guava/src/com/google/common/base/Suppliers.java - platform/external/guava - Git at Google

 /*
  * 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 com.google.common.annotations.Beta;
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.annotations.VisibleForTesting;

 import java.io.Serializable;
 import java.util.concurrent.TimeUnit;

 import javax.annotation.Nullable;

 /**
  * Useful suppliers.
  *
  * <p>All methods return serializable suppliers as long as they're given
  * serializable parameters.
  *
  * @author Laurence Gonsalves
  * @author Harry Heymann
  * @since 2.0 (imported from Google Collections Library)
  */
 @GwtCompatible
 public final class Suppliers {
   private Suppliers() {}

   /**
    * Returns a new supplier which is the composition of the provided function
    * and supplier. In other words, the new supplier's value will be computed by
    * retrieving the value from {@code supplier}, and then applying
    * {@code function} to that value. Note that the resulting supplier will not
    * call {@code supplier} or invoke {@code function} until it is called.
    */
   public static <F, T> Supplier<T> compose(
       Function<? super F, T> function, Supplier<F> supplier) {
     Preconditions.checkNotNull(function);
     Preconditions.checkNotNull(supplier);
     return new SupplierComposition<F, T>(function, supplier);
   }

   private static class SupplierComposition<F, T>
       implements Supplier<T>, Serializable {
     final Function<? super F, T> function;
     final Supplier<F> supplier;

     SupplierComposition(Function<? super F, T> function, Supplier<F> supplier) {
       this.function = function;
       this.supplier = supplier;
     }

     @Override public T get() {
       return function.apply(supplier.get());
     }

     @Override public boolean equals(@Nullable Object obj) {
       if (obj instanceof SupplierComposition) {
         SupplierComposition<?, ?> that = (SupplierComposition<?, ?>) obj;
         return function.equals(that.function) && supplier.equals(that.supplier);
       }
       return false;
     }

     @Override public int hashCode() {
       return Objects.hashCode(function, supplier);
     }

     @Override public String toString() {
       return "Suppliers.compose(" + function + ", " + supplier + ")";
     }

     private static final long serialVersionUID = 0;
   }

   /**
    * Returns a supplier which caches the instance retrieved during the first
    * call to {@code get()} and returns that value on subsequent calls to
    * {@code get()}. See:
    * <a href="http://en.wikipedia.org/wiki/Memoization">memoization</a>
    *
    * <p>The returned supplier is thread-safe. The supplier's serialized form
    * does not contain the cached value, which will be recalculated when {@code
    * get()} is called on the reserialized instance.
    *
    * <p>If {@code delegate} is an instance created by an earlier call to {@code
    * memoize}, it is returned directly.
    */
   public static <T> Supplier<T> memoize(Supplier<T> delegate) {
     return (delegate instanceof MemoizingSupplier)
         ? delegate
         : new MemoizingSupplier<T>(Preconditions.checkNotNull(delegate));
   }

   @VisibleForTesting
   static class MemoizingSupplier<T> implements Supplier<T>, Serializable {
     final Supplier<T> delegate;
     transient volatile boolean initialized;
     // "value" does not need to be volatile; visibility piggy-backs
     // on volatile read of "initialized".
     transient T value;

     MemoizingSupplier(Supplier<T> delegate) {
       this.delegate = delegate;
     }

     @Override public T get() {
       // A 2-field variant of Double Checked Locking.
       if (!initialized) {
         synchronized (this) {
           if (!initialized) {
             T t = delegate.get();
             value = t;
             initialized = true;
             return t;
           }
         }
       }
       return value;
     }

     @Override public String toString() {
       return "Suppliers.memoize(" + delegate + ")";
     }

     private static final long serialVersionUID = 0;
   }

   /**
    * Returns a supplier that caches the instance supplied by the delegate and
    * removes the cached value after the specified time has passed. Subsequent
    * calls to {@code get()} return the cached value if the expiration time has
    * not passed. After the expiration time, a new value is retrieved, cached,
    * and returned. See:
    * <a href="http://en.wikipedia.org/wiki/Memoization">memoization</a>
    *
    * <p>The returned supplier is thread-safe. The supplier's serialized form
    * does not contain the cached value, which will be recalculated when {@code
    * get()} is called on the reserialized instance.
    *
    * @param duration the length of time after a value is created that it
    *     should stop being returned by subsequent {@code get()} calls
    * @param unit the unit that {@code duration} is expressed in
    * @throws IllegalArgumentException if {@code duration} is not positive
    * @since 2.0
    */
   public static <T> Supplier<T> memoizeWithExpiration(
       Supplier<T> delegate, long duration, TimeUnit unit) {
     return new ExpiringMemoizingSupplier<T>(delegate, duration, unit);
   }

