org.multiverse.api

Interface TxnObject

public interface TxnObject

The interface each transactional object needs to implement.

A TxnObject is an object where all reads/writes are managed through a Txn (unless an atomic method is used).

Each TxnObject belongs to 1 Stm instance.

All methods are threadsafe.

Method Summary

Modifier and Type	Method and Description
java.lang.String	atomicToString() Returns a String representation of the object using the provided transaction without looking at a TxnThreadLocal.
void	ensure() Does an ensure.
void	ensure(Txn self) Does an ensure.
TxnLock	getLock() Gets the TxnLock that belongs to this TxnObject.
Stm	getStm() Returns the Stm this TxnObject is part of.
long	getVersion() Returns the current version of the transactional object.
java.lang.String	toDebugString() Returns a debug representation of the TxnObject.
java.lang.String	toString() Returns a String representation of the Object using the Txn on the TxnThreadLocal.
java.lang.String	toString(Txn txn) Returns a String representation of the object using the provided Txn.

Method Detail

getStm

Stm getStm()

Returns the Stm this TxnObject is part of. Once a TxnObject is created using some Stm, it will never become part of another Stm.

Returns:

the Stm this TxnObject is part of. Returned value will never be null.

getLock

TxnLock getLock()

Gets the TxnLock that belongs to this TxnObject. This call doesn't cause any locking, it only provides access to the object that is able to lock. The returned value will never be null.

This call also doesn't rely on a Txn.

Returns:

the TxnLock

Throws:

java.lang.UnsupportedOperationException - if this operation is not supported.

getVersion

long getVersion()

Returns the current version of the transactional object. Each time an update happens, the value is increased. It depends on the stm implementation if the version over references has any meaning. With the MVCC there is a relation, but with the SkySTM isn't.

This method doesn't look at the TxnThreadLocal.

Returns:

the current version.

ensure

void ensure()

Does an ensure. What is means is that at the end of the transaction (so deferred), the transaction checks if no other transaction has made an update, if this TxnObject only is read. The ensure is a way to prevent to writeskew problem on the ref level (see IsolationLevel for more detail about the writeskew problem}

This can safely be called on an TxnObject that already is locked, although it doesn't provide much value since with a locked TxnObject, since the writeskew problem can't occur anymore because it can't be changed.

Unlike the TxnLock.acquire(LockMode) which is pessimistic, ensure is optimistic. This means that a conflict can be detected once the transaction commits.

This method has no effect if the Txn is readonly, because a writeskew is not possible with a readonly transaction.

This call lifts on the Txn stored in the TxnThreadLocal.

Throws:

org.multiverse.api.exceptions.TxnExecutionException

org.multiverse.api.exceptions.ControlFlowError

See Also:

ensure(Txn)

ensure

void ensure(Txn self)

Does an ensure. What is means is that at the end of the transaction (so deferred), the transaction checks if no other transaction has made an update, if this TxnObject only is read. The ensure is a way to prevent to writeskew problem on the ref level (see IsolationLevel for more detail about the writeskew problem}

This can safely be called on an TxnObject that already is locked, although it doesn't provide much value since with a locked TxnObject, since the writeskew problem can't occur anymore because it can't be changed.

Unlike the TxnLock.acquire(LockMode) which is pessimistic, ensure is optimistic. This means that a conflict can be detected once the transaction commits.

This method has no effect if the Txn is readonly, because a writeskew is not possible with a readonly transaction.

Parameters:

self - the Txn this call lifts on.

Throws:

java.lang.NullPointerException - if self is null.

org.multiverse.api.exceptions.TxnExecutionException

org.multiverse.api.exceptions.ControlFlowError

See Also:

ensure()

toDebugString

java.lang.String toDebugString()

Returns a debug representation of the TxnObject. The data used doesn't have to be consistent, it is a best effort. This method doesn't rely on a running transaction.

Returns:

the debug representation of the TxnObject.

toString

java.lang.String toString()

Returns a String representation of the Object using the Txn on the TxnThreadLocal.

Overrides:

toString in class java.lang.Object

Returns:

the toString representation

Throws:

org.multiverse.api.exceptions.TxnExecutionException

org.multiverse.api.exceptions.ControlFlowError

toString

java.lang.String toString(Txn txn)

Returns a String representation of the object using the provided Txn.

Parameters:

txn - the Txn used.

Returns:

the String representation of the object.

Throws:

java.lang.NullPointerException - if tx is null.

org.multiverse.api.exceptions.ControlFlowError

atomicToString

java.lang.String atomicToString()

Returns a String representation of the object using the provided transaction without looking at a TxnThreadLocal. The outputted value doesn't need to be consistent from some point in time, only a best effort is made.

Returns:

the String representation.