Lock.java

package com.sleepycat.je.txn;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.dbi.MemoryBudget;
import de.ovgu.cide.jakutil.*;
/** 
 * A Lock embodies the lock state of a NodeId.  It includes a set of owners and
 * a list of waiters.
 */
public class Lock {
  /** 
 * A single locker always appears only once in the logical set of owners.
 * The owners set is always in one of the following states.
 * 1- Empty
 * 2- A single writer
 * 3- One or more readers
 * 4- Multiple writers or a mix of readers and writers, all for
 * txns which share locks (all ThreadLocker instances for the same
 * thread)
 * Both ownerSet and waiterList are a collection of LockInfo.  Since the
 * common case is that there is only one owner or waiter, we have added an
 * optimization to avoid the cost of collections.  FirstOwner and
 * firstWaiter are used for the first owner or waiter of the lock, and the
 * corresponding collection is instantiated and used only if more owners
 * arrive.
 * In terms of memory accounting, we count up the cost of each added or
 * removed LockInfo, but not the cost of the HashSet/List entry
 * overhead. We could do the latter for more precise accounting.
 */
  private LockInfo firstOwner;
  private Set ownerSet;
  private LockInfo firstWaiter;
  private List waiterList;
  private Long nodeId;
  /** 
 * Create a Lock.
 */
  Lock(  Long nodeId){
    this.nodeId=nodeId;
  }
  public Lock(){
  }
  Long getNodeId(){
    return nodeId;
  }
  /** 
 * The first waiter goes into the firstWaiter member variable.  Once the
 * waiterList is made, all appended waiters go into waiterList, even after
 * the firstWaiter goes away and leaves that field null, so as to leave the
 * list ordered.
 */
  private void addWaiterToEndOfList(  LockInfo waiter,  MemoryBudget mb,  int lockTableIndex){
    if (waiterList == null) {
      if (firstWaiter == null) {
        firstWaiter=waiter;
      }
 else {
        waiterList=new ArrayList();
        waiterList.add(waiter);
      }
    }
 else {
      waiterList.add(waiter);
    }
    this.hook760(mb,lockTableIndex);
  }
  /** 
 * Add this waiter to the front of the list.
 */
  private void addWaiterToHeadOfList(  LockInfo waiter,  MemoryBudget mb,  int lockTableIndex){
    if (firstWaiter != null) {
      if (waiterList == null) {
        waiterList=new ArrayList();
      }
      waiterList.add(0,firstWaiter);
    }
    firstWaiter=waiter;
    this.hook761(mb,lockTableIndex);
  }
  /** 
 * Get a list of waiters for debugging and error messages.
 */
  List getWaitersListClone(){
    List dumpWaiters=new ArrayList();
    if (firstWaiter != null) {
      dumpWaiters.add(firstWaiter);
    }
    if (waiterList != null) {
      dumpWaiters.addAll(waiterList);
    }
    return dumpWaiters;
  }
  /** 
 * Remove this locker from the waiter list.
 */
  void flushWaiter(  Locker locker,  MemoryBudget mb,  int lockTableIndex){
    if ((firstWaiter != null) && (firstWaiter.getLocker() == locker)) {
      firstWaiter=null;
      this.hook762(mb,lockTableIndex);
    }
 else     if (waiterList != null) {
      Iterator iter=waiterList.iterator();
      while (iter.hasNext()) {
        LockInfo info=(LockInfo)iter.next();
        if (info.getLocker() == locker) {
          iter.remove();
          this.hook763(mb,lockTableIndex);
          return;
        }
      }
    }
  }
  private void addOwner(  LockInfo newLock,  MemoryBudget mb,  int lockTableIndex){
    if (firstOwner == null) {
      firstOwner=newLock;
    }
 else {
      if (ownerSet == null) {
        ownerSet=new HashSet();
      }
      ownerSet.add(newLock);
    }
    this.hook764(mb,lockTableIndex);
  }
  /** 
 * Get a new Set of the owners.
 */
  Set getOwnersClone(){
    Set owners;
    if (ownerSet != null) {
      owners=new HashSet(ownerSet);
    }
 else {
      owners=new HashSet();
    }
    if (firstOwner != null) {
      owners.add(firstOwner);
    }
    return owners;
  }
  /** 
 * Remove this LockInfo from the owner set.
