Package org.apache.druid.segment

Class ReferenceCountedSegmentProvider

java.lang.Object

org.apache.druid.segment.ReferenceCountingCloseableObject<Segment>

org.apache.druid.segment.ReferenceCountedSegmentProvider

All Implemented Interfaces:

Closeable, AutoCloseable, ReferenceCountedObjectProvider<Segment>

public class ReferenceCountedSegmentProvider
extends ReferenceCountingCloseableObject<Segment>
implements ReferenceCountedObjectProvider<Segment>

Helper object to assist in managing Segment storage lifecycle. Provides access to the Segment tracked with reference counting, releasing the reference on close. Closing this provider closes the underlying Segment once all references are returned, ensuring that a segment cannot be dropped while it is actively being used.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	ReferenceCountedSegmentProvider.CloseableWrappedReference
static class	ReferenceCountedSegmentProvider.LeafReference	Base type to mark Segment returned by ReferenceCountedObjectProvider<Segment> as 'leaf' segments, to distinguish from other transformations which can be done on top of this segment, such as by SegmentMapFunction
final class	ReferenceCountedSegmentProvider.ReferenceClosingSegment	Wraps a Segment and decrements reference to this segment of ReferenceCountedSegmentProvider on close (instead of closing the segment itself which is managed through the provider)
static final class	ReferenceCountedSegmentProvider.UnmanagedReference

Field Summary

Fields inherited from class org.apache.druid.segment.ReferenceCountingCloseableObject

baseObject, referents

Constructor Summary

Constructors

Constructor	Description
ReferenceCountedSegmentProvider(Segment baseSegment)

Method Summary

Modifier and Type	Method	Description
Optional<Segment>	acquireReference()	This method increments a reference count and provides a Closeable that decrements the reference count when closed.
Segment	getBaseSegment()
static ReferenceCountedSegmentProvider	of(Segment segment)
static Optional<Segment>	unmanaged(Segment segment)	Make a wrapper for a Segment that does not close the underlying segment on close
static Optional<Segment>	wrapCloseable(ReferenceCountedSegmentProvider.LeafReference segment, Closeable closeable)

Methods inherited from class org.apache.druid.segment.ReferenceCountingCloseableObject

close, decrement, decrementOnceCloseable, getNumReferences, increment, incrementReferenceAndDecrementOnceCloseable, isClosed

Methods inherited from class java.lang.Object

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

Constructor Details

ReferenceCountedSegmentProvider

public ReferenceCountedSegmentProvider(Segment baseSegment)

Method Details

of

public static ReferenceCountedSegmentProvider of(Segment segment)

unmanaged

public static Optional<Segment> unmanaged(Segment segment)

Make a wrapper for a Segment that does not close the underlying segment on close

wrapCloseable

public static Optional<Segment> wrapCloseable(ReferenceCountedSegmentProvider.LeafReference segment,
 Closeable closeable)

getBaseSegment

@Nullable
public Segment getBaseSegment()

acquireReference

public Optional<Segment> acquireReference()

Description copied from interface: ReferenceCountedObjectProvider

This method increments a reference count and provides a Closeable that decrements the reference count when closed. The object returned by this method may or may not be thread-safe, it is best to check with the implementation.

IMPORTANT NOTE: to fulfill the contract of this method, implementors must return a closeable to indicate that the reference can be acquired, even if there is nothing to close. Implementors should ideally avoid allowing this method to throw exceptions, but callers are responsible for closing the returned object should any operations on it throw exceptions.

For callers: if this method returns non-empty, IT MUST BE CLOSED, else reference counts can potentially leak.

Specified by:

acquireReference in interface ReferenceCountedObjectProvider<Segment>