TransactionCoordinator (Apache Jena - DBOE Transactions 3.14.0)

java.lang.Object
- org.apache.jena.dboe.transaction.txn.TransactionCoordinator

```
public final class TransactionCoordinator
extends Object
```
One TransactionCoordinator per group of TransactionalComponents. TransactionalComponents can not be shared across TransactionCoordinators.
This is a general engine although tested and most used for multiple-reader and single-writer (MR+SW). TransactionalComponentLifecycle provides the per-thread style.
Contrast to MRSW: multiple-reader or single-writer.
Block writers
Block until no writers are active. When this returns, this guarantees that the database is not changing and the journal is flushed to disk.
See blockWriters(), enableWriters(), execAsWriter(Runnable)
Exclusive mode
Exclusive mode is when the current thread is the only active code : no readers, no writers.
See startExclusiveMode()/tryExclusiveMode() finishExclusiveMode(), execExclusive(Runnable)

See Also:

Transaction, TransactionalComponent, TransactionalSystem

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static interface TransactionCoordinator.ShutdownHook

Nested Classes
Modifier and Type	Class and Description
`static interface`	`TransactionCoordinator.ShutdownHook`

Constructor Summary

Constructors
Constructor and Description
`TransactionCoordinator(Journal journal)` Create a TransactionCoordinator, initially with no associated `TransactionalComponents`.
`TransactionCoordinator(Journal journal, List<TransactionalComponent> components)` Create a TransactionCoordinator, initially with `TransactionalComponents` in the ComponentGroup
`TransactionCoordinator(Location location)` Create a TransactionCoordinator, initially with no associated `TransactionalComponent`s

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`TransactionCoordinator`	`add(TransactionalComponent elt)` Add a `TransactionalComponent`.
`void`	`add(TransactionCoordinator.ShutdownHook hook)` Add a shutdown hook.
`TransactionCoordinator`	`addListener(TransactionListener listener)`
`void`	`attach(TransactionCoordinatorState coordinatorState)`
`Transaction`	`begin(TxnType txnType)` Start a transaction.
`Transaction`	`begin(TxnType txnType, boolean canBlock)` Start a transaction.
`void`	`blockWriters()` Block until no writers are active.
`long`	`countActive()`
`long`	`countActiveReaders()`
`long`	`countActiveWriter()`
`long`	`countBegin()`
`long`	`countBeginRead()`
`long`	`countBeginWrite()`
`long`	`countFinished()`
`TransactionCoordinatorState`	`detach(Transaction txn)`
`void`	`enableWriters()` Allow writers.
`void`	`execAsWriter(Runnable action)` Execute an action in as if a Write but no write transaction started.
`void`	`execExclusive(Runnable action)` Execute an action in exclusive mode.
`void`	`finishExclusiveMode()` Return to normal (release waiting transactions, allow new transactions).
`Journal`	`getJournal()`
`Location`	`getLocation()`
`void`	`modifyConfig(Runnable action)` Perform modification of this `TransactionCoordiator` after it has been started.
`TransactionCoordinator`	`remove(TransactionalComponent elt)` Remove a `TransactionalComponent`.
`void`	`remove(TransactionCoordinator.ShutdownHook hook)` Remove a shutdown hook
`TransactionCoordinator`	`removeListener(TransactionListener listener)`
`void`	`setQuorumGenerator(QuorumGenerator qGen)`
`void`	`setTxnIdGenerator(TxnIdGenerator generator)`
`void`	`shutdown()`
`void`	`shutdown(boolean silent)`
`void`	`start()`
`void`	`startExclusiveMode()` Enter exclusive mode; block if necessary.
`boolean`	`tryBlockWriters()` Try to block all writers, or return if can't at the moment.
`boolean`	`tryBlockWriters(boolean canBlock)` Block until no writers are active, optionally blocking or returning if can't at the moment.
`boolean`	`tryExclusiveMode()` Try to enter exclusive mode.
`boolean`	`tryExclusiveMode(boolean canBlock)` Try to enter exclusive mode.

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - TransactionCoordinator
```
public TransactionCoordinator(Location location)
```
    Create a TransactionCoordinator, initially with no associated TransactionalComponents
  - TransactionCoordinator
```
public TransactionCoordinator(Journal journal)
```
    Create a TransactionCoordinator, initially with no associated TransactionalComponents.
  - TransactionCoordinator
```
public TransactionCoordinator(Journal journal,
                              List<TransactionalComponent> components)
```
    Create a TransactionCoordinator, initially with TransactionalComponents in the ComponentGroup
- Method Detail
  - add
```
public TransactionCoordinator add(TransactionalComponent elt)
```
    Add a TransactionalComponent. Safe to call at any time but it is good practice is to add all the components before any transactions start. Internally, the coordinator ensures the add will safely happen but it does not add the component to existing transactions. This must be setup before recovery is attempted.
  - remove
```
public TransactionCoordinator remove(TransactionalComponent elt)
```
    Remove a TransactionalComponent.
    
