fix(platform-wallet): never drop a wallet event on the wallets-map lock - #4557
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The manager's `wallets` map was a `tokio::sync::RwLock`, and the two synchronous event handlers that resolve a wallet through it cannot await: `BalanceUpdateHandler` probed with `try_read()` and dropped the event's balance snapshot whenever a manager lifecycle write (create / remove / load) was in flight, and `SpendObservationHandler` carried a whole deferral queue to survive the same probe failing. The bus neither retries nor coalesces, so a dropped snapshot leaves superseded totals on screen until some later balance-bearing event happens to arrive, and nothing guarantees one does. Convert the map to `arc_swap::ArcSwap` (already this crate's idiom for rare-write / hot-read state): readers take a wait-free snapshot that can never fail or block, so the drop window no longer exists rather than being papered over. The rare lifecycle writers publish via `rcu`, preserving the generation-checked removal's check-and-remove atomicity, and the sync-context accessors that used `blocking_read()` become wait-free loads, removing their panic-inside-runtime hazard. With the read infallible, `SpendObservationHandler`'s pending queue loses its premise: there is no contention outcome left to defer, so the queue, its 4096-outpoint cap and the shedding warning go, and the handler applies every observation at delivery. Its regression test keeps `#4309` pinned against the closest window the new type admits — a lifecycle writer parked mid-`rcu` across the delivery — as does the balance handler's own test, which asserts the snapshot lands before that writer commits.
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🕓 Ready for review — 49 ahead in queue (commit 6fda0ec) |
📝 WalkthroughWalkthroughThe wallet map changes from an ChangesWallet map synchronization
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🟡 Moderate · up to A failed wallet load can currently roll back a newer wallet generation that reused the same ID, potentially removing valid wallet state. The PR should not merge until rollback is generation-aware. Sequence Diagram(s)sequenceDiagram
participant Lifecycle
participant ArcSwapWallets
participant BalanceUpdateHandler
participant PlatformWallet
Lifecycle->>ArcSwapWallets: start rcu map update
BalanceUpdateHandler->>ArcSwapWallets: load wallet snapshot
ArcSwapWallets-->>BalanceUpdateHandler: return current snapshot
BalanceUpdateHandler->>PlatformWallet: update balance atomics
ArcSwapWallets-->>Lifecycle: commit updated map
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✅ Passed checks (4 passed)
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In `@packages/rs-platform-wallet/src/manager/load.rs`:
- Line 228: The load_from_persistor rollback currently tracks only WalletId,
allowing a newer wallet generation to be removed after concurrent replacement.
Track each inserted wallet’s generation, and during both wallets rollback and
wm.remove_wallet rollback remove only when the current entry still matches that
generation. Add a regression test covering removal, same-ID re-registration, and
a subsequent load failure.
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📒 Files selected for processing (10)
packages/rs-platform-wallet/src/manager/accessors.rspackages/rs-platform-wallet/src/manager/dashpay_sync.rspackages/rs-platform-wallet/src/manager/dpns_sync.rspackages/rs-platform-wallet/src/manager/load.rspackages/rs-platform-wallet/src/manager/mod.rspackages/rs-platform-wallet/src/manager/platform_address_sync.rspackages/rs-platform-wallet/src/manager/wallet_lifecycle.rspackages/rs-platform-wallet/src/wallet/core/balance_handler.rspackages/rs-platform-wallet/src/wallet/core/broadcast.rspackages/rs-platform-wallet/src/wallet/core/spend_observer.rs
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…shed Two follow-ups on the review of this PR. `cargo fmt` on the `wallets_map` test helper, whose return type the ArcSwap change left wrapped. And the rollback in `load_from_persistor` tracked only `WalletId`, so it removed by id alone. That is safe while nothing else touches the map, and this is the interleaving where something does: this load publishes a generation under an id, a concurrent `remove_wallet` frees that id, a registration publishes a NEW generation under it, and only then does a later iteration fail and reach the rollback. Removing by id would delete that new registration — a live wallet this call never created and whose owner is still using it — and the inner-manager unwind that follows would strip its backing too. The rollback is now generation-checked, the same rule `remove_wallet` applies to its own removal: an entry is reclaimed only while it still holds the `Arc<WalletGeneration>` this load inserted, and the inner-manager unwind keys off that same answer. An id that never reached `self.wallets` — this call failed between the two inserts — has no such owner and unwinds as before. The decision is a pure `rollback_targets`, so the invariant is pinned without racing a real load against a real re-registration: `rollback_only_reclaims_the_generation_this_load_published` asserts both halves — reclaimed while ours, refused once superseded. Pre-existing: the id-only removal predates the ArcSwap change, which altered how the map is written, not what the rollback matched on.
