# Description
V2 subscription engine feature parity round to make the classic engine
eligible for deprecation. Splits the test surface so the classic and V2
engines can evolve independently, ports the gaps the classic-engine
integration tests had been exercising, and lands the public V2 API
additions needed to close them.
- Splits `Tests/Opc.Ua.Subscriptions.Tests` into a classic
(`Opc.Ua.Subscriptions.Classic.Tests`) and a V2
(`Opc.Ua.Subscriptions.Tests`) project to shrink CI time and let the two
engines diverge cleanly.
- Adds the V2 public-surface gaps required by the test ports
(`Subscription.ServerId` on the class, `SetSubscriptionDurableAsync`,
`SendInitialValuesOnTransfer`, unified `OnSubscriptionStateChangedAsync`
handler callback, per-item `ConditionRefreshAsync`, fluent
`LoadSubscriptionsAsync(Stream, …)` and `Subscription.Snapshot()` /
`RestoreAsync()` for save/load + transfer).
- Lands handler-centric design (no `PublishingStopped` property handlers
maintain derived state); always-sequential per-subscription delivery
documented + tested.
- **Adds short and long haul stability tests for the V2 `ManagedSession`
+ subscription engine. Closes #3744** (see "Issue #3744 Haul tests"
below).
- **Migrates SubscriptionStateSnapshot / MonitoredItemStateSnapshot to
`[DataType]` source-generator codecs**.
- `SubscriptionDurableV2Tests.cs` 5 V2 ports of the classic durable test
patterns.
- `V2FollowUpCoverageTests.cs` handler state-change callback, fluent
stream-based `LoadSubscriptionsAsync`, `SendInitialValuesOnTransfer`,
snapshot edge cases (empty / `DataChangeFilter` round-trip / concurrent
mutation).
- `SubscriptionFailoverV2Tests.cs` forced channel-break with and without
`WithTransferSubscriptionsOnRecreate`.
- `MonitoredItemConditionRefreshLiveV2Tests.cs` ΓÇö live
`ConditionRefresh` against the reference server's event source; asserts
`RefreshStart` / `RefreshEnd` events flow through the handler.
## Fixes
- #3744 Haul tests (V2 ManagedSession + subscription engine)
`Tests/Opc.Ua.Sessions.Tests/ManagedSessionStabilityTest.cs` adds the
short/long haul coverage requested by
[#3744](https://github.com/OPCFoundation/UA-.NETStandard/issues/3744)
plus the bonus fault-injection variant:
| Test | Duration | Category | Purpose |
|---|---|---|---|
| `ShortHaulManagedSessionV2Async` | 2 minutes | `ManagedSessionHaul`
(`[Explicit]`) | Quick local sanity check of the V2 monotonicity
contract. |
| `LongHaulManagedSessionV2Async` | 90 minutes (configurable via
`TEST_DURATION_MINUTES`) | `ManagedSessionHaul` (`[Explicit]`) |
Long-running V2 stability + monotonicity. |
| `LongHaulManagedSessionWithFaultInjectionV2Async` | 90 minutes
(configurable) + fault every `FAULT_INJECTION_INTERVAL_SECONDS` (default
60s) | `ManagedSessionHaul` (`[Explicit]`) | **Bonus** ΓÇö force-closes
the subscriber transport channel periodically; verifies V2 manager
transfers/recreates the subscription and continues monotonic delivery
across reconnects. |
**Pattern.** A writer `ManagedSession` increments a `uint32` counter and
writes it into `Scalar_Static_Mass_UInt32_UInt32_00` every 250ms. A
subscriber `ManagedSession` runs a V2 subscription with a single
monitored item on the same node. `MonotonicCounterHandler` asserts each
received sample is *strictly greater than* the previous one. V2
`ISubscriptionNotificationHandler` per-subscription ordering guarantee.
Skipped values (sampling rate < write rate) are tolerated; duplicates
and reorderings are violations.
* GC reduction via IPooledEncodeable activator pooling
Add opt-in activator-level pooling for IEncodeable instances decoded
during V2 subscription publish dispatch. The design replaces the
earlier IAllocator-on-IServiceMessageContext approach (which had a
cross-contamination hazard for non-publish decodes) with a clean
factory-based model where pooling lives on the encodeable activator.
New public API:
- IPooledEncodeable : IEncodeable - opt-in marker with Reuse() method
- PooledEncodeableType<T> : EncodeableType<T> - activator base with
BoundedObjectPool<T> (lock-free, no new package dependency)
- ISubscriptionManager.PoolNotifications { get; set; }
- ManagedSessionOptions.PoolNotifications { get; init; }
- ManagedSessionBuilder.WithPoolNotifications(bool)
Source-gen:
- All concrete non-abstract structure types (including service
request/response types) are generated with PooledEncodeableType<T>
activators and IPooledEncodeable.Reuse() bodies by default
- Derived types use 'new' to hide inherited Reuse/ClearPooledSentinel
so each concrete type routes through its own activator's pool
- No changes to external design XML files (UA Core Services.xml etc.)
- poolable selection is hardcoded in the generator
Benchmarks (MonitoredItemNotification, 1000 ops):
- Allocations: 128 KB -> 408 B (~315x reduction)
- Gen0 collections: 29.75 -> 0.09 per 1000 ops
No interface changes to IEncodeable, IDecoder, IServiceMessageContext,
or ISubscriptionNotificationHandler. Handlers retain by copy when
pooling is enabled.
Call IPooledEncodeable.Reuse() on decoded IServiceRequest and
IServiceResponse after the server is done with them:
- TcpTransportListener.OnRequestReceivedAsync: reuse both request
and response in a finally block after ProcessRequestAsync +
SendResponse complete
- EndpointBase.InvokeServiceAsync (HTTPS path): same pattern after
ProcessRequestAsync + BinaryEncoder.EncodeMessage
Walk acknowledged, overflow-evicted, and disposed NotificationMessage
objects and call IPooledEncodeable.Reuse() on their notification
payloads (MonitoredItemNotification, DataChangeNotification,
EventFieldList, EventNotificationList).
Insertion points in Subscription.cs:
- Acknowledge(): after RemoveAt from m_sentMessages
- InnerPublish() overflow: before RemoveRange/Clear on m_sentMessages
- Dispose(): before m_sentMessages.Clear()
- InnerPublish() unsent-message overflow: before RemoveRange on
the messages list
Replace new T() with XxxActivator.Instance.CreateInstance() for all
server-side notification payload types so instances are rented from
the activator pool instead of heap-allocated:
New static helper ReuseNotificationPayloads() walks the
NotificationMessage.NotificationData, extracts DataChangeNotification
and EventNotificationList via TryGetValue, iterates their items, and
calls Reuse() on each pooled payload.
- Add new managed session, wrapping session and providing connection management and failover handling
- Add new Subscription engine that can act as alternative to current engine, but is based on channels with worker tasks
- Add a fluent builder for managed session clients
- Replace NodeCache with LruNodeCache, rename ILruNodeCache and LruNodeCache to INodeCache and NodeCache
- Update migration guide and document new functionality.
Marc Schier