Uses of Package
org.apache.cassandra.utils.concurrent

Packages that use org.apache.cassandra.utils.concurrent

Package	Description
org.apache.cassandra.audit
org.apache.cassandra.batchlog
org.apache.cassandra.cache
org.apache.cassandra.concurrent
org.apache.cassandra.cql3
org.apache.cassandra.db
org.apache.cassandra.db.commitlog
org.apache.cassandra.db.compaction
org.apache.cassandra.db.compaction.unified
org.apache.cassandra.db.compaction.writers
org.apache.cassandra.db.lifecycle
org.apache.cassandra.db.memtable
org.apache.cassandra.db.partitions
org.apache.cassandra.db.repair
org.apache.cassandra.db.rows
org.apache.cassandra.db.streaming	File transfer
org.apache.cassandra.dht
org.apache.cassandra.fql
org.apache.cassandra.hints	Hints subsystem consists of several components.
org.apache.cassandra.index
org.apache.cassandra.index.sai
org.apache.cassandra.index.sasi.disk
org.apache.cassandra.io.compress
org.apache.cassandra.io.sstable
org.apache.cassandra.io.sstable.format
org.apache.cassandra.io.sstable.format.big
org.apache.cassandra.io.sstable.format.bti
org.apache.cassandra.io.sstable.indexsummary
org.apache.cassandra.io.util
org.apache.cassandra.net
org.apache.cassandra.repair
org.apache.cassandra.repair.autorepair
org.apache.cassandra.repair.consistent
org.apache.cassandra.repair.messages
org.apache.cassandra.schema
org.apache.cassandra.service
org.apache.cassandra.service.paxos.cleanup
org.apache.cassandra.service.paxos.v1
org.apache.cassandra.service.reads
org.apache.cassandra.service.reads.repair
org.apache.cassandra.streaming
org.apache.cassandra.streaming.async	Non-blocking streaming with netty
org.apache.cassandra.transport
org.apache.cassandra.utils
org.apache.cassandra.utils.concurrent
org.apache.cassandra.utils.memory
org.apache.cassandra.utils.obs

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.audit

Class	Description
WeightedQueue.Weighable

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.batchlog

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.cache

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.concurrent

Class	Description
AbstractFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
Awaitable	A generic signal consumer, supporting all of the typical patterns used in Cassandra.
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
RunnableFuture
SyncFuture	Netty's DefaultPromise uses a mutex to coordinate notifiers AND waiters between the eventLoop and the other threads.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.cql3

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
OpOrder	A class for providing synchronization between producers and consumers that do not communicate directly with each other, but where the consumers need to process their work in contiguous batches.
OpOrder.Barrier	This class represents a synchronisation point providing ordering guarantees on operations started against the enclosing OpOrder.
OpOrder.Group	Represents a group of identically ordered operations, i.e.
Refs	A collection of managed Ref references to RefCounted objects, and the objects they are referencing.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.commitlog

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
Semaphore
WaitQueue	A relatively easy to use utility for general purpose thread signalling.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.compaction

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
Refs	A collection of managed Ref references to RefCounted objects, and the objects they are referencing.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.compaction.unified

Class	Description
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.compaction.writers

Class	Description
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.lifecycle

Class	Description
OpOrder.Group	Represents a group of identically ordered operations, i.e.
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.memtable

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
OpOrder.Barrier	This class represents a synchronisation point providing ordering guarantees on operations started against the enclosing OpOrder.
OpOrder.Group	Represents a group of identically ordered operations, i.e.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.partitions

Class	Description
OpOrder.Group	Represents a group of identically ordered operations, i.e.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.repair

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
Refs	A collection of managed Ref references to RefCounted objects, and the objects they are referencing.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.rows

Class	Description
OpOrder.Group	Represents a group of identically ordered operations, i.e.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.db.streaming

Class

Description

Ref

An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.dht

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.fql

Class	Description
WeightedQueue.Weighable

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.hints

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.index

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.index.sai

Class	Description
SharedCloseable	A simple extension of AutoCloseable, that represents a resource that can be utilised in multiple locations, each managing their own closure of the resource, so that when the last such instance is closed all are.
SharedCloseableImpl	A simple abstract implementation of SharedCloseable

