ThreadCount.java

package org.opensha2.calc;

import com.google.common.util.concurrent.MoreExecutors;

import java.util.concurrent.ExecutorService;

/**
 * The number of threads with which to intialize thread pools. Values reference
 * the number of non-competing threads that could be supported on a particular
 * system as determined by calling {@link Runtime#availableProcessors()}.
 *
 * @author Peter Powers
 */
public enum ThreadCount {

  /**
   * A single thread. This identifier will typically cause a program to either
   * use Guava's {@link MoreExecutors#directExecutor()} or skip using an
   * {@link ExecutorService} altogether, and all calculations will be run on the
   * thread from which a program was called. This is useful for debugging.
   */
  ONE {
    @Override
    public int value() {
      return 1;
    }
  },

  /**
   * Half of {@code ALL}.
   */
  HALF {
    @Override
    public int value() {
      return Math.max(1, CORES / 2);
    }
  },

  /**
   * Two less than {@code ALL}, so as to not commandeer all available resources.
   */
  N_MINUS_2 {
    @Override
    public int value() {
      return Math.max(1, CORES - 2);
    }
  },

  /**
   * All possible non-competing threads. The number of threads will equal the
   * number of available processors.
   */
  ALL {
    @Override
    public int value() {
      return CORES;
    }
  };

  private static final int CORES = Runtime.getRuntime().availableProcessors();

  /**
   * The number of threads relative to the number of available processors on a
   * system. The value returned will never be less than one.
   */
  public abstract int value();

}