SyncFuture (Apache HBase 1.2.12 API)

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 the ringbuffer and into a sync runner 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. Unimplemented methods throw UnsupportedOperationException.
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`	`doneSequence` The sequence that was set in here when we were marked done.
`private static long`	`NOT_DONE`
`private long`	`ringBufferSequence` The sequence at which we were added to the ring buffer.
`private org.apache.htrace.Span`	`span` Optionally carry a disconnected scope to the SyncRunner.
`private Thread`	`t`
`private Throwable`	`throwable` If error, the associated throwable.

Constructor Summary

Constructors
Constructor and Description

SyncFuture()

Constructors
Constructor and Description
`SyncFuture()`

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`cancel(boolean mayInterruptIfRunning)`
`(package private) boolean`	`done(long sequence, Throwable t)`
`long`	`get(long timeout)`
`Long`	`get(long timeout, TimeUnit unit)`
`(package private) long`	`getRingBufferSequence()`
`(package private) org.apache.htrace.Span`	`getSpan()` Retrieve the `span` instance from this Future.
`(package private) Throwable`	`getThrowable()`
`boolean`	`isCancelled()`
`(package private) boolean`	`isDone()`
`(package private) boolean`	`isThrowable()`
`(package private) SyncFuture`	`reset(long sequence)` Call this method to clear old usage and get it ready for new deploy.
`(package private) SyncFuture`	`reset(long sequence, org.apache.htrace.Span span)` Call this method to clear old usage and get it ready for new deploy.
`(package private) void`	`setSpan(org.apache.htrace.Span span)` Used to re-attach a `span` to the Future.
`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
  - ringBufferSequence
```
private long ringBufferSequence
```
    The sequence at which we were added to the ring buffer.
  - doneSequence
```
private long doneSequence
```
    The sequence that was set in here when we were marked done. Should be equal or > ringBufferSequence. Put this data member into the NOT_DONE state while this class is in use. But for the first position on construction, let it be -1 so we can immediately call reset(long, Span) below and it will work.
  - throwable
```
private Throwable throwable
```
    If error, the associated throwable. Set when the future is 'done'.
  - t
```
private Thread t
```
  - span
```
private org.apache.htrace.Span span
```
    Optionally carry a disconnected scope to the SyncRunner.
- Constructor Detail
  - SyncFuture
```
SyncFuture()
```
- Method Detail
  - reset
```
SyncFuture reset(long sequence)
```
    Call this method to clear old usage and get it ready for new deploy. Call this method even if it is being used for the first time.
    
    Parameters:
    sequence - sequenceId from this Future's position in the RingBuffer
    
    Returns:
    this
  - reset
```
SyncFuture reset(long sequence,
               org.apache.htrace.Span span)
```
    Call this method to clear old usage and get it ready for new deploy. Call this method even if it is being used for the first time.
    
    Parameters:
    sequence - sequenceId from this Future's position in the RingBuffer
    span - curren span, detached from caller. Don't forget to attach it when resuming after a call to #get().
    
    Returns:
    this
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object
  - getRingBufferSequence
```
long getRingBufferSequence()
```
  - getSpan
```
org.apache.htrace.Span getSpan()
```
    Retrieve the span instance from this Future. EventHandler calls this method to continue the span. Thread waiting on this Future musn't call this method until AFTER calling #get() and the future has been released back to the originating thread.
  - setSpan
```
void setSpan(org.apache.htrace.Span span)
```
    Used to re-attach a span to the Future. Called by the EventHandler after a it has completed processing and detached the span from its scope.
  - done
```
boolean done(long sequence,
           Throwable t)
```
    Parameters:
    sequence - Sync sequence 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
```
public boolean cancel(boolean mayInterruptIfRunning)
```
  - get
```
public long get(long timeout)
         throws InterruptedException,
                ExecutionException,
                TimeoutIOException
```
    Throws:
    
    InterruptedException
    
    ExecutionException
    
    TimeoutIOException
  - get
```
public Long get(long timeout,
       TimeUnit unit)
         throws InterruptedException,
                ExecutionException
```
    Throws:
    
    InterruptedException
    
    ExecutionException
  - isCancelled
```
public boolean isCancelled()
```
  - isDone
```
boolean isDone()
```
  - isThrowable
```
boolean isThrowable()
```
  - getThrowable
```
Throwable getThrowable()
```

Class SyncFuture

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

NOT_DONE

ringBufferSequence

doneSequence

throwable

t

span

Constructor Detail

SyncFuture

Method Detail

reset

reset

toString

getRingBufferSequence

getSpan

setSpan

done

cancel

get

get

isCancelled

isDone

isThrowable

getThrowable