sos.db
Class DefaultTransactionPolicy

java.lang.Object
  sos.db.AbstractTransactionPolicy
      sos.db.DefaultTransactionPolicy

All Implemented Interfaces:

java.io.Serializable, TransactionPolicy

public class DefaultTransactionPolicy
extends AbstractTransactionPolicy
implements TransactionPolicy

A transaction policy that uses a single database lock to ensure that transactions appear to execute sequentially. For any transaction to make progress it must hold the single database lock. An instance of this class should not be shared among databases.

With this policy, there is no chance for deadlock. If the transaction holding the lock never commits or aborts, however, then another transaction would wait forever and no progress would be made. To avoid this starvation, a timeout interval is used. A transaction will wait for a lock the number of milliseconds specified in the constructor.

This policy allows no concurrency in transactions. To allow operations on different objects to execute concurrently, consider using DefaultReadWriteTransactionPolicy instead of this class.

This policy is adequate for applications in which all transactions execute on the same thread or for applications in which there is high transaction contention.

Since:

1.0

See Also:

DefaultReadWriteTransactionPolicy

Constructor Summary

DefaultTransactionPolicy()
Creates an instance of DefaultTransactionPolicy with a default lock timeout of Long.MAX_VALUE milliseconds.

DefaultTransactionPolicy(long timeout)
Creates an instance of DefaultTransactionPolicy with the specified lock timeout.

Method Summary

protected void	logLockAcquired(java.lang.String databaseName) Records that the database lock has been acquired.
protected void	logLockReleased(java.lang.String databaseName) Records that the database lock has been released.
void	startTransaction(TransactionSupport support) Notifies this policy that a top-level transaction is starting for the executing thread.

Methods inherited from class sos.db.AbstractTransactionPolicy

getMethodStatus, invoke, logMethodInvocation, prepareForReadOnlyInvocation, prepareForWriteInvocation, registerObject, unregisterObjects

Methods inherited from class java.lang.Object

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

Methods inherited from interface sos.db.TransactionPolicy

invoke, registerObject, unregisterObjects

Constructor Detail

DefaultTransactionPolicy

public DefaultTransactionPolicy()

Creates an instance of DefaultTransactionPolicy with a default lock timeout of Long.MAX_VALUE milliseconds.

See Also:

DefaultTransactionPolicy(long)

DefaultTransactionPolicy

public DefaultTransactionPolicy(long timeout)

Creates an instance of DefaultTransactionPolicy with the specified lock timeout.

Parameters:

timeout - maximum time to wait (in milliseconds) for the database lock

Method Detail

logLockAcquired

protected void logLockAcquired(java.lang.String databaseName)

Records that the database lock has been acquired.

This implementation uses the localized message for key "logLockAcquired". The message takes two parameters: the database name and the transaction thread.

Parameters:

databaseName - name of the database

Since:

2.0

logLockReleased

protected void logLockReleased(java.lang.String databaseName)

Records that the database lock has been released.

This implementation uses the localized message for key "logLockReleased". The message takes two parameters: the database name and the transaction thread.

Parameters:

databaseName - name of the database

Since:

2.0

startTransaction

public void startTransaction(TransactionSupport support)
                      throws java.io.IOException

Description copied from interface: TransactionPolicy

Notifies this policy that a top-level transaction is starting for the executing thread. The database calls this method when a top-level transaction is starting.

Specified by:

startTransaction in interface TransactionPolicy

Overrides:

startTransaction in class AbstractTransactionPolicy

Parameters:

support - object to assist in transaction management

Throws:

java.io.IOException - if an I/O error occurs