guava-tests/test/com/google/common/util/concurrent/RateLimiterTest.java - platform/external/guava - Git at Google

 /*
  * 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 com.google.common.testing.NullPointerTester;
 import com.google.common.testing.NullPointerTester.Visibility;

 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 {
   private static final double EPSILON = 1e-8;

   /**
    * 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 testImmediateTryAcquire() {
     RateLimiter r = RateLimiter.create(1);
     assertTrue("Unable to acquire initial permit", r.tryAcquire());
     assertFalse("Capable of acquiring secondary permit", r.tryAcquire());
   }

   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 testSimpleAcquireReturnValues() {
     RateLimiter limiter = RateLimiter.create(ticker, 5.0);
     assertEquals(0.0, limiter.acquire(), EPSILON);  // R0.00
     ticker.sleepMillis(200);                        // U0.20, we are ready for the next request...
     assertEquals(0.0, limiter.acquire(), EPSILON);  // R0.00, ...which is granted immediately
     assertEquals(0.2, limiter.acquire(), EPSILON);  // 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.createWithCapacity(ticker, 1.0, 10, TimeUnit.SECONDS);
     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));
       }
     }
   }

   public void testNulls() {
     NullPointerTester tester = new NullPointerTester()
         .setDefault(RateLimiter.SleepingTicker.class, ticker);
     tester.testStaticMethods(RateLimiter.class, Visibility.PACKAGE);
     tester.testInstanceMethods(RateLimiter.create(ticker, 5.0), Visibility.PACKAGE);
   }

   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.toString(events), 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();
     }
   }
 }
	/*
	* 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 com.google.common.testing.NullPointerTester;
	import com.google.common.testing.NullPointerTester.Visibility;

	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 {
	private static final double EPSILON = 1e-8;

	/**
	* 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 testImmediateTryAcquire() {
	RateLimiter r = RateLimiter.create(1);
	assertTrue("Unable to acquire initial permit", r.tryAcquire());
	assertFalse("Capable of acquiring secondary permit", r.tryAcquire());
	}

	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 testSimpleAcquireReturnValues() {
	RateLimiter limiter = RateLimiter.create(ticker, 5.0);
	assertEquals(0.0, limiter.acquire(), EPSILON); // R0.00
	ticker.sleepMillis(200); // U0.20, we are ready for the next request...
	assertEquals(0.0, limiter.acquire(), EPSILON); // R0.00, ...which is granted immediately
	assertEquals(0.2, limiter.acquire(), EPSILON); // 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.createWithCapacity(ticker, 1.0, 10, TimeUnit.SECONDS);
	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));
	}
	}
	}

	public void testNulls() {
	NullPointerTester tester = new NullPointerTester()
	.setDefault(RateLimiter.SleepingTicker.class, ticker);
	tester.testStaticMethods(RateLimiter.class, Visibility.PACKAGE);
	tester.testInstanceMethods(RateLimiter.create(ticker, 5.0), Visibility.PACKAGE);
	}

	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.toString(events), 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();
	}
	}
	}