T
- the type of elements returned by the cursor@API(value=EXPERIMENTAL) public class UnorderedUnionCursor<T> extends Object
If there are limits applied to the children of this cursor, this cursor will continue to emit elements as long as
there remains at least one child cursor who has not yet returned its last result. (For example, if this cursor
has two children and one of them completes faster than the other due to hitting some limit, then the union cursor
will continue returning results from the other cursor.) This differs from the behavior of the ordered
UnionCursor
.
RecordCursor.NoNextReason
Modifier | Constructor and Description |
---|---|
protected |
UnorderedUnionCursor(List<com.apple.foundationdb.record.provider.foundationdb.cursors.MergeCursorState<T>> cursorStates,
FDBStoreTimer timer) |
Modifier and Type | Method and Description |
---|---|
boolean |
accept(RecordCursorVisitor visitor)
Accept a visit from hierarchical visitor, which implements
RecordCursorVisitor . |
void |
close() |
static <T> UnorderedUnionCursor<T> |
create(List<Function<byte[],RecordCursor<T>>> cursorFunctions,
byte[] continuation,
FDBStoreTimer timer)
Create a union cursor from two or more cursors.
|
byte[] |
getContinuation()
Deprecated.
|
Executor |
getExecutor() |
RecordCursor.NoNextReason |
getNoNextReason()
Deprecated.
|
FDBStoreTimer |
getTimer()
Get the
FDBStoreTimer used to instrument events of this cursor. |
protected RecordCursor.NoNextReason |
mergeNoNextReasons()
Merges all of the cursors and whether they have stopped and returns the "strongest" reason for the result to stop.
|
U |
next()
Deprecated.
|
CompletableFuture<Boolean> |
onHasNext()
Deprecated.
|
CompletableFuture<RecordCursorResult<U>> |
onNext()
Asynchronously return the next result from this cursor.
|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
asIterator, asList, empty, empty, filter, filterAsync, filterAsyncInstrumented, filterAsyncInstrumented, filterInstrumented, filterInstrumented, first, flatMapPipelined, flatMapPipelined, flatMapPipelined, forEach, forEachAsync, forEachResult, forEachResultAsync, fromFuture, fromFuture, fromIterator, fromIterator, fromList, fromList, fromList, fromList, getCount, getNext, hasNext, limitRowsTo, limitTo, map, mapEffect, mapEffect, mapFuture, mapPipelined, orElse, reduce, skip, skipThenLimit
forEachRemaining, remove
protected UnorderedUnionCursor(@Nonnull List<com.apple.foundationdb.record.provider.foundationdb.cursors.MergeCursorState<T>> cursorStates, @Nullable FDBStoreTimer timer)
@Nonnull public static <T> UnorderedUnionCursor<T> create(@Nonnull List<Function<byte[],RecordCursor<T>>> cursorFunctions, @Nullable byte[] continuation, @Nullable FDBStoreTimer timer)
UnionCursor
, this does
not require that the child cursors return values in any particular order. The trade-off, however,
is that this cursor will not attempt to remove any duplicates from its children. It will return
results from its children as they become available.T
- the type of elements returned by this cursorcursorFunctions
- a list of functions to produce RecordCursor
s from a continuationcontinuation
- any continuation from a previous scantimer
- the timer used to instrument events@Nonnull protected RecordCursor.NoNextReason mergeNoNextReasons()
SOURCE_EXHAUSTED
if all of the cursors are exhausted.@Nonnull public CompletableFuture<RecordCursorResult<U>> onNext()
RecordCursor
RecordCursorResult
, which represents exactly one of the following:
T
produced by the cursor. In addition to the next record, this result
includes a RecordCursorContinuation
that can be used to continue the cursor after the last record
returned. The returned continuation is guaranteed not to be an "end continuation" representing the end of
the cursor: specifically, RecordCursorContinuation.isEnd()
is always false
on the returned
continuation.
RecordCursor.NoNextReason
that
explains why no record could be produced. The result include a continuation that can be used to continue
the cursor after the last record returned.
If the result's NoNextReason
is anything other than RecordCursor.NoNextReason.SOURCE_EXHAUSTED
, the
returned continuation must not be an end continuation. Conversely, if the result's NoNextReason
is SOURCE_EXHAUSTED
, then the returned continuation must be an an "end continuation".
RecordCursorContinuation
can be serialized to an opaque byte array using
RecordCursorContinuation.toBytes()
. This can be passed back into a new cursor of the same type, with all
other parameters remaining the same.onNext
in interface RecordCursor<U>
RecordCursorResult
,
RecordCursorContinuation
@Nonnull @Deprecated public CompletableFuture<Boolean> onHasNext()
RecordCursor
onHasNext
in interface RecordCursor<U>
true
if RecordCursor.next()
would return a record.AsyncIterator.onHasNext()
@Nullable @Deprecated public U next()
RecordCursor
@Nullable @Deprecated public byte[] getContinuation()
RecordCursor
getContinuation
in interface RecordCursor<U>
null
if the underlying source is completely exhausted, independent of any limit
passed to the cursor creator. Since such creators generally accept null
to mean no continuation,
that is, start from the beginning, one must check for null
from getContinuation
to
keep from starting over.
Result is not always defined if called before onHasNext
or before next
after
onHasNext
has returned true
. That is, a continuation is only guaranteed when called
"between" records from a while (hasNext) next
loop or after its end.@Nonnull @Deprecated public RecordCursor.NoNextReason getNoNextReason()
RecordCursor
false
for RecordCursor.hasNext()
.
If hasNext
was not called or returned true
last time, the result is undefined and
may be an exception.getNoNextReason
in interface RecordCursor<U>
public void close()
close
in interface RecordCursor<U>
close
in interface AutoCloseable
@Nonnull public Executor getExecutor()
getExecutor
in interface RecordCursor<U>
@Nullable public FDBStoreTimer getTimer()
FDBStoreTimer
used to instrument events of this cursor.public boolean accept(@Nonnull RecordCursorVisitor visitor)
RecordCursor
RecordCursorVisitor
.
By contract, implementations of this method must return the value of visitor.visitLeave(this)
,
which determines whether or not subsequent siblings of this cursor should be visited.accept
in interface RecordCursor<U>
visitor
- a hierarchical visitortrue
if the subsequent siblings of the cursor
should be visited, and false
otherwise