sos.db
Class DefaultReadWriteTransactionPolicy

java.lang.Object
  sos.db.AbstractTransactionPolicy
      sos.db.DefaultReadWriteTransactionPolicy

All Implemented Interfaces:

java.io.Serializable, TransactionPolicy

public class DefaultReadWriteTransactionPolicy
extends AbstractTransactionPolicy
implements TransactionPolicy

A transaction policy that uses strict two phase locking (2PL) to ensure that transactions appear to execute sequentially and that uses lock timeouts to break potential deadlock.

With this policy, transactions on different objects are allowed to execute concurrently. Also, transactions invoking read-only methods on the same objects are allowed to execute concurrently.

With this policy, transactions in high contention may deadlock, and repeated attempts at these transactions may lead to thrashing, causing no transaction to make progress. To avoid the thrashing, consider using DefaultTransactionPolicy instead of this class.

This policy is adequate for applications in which transactions execute on different threads and without much contention.

Logging

This class logs fine-grained activity, as given by the following table:

Activity	Severity
A read lock is acquired	FINEST
A read lock is released	FINEST
A write lock is acquired	FINEST
A write lock is released	FINEST
A method is invoked	FINEST

Subclasses may change the log messages or severity by overriding the logXxx methods.

Since:

1.0

See Also:

DefaultTransactionPolicy

Constructor Summary

DefaultReadWriteTransactionPolicy()
Creates an instance of DefaultReadWriteTransactionPolicy with default timeout intervals of one minute each.

DefaultReadWriteTransactionPolicy(long readTimeout, long writeTimeout)
Creates an instance of DefaultReadWriteTransactionPolicy with the specified timeout intervals.

Method Summary

protected void	acquireReadLock(TransactionSupport support) Acquires a read lock for the key referenced by support.
protected void	acquireWriteLock(TransactionSupport support) Acquires a write lock for the key referenced by support.
protected void	logReadLockAcquired(java.lang.String databaseName, java.lang.Object key) Records that the read lock associated with key has been acquired.
protected void	logReadLockReleased(java.lang.String databaseName, java.lang.Object key) Records that the read lock associated with key has been released.
protected void	logWriteLockAcquired(java.lang.String databaseName, java.lang.Object key) Records that the write lock associated with key has been acquired.
protected void	logWriteLockReleased(java.lang.String databaseName, java.lang.Object key) Records that the write lock associated with key has been released.
protected void	prepareForReadOnlyInvocation(TransactionSupport support) Prepares for the invocation of a read-only method on the object referenced by support.
protected void	prepareForWriteInvocation(TransactionSupport support) Prepares for the invocation of a non-read-only method on the object referenced by support.
void	registerObject(TransactionSupport support, java.lang.Object object) Notifies this policy that there is a new database object.

Methods inherited from class sos.db.AbstractTransactionPolicy

getMethodStatus, invoke, logMethodInvocation, startTransaction, 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, startTransaction, unregisterObjects

Constructor Detail

DefaultReadWriteTransactionPolicy

public DefaultReadWriteTransactionPolicy()

Creates an instance of DefaultReadWriteTransactionPolicy with default timeout intervals of one minute each.

See Also:

DefaultReadWriteTransactionPolicy(long,long)

DefaultReadWriteTransactionPolicy

public DefaultReadWriteTransactionPolicy(long readTimeout,
                                         long writeTimeout)

Creates an instance of DefaultReadWriteTransactionPolicy with the specified timeout intervals.

Parameters:

readTimeout - maximum time to wait (in milliseconds) for a read lock

writeTimeout - maximum time to wait (in milliseconds) for a write lock

Method Detail

acquireReadLock

protected void acquireReadLock(TransactionSupport support)
                        throws java.io.IOException

Acquires a read lock for the key referenced by support.

Parameters:

support - object that holds the key for which to acquire the read lock

Throws:

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

acquireWriteLock

protected void acquireWriteLock(TransactionSupport support)
                         throws java.io.IOException

Acquires a write lock for the key referenced by support.

Parameters:

support - object that holds the key for which to acquire the write lock

Throws:

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

logReadLockAcquired

protected void logReadLockAcquired(java.lang.String databaseName,
                                   java.lang.Object key)

Records that the read lock associated with key has been acquired.

It is safe to invoke toString on key.

This implementation uses the localized message for key "logReadLockAcquired". The message takes three parameters: the database name, the transaction thread, and the key.

Parameters:

databaseName - name of the database

key - unique key of object being read

logReadLockReleased

protected void logReadLockReleased(java.lang.String databaseName,
                                   java.lang.Object key)

Records that the read lock associated with key has been released.

It is safe to invoke toString on key.

This implementation uses the localized message for key "logReadLockReleased". The message takes three parameters: the database name, the transaction thread, and the key.

Parameters:

databaseName - name of the database

key - unique key of object being read

logWriteLockAcquired

protected void logWriteLockAcquired(java.lang.String databaseName,
                                    java.lang.Object key)

Records that the write lock associated with key has been acquired.

It is safe to invoke toString on key.

This implementation uses the localized message for key "logWriteLockAcquired". The message takes three parameters: the database name, the transaction thread, and the key.

Parameters:

databaseName - name of the database

key - unique key of object being written

logWriteLockReleased

protected void logWriteLockReleased(java.lang.String databaseName,
                                    java.lang.Object key)

Records that the write lock associated with key has been released.

It is safe to invoke toString on key.

This implementation uses the localized message for key "logWriteLockReleased". The message takes three parameters: the database name, the transaction thread, and the key.

Parameters:

databaseName - name of the database

key - unique key of object being written

prepareForReadOnlyInvocation

protected void prepareForReadOnlyInvocation(TransactionSupport support)
                                     throws java.io.IOException

Description copied from class: AbstractTransactionPolicy

Prepares for the invocation of a read-only method on the object referenced by support.

This implementation does nothing. Subclasses can override this method to provide a more meaningful implementation. For example, they can use this method to acquire a read lock.

Overrides:

prepareForReadOnlyInvocation in class AbstractTransactionPolicy

Parameters:

support - object that holds information about the receiver object, including a key that uniquely identifies it

Throws:

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

See Also:

AbstractTransactionPolicy.prepareForWriteInvocation(sos.db.TransactionSupport)

prepareForWriteInvocation

protected void prepareForWriteInvocation(TransactionSupport support)
                                  throws java.io.IOException

Description copied from class: AbstractTransactionPolicy

Prepares for the invocation of a non-read-only method on the object referenced by support.

This implementation does nothing. Subclasses can override this method to provide a more meaningful implementation. For example, they can use this method to acquire a write lock.

Overrides:

prepareForWriteInvocation in class AbstractTransactionPolicy

Parameters:

support - object that holds information about the receiver object, including a key that uniquely identifies it

Throws:

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

See Also:

AbstractTransactionPolicy.prepareForReadOnlyInvocation(sos.db.TransactionSupport)

registerObject

public void registerObject(TransactionSupport support,
                           java.lang.Object object)
                    throws java.io.IOException

Description copied from interface: TransactionPolicy

Notifies this policy that there is a new database object. The database calls this method when an object is added to the database.

Specified by:

registerObject in interface TransactionPolicy

Overrides:

registerObject in class AbstractTransactionPolicy

Parameters:

support - object to assist in transaction management

object - the object added to the database

Throws:

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