   @VisibleForTesting static class ExpiringMemoizingSupplier<T>
       implements Supplier<T>, Serializable {
     final Supplier<T> delegate;
     final long durationNanos;
     transient volatile T value;
     // The special value 0 means "not yet initialized".
     transient volatile long expirationNanos;

     ExpiringMemoizingSupplier(
         Supplier<T> delegate, long duration, TimeUnit unit) {
       this.delegate = Preconditions.checkNotNull(delegate);
       this.durationNanos = unit.toNanos(duration);
       Preconditions.checkArgument(duration > 0);
     }

     @Override public T get() {
       // Another variant of Double Checked Locking.
       //
       // We use two volatile reads.  We could reduce this to one by
       // putting our fields into a holder class, but (at least on x86)
       // the extra memory consumption and indirection are more
       // expensive than the extra volatile reads.
       long nanos = expirationNanos;
       long now = Platform.systemNanoTime();
       if (nanos == 0 || now - nanos >= 0) {
         synchronized (this) {
           if (nanos == expirationNanos) {  // recheck for lost race
             T t = delegate.get();
             value = t;
             nanos = now + durationNanos;
             // In the very unlikely event that nanos is 0, set it to 1;
             // no one will notice 1 ns of tardiness.
             expirationNanos = (nanos == 0) ? 1 : nanos;
             return t;
           }
         }
       }
       return value;
     }

     @Override public String toString() {
       // This is a little strange if the unit the user provided was not NANOS,
       // but we don't want to store the unit just for toString
       return "Suppliers.memoizeWithExpiration(" + delegate + ", " +
           durationNanos + ", NANOS)";
     }

     private static final long serialVersionUID = 0;
   }

   /**
    * Returns a supplier that always supplies {@code instance}.
    */
   public static <T> Supplier<T> ofInstance(@Nullable T instance) {
     return new SupplierOfInstance<T>(instance);
   }

   private static class SupplierOfInstance<T>
       implements Supplier<T>, Serializable {
     final T instance;

     SupplierOfInstance(@Nullable T instance) {
       this.instance = instance;
     }

     @Override public T get() {
       return instance;
     }

     @Override public boolean equals(@Nullable Object obj) {
       if (obj instanceof SupplierOfInstance) {
         SupplierOfInstance<?> that = (SupplierOfInstance<?>) obj;
         return Objects.equal(instance, that.instance);
       }
       return false;
     }

     @Override public int hashCode() {
       return Objects.hashCode(instance);
     }

     @Override public String toString() {
       return "Suppliers.ofInstance(" + instance + ")";
     }

     private static final long serialVersionUID = 0;
   }

   /**
    * Returns a supplier whose {@code get()} method synchronizes on
    * {@code delegate} before calling it, making it thread-safe.
    */
   public static <T> Supplier<T> synchronizedSupplier(Supplier<T> delegate) {
     return new ThreadSafeSupplier<T>(Preconditions.checkNotNull(delegate));
   }

   private static class ThreadSafeSupplier<T>
       implements Supplier<T>, Serializable {
     final Supplier<T> delegate;

     ThreadSafeSupplier(Supplier<T> delegate) {
       this.delegate = delegate;
     }

     @Override public T get() {
       synchronized (delegate) {
         return delegate.get();
       }
     }

     @Override public String toString() {
       return "Suppliers.synchronizedSupplier(" + delegate + ")";
     }

     private static final long serialVersionUID = 0;
   }

   /**
    * Returns a function that accepts a supplier and returns the result of
    * invoking {@link Supplier#get} on that supplier.
    *
    * @since 8.0
    */
   @Beta
   public static <T> Function<Supplier<T>, T> supplierFunction() {
     @SuppressWarnings("unchecked") // implementation is "fully variant"
     SupplierFunction<T> sf = (SupplierFunction<T>) SupplierFunctionImpl.INSTANCE;
     return sf;
   }

   private interface SupplierFunction<T> extends Function<Supplier<T>, T> {}

   private enum SupplierFunctionImpl implements SupplierFunction<Object> {
     INSTANCE;

     // Note: This makes T a "pass-through type"
     @Override public Object apply(Supplier<Object> input) {
       return input.get();
     }

