com.sun.sgs.impl.util.lock
Class TxnLockManager<K>

java.lang.Object
  com.sun.sgs.impl.util.lock.LockManager<K>
      com.sun.sgs.impl.util.lock.TxnLockManager<K>

Type Parameters:

K - the type of key

public final class TxnLockManager<K>
extends LockManager<K>

A class for managing lock conflicts of a transaction. Calls on behalf of a locker should only be made from a single thread at a time. All Locker objects supplied to this class should be instances of TxnLocker.

This implementation checks for deadlock whenever a lock request is blocked due to a conflict. It selects as the deadlock victim the locker with the latest requested start time. The implementation does not deny requests that would not result in deadlock. When requests block, it services the requests in the order that they arrive.

This class and its superclass use the Logger named com.sun.sgs.impl.util.lock to log information at the following logging levels:

• FINER - Releasing locks; requesting, waiting for, and returning from lock requests
• FINEST - Notifying new lock owners, results of requesting locks before waiting, releasing locks, results of attempting to assign locks to waiters

Field Summary

Fields inherited from class com.sun.sgs.impl.util.lock.LockManager

currentKeySync, currentLockerSync, logger

Constructor Summary

TxnLockManager(long lockTimeout, int numKeyMaps)
Creates an instance of this class.

Method Summary

LockConflict<K>	lock(Locker<K> locker, K key, boolean forWrite) Attempts to acquire a lock, waiting if needed.
LockConflict<K>	lockNoWait(Locker<K> locker, K key, boolean forWrite) Attempts to acquire a lock, returning immediately.
(package private) LockConflict<K>	lockNoWaitInternal(Locker<K> locker, K key, boolean forWrite) Attempts to acquire a lock, returning immediately.
LockConflict<K>	waitForLock(Locker<K> locker) Waits for a previous attempt to obtain a lock that blocked.

Methods inherited from class com.sun.sgs.impl.util.lock.LockManager

getKeyMap, getLock, getOwners, getWaiters, releaseLock, releaseLockInternal, waitForLockInternal

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TxnLockManager

public TxnLockManager(long lockTimeout,
                      int numKeyMaps)

Creates an instance of this class.

Parameters:

lockTimeout - the maximum number of milliseconds to acquire a lock

numKeyMaps - the number of separate maps to use for storing keys

Throws:

IllegalArgumentException - if lockTimeout or numKeyMaps is less than 1

Method Detail

lock

public LockConflict<K> lock(Locker<K> locker,
                            K key,
                            boolean forWrite)

Attempts to acquire a lock, waiting if needed. Returns information about conflicts that occurred while attempting to acquire the lock that prevented the lock from being acquired, or else null if the lock was acquired. If the type field of the return value is DEADLOCK, then the caller should abort the transaction, and any subsequent lock or wait requests will throw IllegalStateException. Otherwise, the caller can repeat this call, and any conflicts from earlier calls will be ignored.

Overrides:

lock in class LockManager<K>

Parameters:

locker - the locker requesting the lock

key - the key identifying the lock

forWrite - whether to request a write lock

Returns:

lock conflict information, or null if there was no conflict

Throws:

IllegalArgumentException - if locker has a different lock manager, or if locker is not an instance of TxnLocker

lockNoWait

public LockConflict<K> lockNoWait(Locker<K> locker,
                                  K key,
                                  boolean forWrite)

Attempts to acquire a lock, returning immediately. Returns information about any conflict that occurred while attempting to acquire the lock, or else null if the lock was acquired. If the attempt to acquire the lock was blocked, returns a value with a type field of BLOCKED rather than waiting. If the type field of the return value is DEADLOCK, then the caller should abort the transaction, and any subsequent lock or wait requests will throw IllegalStateException. Otherwise, the caller can repeat this call, and any conflicts from earlier calls will be ignored.

Overrides:

lockNoWait in class LockManager<K>

Parameters:

locker - the locker requesting the lock

key - the key identifying the lock

forWrite - whether to request a write lock

Returns:

lock conflict information, or null if there was no conflict

Throws:

IllegalArgumentException - if locker has a different lock manager, or if locker is not an instance of TxnLocker

waitForLock

public LockConflict<K> waitForLock(Locker<K> locker)

Waits for a previous attempt to obtain a lock that blocked. Returns information about any conflict that occurred while attempting to acquire the lock, or else null if the lock was acquired or the transaction was not waiting. If the type field of the return value is DEADLOCK, then the caller should abort the transaction, and any subsequent lock or wait requests will throw IllegalStateException.

Overrides:

waitForLock in class LockManager<K>

Parameters:

locker - the locker requesting the lock

Returns:

lock conflict information, or null if there was no conflict

Throws:

IllegalArgumentException - if locker has a different lock manager, or if locker is not an instance of TxnLocker

lockNoWaitInternal

LockConflict<K> lockNoWaitInternal(Locker<K> locker,
                                   K key,
                                   boolean forWrite)

Attempts to acquire a lock, returning immediately. Like LockManager.lockNoWait(com.sun.sgs.impl.util.lock.Locker, K, boolean), but does not check that the correct lock manager was supplied.

This implementation calls the deadlock checker if the request blocks.

Overrides:

lockNoWaitInternal in class LockManager<K>

Parameters:

locker - the locker requesting the lock

key - the key identifying the lock

forWrite - whether to request a write lock

Returns:

lock conflict information, or null if there was no conflict

Throws:

IllegalStateException - if an earlier lock attempt for this transaction produced a deadlock, or if still waiting for an earlier attempt to complete