DelegateExecutionManager.java

package games.strategy.engine.delegate;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.logging.Level;
import java.util.logging.Logger;

import games.strategy.engine.GameOverException;
import games.strategy.engine.framework.headlessGameServer.HeadlessGameServer;
import games.strategy.engine.message.MessengerException;
import games.strategy.triplea.util.WrappedInvocationHandler;

/**
 * Manages when delegates are allowed to execute.
 *
 * <p>
 * When saving a game, we want to ensure that no delegate is executing, otherwise the delegate could modify the state of
 * the game while the
 * game is being saved, resulting in an invalid save game.
 * </p>
 *
 * <p>
 * This class effectivly keeps a count of how many threads are executing in the delegates, and provides a way of
 * blocking further threads
 * from starting execution in a delegate.
 * </p>
 */
public class DelegateExecutionManager {
  private final Logger sm_logger = Logger.getLogger(DelegateExecutionManager.class.getName());
  /*
   * Delegate execution can be thought of as a read/write lock.
   * Many delegates can be executing at one time (to execute you acquire the read lock), but
   * only 1 block can be held (the block is equivalent to the read lock).
   */
  private final ReentrantReadWriteLock m_readWriteLock = new ReentrantReadWriteLock();
  private final ThreadLocal<Boolean> m_currentThreadHasReadLock = new ThreadLocal<>();
  private volatile boolean m_isGameOver = false;

  public void setGameOver() {
    m_isGameOver = true;
  }

  /**
   * When this method returns true, threads will not be able to enter delegates until
   * a call to resumeDelegateExecution is made.
   *
   * <p>
   * When delegateExecution is blocked, it also blocks subsequent cals to blockDelegateExecution(...)
   * </p>
   *
   * <p>
   * If timeToWaitMS is > 0, we will give up trying to block delegate execution after timeTiWaitMS has elapsed.
   * </p>
   */
  public boolean blockDelegateExecution(final int timeToWaitMS) throws InterruptedException {
    final boolean rVal = m_readWriteLock.writeLock().tryLock(timeToWaitMS, TimeUnit.MILLISECONDS);
    if (!rVal) {
      if (sm_logger.isLoggable(Level.FINE)) {
        sm_logger.fine("Could not block delegate execution. Read Lock count: " + m_readWriteLock.getReadLockCount()
            + " Write Hold count: " + m_readWriteLock.getWriteHoldCount() + " Queue Length: "
            + m_readWriteLock.getQueueLength() + " Current Thread Has Lock: "
            + m_readWriteLock.isWriteLockedByCurrentThread() + " Has Queued Threads: "
            + m_readWriteLock.hasQueuedThreads() + " Is Write Locked: " + m_readWriteLock.isWriteLocked()
            + " toString: " + m_readWriteLock.toString());
      } else {
        HeadlessGameServer.log("Could not block delegate execution. Read Lock count: "
            + m_readWriteLock.getReadLockCount() + " Write Hold count: " + m_readWriteLock.getWriteHoldCount()
            + " Queue Length: " + m_readWriteLock.getQueueLength() + " Current Thread Has Lock: "
            + m_readWriteLock.isWriteLockedByCurrentThread() + " Has Queued Threads: "
            + m_readWriteLock.hasQueuedThreads() + " Is Write Locked: " + m_readWriteLock.isWriteLocked()
            + " toString: " + m_readWriteLock.toString());
      }
    } else {
      if (sm_logger.isLoggable(Level.FINE)) {
        sm_logger.fine(Thread.currentThread().getName() + " block delegate execution.");
      }
    }
    return rVal;
  }

  /**
   * Allow delegate execution to resume.
   */
  public void resumeDelegateExecution() {
    if (sm_logger.isLoggable(Level.FINE)) {
      sm_logger.fine(Thread.currentThread().getName() + " resumes delegate execution.");
    }
    m_readWriteLock.writeLock().unlock();
  }

  private boolean currentThreadHasReadLock() {
    return m_currentThreadHasReadLock.get() == Boolean.TRUE;
  }

  /**
   * Used to create an object the exits delegate execution.
   *
   * <p>
   * Objects on this method will decrement the thread lock count when called, and will increment it again when execution
   * is finished.
   * </p>
   */
  public Object createOutboundImplementation(final Object implementor, final Class<?>[] interfaces) {
    assertGameNotOver();
    final InvocationHandler ih = (proxy, method, args) -> {
      assertGameNotOver();
      final boolean threadLocks = currentThreadHasReadLock();
      if (threadLocks) {
        leaveDelegateExecution();
      }
      try {
        return method.invoke(implementor, args);
      } catch (final MessengerException me) {
        throw new GameOverException("Game Over!");
      } catch (final InvocationTargetException ite) {
        assertGameNotOver();
        throw ite;
      } finally {
        if (threadLocks) {
          enterDelegateExecution();
        }
      }
    };
    return Proxy.newProxyInstance(implementor.getClass().getClassLoader(), interfaces, ih);
  }

  private void assertGameNotOver() {
    if (m_isGameOver) {
      throw new GameOverException("Game Over");
    }
  }

  /**
   * Use to create an object that begins delegate execution.
   *
   * <p>
   * Objects on this method will increment the thread lock count when called, and will decrement it again when execution
   * is finished.
   * </p>
   */
  public Object createInboundImplementation(final Object implementor, final Class<?>[] interfaces) {
    assertGameNotOver();
    final InvocationHandler ih = new WrappedInvocationHandler(implementor) {
      @Override
      public Object invoke(final Object proxy, final Method method, final Object[] args) throws Throwable {
        if (super.shouldHandle(method, args)) {
          return super.handle(method, args);
        }
        assertGameNotOver();
        enterDelegateExecution();
        try {
          return method.invoke(implementor, args);
        } catch (final InvocationTargetException ite) {
          assertGameNotOver();
          throw ite.getCause();
        } catch (final RuntimeException re) {
          assertGameNotOver();
          throw re;
        } finally {
          leaveDelegateExecution();
        }
      }
    };
    return Proxy.newProxyInstance(implementor.getClass().getClassLoader(), interfaces, ih);
  }

  public void leaveDelegateExecution() {
    if (sm_logger.isLoggable(Level.FINE)) {
      sm_logger.fine(Thread.currentThread().getName() + " leaves delegate execution.");
    }
    m_readWriteLock.readLock().unlock();
    m_currentThreadHasReadLock.set(null);
  }

  public void enterDelegateExecution() {
    if (sm_logger.isLoggable(Level.FINE)) {
      sm_logger.fine(Thread.currentThread().getName() + " enters delegate execution.");
    }
    if (currentThreadHasReadLock()) {
      throw new IllegalStateException("Already locked?");
    }
    m_readWriteLock.readLock().lock();
    m_currentThreadHasReadLock.set(Boolean.TRUE);
  }
}