    See Also:
    
    add(org.apache.jena.dboe.transaction.txn.TransactionalComponent)
  - addListener
```
public TransactionCoordinator addListener(TransactionListener listener)
```
  - removeListener
```
public TransactionCoordinator removeListener(TransactionListener listener)
```
  - modifyConfig
```
public void modifyConfig(Runnable action)
```
    Perform modification of this TransactionCoordiator after it has been started.
    This operation enters exclusive mode, releases the configuration lock, then calls the action. On exit from the action, it resets the configuration lock, and exits exclusive mode.
    Do not call inside a transaction, it may cause a deadlock.
    Use with care!
  - add
```
public void add(TransactionCoordinator.ShutdownHook hook)
```
    Add a shutdown hook. Shutdown is not guaranteed to be called and hence hooks may not get called.
  - remove
```
public void remove(TransactionCoordinator.ShutdownHook hook)
```
    Remove a shutdown hook
  - setQuorumGenerator
```
public void setQuorumGenerator(QuorumGenerator qGen)
```
  - start
```
public void start()
```
  - setTxnIdGenerator
```
public void setTxnIdGenerator(TxnIdGenerator generator)
```
  - getJournal
```
public Journal getJournal()
```
  - getLocation
```
public Location getLocation()
```
  - detach
```
public TransactionCoordinatorState detach(Transaction txn)
```
  - attach
```
public void attach(TransactionCoordinatorState coordinatorState)
```
  - shutdown
```
public void shutdown()
```
  - shutdown
```
public void shutdown(boolean silent)
```
  - startExclusiveMode
```
public void startExclusiveMode()
```
    Enter exclusive mode; block if necessary. There are no active transactions on return; new transactions will be held up in 'begin'. Return to normal (release waiting transactions, allow new transactions) with finishExclusiveMode().
    Do not call inside an existing transaction.
  - tryExclusiveMode
```
public boolean tryExclusiveMode()
```
    Try to enter exclusive mode. If return is true, then there are no active transactions on return and new transactions will be held up in 'begin'. If false, there were in-progress transactions. Return to normal (release waiting transactions, allow new transactions) with finishExclusiveMode().
    Do not call inside an existing transaction.
  - tryExclusiveMode
```
public boolean tryExclusiveMode(boolean canBlock)
```
    Try to enter exclusive mode. If return is true, then there are no active transactions on return and new transactions will be held up in 'begin'. If false, there were in-progress transactions. Return to normal (release waiting transactions, allow new transactions) with finishExclusiveMode().
    Do not call inside an existing transaction.
    
    Parameters:
    
    canBlock - Allow the operation block and wait for the exclusive mode lock.
  - finishExclusiveMode
```
public void finishExclusiveMode()
```
    Return to normal (release waiting transactions, allow new transactions). Must be paired with an earlier startExclusiveMode().
  - execExclusive
```
public void execExclusive(Runnable action)
```
    Execute an action in exclusive mode. This method can block. Equivalent to:
```
  startExclusiveMode();
  try { action.run(); }
  finally { finishExclusiveMode(); }
 
```
    Parameters:
    
    action -
  - blockWriters
```
public void blockWriters()
```
    Block until no writers are active. When this returns, this guarantees that the database is not changing and the journal is flushed to disk.
    The application must call enableWriters() later.
    This operation must not be nested (it will block).
    
    See Also:
    
    tryBlockWriters(), enableWriters()
  - tryBlockWriters
```
public boolean tryBlockWriters()
```
    Try to block all writers, or return if can't at the moment.
    Unlike a write transction, there is no associated transaction.
    If it returns true, the application must call enableWriters() later.
    
    Returns:
    
    true if the operation succeeded and writers are blocked
    
    See Also:
    
    blockWriters(), enableWriters()
  - tryBlockWriters
```
public boolean tryBlockWriters(boolean canBlock)
```
    Block until no writers are active, optionally blocking or returning if can't at the moment.
    Unlike a write transaction, there is no associated transaction.
    If it returns true, the application must call enableWriters() later.
    
    Parameters:
    
    canBlock -
    
    Returns:
    
    true if the operation succeeded and writers are blocked
  - enableWriters
```
public void enableWriters()
```
    Allow writers. This must be used in conjunction with blockWriters() or tryBlockWriters()
    
    See Also:
    
    blockWriters(), tryBlockWriters()
  - execAsWriter
```
public void execAsWriter(Runnable action)
```
    Execute an action in as if a Write but no write transaction started. This method can block.
    Equivalent to:
```
  blockWriters();
  try { action.run(); }
  finally { enableWriters(); }
 
```
    Parameters:
    
    action -
  - begin
```
public Transaction begin(TxnType txnType)
```
    Start a transaction. This may block.
  - begin
```
public Transaction begin(TxnType txnType,
                         boolean canBlock)
```
    Start a transaction. Returns null if this operation would block. Readers can start at any time. A single writer policy is currently imposed so a "begin(WRITE)" may block.
  - countActiveReaders
```
public long countActiveReaders()
```
  - countActiveWriter
```
public long countActiveWriter()
```
  - countActive
```
public long countActive()
```
  - countBegin
```
public long countBegin()
```
  - countBeginRead
```
public long countBeginRead()
```
  - countBeginWrite
```
public long countBeginWrite()
```
  - countFinished
```
public long countFinished()
```

Class TransactionCoordinator

Block writers

Exclusive mode

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

TransactionCoordinator

TransactionCoordinator

TransactionCoordinator

Method Detail

add

remove

addListener

removeListener

modifyConfig

add

remove

setQuorumGenerator

start

setTxnIdGenerator

getJournal

getLocation

detach

attach

shutdown

shutdown

startExclusiveMode

tryExclusiveMode

tryExclusiveMode

finishExclusiveMode

execExclusive

blockWriters

tryBlockWriters

tryBlockWriters

enableWriters

execAsWriter

begin

begin

countActiveReaders

countActiveWriter

countActive

countBegin

countBeginRead

countBeginWrite

countFinished