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Approving.
The RwLock → ArcSwap migration is complete — no read()/write()/try_read()/blocking_read() on wallets remains in the crate — and all three write sites use rcu correctly. The property the generation checks depend on (the closure sees exactly the map the CAS compares against, and the last invocation is the committing one) holds, so remove_wallet's check-and-remove stays atomic. The rollback_targets commit closes a real hole: a failed load_from_persistor could previously evict a foreign generation re-registered under the same id. The "insert into the inner manager → publish into self.wallets" window stays closed against a concurrent registration (insert_wallet returns WalletAlreadyExists), so the rollback ordering is sound. No guard is held across an .await anywhere, which is the new foot-gun this type introduces.
Three non-blocking notes:
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spend_observer.rs— dropping the deferral queue leaves the window betweeninsert_walletand theself.walletspublish (which spans theawaiton platform-address initialization) as an unconditional drop for spend observations. For a wallet id re-registered after a removal, the inherited in-broadcast fences mean a lost observation leaves the outpoint fenced for the manager's lifetime — the #4309 symptom. The oldtry_readlost that same window too, except for the sliver the queue rescued, so this isn't a regression introduced here; but it may be worth releasing/re-seeding fences right after thercupublish, the way the balance atomics already are, before considering #4309 fully closed. -
manager/mod.rsfield doc says thercuclosure "must stay pure map manipulation", while two of the three call sites deliberately write captured state (Cellinwallet_lifecycle.rs,RefCellinload.rs) and rely on last-invocation-commits. The code is right; the doc tells a future editor the opposite. Stating the actual rule — captured state must be overwritten per attempt, never accumulated — would protect the invariant better. -
load.rsrollback warning ("a new generation was registered under this id") also fires when the entry was simply removed concurrently and nothing replaced it. Harmless, but misleading during triage.
…rrect what the docs claim Review follow-ups on this PR. One real defect, the rest are the code telling a future reader something that is not true. `load_from_persistor` seeded the balance atomic BEFORE `insert_wallet`, and the wallet becomes SPV-visible the moment that insert lands — several `.await`s before the `rcu` publishes it. A `BlockProcessed` arriving in that window finds the wallet absent from the map and its snapshot is dropped, leaving a restored wallet showing the persisted total while the inner balance has moved on, with no later event guaranteed to correct it. `register_wallet` already re-seeds after its publish and its comment claimed the restore path did too; now it does. Both sites note the ordering they accept: the seed can briefly lose a race with the handler, and the next event corrects that — worth more than the window it closes. The field doc said an `rcu` closure "must stay pure map manipulation", while two of the three call sites deliberately write captured state and are correct in doing so. It now states the rule they actually rely on: only the invocation whose compare-and-swap succeeds is published, so captured state must be overwritten per attempt, never accumulated. The rollback's warning claimed a new generation had been registered under the id whenever the entry was not ours — including when something else had simply removed it and nothing replaced it, which sends anyone reading it after a wallet-disappeared report after a generation that does not exist. The two states are now distinguished. `get_wallet` and `wallet_ids` became character-for-character copies of their `_blocking` twins, so they delegate rather than drift; their `async` signatures stay for source compatibility, with the doc saying they no longer suspend. Tests: `a_failed_load_rolls_back_the_wallet_it_had_already_published` fails a load after a wallet is published, so the rollback's `rcu` closure, its per-attempt verdict hand-off and the branch deciding whether the inner-manager entry is removed all execute — none of which the pure-function test reaches. And both rendezvous closures now park once: `rcu` may re-run its closure, and a second `recv()` on a send-once channel would hang the suite rather than fail it.
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@llbartekll thanks — all three notes landed somewhere, two as fixes and one as a correction to the docs instead. 2 (the 3 (the rollback warning). Fixed. The two states are now distinguished: an id still in the map after the rollback means a same-id re-registration owns it and something is genuinely left in place; an id that is simply gone gets "already removed by something else; nothing left to roll back". A wait-free load after the rollback is enough for a log line. 1 (the spend-observation publish window). Not fixed, and I want to be explicit rather than quietly skip it. I agree with your framing — the old That claim also turned out to be false for one of the two paths, which is the one real defect this round: Also in this push: Corrected the PR description too: it claimed the Local before pushing: 927 tests, |
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## v4.2-dev #4557 +/- ##
============================================
- Coverage 87.57% 85.89% -1.69%
============================================
Files 2748 2786 +38
Lines 357005 367366 +10361
============================================
+ Hits 312647 315535 +2888
- Misses 44358 51831 +7473
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Re-approving after 6fda0ecf7 (my earlier approval was dismissed as stale by the new commit).
