Transaction

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org.odmg
Interface Transaction

public interface Transaction

This interfaces provides the operations necessary to perform database transactions. All access, creation, and modification of persistent objects and their fields must be done within a transaction. Before performing any database operations, a thread must explicitly create a transaction object or associate itself with an existing transaction object (by calling join), and that transaction must be open (through a call to begin). All subsequent operations by the thread, including reads, writes, and lock acquisitions, are done under the thread’s current transaction.

A thread may only operate on its current transaction. For example, a TransactionNotInProgressException is thrown if a thread attempts to begin, commit, checkpoint, or abort a transaction prior to joining itself to that transaction.

A transaction is either open or closed. A transaction is open if a call has been made to begin, but no call has been made to commit or abort. Once commit or abort is called, the transaction is closed. The method isOpen can be called to determine the state of the transaction.

Read locks are implicitly obtained on objects as they are accessed. Write locks are implicitly obtained as objects are modified. Transaction objects are transient, they cannot be stored in the database.

Version:: ODMG 3.0

Field Summary

static int READ
          Read lock mode.

static int UPGRADE
          Upgrade lock mode.

static int WRITE
          Write lock mode.

Method Summary

void abort()
          Abort and close the transaction.

void begin()
          Start a transaction.

void checkpoint()
          Commit the transaction, but reopen the transaction, retaining all locks.

void commit()
          Commit and close the transaction.

boolean isOpen()
          Determine whether the transaction is open or not.

void join()
          Attach the caller's thread to this Transaction and detach the thread from any former Transaction the thread may have been associated with.

void leave()
          Detach the caller's thread from this Transaction, but do not attach the thread to another Transaction.

void lock(java.lang.Object obj, int lockMode)
          Upgrade the lock on the given object to the given lock mode.

boolean tryLock(java.lang.Object obj, int lockMode)
          Upgrade the lock on the given object to the given lock mode.

Field Detail

READ

public static final int READ

Read lock mode.

See Also:: Constant Field Values

UPGRADE

public static final int UPGRADE

Upgrade lock mode.

See Also:: Constant Field Values

WRITE

public static final int WRITE

Write lock mode.

See Also:: Constant Field Values

Method Detail

join

public void join()

Attach the caller's thread to this Transaction and detach the thread from any former Transaction the thread may have been associated with.

leave

public void leave()

Detach the caller's thread from this Transaction, but do not attach the thread to another Transaction.

begin

public void begin()

Start a transaction. Calling begin multiple times on the same transaction object, without an intervening call to commit or abort, causes the exception TransactionInProgressException to be thrown on the second and subsequent calls. Operations executed before a transaction has been opened, or before reopening after a transaction is aborted or committed, have undefined results; these may throw a TransactionNotInProgressException exception.

isOpen

public boolean isOpen()

Determine whether the transaction is open or not. A transaction is open if a call has been made to begin, but a subsequent call to either commit or abort has not been made.

commit

public void commit()

Commit and close the transaction. Calling commit commits to the database all persistent object modifications within the transaction and releases any locks held by the transaction. A persistent object modification is an update of any field of an existing persistent object, or an update or creation of a new named object in the database. If a persistent object modification results in a reference from an existing persistent object to a transient object, the transient object is moved to the database, and all references to it updated accordingly. Note that the act of moving a transient object to the database may create still more persistent references to transient objects, so its referents must be examined and moved as well. This process continues until the database contains no references to transient objects, a condition that is guaranteed as part of transaction commit. Committing a transaction does not remove from memory transient objects created during the transaction

abort

public void abort()

Abort and close the transaction. Calling abort abandons all persistent object modifications and releases the associated locks. Aborting a transaction does not restore the state of modified transient objects

checkpoint

public void checkpoint()

Commit the transaction, but reopen the transaction, retaining all locks. Calling checkpoint commits persistent object modifications made within the transaction since the last checkpoint to the database. The transaction retains all locks it held on those objects at the time the checkpoint was invoked.

lock

public void lock(java.lang.Object obj,
                 int lockMode)
          throws LockNotGrantedException

Upgrade the lock on the given object to the given lock mode. The call has no effect if the object's current lock is already at or above that level of lock mode.

tryLock

public boolean tryLock(java.lang.Object obj,
                       int lockMode)

Upgrade the lock on the given object to the given lock mode. Method tryLock is the same as lock except it returns a boolean indicating whether the lock was granted instead of generating an exception.