 */
  private boolean flushOwner(  LockInfo oldOwner,  MemoryBudget mb,  int lockTableIndex){
    boolean removed=false;
    if (oldOwner != null) {
      if (firstOwner == oldOwner) {
        firstOwner=null;
        return true;
      }
      if (ownerSet != null) {
        removed=ownerSet.remove(oldOwner);
      }
    }
    this.hook765(mb,lockTableIndex,removed);
    return removed;
  }
  /** 
 * Remove this locker from the owner set.
 */
  private LockInfo flushOwner(  Locker locker,  MemoryBudget mb,  int lockTableIndex){
    LockInfo flushedInfo=null;
    if ((firstOwner != null) && (firstOwner.getLocker() == locker)) {
      flushedInfo=firstOwner;
      firstOwner=null;
    }
 else     if (ownerSet != null) {
      Iterator iter=ownerSet.iterator();
      while (iter.hasNext()) {
        LockInfo o=(LockInfo)iter.next();
        if (o.getLocker() == locker) {
          iter.remove();
          flushedInfo=o;
        }
      }
    }
    this.hook766(mb,lockTableIndex,flushedInfo);
    return flushedInfo;
  }
  /** 
 * Returns the owner LockInfo for a locker, or null if locker is not an
 * owner.
 */
  private LockInfo getOwnerLockInfo(  Locker locker){
    if ((firstOwner != null) && (firstOwner.getLocker() == locker)) {
      return firstOwner;
    }
    if (ownerSet != null) {
      Iterator iter=ownerSet.iterator();
      while (iter.hasNext()) {
        LockInfo o=(LockInfo)iter.next();
        if (o.getLocker() == locker) {
          return o;
        }
      }
    }
    return null;
  }
  /** 
 * Return true if locker is an owner of this Lock for lockType,
 * false otherwise.
 * This method is only used by unit tests.
 */
  boolean isOwner(  Locker locker,  LockType lockType){
    LockInfo o=getOwnerLockInfo(locker);
    if (o != null) {
      LockType ownedLockType=o.getLockType();
      if (lockType == ownedLockType) {
        return true;
      }
      LockUpgrade upgrade=ownedLockType.getUpgrade(lockType);
      if (!upgrade.getPromotion()) {
        return true;
      }
    }
    return false;
  }
  /** 
 * Return true if locker is an owner of this Lock and this is a write
 * lock.
 */
  boolean isOwnedWriteLock(  Locker locker){
    LockInfo o=getOwnerLockInfo(locker);
    return o != null && o.getLockType().isWriteLock();
  }
  /** 
 * Return true if locker is a waiter on this Lock.
 * This method is only used by unit tests.
 */
  boolean isWaiter(  Locker locker){
    if (firstWaiter != null) {
      if (firstWaiter.getLocker() == locker) {
        return true;
      }
    }
    if (waiterList != null) {
      Iterator iter=waiterList.iterator();
      while (iter.hasNext()) {
        LockInfo info=(LockInfo)iter.next();
        if (info.getLocker() == locker) {
          return true;
        }
      }
    }
    return false;
  }
  int nWaiters(){
    int count=0;
    if (firstWaiter != null) {
      count++;
    }
    if (waiterList != null) {
      count+=waiterList.size();
    }
    return count;
  }
  int nOwners(){
    int count=0;
    if (firstOwner != null) {
      count++;
    }
    if (ownerSet != null) {
      count+=ownerSet.size();
    }
    return count;
  }
  /** 
 * Attempts to acquire the lock and returns the LockGrantType.
 * Assumes we hold the lockTableLatch when entering this method.