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.index.sasi.disk

Class	Description
CountDownLatch

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.io.compress

Class	Description
Ref.IdentityCollection
SharedCloseable	A simple extension of AutoCloseable, that represents a resource that can be utilised in multiple locations, each managing their own closure of the resource, so that when the last such instance is closed all are.
SharedCloseableImpl	A simple abstract implementation of SharedCloseable
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.
WrappedSharedCloseable	An implementation of SharedCloseable that wraps a normal AutoCloseable, ensuring its close method is only called when all instances of SharedCloseable have been

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.io.sstable

Class	Description
OpOrder.Barrier	This class represents a synchronisation point providing ordering guarantees on operations started against the enclosing OpOrder.
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.io.sstable.format

Class	Description
Ref	An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope.
Ref.IdentityCollection
RefCounted	An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope.
RefCounted.Tidy
SelfRefCounted
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.io.sstable.format.big

Class	Description
RefCounted	An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope.
SelfRefCounted
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.io.sstable.format.bti

Class	Description
Ref.IdentityCollection
RefCounted	An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope.
SelfRefCounted
SharedCloseable	A simple extension of AutoCloseable, that represents a resource that can be utilised in multiple locations, each managing their own closure of the resource, so that when the last such instance is closed all are.
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.io.sstable.indexsummary

Class	Description
Ref.IdentityCollection
SharedCloseable	A simple extension of AutoCloseable, that represents a resource that can be utilised in multiple locations, each managing their own closure of the resource, so that when the last such instance is closed all are.
SharedCloseableImpl	A simple abstract implementation of SharedCloseable
WrappedSharedCloseable	An implementation of SharedCloseable that wraps a normal AutoCloseable, ensuring its close method is only called when all instances of SharedCloseable have been

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.io.util

Class	Description
Ref.IdentityCollection
RefCounted.Tidy
SharedCloseable	A simple extension of AutoCloseable, that represents a resource that can be utilised in multiple locations, each managing their own closure of the resource, so that when the last such instance is closed all are.
SharedCloseableImpl	A simple abstract implementation of SharedCloseable
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional	A simple abstract implementation of Transactional behaviour.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.net

Class	Description
AbstractFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncPromise	Extends AsyncFuture to implement the Promise interface.
AsyncPromise.WithExecutor
Awaitable	A generic signal consumer, supporting all of the typical patterns used in Cassandra.
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
Promise	A Promise that integrates Promise with our Future API to improve clarity and coherence in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.repair

Class	Description
AbstractFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
Awaitable	A generic signal consumer, supporting all of the typical patterns used in Cassandra.
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.repair.autorepair

Class	Description
Condition	Simpler API than java.util.concurrent.Condition; would be nice to extend it, but also nice to share API with Future, for which Netty's API is incompatible with java.util.concurrent.Condition Awaitable for explicit external signals.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.repair.consistent

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.repair.messages

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.schema

Class	Description
Awaitable	A generic signal consumer, supporting all of the typical patterns used in Cassandra.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.service

Class	Description
Condition	Simpler API than java.util.concurrent.Condition; would be nice to extend it, but also nice to share API with Future, for which Netty's API is incompatible with java.util.concurrent.Condition Awaitable for explicit external signals.
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
IntrusiveStack	An efficient stack/list that is expected to be ordinarily either empty or close to, and for which we need concurrent insertions and do not need to support removal - i.e.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.service.paxos.cleanup

Class	Description
AbstractFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
Awaitable	A generic signal consumer, supporting all of the typical patterns used in Cassandra.
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.service.paxos.v1

Class	Description
CountDownLatch

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.service.reads

Class	Description
Accumulator	A simple append-only collection supporting an unbounded number of concurrent readers/writers, but a bounded number of items.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.service.reads.repair

Class	Description
AbstractFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
Awaitable	A generic signal consumer, supporting all of the typical patterns used in Cassandra.
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.streaming

Class	Description
AbstractFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
Awaitable	A generic signal consumer, supporting all of the typical patterns used in Cassandra.
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.streaming.async

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.transport

Class	Description
NonBlockingRateLimiter	A rate limiter implementation that allows callers to reserve permits that may only be available in the future, delegating to them decisions about how to schedule/delay work and whether or not to block execution to do so.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.utils

