common/base/SuppliersTest.java

/*
 * Copyright (C) 2007 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.base;

import static com.google.common.testing.SerializableTester.reserialize;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.Lists;
import com.google.common.testing.NullPointerTester;

import junit.framework.TestCase;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;

/**
 * Tests com.google.common.base.Suppliers.
 *
 * @author Laurence Gonsalves
 * @author Harry Heymann
 */
@GwtCompatible(emulated = true)
public class SuppliersTest extends TestCase {
  public void testCompose() {
    Supplier<Integer> fiveSupplier = new Supplier<Integer>() {
      @Override
      public Integer get() {
        return 5;
      }
    };

    Function<Number, Integer> intValueFunction =
        new Function<Number, Integer>() {
          @Override
          public Integer apply(Number x) {
            return x.intValue();
          }
        };

    Supplier<Integer> squareSupplier = Suppliers.compose(intValueFunction,
        fiveSupplier);

    assertEquals(Integer.valueOf(5), squareSupplier.get());
  }

  public void testComposeWithLists() {
    Supplier<ArrayList<Integer>> listSupplier
        = new Supplier<ArrayList<Integer>>() {
      @Override
      public ArrayList<Integer> get() {
        return Lists.newArrayList(0);
      }
    };

    Function<List<Integer>, List<Integer>> addElementFunction =
        new Function<List<Integer>, List<Integer>>() {
          @Override
          public List<Integer> apply(List<Integer> list) {
            ArrayList<Integer> result = Lists.newArrayList(list);
            result.add(1);
            return result;
          }
        };

    Supplier<List<Integer>> addSupplier = Suppliers.compose(addElementFunction,
        listSupplier);

    List<Integer> result = addSupplier.get();
    assertEquals(Integer.valueOf(0), result.get(0));
    assertEquals(Integer.valueOf(1), result.get(1));
  }

  static class CountingSupplier implements Supplier<Integer>, Serializable {
    private static final long serialVersionUID = 0L;
    transient int calls = 0;
    @Override
    public Integer get() {
      calls++;
      return calls * 10;
    }
  }

  public void testMemoize() {
    CountingSupplier countingSupplier = new CountingSupplier();
    Supplier<Integer> memoizedSupplier = Suppliers.memoize(countingSupplier);
    checkMemoize(countingSupplier, memoizedSupplier);
  }

  public void testMemoize_redudantly() {
    CountingSupplier countingSupplier = new CountingSupplier();
    Supplier<Integer> memoizedSupplier = Suppliers.memoize(countingSupplier);
    assertSame(memoizedSupplier, Suppliers.memoize(memoizedSupplier));
  }

  @GwtIncompatible("SerializableTester")
  public void testMemoizeSerialized() {
    CountingSupplier countingSupplier = new CountingSupplier();
    Supplier<Integer> memoizedSupplier = Suppliers.memoize(countingSupplier);
    checkMemoize(countingSupplier, memoizedSupplier);
    // Calls to the original memoized supplier shouldn't affect its copy.
    memoizedSupplier.get();

    Supplier<Integer> copy = reserialize(memoizedSupplier);
    memoizedSupplier.get();

    CountingSupplier countingCopy = (CountingSupplier)
        ((Suppliers.MemoizingSupplier<Integer>) copy).delegate;
    checkMemoize(countingCopy, copy);
  }

  private void checkMemoize(
      CountingSupplier countingSupplier, Supplier<Integer> memoizedSupplier) {
    // the underlying supplier hasn't executed yet
    assertEquals(0, countingSupplier.calls);

    assertEquals(10, (int) memoizedSupplier.get());

    // now it has
    assertEquals(1, countingSupplier.calls);

    assertEquals(10, (int) memoizedSupplier.get());

    // it still should only have executed once due to memoization
    assertEquals(1, countingSupplier.calls);
  }

  public void testMemoizeExceptionThrown() {
    Supplier<Integer> exceptingSupplier = new Supplier<Integer>() {
      @Override
      public Integer get() {
        throw new NullPointerException();
      }
    };

    Supplier<Integer> memoizedSupplier = Suppliers.memoize(exceptingSupplier);