All three follow-ups are addressed, and the restore-path balance window you found on the way is a real defect worth its own fix — load_from_persistor seeding before insert_wallet left a restored wallet showing the persisted total with no later event guaranteed to correct it, and the two creation paths now close that window the same way. a_failed_load_rolls_back_the_wallet_it_had_already_published is the test the rollback was missing: the pure-function test could stay green while the inner-manager branch was inverted.
I checked the one thing in the new commit that looked worth a second pass — let still_mapped = self.wallets.load() is held across wallet_manager.write().await in the rollback. It is fine: arc_swap's wait_for_readers goes to Debt::pay_all, which pays the outstanding slots by taking a ref count rather than spinning, so a live guard cannot stall an rcu writer, and Guard is Send (HybridProtection is Option<&'static Debt> over an AtomicUsize plus the Arc). Taking the snapshot before the lock is also the more accurate reading, since it sits closer in time to the rcu that produced rolled_back. load_full() would state the "owned snapshot, not a guard" intent more plainly if you touch it again, but nothing needs changing.
Two nits, neither blocking:
wallet_lifecycle.rs, the new note on the re-seed: "and during the rescan this exists for those arrive continuously" is garbled — theload.rstwin reads correctly ("during catch-up those arrive continuously").- The parked-once rendezvous guard is the right call, but the two copies are now identical eight-line comments over identical code in
mod.rsandbroadcast.rs. Fine as is; worth a shared test helper if a third rendezvous ever shows up.
4 participants
Issue being fixed or feature implemented
The manager's
walletsmap is atokio::sync::RwLock, and the two event handlers that resolve a wallet through it are synchronous and cannot await:BalanceUpdateHandlerprobed it withtry_read()and dropped the event's balance snapshot whenever a lifecycle write (wallet create / remove / load) was in flight. The event bus neither retries nor coalesces, so a dropped snapshot leaves superseded totals on screen until some later balance-bearing event happens to arrive — and nothing guarantees one does.SpendObservationHandlercarries an entire deferral queue whose only reason to exist is that sametry_read()failing (dashpay/platform#4309).Extracted from #4406, where it was one commit among many. It is independent of that PR's subject and is a live fix on its own.
What was done?
PlatformWalletManager::walletsbecomesarc_swap::ArcSwap— already this crate's idiom for rare-write / hot-read state. Readers take a wait-free snapshot that can never fail or block, so the drop window no longer exists rather than being papered over.rcu, preserving the generation-checked removal's check-and-remove atomicity (wallet_lifecycle.rs,load.rs).blocking_read()become wait-free loads, removing that map's panic-inside-runtime hazard (accessors.rs). Scoped deliberately: the same functions still take other locks the ordinary way —platform_address_provider_state_blockingkeepsprovider_lock.blocking_read(), andwallet_network_blocking/tracked_asset_locks_blockingkeepwallet_manager.blocking_read()— so their "must not be called from inside a tokio async task" contract is unchanged. This PR narrows the hazard to those locks; it does not remove it from these entry points.SpendObservationHandler's pending queue loses its premise: there is no contention outcome left to defer. The queue, itsMAX_QUEUED_SPEND_OBSERVATIONScap and the shedding warning are removed, and the handler applies every observation at delivery (spend_observer.rs, −181 lines).How Has This Been Tested?
cargo test -p platform-wallet— 928 tests pass.Two regression tests pin the behaviour against the closest window the new type admits — a lifecycle writer parked mid-
rcuacross the delivery:manager::tests::balance_snapshot_survives_wallets_map_write_contention— the snapshot must land in the wallet's balance atomics before that writer commits.wallet::core::broadcast::tests::a_wallets_map_write_in_flight_does_not_cost_a_spend_observation— the in-broadcast fence must clear anyway (replaces the old contention/deferral test, whose scenario is now unreachable).Breaking Changes
None.
walletsis not part of the public API surface;get_wallet_blockingkeeps its name and signature (it is simply no longer blocking).Checklist:
For repository code-owners and collaborators only
Summary by CodeRabbit
Performance Improvements
Reliability