     @Override public String toString() {
       return "Suppliers.supplierFunction()";
     }
   }
 }
	/*
	* 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 com.google.common.annotations.Beta;
	import com.google.common.annotations.GwtCompatible;
	import com.google.common.annotations.VisibleForTesting;

	import java.io.Serializable;
	import java.util.concurrent.TimeUnit;

	import javax.annotation.Nullable;

	/**
	* Useful suppliers.
	*
	* <p>All methods return serializable suppliers as long as they're given
	* serializable parameters.
	*
	* @author Laurence Gonsalves
	* @author Harry Heymann
	* @since 2.0 (imported from Google Collections Library)
	*/
	@GwtCompatible
	public final class Suppliers {
	private Suppliers() {}

	/**
	* Returns a new supplier which is the composition of the provided function
	* and supplier. In other words, the new supplier's value will be computed by
	* retrieving the value from {@code supplier}, and then applying
	* {@code function} to that value. Note that the resulting supplier will not
	* call {@code supplier} or invoke {@code function} until it is called.
	*/
	public static <F, T> Supplier<T> compose(
	Function<? super F, T> function, Supplier<F> supplier) {
	Preconditions.checkNotNull(function);
	Preconditions.checkNotNull(supplier);
	return new SupplierComposition<F, T>(function, supplier);
	}

	private static class SupplierComposition<F, T>
	implements Supplier<T>, Serializable {
	final Function<? super F, T> function;
	final Supplier<F> supplier;

	SupplierComposition(Function<? super F, T> function, Supplier<F> supplier) {
	this.function = function;
	this.supplier = supplier;
	}

	@Override public T get() {
	return function.apply(supplier.get());
	}

	@Override public boolean equals(@Nullable Object obj) {
	if (obj instanceof SupplierComposition) {
	SupplierComposition<?, ?> that = (SupplierComposition<?, ?>) obj;
	return function.equals(that.function) && supplier.equals(that.supplier);
	}
	return false;
	}

	@Override public int hashCode() {
	return Objects.hashCode(function, supplier);
	}

	@Override public String toString() {
	return "Suppliers.compose(" + function + ", " + supplier + ")";
	}

	private static final long serialVersionUID = 0;
	}

	/**
	* Returns a supplier which caches the instance retrieved during the first
	* call to {@code get()} and returns that value on subsequent calls to
	* {@code get()}. See:
	* <a href="http://en.wikipedia.org/wiki/Memoization">memoization</a>
	*
	* <p>The returned supplier is thread-safe. The supplier's serialized form
	* does not contain the cached value, which will be recalculated when {@code
	* get()} is called on the reserialized instance.
	*
	* <p>If {@code delegate} is an instance created by an earlier call to {@code
	* memoize}, it is returned directly.
	*/
	public static <T> Supplier<T> memoize(Supplier<T> delegate) {
	return (delegate instanceof MemoizingSupplier)
	? delegate
	: new MemoizingSupplier<T>(Preconditions.checkNotNull(delegate));
	}

	@VisibleForTesting
	static class MemoizingSupplier<T> implements Supplier<T>, Serializable {
	final Supplier<T> delegate;
	transient volatile boolean initialized;
	// "value" does not need to be volatile; visibility piggy-backs
	// on volatile read of "initialized".
	transient T value;

	MemoizingSupplier(Supplier<T> delegate) {
	this.delegate = delegate;
	}

	@Override public T get() {
	// A 2-field variant of Double Checked Locking.
	if (!initialized) {
	synchronized (this) {
	if (!initialized) {
	T t = delegate.get();
	value = t;
	initialized = true;
	return t;
	}
	}
	}
	return value;
	}

	@Override public String toString() {
	return "Suppliers.memoize(" + delegate + ")";
	}

	private static final long serialVersionUID = 0;
	}

	/**
	* Returns a supplier that caches the instance supplied by the delegate and
	* removes the cached value after the specified time has passed. Subsequent
	* calls to {@code get()} return the cached value if the expiration time has
	* not passed. After the expiration time, a new value is retrieved, cached,
	* and returned. See:
	* <a href="http://en.wikipedia.org/wiki/Memoization">memoization</a>
	*
	* <p>The returned supplier is thread-safe. The supplier's serialized form
	* does not contain the cached value, which will be recalculated when {@code
	* get()} is called on the reserialized instance.
	*
	* @param duration the length of time after a value is created that it
	* should stop being returned by subsequent {@code get()} calls
	* @param unit the unit that {@code duration} is expressed in
	* @throws IllegalArgumentException if {@code duration} is not positive
	* @since 2.0
	*/
	public static <T> Supplier<T> memoizeWithExpiration(
	Supplier<T> delegate, long duration, TimeUnit unit) {
	return new ExpiringMemoizingSupplier<T>(delegate, duration, unit);
	}

