Transactional (Apache Jena ARQ)

All Known Subinterfaces:

Dataset, DatasetGraph, DatasetGraphWrapperView, GraphStore, TransactionalNotSupportedMixin

All Known Implementing Classes:

DatasetGraphBase, DatasetGraphBaseFind, DatasetGraphCollection, DatasetGraphFilteredView, DatasetGraphInMemory, DatasetGraphMap, DatasetGraphMapLink, DatasetGraphMonitor, DatasetGraphNull, DatasetGraphOne, DatasetGraphQuads, DatasetGraphReadOnly, DatasetGraphSink, DatasetGraphTrackActive, DatasetGraphTriplesQuads, DatasetGraphViewGraphs, DatasetGraphWrapper, DatasetGraphZero, DatasetImpl, DatasetOne, DifferenceDatasetGraph, DyadicDatasetGraph, DynamicDatasets.DynamicDatasetGraph, GraphStoreBasic, IntersectionDatasetGraph, TransactionalLock, TransactionalNotSupported, TransactionalNull, TxnCounter, TxnDataset2Graph, UnionDatasetGraph
```
public interface Transactional
```
Interface that encapsulates the begin/abort|commit/end operations.
The read lifecycle is:
```
 begin(READ) ... end()
```
commit and abort are allowed.
The write lifecycle is:
```
 begin(WRITE) ... abort() or commit()
```
end() is optional but preferred.
Helper code is available Txn so, for example:
```
Txn.executeRead(dataset,  ()-> { ... sparql query ... });
```
```
Txn.executeWrite(dataset,  ()-> { ... sparql update ... });
```
or use one of Txn.calculateRead and Txn.executeWrite to return a value for the transaction block.
Directly called, code might look like:
```
     Transactional object = ...
     object.begin(TxnMode.READ) ;
     try {
       ... actions inside a read transaction ...
     } finally { object.end() ; }
 
```
or
```
     Transactional object = ...
     object.begin(TxnMode.WRITE) ;
     try {
        ... actions inside a write transaction ...
        object.commit() ;
     } finally {
        // This causes an abort if  commit has not been called.
        object.end() ;
     }
 
```

Nested Class Summary

Nested Classes
Modifier and Type Interface and Description

static class Transactional.Promote

Nested Classes
Modifier and Type	Interface and Description
`static class`	`Transactional.Promote`

Method Summary

All Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method and Description
`void`	`abort()` Abort a transaction - finish the transaction and undo any changes (if a "write" transaction)
`default void`	`begin()` Start a transaction which is READ mode and which will switch to WRITE if an update is attempted but only if no intermediate transaction has performed an update.
`void`	`begin(ReadWrite readWrite)` Start either a READ or WRITE transaction.
`void`	`begin(TxnType type)` Start a transaction. READ or WRITE transactions start in that state and do not change for the lifetime of the transaction.
`void`	`commit()` Commit a transaction - finish the transaction and make any changes permanent (if a "write" transaction)
`void`	`end()` Finish the transaction - if a write transaction and commit() has not been called, then abort
`boolean`	`isInTransaction()` Say whether inside a transaction.
`default boolean`	`promote()` Attempt to promote a transaction from "read" to "write" when the transaction started with a "promote" mode (`READ_PROMOTE` or `READ_COMMITTED_PROMOTE`).
`boolean`	`promote(Transactional.Promote mode)` Attempt to promote a transaction from "read" mode to "write" and the transaction.
`ReadWrite`	`transactionMode()` Return the current mode of the transaction - "read" or "write".
`TxnType`	`transactionType()` Return the transaction type used in `begin(TxnType)`.

- Method Detail
  - begin
```
default void begin()
```
    Start a transaction which is READ mode and which will switch to WRITE if an update is attempted but only if no intermediate transaction has performed an update.
    See begin(TxnType) for more details an options.
    May not be implemented. See begin(ReadWrite) is guaranteed to be provided.
  - begin
```
void begin(TxnType type)
```
    Start a transaction.
    READ or WRITE transactions start in that state and do not change for the lifetime of the transaction.
    - WRITE: this guarantees a WRITE will complete if commit() is called. The same as begin(ReadWrite.WRITE).
    - READ: the transaction can not promote to WRITE,ensuring read-only access to the data. The same as begin(ReadWrite.READ).
    - READ_PROMOTE: the transaction will go from "read" to "write" if an update is attempted and if the dataset has not been changed by another write transaction. See also promote().
    - READ_COMMITTED_PROMOTE: Use this with care. The promotion will succeed but changes from other transactions become visible.
    Read committed: at the point transaction attempts promotion from "read" to "write", the system checks if the dataset has change since the transaction started (called begin). If READ_PROMOTE, the dataset must not have changed; if READ_COMMITTED_PROMOTE any intermediate changes are visible but the application can not assume any data it has read in the transaction is the same as it was at the point the transaction started.
    This operation is optional and some implementations may throw a JenaTransactionException exception for some or all TxnType values.
    See begin(ReadWrite) for a form that is required of implementations.
  - begin
```
void begin(ReadWrite readWrite)
```
    Start either a READ or WRITE transaction.
  - promote
```
default boolean promote()
```
    Attempt to promote a transaction from "read" to "write" when the transaction started with a "promote" mode (READ_PROMOTE or READ_COMMITTED_PROMOTE).
    Returns "true" if the transaction is in write mode after the call. The method always succeeds of the transaction is already "write".
    A READ_COMMITTED_PROMOTE can always be promoted, but the call may need to wait.
    This method returns true if a READ_PROMOTE or READ_COMMITTED_PROMOTE is promoted.
    This method returns false if a READ_PROMOTE can't be promoted - the transaction is still valid and in "read" mode. Any further calls to promote() will also return false.
    
    This method returns false if there is an attempt to promote a "READ" transaction.
  - promote
```
boolean promote(Transactional.Promote mode)
```
    Attempt to promote a transaction from "read" mode to "write" and the transaction. This method allows the form of promotion to be specified. The transaction must not have been started with READ, which is read-only.
    An argument of READ_PROMOTE treats the promotion as if the transaction was started with READ_PROMOTE (any other writer commiting since the transaction started blocks promotion) and READ_COMMITTED_PROMOTE treats the promotion as if the transaction was started with READ_COMMITTED_PROMOTE (intemediate writer commits become visible).
    Returns "true" if the transaction is in write mode after the call. The method always succeeds of the transaction is already "write".
    This method returns true if a READ_PROMOTE or READ_COMMITTED_PROMOTE is promoted.
    This method returns false if a READ_PROMOTE can't be promoted - the transaction is still valid and in "read" mode.
    This method throws an exception if there is an attempt to promote a READ transaction.
  - commit
```
void commit()
```
    Commit a transaction - finish the transaction and make any changes permanent (if a "write" transaction)
  - abort
```
void abort()
```
    Abort a transaction - finish the transaction and undo any changes (if a "write" transaction)
  - end
```
void end()
```
    Finish the transaction - if a write transaction and commit() has not been called, then abort
  - transactionMode
```
ReadWrite transactionMode()
```
    Return the current mode of the transaction - "read" or "write". If the caller is not in a transaction, this method returns null.
  - transactionType
```
TxnType transactionType()
```
    Return the transaction type used in begin(TxnType). If the caller is not in a transaction, this method returns null.
  - isInTransaction
```
boolean isInTransaction()
```
    Say whether inside a transaction.

Interface Transactional

Nested Class Summary

Method Summary

Method Detail

begin

begin

begin

promote

promote

commit

abort

end

transactionMode

transactionType

isInTransaction