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
Ref.IdentityCollection
SharedCloseable	A simple extension of AutoCloseable, that represents a resource that can be utilised in multiple locations, each managing their own closure of the resource, so that when the last such instance is closed all are.
SharedCloseableImpl	A simple abstract implementation of SharedCloseable
WrappedSharedCloseable	An implementation of SharedCloseable that wraps a normal AutoCloseable, ensuring its close method is only called when all instances of SharedCloseable have been

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.utils.concurrent

Class	Description
AbstractFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncFuture	Our default Future implementation, with all state being managed without locks (except those used by the JVM).
AsyncPromise	Extends AsyncFuture to implement the Promise interface.
Awaitable	A generic signal consumer, supporting all of the typical patterns used in Cassandra.
Awaitable.AbstractAwaitable
Awaitable.AsyncAwaitable	A barebones asynchronous Awaitable.
Awaitable.SyncAwaitable	A barebones Awaitable that uses mutual exclusion.
Condition	Simpler API than java.util.concurrent.Condition; would be nice to extend it, but also nice to share API with Future, for which Netty's API is incompatible with java.util.concurrent.Condition Awaitable for explicit external signals.
Condition.Async	An asynchronous Condition.
ConditionAsConsumer
CountDownLatch
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
FutureCombiner	Netty's PromiseCombiner is not threadsafe, and we combine futures from multiple event executors.
ImmediateFuture
IntrusiveStack	An efficient stack/list that is expected to be ordinarily either empty or close to, and for which we need concurrent insertions and do not need to support removal - i.e.
IntrusiveStack.Setter
LightweightRecycler	A simple thread local object reuse facility with limited capacity and no attempt at rebalancing pooling between threads.
LoadingMap.UnloadExecutionException	Thrown when unloading a value failed.
NonBlockingRateLimiter	A rate limiter implementation that allows callers to reserve permits that may only be available in the future, delegating to them decisions about how to schedule/delay work and whether or not to block execution to do so.
OpOrder.Barrier	This class represents a synchronisation point providing ordering guarantees on operations started against the enclosing OpOrder.
OpOrder.Group	Represents a group of identically ordered operations, i.e.
Promise	A Promise that integrates Promise with our Future API to improve clarity and coherence in the codebase.
Ref	An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope.
Ref.IdentityCollection
Ref.OnLeak
RefCounted	An object that needs ref counting does the two following: - defines a Tidy object that will cleanup once it's gone, (this must retain no references to the object we're tracking (only its resources and how to clean up)) Then, one of two options: 1) Construct a Ref directly pointing to it, and always use this Ref; or 2) - implements RefCounted - encapsulates a Ref, we'll call selfRef, to which it proxies all calls to RefCounted behaviours - users must ensure no references to the selfRef leak, or are retained outside of a method scope.
RefCounted.Tidy
Refs	A collection of managed Ref references to RefCounted objects, and the objects they are referencing.
SelfRefCounted
Semaphore
SharedCloseable	A simple extension of AutoCloseable, that represents a resource that can be utilised in multiple locations, each managing their own closure of the resource, so that when the last such instance is closed all are.
SharedCloseableImpl	A simple abstract implementation of SharedCloseable
SyncFuture	Netty's DefaultPromise uses a mutex to coordinate notifiers AND waiters between the eventLoop and the other threads.
SyncPromise	Extends SyncFuture to implement the Promise interface.
Transactional	An abstraction for Transactional behaviour.
Transactional.AbstractTransactional.State
UncheckedInterruptedException	Unchecked InterruptedException, to be thrown in places where an interrupt is unexpected
WaitQueue	A relatively easy to use utility for general purpose thread signalling.
WaitQueue.Signal	A Signal is a one-time-use mechanism for a thread to wait for notification that some condition state has transitioned that it may be interested in (and hence should check if it is).
WeightedQueue.Weigher
WrappedSharedCloseable	An implementation of SharedCloseable that wraps a normal AutoCloseable, ensuring its close method is only called when all instances of SharedCloseable have been

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.utils.memory

Class	Description
Future	A Future that integrates several different (but equivalent) APIs used within Cassandra into a single concept, integrating also with our Awaitable abstraction, to overall improve coherency and clarity in the codebase.
OpOrder.Group	Represents a group of identically ordered operations, i.e.
WaitQueue	A relatively easy to use utility for general purpose thread signalling.

Classes in org.apache.cassandra.utils.concurrent used by org.apache.cassandra.utils.obs

Class	Description
Ref.IdentityCollection