    // call get() twice to make sure that memoization doesn't interfere
    // with throwing the exception
    for (int i = 0; i < 2; i++) {
      try {
        memoizedSupplier.get();
        fail("failed to throw NullPointerException");
      } catch (NullPointerException e) {
        // this is what should happen
      }
    }
  }

  @GwtIncompatible("Thread.sleep")
  public void testMemoizeWithExpiration() throws InterruptedException {
    CountingSupplier countingSupplier = new CountingSupplier();

    Supplier<Integer> memoizedSupplier = Suppliers.memoizeWithExpiration(
        countingSupplier, 75, TimeUnit.MILLISECONDS);

    checkExpiration(countingSupplier, memoizedSupplier);
  }

  @GwtIncompatible("Thread.sleep, SerializationTester")
  public void testMemoizeWithExpirationSerialized()
      throws InterruptedException {
    CountingSupplier countingSupplier = new CountingSupplier();

    Supplier<Integer> memoizedSupplier = Suppliers.memoizeWithExpiration(
        countingSupplier, 75, TimeUnit.MILLISECONDS);
    // Calls to the original memoized supplier shouldn't affect its copy.
    memoizedSupplier.get();

    Supplier<Integer> copy = reserialize(memoizedSupplier);
    memoizedSupplier.get();

    CountingSupplier countingCopy = (CountingSupplier)
        ((Suppliers.ExpiringMemoizingSupplier<Integer>) copy).delegate;
    checkExpiration(countingCopy, copy);
  }

  @GwtIncompatible("Thread.sleep")
  private void checkExpiration(
      CountingSupplier countingSupplier, Supplier<Integer> memoizedSupplier)
      throws InterruptedException {
    // the underlying supplier hasn't executed yet
    assertEquals(0, countingSupplier.calls);

    assertEquals(10, (int) memoizedSupplier.get());
    // now it has
    assertEquals(1, countingSupplier.calls);

    assertEquals(10, (int) memoizedSupplier.get());
    // it still should only have executed once due to memoization
    assertEquals(1, countingSupplier.calls);

    Thread.sleep(150);

    assertEquals(20, (int) memoizedSupplier.get());
    // old value expired
    assertEquals(2, countingSupplier.calls);

    assertEquals(20, (int) memoizedSupplier.get());
    // it still should only have executed twice due to memoization
    assertEquals(2, countingSupplier.calls);
  }

  public void testOfInstanceSuppliesSameInstance() {
    Object toBeSupplied = new Object();
    Supplier<Object> objectSupplier = Suppliers.ofInstance(toBeSupplied);
    assertSame(toBeSupplied,objectSupplier.get());
    assertSame(toBeSupplied,objectSupplier.get()); // idempotent
  }

  public void testOfInstanceSuppliesNull() {
    Supplier<Integer> nullSupplier = Suppliers.ofInstance(null);
    assertNull(nullSupplier.get());
  }

  @GwtIncompatible("Thread")

  public void testExpiringMemoizedSupplierThreadSafe() throws Throwable {
    Function<Supplier<Boolean>, Supplier<Boolean>> memoizer =
        new Function<Supplier<Boolean>, Supplier<Boolean>>() {
      @Override public Supplier<Boolean> apply(Supplier<Boolean> supplier) {
        return Suppliers.memoizeWithExpiration(
            supplier, Long.MAX_VALUE, TimeUnit.NANOSECONDS);
      }
    };
    testSupplierThreadSafe(memoizer);
  }

  @GwtIncompatible("Thread")

  public void testMemoizedSupplierThreadSafe() throws Throwable {
    Function<Supplier<Boolean>, Supplier<Boolean>> memoizer =
        new Function<Supplier<Boolean>, Supplier<Boolean>>() {
      @Override public Supplier<Boolean> apply(Supplier<Boolean> supplier) {
        return Suppliers.memoize(supplier);
      }
    };
    testSupplierThreadSafe(memoizer);
  }