 */
  LockGrantType lock(  LockType requestType,  Locker locker,  boolean nonBlockingRequest,  MemoryBudget mb,  int lockTableIndex){
    assert validateRequest(locker);
    LockInfo newLock=new LockInfo(locker,requestType);
    LockGrantType grant=tryLock(newLock,nWaiters() == 0,mb,lockTableIndex);
    if (grant == LockGrantType.WAIT_NEW || grant == LockGrantType.WAIT_PROMOTION || grant == LockGrantType.WAIT_RESTART) {
      if (requestType.getCausesRestart() && grant != LockGrantType.WAIT_RESTART) {
        LockInfo waiter=null;
        Iterator iter=null;
        if (waiterList != null) {
          iter=waiterList.iterator();
        }
        if (firstWaiter != null) {
          waiter=firstWaiter;
        }
 else         if ((iter != null) && (iter.hasNext())) {
          waiter=(LockInfo)iter.next();
        }
        while (waiter != null) {
          Locker waiterLocker=waiter.getLocker();
          LockType waiterType=waiter.getLockType();
          if (waiterType != LockType.RESTART && locker != waiterLocker && !locker.sharesLocksWith(waiterLocker)) {
            LockConflict conflict=waiterType.getConflict(requestType);
            if (conflict.getRestart()) {
              grant=LockGrantType.WAIT_RESTART;
              break;
            }
          }
          if ((iter != null) && (iter.hasNext())) {
            waiter=(LockInfo)iter.next();
          }
 else {
            waiter=null;
          }
        }
      }
      if (nonBlockingRequest) {
        grant=LockGrantType.DENIED;
      }
 else {
        if (grant == LockGrantType.WAIT_PROMOTION) {
          addWaiterToHeadOfList(newLock,mb,lockTableIndex);
        }
 else {
          assert grant == LockGrantType.WAIT_NEW || grant == LockGrantType.WAIT_RESTART;
          if (grant == LockGrantType.WAIT_RESTART) {
            newLock.setLockType(LockType.RESTART);
          }
          addWaiterToEndOfList(newLock,mb,lockTableIndex);
        }
      }
    }
    return grant;
  }
  /** 
 * Releases a lock and moves the next waiter(s) to the owners.
 * @returnnull if we were not the owner,
 * a non-empty set if owners should be notified after releasing,
 * an empty set if no notification is required.
 */
  Set release(  Locker locker,  MemoryBudget mb,  int lockTableIndex){
    LockInfo removedLock=flushOwner(locker,mb,lockTableIndex);
    if (removedLock == null) {
      return null;
    }
    Set lockersToNotify=Collections.EMPTY_SET;
    if (nWaiters() == 0) {
      return lockersToNotify;
    }
    LockInfo waiter=null;
    Iterator iter=null;
    boolean isFirstWaiter=false;
    if (waiterList != null) {
      iter=waiterList.iterator();
    }
    if (firstWaiter != null) {
      waiter=firstWaiter;
      isFirstWaiter=true;
    }
 else     if ((iter != null) && (iter.hasNext())) {
      waiter=(LockInfo)iter.next();
    }
    while (waiter != null) {
      LockType waiterType=waiter.getLockType();
      Locker waiterLocker=waiter.getLocker();
      LockGrantType grant;
      if (waiterType == LockType.RESTART) {
        grant=rangeInsertConflict(waiterLocker) ? LockGrantType.WAIT_NEW : LockGrantType.NEW;
      }
 else {
        grant=tryLock(waiter,true,mb,lockTableIndex);
      }
      if (grant == LockGrantType.NEW || grant == LockGrantType.EXISTING || grant == LockGrantType.PROMOTION) {
        if (isFirstWaiter) {
          firstWaiter=null;
        }
 else {
          iter.remove();
        }
        if (lockersToNotify == Collections.EMPTY_SET) {
          lockersToNotify=new HashSet();
        }
        lockersToNotify.add(waiterLocker);
        this.hook767(mb,lockTableIndex);
      }
 else {
        assert grant == LockGrantType.WAIT_NEW || grant == LockGrantType.WAIT_PROMOTION || grant == LockGrantType.WAIT_RESTART;
        break;
      }
      if ((iter != null) && (iter.hasNext())) {
        waiter=(LockInfo)iter.next();
        isFirstWaiter=false;
      }
 else {
        waiter=null;
      }
    }
    return lockersToNotify;
  }
  /** 
 * Called from lock() to try locking a new request, and from release() to
 * try locking a waiting request.
 * @param newLock is the lock that is requested.