	@VisibleForTesting static class ExpiringMemoizingSupplier<T>
	implements Supplier<T>, Serializable {
	final Supplier<T> delegate;
	final long durationNanos;
	transient volatile T value;
	// The special value 0 means "not yet initialized".
	transient volatile long expirationNanos;

	ExpiringMemoizingSupplier(
	Supplier<T> delegate, long duration, TimeUnit unit) {
	this.delegate = Preconditions.checkNotNull(delegate);
	this.durationNanos = unit.toNanos(duration);
	Preconditions.checkArgument(duration > 0);
	}

	@Override public T get() {
	// Another variant of Double Checked Locking.
	//
	// We use two volatile reads. We could reduce this to one by
	// putting our fields into a holder class, but (at least on x86)
	// the extra memory consumption and indirection are more
	// expensive than the extra volatile reads.
	long nanos = expirationNanos;
	long now = Platform.systemNanoTime();
	if (nanos == 0 \|\| now - nanos >= 0) {
	synchronized (this) {
	if (nanos == expirationNanos) { // recheck for lost race
	T t = delegate.get();
	value = t;
	nanos = now + durationNanos;
	// In the very unlikely event that nanos is 0, set it to 1;
	// no one will notice 1 ns of tardiness.
	expirationNanos = (nanos == 0) ? 1 : nanos;
	return t;
	}
	}
	}
	return value;
	}

	@Override public String toString() {
	// This is a little strange if the unit the user provided was not NANOS,
	// but we don't want to store the unit just for toString
	return "Suppliers.memoizeWithExpiration(" + delegate + ", " +
	durationNanos + ", NANOS)";
	}

	private static final long serialVersionUID = 0;
	}

	/**
	* Returns a supplier that always supplies {@code instance}.
	*/
	public static <T> Supplier<T> ofInstance(@Nullable T instance) {
	return new SupplierOfInstance<T>(instance);
	}

	private static class SupplierOfInstance<T>
	implements Supplier<T>, Serializable {
	final T instance;

	SupplierOfInstance(@Nullable T instance) {
	this.instance = instance;
	}

	@Override public T get() {
	return instance;
	}

	@Override public boolean equals(@Nullable Object obj) {
	if (obj instanceof SupplierOfInstance) {
	SupplierOfInstance<?> that = (SupplierOfInstance<?>) obj;
	return Objects.equal(instance, that.instance);
	}
	return false;
	}

	@Override public int hashCode() {
	return Objects.hashCode(instance);
	}

	@Override public String toString() {
	return "Suppliers.ofInstance(" + instance + ")";
	}

	private static final long serialVersionUID = 0;
	}

	/**
	* Returns a supplier whose {@code get()} method synchronizes on
	* {@code delegate} before calling it, making it thread-safe.
	*/
	public static <T> Supplier<T> synchronizedSupplier(Supplier<T> delegate) {
	return new ThreadSafeSupplier<T>(Preconditions.checkNotNull(delegate));
	}

	private static class ThreadSafeSupplier<T>
	implements Supplier<T>, Serializable {
	final Supplier<T> delegate;

	ThreadSafeSupplier(Supplier<T> delegate) {
	this.delegate = delegate;
	}

	@Override public T get() {
	synchronized (delegate) {
	return delegate.get();
	}
	}

	@Override public String toString() {
	return "Suppliers.synchronizedSupplier(" + delegate + ")";
	}

	private static final long serialVersionUID = 0;
	}

	/**
	* Returns a function that accepts a supplier and returns the result of
	* invoking {@link Supplier#get} on that supplier.
	*
	* @since 8.0
	*/
	@Beta
	public static <T> Function<Supplier<T>, T> supplierFunction() {
	@SuppressWarnings("unchecked") // implementation is "fully variant"
	SupplierFunction<T> sf = (SupplierFunction<T>) SupplierFunctionImpl.INSTANCE;
	return sf;
	}

	private interface SupplierFunction<T> extends Function<Supplier<T>, T> {}

	private enum SupplierFunctionImpl implements SupplierFunction<Object> {
	INSTANCE;

	// Note: This makes T a "pass-through type"
	@Override public Object apply(Supplier<Object> input) {
	return input.get();
	}

	@Override public String toString() {
	return "Suppliers.supplierFunction()";
	}
	}
	}