org.apache.hadoop.hbase.regionserver.wal

Class SyncFuture

java.lang.Object

org.apache.hadoop.hbase.regionserver.wal.SyncFuture

@InterfaceAudience.Private
class SyncFuture
extends Object

A Future on a filesystem sync call. It given to a client or 'Handler' for it to wait on till the sync completes.

Handlers coming in call append, append, append, and then do a flush/sync of the edits they have appended the WAL before returning. Since sync takes a while to complete, we give the Handlers back this sync future to wait on until the actual HDFS sync completes. Meantime this sync future goes across a queue and is handled by a background thread; when it completes, it finishes up the future, the handler get or failed check completes and the Handler can then progress.

This is just a partial implementation of Future; we just implement get and failure.

There is not a one-to-one correlation between dfs sync invocations and instances of this class. A single dfs sync call may complete and mark many SyncFutures as done; i.e. we batch up sync calls rather than do a dfs sync call every time a Handler asks for it.

SyncFutures are immutable but recycled. Call #reset(long, Span) before use even if it the first time, start the sync, then park the 'hitched' thread on a call to #get().

Field Summary

Fields

Modifier and Type	Field and Description
private long	doneTxid The transaction id that was set in here when we were marked done.
private static long	NOT_DONE
private Thread	t
private Throwable	throwable If error, the associated throwable.
private long	txid The transaction id of this operation, monotonically increases.

Constructor Summary

Constructors

Constructor and Description
SyncFuture()

Method Summary

Modifier and Type	Method and Description
(package private) boolean	cancel(boolean mayInterruptIfRunning)
(package private) boolean	done(long txid, Throwable t)
(package private) long	get(long timeoutNs)
(package private) Throwable	getThrowable()
(package private) long	getTxid()
(package private) boolean	isDone()
(package private) boolean	isThrowable()
(package private) SyncFuture	reset(long txid) Call this method to clear old usage and get it ready for new deploy.
String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

NOT_DONE

private static final long NOT_DONE

See Also:

Constant Field Values

txid

private long txid

The transaction id of this operation, monotonically increases.

doneTxid

private long doneTxid

The transaction id that was set in here when we were marked done. Should be equal or > txnId. Put this data member into the NOT_DONE state while this class is in use.

throwable

private Throwable throwable

If error, the associated throwable. Set when the future is 'done'.

t

private Thread t

Constructor Detail

SyncFuture

SyncFuture()

Method Detail

reset

SyncFuture reset(long txid)

Call this method to clear old usage and get it ready for new deploy.

Parameters:

txid - the new transaction id

Returns:

this

toString

public String toString()

Overrides:

toString in class Object

getTxid

long getTxid()

done

boolean done(long txid,
             Throwable t)

Parameters:

txid - the transaction id at which this future 'completed'.

t - Can be null. Set if we are 'completing' on error (and this 't' is the error).

Returns:

True if we successfully marked this outstanding future as completed/done. Returns false if this future is already 'done' when this method called.

cancel

boolean cancel(boolean mayInterruptIfRunning)

get

long get(long timeoutNs)
  throws InterruptedException,
         ExecutionException,
         TimeoutIOException

Throws:

InterruptedException

ExecutionException

TimeoutIOException

isDone

boolean isDone()

isThrowable

boolean isThrowable()

getThrowable

Throwable getThrowable()