  @GwtIncompatible("Thread")
  public void testSupplierThreadSafe(
      Function<Supplier<Boolean>, Supplier<Boolean>> memoizer)
      throws Throwable {
    final AtomicInteger count = new AtomicInteger(0);
    final AtomicReference<Throwable> thrown =
        new AtomicReference<Throwable>(null);
    final int numThreads = 3;
    final Thread[] threads = new Thread[numThreads];
    final long timeout = TimeUnit.SECONDS.toNanos(60);

    final Supplier<Boolean> supplier = new Supplier<Boolean>() {
      boolean isWaiting(Thread thread) {
        switch (thread.getState()) {
          case BLOCKED:
          case WAITING:
          case TIMED_WAITING:
          return true;
          default:
          return false;
        }
      }

      int waitingThreads() {
        int waitingThreads = 0;
        for (Thread thread : threads) {
          if (isWaiting(thread)) {
            waitingThreads++;
          }
        }
        return waitingThreads;
      }

      @Override
      public Boolean get() {
        // Check that this method is called exactly once, by the first
        // thread to synchronize.
        long t0 = System.nanoTime();
        while (waitingThreads() != numThreads - 1) {
          if (System.nanoTime() - t0 > timeout) {
            thrown.set(new TimeoutException(
                "timed out waiting for other threads to block" +
                " synchronizing on supplier"));
            break;
          }
          Thread.yield();
        }
        count.getAndIncrement();
        return Boolean.TRUE;
      }
    };

    final Supplier<Boolean> memoizedSupplier = memoizer.apply(supplier);

    for (int i = 0; i < numThreads; i++) {
      threads[i] = new Thread() {
        @Override public void run() {
          assertSame(Boolean.TRUE, memoizedSupplier.get());
        }
      };
    }
    for (Thread t : threads) {
      t.start();
    }
    for (Thread t : threads) {
      t.join();
    }

    if (thrown.get() != null) {
      throw thrown.get();
    }
    assertEquals(1, count.get());
  }

  @GwtIncompatible("Thread")

  public void testSynchronizedSupplierThreadSafe()
      throws InterruptedException {
    final Supplier<Integer> nonThreadSafe = new Supplier<Integer>() {
      int counter = 0;
      @Override
      public Integer get() {
        int nextValue = counter + 1;
        Thread.yield();
        counter = nextValue;
        return counter;
      }
    };

    final int numThreads = 10;
    final int iterations = 1000;
    Thread[] threads = new Thread[numThreads];
    for (int i = 0; i < numThreads; i++) {
      threads[i] = new Thread() {
        @Override public void run() {
          for (int j = 0; j < iterations; j++) {
            Suppliers.synchronizedSupplier(nonThreadSafe).get();
          }
        }
      };
    }
    for (Thread t : threads) {
      t.start();
    }
    for (Thread t : threads) {
      t.join();
    }

    assertEquals(numThreads * iterations + 1, (int) nonThreadSafe.get());
  }

  public void testSupplierFunction() {
    Supplier<Integer> supplier = Suppliers.ofInstance(14);
    Function<Supplier<Integer>, Integer> supplierFunction =
        Suppliers.supplierFunction();

    assertEquals(14, (int) supplierFunction.apply(supplier));
  }

  @GwtIncompatible("SerializationTester")
  public void testSerialization() {
    assertEquals(
        Integer.valueOf(5), reserialize(Suppliers.ofInstance(5)).get());
    assertEquals(Integer.valueOf(5), reserialize(Suppliers.compose(
        Functions.identity(), Suppliers.ofInstance(5))).get());
    assertEquals(Integer.valueOf(5),
        reserialize(Suppliers.memoize(Suppliers.ofInstance(5))).get());
    assertEquals(Integer.valueOf(5),
        reserialize(Suppliers.memoizeWithExpiration(
            Suppliers.ofInstance(5), 30, TimeUnit.SECONDS)).get());
    assertEquals(Integer.valueOf(5), reserialize(
        Suppliers.synchronizedSupplier(Suppliers.ofInstance(5))).get());
  }

  @GwtIncompatible("NullPointerTest")
  public void testNullPointers() throws Exception {
    NullPointerTester tester = new NullPointerTester();
    tester.testAllPublicStaticMethods(Suppliers.class);
  }
}