiter = RateLimiter.create(ticker, Double.POSITIVE_INFINITY);
limiter.acquire(Integer.MAX_VALUE / 4);
limiter.acquire(Integer.MAX_VALUE / 2);
limiter.acquire(Integer.MAX_VALUE);
assertEvents("R0.00", "R0.00", "R0.00"); // no wait, infinite rate!
limiter.setRate(1.0);
limiter.acquire();
limiter.acquire();
limiter.acquire();
assertEvents("R0.00", "R1.00", "R1.00"); // we repay the last request (but that had no cost)
// and then we go to 1 second per request mode
limiter.setRate(Double.POSITIVE_INFINITY);
limiter.acquire();
limiter.acquire();
limiter.acquire();
assertEvents("R1.00", "R0.00", "R0.00"); // we repay the last request (1sec), then back to +oo
}
public void testInfinity_WarmUp() {
RateLimiter limiter = RateLimiter.create(
ticker, Double.POSITIVE_INFINITY, 10, TimeUnit.SECONDS);
limiter.acquire(Integer.MAX_VALUE / 4);
limiter.acquire(Integer.MAX_VALUE / 2);
limiter.acquire(Integer.MAX_VALUE);
assertEvents("R0.00", "R0.00", "R0.00");
limiter.setRate(1.0);
limiter.acquire();
limiter.acquire();
limiter.acquire();
assertEvents("R0.00", "R1.00", "R1.00");
limiter.setRate(Double.POSITIVE_INFINITY);
limiter.acquire();
limiter.acquire();
limiter.acquire();
assertEvents("R1.00", "R0.00", "R0.00");
}
/**
* Make sure that bursts can never go above 1-second-worth-of-work for the current
* rate, even when we change the rate.
*/
public void testWeNeverGetABurstMoreThanOneSec() {
RateLimiter limiter = RateLimiter.create(ticker, 1.0);
int[] rates = { 1000, 1, 10, 1000000, 10, 1};
for (int rate : rates) {
int oneSecWorthOfWork = rate;
ticker.sleepMillis(rate * 1000);
limiter.setRate(rate);
long burst = measureTotalTimeMillis(limiter, oneSecWorthOfWork, new Random());
// we allow one second worth of work to go in a burst (i.e. take less than a second)
assertTrue(burst <= 1000);
long afterBurst = measureTotalTimeMillis(limiter, oneSecWorthOfWork, new Random());
// but work beyond that must take at least one second
assertTrue(afterBurst >= 1000);
}
}
/**
* This neat test shows that no matter what weights we use in our requests, if we push X
* amount of permits in a cool state, where X = rate * timeToCoolDown, and we have
* specified a timeToWarmUp() period, it will cost as the prescribed amount of time. E.g.,
* calling [acquire(5), acquire(1)] takes exactly the same time as
* [acquire(2), acquire(3), acquire(1)].
*/
public void testTimeToWarmUpIsHonouredEvenWithWeights() {
Random random = new Random();
int maxPermits = 10;
double[] qpsToTest = { 4.0, 2.0, 1.0, 0.5, 0.1 };
for (int trial = 0; trial < 100; trial++) {
for (double qps : qpsToTest) {
// Since we know that: maxPermits = 0.5 * warmup / stableInterval;
// then if maxPermits == 10, we have:
// warmupSeconds = 20 / qps
long warmupMillis = (long) ((2 * maxPermits / qps) * 1000.0);
RateLimiter rateLimiter = RateLimiter.create(
ticker, qps, warmupMillis, TimeUnit.MILLISECONDS);
assertEquals(warmupMillis, measureTotalTimeMillis(rateLimiter, maxPermits, random));
}
}
}
private long measureTotalTimeMillis(RateLimiter rateLimiter, int permits, Random random) {
long startTime = ticker.instant;
while (permits > 0) {
int nextPermitsToAcquire = Math.max(1, random.nextInt(permits));
permits -= nextPermitsToAcquire;
rateLimiter.acquire(nextPermitsToAcquire);
}
rateLimiter.acquire(1); // to repay for any pending debt
return TimeUnit.NANOSECONDS.toMillis(ticker.instant - startTime);
}
private void assertEvents(String... events) {
assertEquals(Arrays.asList(events).toString(), ticker.readEventsAndClear());
}
private static class FakeTicker extends RateLimiter.SleepingTicker {
long instant = 0L;
final List<String> events = Lists.newArrayList();
@Override
public long read() {
return instant;
}
void sleepMillis(int millis) {
sleepMicros("U", TimeUnit.MILLISECONDS.toMicros(millis));
}
void sleepMicros(String caption, long micros) {
instant += TimeUnit.MICROSECONDS.toNanos(micros);
events.add(caption + String.format("%3.2f", (micros / 1000000.0)));
}
@Override
void sleepMicrosUninterruptibly(long micros) {
sleepMicros("R", micros);
}
String readEventsAndClear() {
try {
return events.toString();
} finally {
events.clear();
}
}
@Override
public String toString() {
return events.toString();
}
}
}