com.continuent.tungsten.replicator.thl
Class THLParallelReadQueue

java.lang.Object
  com.continuent.tungsten.replicator.thl.THLParallelReadQueue

public class THLParallelReadQueue
extends java.lang.Object

Implements a queue that returns in total order the most recently read events from its parent read task and pending control events required to process watches properly. Items in this queue come from the following sources:

1. Events read from the log. The THLParallelReadTask thread supplies these as it reads them.
2. Out-of-band control events. The THLParallelQueue inserts these to implement synchronization between channels, i.e., stage tasks. They must be merged in sequence number order into the queue so that the stage task sees them.
3. Control events generated from watch predicates. These ensure that stage tasks commit their current position so that watches can be fulfilled.

The main responsibility of this class is to merge these events so the get() method returns them in total order. The APIs of this class match standard queue interfaces.

Access to this class is highly concurrent. Methods that merge queue contents are synchronized to ensure atomicity of changes across queue structures. Failure to do this could result in ordering violations. The event queue is protected by a concurrent collection. Methods that access this as well as statistical information are not synchronized, as doing so would raise the risk of deadlocks.

Version:

1.0

Author:

Robert Hodges

Constructor Summary

THLParallelReadQueue(int taskId, int maxSize, int maxControlEvents, long startingSeqno, int syncInterval, ReplDBMSHeader lastHeader, AtomicIntervalGuard<?> intervalGuard)
Instantiates a new read queue.

Method Summary

void	addWatchSyncPredicate(WatchPredicate<ReplDBMSHeader> predicate) Add a new predicate to the list of predicates that should generate sync events.
long	getAcceptCount() Return count of accepted events.
long	getDiscardCount() Return count of discarded events.
long	getReadSeqno() Returns current sequence number we have read.
boolean	isLastFrag() Returns whether last event read was the end of a transaction.
ReplEvent	peek() Returns but does not remove next event from the queue if it exists or returns null if queue is empty.
void	post(THLEvent thlEvent) Post a normal event which will be enqueued immediately.
void	postOutOfBand(ReplControlEvent controlEvent) Post a control event, which will either be immediately added to the event queue or buffered in the control event queue until it is time to merge it.
void	release() Frees resources including all queues and lists.
int	size() Returns the current queue size.
ReplEvent	take() Removes the next event from the queue, waiting indefinitely for something to arrive.
ReplEvent	take(long timeout, java.util.concurrent.TimeUnit unit) Removes the next element from the event queue, returning null if it cannot be found within the timeout.

Methods inherited from class java.lang.Object

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

Constructor Detail

THLParallelReadQueue

public THLParallelReadQueue(int taskId,
                            int maxSize,
                            int maxControlEvents,
                            long startingSeqno,
                            int syncInterval,
                            ReplDBMSHeader lastHeader,
                            AtomicIntervalGuard<?> intervalGuard)

Instantiates a new read queue.

Parameters:

taskId - Task to which this queue belongs

maxSize - Maximum number of all events to buffer

maxControlEvents - Maximum number of control events to buffer

startingSeqno - Sequence number of next transaction

syncInterval - Interval at which to generate synchronization events

lastHeader - Header of last transaction processed before start

intervalGuard - Interval guard to track read position

Method Detail

getReadSeqno

public long getReadSeqno()

Returns current sequence number we have read.

isLastFrag

public boolean isLastFrag()

Returns whether last event read was the end of a transaction.

getAcceptCount

public long getAcceptCount()

Return count of accepted events.

getDiscardCount

public long getDiscardCount()

Return count of discarded events.

release

public void release()

Frees resources including all queues and lists.

addWatchSyncPredicate

public void addWatchSyncPredicate(WatchPredicate<ReplDBMSHeader> predicate)
                           throws java.lang.InterruptedException

Add a new predicate to the list of predicates that should generate sync events. If we are at the end of a transaction, see if the event should be posted immediately.

Parameters:

predicate - Watch predicate

Throws:

java.lang.InterruptedException

postOutOfBand

public void postOutOfBand(ReplControlEvent controlEvent)
                   throws java.lang.InterruptedException

Post a control event, which will either be immediately added to the event queue or buffered in the control event queue until it is time to merge it. The control event is ordered by seqno then by order of insertion in cases where there are multiple control events for a single seqno.

Note that if you post a control event whose seqno is prior to the current seqno in the queue, the control event seqno will be altered to use the current seqno. This is required to prevent seqno values from appearing to move backwards, which could provoke bugs in downstream tasks that expect sequence numbers to increase monotonically.

Parameters:

controlEvent - Control event to post or buffer

Throws:

java.lang.InterruptedException

post

public void post(THLEvent thlEvent)
          throws java.lang.InterruptedException

Post a normal event which will be enqueued immediately. Synchronize position to update counters and merge any pending control events or predicates as well.

Parameters:

thlEvent - Event to post.

Throws:

java.lang.InterruptedException

size

public int size()

Returns the current queue size.

take

public ReplEvent take()
               throws java.lang.InterruptedException

Removes the next event from the queue, waiting indefinitely for something to arrive.

Returns:

An event

Throws:

java.lang.InterruptedException - Thrown if thread is interrupted.

take

public ReplEvent take(long timeout,
                      java.util.concurrent.TimeUnit unit)
               throws java.lang.InterruptedException

Removes the next element from the event queue, returning null if it cannot be found within the timeout.

Parameters:

timeout - Interval to wait

unit - Unit of time

Returns:

An event or null if we time out

Throws:

java.lang.InterruptedException - Thrown if thread is interrupted.

peek

public ReplEvent peek()
               throws java.lang.InterruptedException

Returns but does not remove next event from the queue if it exists or returns null if queue is empty.

Throws:

java.lang.InterruptedException