/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 2002,2009 Oracle.  All rights reserved.
 *
 * $Id: ThinLockImpl.java,v 1.6.2.1 2009/01/06 04:36:48 cwl Exp $
 */

package com.sleepycat.je.txn;

import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.dbi.MemoryBudget;

/**
 * Implements a lightweight Lock with no waiters and only a single Owner.  If,
 * during an operation (lock, transfer, or transferMultiple) more than one
 * owner or waiter is required, then this will mutate to a LockImpl, perform
 * the requested operation, and return the new LockImpl to the caller.
 *
 * public for Sizeof.
 */
public class ThinLockImpl extends LockInfo implements Lock {

    /**
     * Create a Lock.  Public for Sizeof.
     */
    public ThinLockImpl() {
	super(null, null);
    }

    public List<LockInfo> getWaitersListClone() {
        return Collections.emptyList();
    }

    public void flushWaiter(Locker locker,
			    MemoryBudget mb,
			    int lockTableIndex) {

	/* Do nothing. */
	return;
    }

    public Set<LockInfo> getOwnersClone() {

	Set<LockInfo> ret = new HashSet<LockInfo>();
	if (locker != null) {
	    ret.add(this);
	}
	return ret;
    }

    public boolean isOwner(Locker locker, LockType lockType) {

	if (locker == this.locker) {
	    if (lockType == this.lockType) {
		return true;
	    }

	    if (this.lockType != null) {
		LockUpgrade upgrade = this.lockType.getUpgrade(lockType);
		if (!upgrade.getPromotion()) {
		    return true;
		}
	    }
	} else {
	    return false;
	}
	return false;
    }

    public boolean isOwnedWriteLock(Locker locker) {

	if (locker != this.locker) {
	    return false;
	}

	if (this.lockType != null) {
	    return this.lockType.isWriteLock();
	} else {
	    return false;
	}
    }

    public boolean isWaiter(Locker locker) {

	/* There can never be waiters on Thin Locks. */
        return false;
    }

    public int nWaiters() {
        return 0;
    }

    public int nOwners() {
        return (locker == null ? 0 : 1);
    }

    public LockAttemptResult lock(LockType requestType,
				  Locker locker,
				  boolean nonBlockingRequest,
				  MemoryBudget mb,
				  int lockTableIndex)
	throws DatabaseException {

	if (this.locker != null &&
	    this.locker != locker) {
	    /* Lock is already held by someone else so mutate. */
	    Lock newLock =
		new LockImpl(new LockInfo(this.locker, this.lockType));
	    return newLock.lock(requestType, locker, nonBlockingRequest,
				mb, lockTableIndex);
	}

	LockGrantType grant = null;
	if (this.locker == null) {
	    this.locker = locker;
	    this.lockType = requestType;
	    grant = LockGrantType.NEW;
	} else {

	    /* The requestor holds this lock.  Check for upgrades. */
	    LockUpgrade upgrade = lockType.getUpgrade(requestType);
	    if (upgrade.getUpgrade() == null) {
		grant = LockGrantType.EXISTING;
	    } else {
		LockType upgradeType = upgrade.getUpgrade();
		assert upgradeType != null;
		this.lockType = upgradeType;
		grant = (upgrade.getPromotion() ?
			 LockGrantType.PROMOTION : LockGrantType.EXISTING);
	    }
	}
	return new LockAttemptResult(this, grant, false);
    }

    public Set<Locker> release(Locker locker, 
                               MemoryBudget mb, 
                               int lockTableIndex) {

	if (locker == this.locker) {
	    this.locker = null;
	    this.lockType = null;
	    return Collections.emptySet();
	} else {
	    return null;
	}
    }

    public void demote(Locker locker) {

	if (this.lockType.isWriteLock()) {
	    this.lockType = (lockType == LockType.RANGE_WRITE) ?
		LockType.RANGE_READ : LockType.READ;
	}
    }

    public Lock transfer(Long nodeId,
			 Locker currentLocker,
			 Locker destLocker,
			 MemoryBudget mb,
			 int lockTableIndex)
        throws DatabaseException {

	Lock newLock = new LockImpl(new LockInfo(this.locker, this.lockType));
	return newLock.transfer(nodeId, currentLocker, destLocker,
				mb, lockTableIndex);
    }

    public Lock transferMultiple(Long nodeId,
				 Locker currentLocker,
				 Locker[] destLockers,
				 MemoryBudget mb,
				 int lockTableIndex)
        throws DatabaseException {

	Lock newLock = new LockImpl(new LockInfo(this.locker, this.lockType));
	return newLock.transferMultiple(nodeId, currentLocker, destLockers,
					mb, lockTableIndex);
    }

    public Locker getWriteOwnerLocker() {

	if (lockType != null &&
	    lockType.isWriteLock()) {
	    return locker;
	} else {
	    return null;
	}
    }

    public boolean isThin() {
	return true;
    }

    @Override
    public String toString() {

        StringBuffer sb = new StringBuffer();
        sb.append(" ThinLockAddr:").append(System.identityHashCode(this));
        sb.append(" Owner:");
        if (nOwners() == 0) {
            sb.append(" (none)");
        } else {
	    sb.append(locker);
        }

        sb.append(" Waiters: (none)");
        return sb.toString();
    }
}