 * @param firstWaiterInLine determines whether to grant the lock when a
 * NEW lock can be granted, but other non-conflicting owners exist; for
 * example, when a new READ lock is requested but READ locks are held by
 * other owners.  This parameter should be true if the requestor is the
 * first waiter in line (or if there are no waiters), and false otherwise.
 * @param mb is the current memory budget.
 * @return LockGrantType.EXISTING, NEW, PROMOTION, WAIT_RESTART, WAIT_NEW
 * or WAIT_PROMOTION.
 */
  private LockGrantType tryLock(  LockInfo newLock,  boolean firstWaiterInLine,  MemoryBudget mb,  int lockTableIndex){
    if (nOwners() == 0) {
      addOwner(newLock,mb,lockTableIndex);
      return LockGrantType.NEW;
    }
    Locker locker=newLock.getLocker();
    LockType requestType=newLock.getLockType();
    LockUpgrade upgrade=null;
    LockInfo lockToUpgrade=null;
    boolean ownerExists=false;
    boolean ownerConflicts=false;
    LockInfo owner=null;
    Iterator iter=null;
    if (ownerSet != null) {
      iter=ownerSet.iterator();
    }
    if (firstOwner != null) {
      owner=firstOwner;
    }
 else     if ((iter != null) && (iter.hasNext())) {
      owner=(LockInfo)iter.next();
    }
    while (owner != null) {
      Locker ownerLocker=owner.getLocker();
      LockType ownerType=owner.getLockType();
      if (locker == ownerLocker) {
        assert (upgrade == null);
        upgrade=ownerType.getUpgrade(requestType);
        if (upgrade.getUpgrade() == null) {
          return LockGrantType.EXISTING;
        }
 else {
          lockToUpgrade=owner;
        }
      }
 else {
        if (!locker.sharesLocksWith(ownerLocker)) {
          LockConflict conflict=ownerType.getConflict(requestType);
          if (conflict.getRestart()) {
            return LockGrantType.WAIT_RESTART;
          }
 else {
            if (!conflict.getAllowed()) {
              ownerConflicts=true;
            }
            ownerExists=true;
          }
        }
      }
      if ((iter != null) && (iter.hasNext())) {
        owner=(LockInfo)iter.next();
      }
 else {
        owner=null;
      }
    }
    if (upgrade != null) {
      LockType upgradeType=upgrade.getUpgrade();
      assert upgradeType != null;
      if (!ownerConflicts) {
        lockToUpgrade.setLockType(upgradeType);
        return upgrade.getPromotion() ? LockGrantType.PROMOTION : LockGrantType.EXISTING;
      }
 else {
        return LockGrantType.WAIT_PROMOTION;
      }
    }
 else {
      if (!ownerConflicts && (!ownerExists || firstWaiterInLine)) {
        addOwner(newLock,mb,lockTableIndex);
        return LockGrantType.NEW;
      }
 else {
        return LockGrantType.WAIT_NEW;
      }
    }
  }
  /** 
 * Called from release() when a RESTART request is waiting to determine if
 * any RANGE_INSERT owners exist.  We can't call tryLock for a RESTART
 * lock because it must never be granted.
 */
  private boolean rangeInsertConflict(  Locker waiterLocker){
    LockInfo owner=null;
    Iterator iter=null;
    if (ownerSet != null) {
      iter=ownerSet.iterator();
    }
    if (firstOwner != null) {
      owner=firstOwner;
    }
 else     if ((iter != null) && (iter.hasNext())) {
      owner=(LockInfo)iter.next();
    }
    while (owner != null) {
      Locker ownerLocker=owner.getLocker();
      if (ownerLocker != waiterLocker && !ownerLocker.sharesLocksWith(waiterLocker) && owner.getLockType() == LockType.RANGE_INSERT) {
        return true;
      }
      if ((iter != null) && (iter.hasNext())) {
        owner=(LockInfo)iter.next();
      }
 else {
        owner=null;
      }
    }
    return false;
  }
  /** 
 * Downgrade a write lock to a read lock.
