File: SynchronizedChar.java

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/*
  File: SynchronizedChar.java

  Originally written by Doug Lea and released into the public domain.
  This may be used for any purposes whatsoever without acknowledgment.
  Thanks for the assistance and support of Sun Microsystems Labs,
  and everyone contributing, testing, and using this code.

  History:
  Date       Who                What
  19Jun1998  dl               Create public version
*/

package EDU.oswego.cs.dl.util.concurrent;

/**
 * A class useful for offloading synch for char instance variables.
 *
 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
 **/

public class SynchronizedChar extends SynchronizedVariable implements Comparable, Cloneable {

  protected char value_;

  /** 
   * Make a new SynchronizedChar with the given initial value,
   * and using its own internal lock.
   **/
  public SynchronizedChar(char initialValue) { 
    super(); 
    value_ = initialValue; 
  }

  /** 
   * Make a new SynchronizedChar with the given initial value,
   * and using the supplied lock.
   **/
  public SynchronizedChar(char initialValue, Object lock) { 
    super(lock); 
    value_ = initialValue; 
  }

  /** 
   * Return the current value 
   **/
  public final char get() { synchronized(lock_) { return value_; } }

  /** 
   * Set to newValue.
   * @return the old value 
   **/

  public char set(char newValue) { 
    synchronized (lock_) {
      char old = value_;
      value_ = newValue; 
      return old;
    }
  }

  /**
   * Set value to newValue only if it is currently assumedValue.
   * @return true if successful
   **/
  public boolean commit(char assumedValue, char newValue) {
    synchronized(lock_) {
      boolean success = (assumedValue == value_);
      if (success) value_ = newValue;
      return success;
    }
  }


  /** 
   * Atomically swap values with another SynchronizedChar.
   * Uses identityHashCode to avoid deadlock when
   * two SynchronizedChars attempt to simultaneously swap with each other.
   * (Note: Ordering via identyHashCode is not strictly guaranteed
   * by the language specification to return unique, orderable
   * values, but in practice JVMs rely on them being unique.)
   * @return the new value 
   **/

  public char swap(SynchronizedChar other) {
    if (other == this) return get();
    SynchronizedChar fst = this;
    SynchronizedChar snd = other;
    if (System.identityHashCode(fst) > System.identityHashCode(snd)) {
      fst = other;
      snd = this;
    }
    synchronized(fst.lock_) {
      synchronized(snd.lock_) {
        fst.set(snd.set(fst.get()));
        return get();
      }
    }
  }

  /** 
   * Add amount to value (i.e., set value += amount)
   * @return the new value 
   **/
  public char add(char amount) { 
    synchronized (lock_) {
      return value_ += amount; 
    }
  }

  /** 
   * Subtract amount from value (i.e., set value -= amount)
   * @return the new value 
   **/
  public char subtract(char amount) { 
    synchronized (lock_) {
      return value_ -= amount; 
    }
  }

  /** 
   * Multiply value by factor (i.e., set value *= factor)
   * @return the new value 
   **/
  public synchronized char multiply(char factor) { 
    synchronized (lock_) {
      return value_ *= factor; 
    }
  }

  /** 
   * Divide value by factor (i.e., set value /= factor)
   * @return the new value 
   **/
  public char divide(char factor) { 
    synchronized (lock_) {
      return value_ /= factor; 
    }
  }

  public int compareTo(char other) {
    char val = get();
    return (val < other)? -1 : (val == other)? 0 : 1;
  }

  public int compareTo(SynchronizedChar other) {
    return compareTo(other.get());
  }

  public int compareTo(Object other) {
    return compareTo((SynchronizedChar)other);
  }

  public boolean equals(Object other) {
    if (other != null &&
        other instanceof SynchronizedChar)
      return get() == ((SynchronizedChar)other).get();
    else
      return false;
  }

  public int hashCode() { // same hash as Char
    return (int)(get());
  }

  public String toString() { return String.valueOf(get()); }

}