 */
  void demote(  Locker locker){
    LockInfo owner=getOwnerLockInfo(locker);
    if (owner != null) {
      LockType type=owner.getLockType();
      if (type.isWriteLock()) {
        owner.setLockType((type == LockType.RANGE_WRITE) ? LockType.RANGE_READ : LockType.READ);
      }
    }
  }
  /** 
 * Transfer a lock from one transaction to another. Make sure that this
 * destination locker is only present as a single reader or writer.
 */
  LockType transfer(  Locker currentLocker,  Locker destLocker,  MemoryBudget mb,  int lockTableIndex) throws DatabaseException {
    LockType lockType=null;
    int numRemovedLockInfos=0;
    if (firstOwner != null) {
      if (firstOwner.getLocker() == destLocker) {
        firstOwner=null;
        numRemovedLockInfos++;
      }
 else       if (firstOwner.getLocker() == currentLocker) {
        lockType=setNewLocker(firstOwner,destLocker);
      }
    }
    if (ownerSet != null) {
      Iterator iter=ownerSet.iterator();
      while (iter.hasNext()) {
        LockInfo owner=(LockInfo)iter.next();
        if (owner.getLocker() == destLocker) {
          iter.remove();
          numRemovedLockInfos++;
        }
 else         if (owner.getLocker() == currentLocker) {
          lockType=setNewLocker(owner,destLocker);
        }
      }
    }
    if ((firstWaiter != null) && (firstWaiter.getLocker() == destLocker)) {
      firstWaiter=null;
      numRemovedLockInfos++;
    }
    if (waiterList != null) {
      Iterator iter=waiterList.iterator();
      while (iter.hasNext()) {
        LockInfo info=(LockInfo)iter.next();
        if (info.getLocker() == destLocker) {
          iter.remove();
          numRemovedLockInfos++;
        }
      }
    }
    this.hook768(mb,lockTableIndex,numRemovedLockInfos);
    return lockType;
  }
  private LockType setNewLocker(  LockInfo owner,  Locker destLocker) throws DatabaseException {
    owner.setLocker(destLocker);
    destLocker.addLock(nodeId,this,owner.getLockType(),LockGrantType.NEW);
    return owner.getLockType();
  }
  /** 
 * Transfer a lock from one transaction to many others. Only really needed
 * for case where a write handle lock is being transferred to multiple read
 * handles.
 */
  LockType transferMultiple(  Locker currentLocker,  Locker[] destLockers,  MemoryBudget mb,  int lockTableIndex) throws DatabaseException {
    LockType lockType=null;
    LockInfo oldOwner=null;
    if (destLockers.length == 1) {
      return transfer(currentLocker,destLockers[0],mb,lockTableIndex);
    }
 else {
      if (firstOwner != null) {
        for (int i=0; i < destLockers.length; i++) {
          if (firstOwner.getLocker() == destLockers[i]) {
            firstOwner=null;
            break;
          }
        }
      }
      if (ownerSet != null) {
        Iterator ownersIter=ownerSet.iterator();
        while (ownersIter.hasNext()) {
          LockInfo o=(LockInfo)ownersIter.next();
          for (int i=0; i < destLockers.length; i++) {
            if (o.getLocker() == destLockers[i]) {
              ownersIter.remove();
              break;
            }
          }
        }
      }
      if (firstOwner != null) {
        oldOwner=cloneLockInfo(firstOwner,currentLocker,destLockers,mb,lockTableIndex);
      }
      if ((ownerSet != null) && (oldOwner == null)) {
        Iterator ownersIter=ownerSet.iterator();
        while (ownersIter.hasNext()) {
          LockInfo o=(LockInfo)ownersIter.next();
          oldOwner=cloneLockInfo(o,currentLocker,destLockers,mb,lockTableIndex);
          if (oldOwner != null) {
            break;
          }
        }
      }
      if (firstWaiter != null) {
        for (int i=0; i < destLockers.length; i++) {
          if (firstWaiter.getLocker() == destLockers[i]) {
            firstWaiter=null;
            break;
          }
        }
      }
      if (waiterList != null) {
        Iterator iter=waiterList.iterator();
        while (iter.hasNext()) {
          LockInfo o=(LockInfo)iter.next();
          for (int i=0; i < destLockers.length; i++) {
            if (o.getLocker() == destLockers[i]) {
              iter.remove();
              break;
            }
          }
        }
      }
    }
    boolean removed=flushOwner(oldOwner,mb,lockTableIndex);
    assert removed;
    return lockType;
  }
  /** 
 * If oldOwner is the current owner, clone it and transform it into a dest
 * locker.
 */
  private LockInfo cloneLockInfo(  LockInfo oldOwner,  Locker currentLocker,  Locker[] destLockers,  MemoryBudget mb,  int lockTableIndex) throws DatabaseException {
    if (oldOwner.getLocker() == currentLocker) {
      try {
        LockType lockType=oldOwner.getLockType();
        for (int i=0; i < destLockers.length; i++) {
          LockInfo clonedLockInfo=(LockInfo)oldOwner.clone();
          clonedLockInfo.setLocker(destLockers[i]);
          destLockers[i].addLock(nodeId,this,lockType,LockGrantType.NEW);
          addOwner(clonedLockInfo,mb,lockTableIndex);
        }
        return oldOwner;
      }
 catch (      CloneNotSupportedException e) {
        throw new DatabaseException(e);
      }
    }
 else {
      return null;
    }
  }
  /** 
 * Return the locker that has a write ownership on this lock. If no
 * write owner exists, return null.
 */
  Locker getWriteOwnerLocker(){
    LockInfo owner=null;
    Iterator iter=null;
    if (ownerSet != null) {
      iter=ownerSet.iterator();
    }
    if (firstOwner != null) {
      owner=firstOwner;
    }
 else     if ((iter != null) && (iter.hasNext())) {
      owner=(LockInfo)iter.next();
    }
    while (owner != null) {
      if (owner.getLockType().isWriteLock()) {
        return owner.getLocker();
      }
      if ((iter != null) && (iter.hasNext())) {
        owner=(LockInfo)iter.next();
      }
 else {
        owner=null;
      }
    }
    return null;
  }
  /** 
 * Debugging aid, validation before a lock request.
 */
  private boolean validateRequest(  Locker locker){
    if (firstWaiter != null) {
      if (firstWaiter.getLocker() == locker) {
        assert false : "locker " + locker + " is already on waiters list.";
      }
    }
    if (waiterList != null) {
      Iterator iter=waiterList.iterator();
      while (iter.hasNext()) {
        LockInfo o=(LockInfo)iter.next();
        if (o.getLocker() == locker) {
          assert false : "locker " + locker + " is already on waiters list.";
        }
      }
    }
    return true;
  }
  /** 
 * Debug dumper.
 */
  public String toString(){
    StringBuffer sb=new StringBuffer();
    sb.append(" NodeId:").append(nodeId);
    sb.append(" Owners:");
    if (nOwners() == 0) {
      sb.append(" (none)");
    }
 else {
      if (firstOwner != null) {
        sb.append(firstOwner);
      }
      if (ownerSet != null) {
        Iterator iter=ownerSet.iterator();
        while (iter.hasNext()) {
          LockInfo info=(LockInfo)iter.next();
          sb.append(info);
        }
      }
    }
    sb.append(" Waiters:");
    if (nWaiters() == 0) {
      sb.append(" (none)");
    }
 else {
      sb.append(getWaitersListClone());
    }
    return sb.toString();
  }
  protected void hook760(  MemoryBudget mb,  int lockTableIndex){
  }
  protected void hook761(  MemoryBudget mb,  int lockTableIndex){
  }
  protected void hook762(  MemoryBudget mb,  int lockTableIndex){
  }
  protected void hook763(  MemoryBudget mb,  int lockTableIndex){
  }
  protected void hook764(  MemoryBudget mb,  int lockTableIndex){
  }
  protected void hook765(  MemoryBudget mb,  int lockTableIndex,  boolean removed){
  }
  protected void hook766(  MemoryBudget mb,  int lockTableIndex,  LockInfo flushedInfo){
  }
  protected void hook767(  MemoryBudget mb,  int lockTableIndex){
  }
  protected void hook768(  MemoryBudget mb,  int lockTableIndex,  int numRemovedLockInfos) throws DatabaseException {
  }
}