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📝 WalkthroughWalkthrough
Sequence Diagram(s)sequenceDiagram
participant Caller
participant ChannelFactory
participant IOEventLoop
participant AddressResolver
Caller->>ChannelFactory: resolveAll(address)
ChannelFactory->>IOEventLoop: schedule lookup
IOEventLoop->>AddressResolver: resolveAll(address)
AddressResolver-->>ChannelFactory: resolved addresses or failure
ChannelFactory-->>Caller: complete CompletionStage
Priority: ⬇️ Low Change: Feature Merge Risk: 🟡 Moderate · up to Concurrent initial lookups can run bootstrap configuration multiple times and lose the promised pinned resolver execution context. Synchronize or atomically initialize the cached resolver state before merge. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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ChannelFactory.resolveAll(SocketAddress) asks the resolver the driver's bootstrap would use for a connect, so a custom AddressResolverGroup installed through NettyOptions.afterBootstrapInitialized is honoured, for every address a name currently maps to. It mirrors Netty's own short-circuits (disabled resolver, unsupported or already-resolved address: the input as is). AddressResolver#resolveAll resolves inline, so the lookup runs on one pinned I/O loop, never on the caller; the hook is asked once. No caller yet: the contact-point expansion follows. Refs: scylladb#890 Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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Code Review by Qodo
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Actionable comments posted: 1
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Inline comments:
In
`@core/src/main/java/com/datastax/oss/driver/internal/core/channel/ChannelFactory.java`:
- Around line 307-322: Make initialization of the cached resolver state in the
resolver lookup flow atomic so concurrent first calls cannot both observe a null
resolverGroup. Synchronize or use an atomic holder around Bootstrap creation,
afterBootstrapInitialized, resolver extraction, and assignment to ensure the
hook and event-loop selection occur once and all callers reuse the same
ResolvedResolverGroup.
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📒 Files selected for processing (4)
core/src/main/java/com/datastax/oss/driver/internal/core/channel/ChannelFactory.javacore/src/main/java/com/datastax/oss/driver/internal/core/context/NettyOptions.javacore/src/test/java/com/datastax/oss/driver/internal/core/channel/ChannelFactoryResolveAllTest.javacore/src/test/java/com/datastax/oss/driver/internal/core/channel/TestAddressResolverGroup.java
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| */ | ||
| @Nullable | ||
| private AddressResolverGroup<?> resolverGroup() { | ||
| ResolvedResolverGroup discovered = this.resolverGroup; |
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[P2] Initialize the cached resolver state atomically
ChannelFactory is @ThreadSafe, but concurrent first resolveAll calls can both pass this null check. They can invoke afterBootstrapInitialized multiple times, create separate resolver groups, and select different event loops. This violates the PR's once-only hook and pinned-loop guarantees and can duplicate DNS resolver resources. Publish the resolver group and executor through one synchronized or atomic holder, and add a concurrent-first-call test; the current sequential test does not exercise this race.
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Fixed in 4623305. resolverGroup() and resolverExecutor() are now one resolverState(): the group and the pinned loop are discovered together, in one critical section, behind a single lock, and published as an immutable holder through a volatile field. A hook that throws still caches nothing.
New test should_run_the_bootstrap_hook_once_when_lookups_race: 8 callers released by a barrier, the hook sleeps 50 ms and builds the group it installs. 8 hook calls against the previous file, 1 now; 15/15 runs green.
| } | ||
| resolver | ||
| .resolveAll(address) | ||
| .addListener( |
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[P2] Fail an in-flight lookup when its event loop terminates
After scheduling succeeds, this listener is the only path that completes result. With Netty 4.1.136 DnsAddressResolverGroup, shutting down the event loop during a pending query cancels its timeout and closes the resolver without completing the resolution future. Reproduced result: both the Netty future and returned stage remain incomplete after shutdownGracefully().sync(). This directly contradicts the PR's no-incomplete-path guarantee. The new shutdown test only covers calls started after shutdown. Race pending lookups against executor.terminationFuture() and remove that listener after normal completion.
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Confirmed and fixed in 4623305. The chain is as you describe: confirmShutdown() cancels scheduled tasks rather than running them, so DnsQueryContext's timeout never fires, and DnsResponseHandler has no channelInactive, so closing the resolver's channel completes nothing either.
failWhenExecutorTerminates races each lookup against executor.terminationFuture() — a promise on GlobalEventExecutor, so it is notified off the loop that is dying — and removes the listener when the stage completes, so a long-lived loop does not accumulate one per lookup. Registered after execute() is accepted, not before: on an already-terminated loop addListener notifies immediately and would otherwise race RejectedExecutionException to the stage, making the existing shutdown test nondeterministic.
New test should_fail_the_stage_when_the_io_loop_terminates_mid_lookup, with a resolver that never answers and a latch proving the lookup is in flight: the stage stayed pending against the previous file, fails now.
The javadoc and the PR body no longer claim an absolute "no path can leave the stage incomplete" — a resolver that never answers on a loop that never terminates still hangs, exactly as a connect's resolution does.
…ER-201) Two review findings, both about guarantees this commit claims. Initialise the resolver group and the pinned loop together, once, behind one lock: two concurrent first calls could each run the bootstrap hook and pin a loop of their own. Fail a lookup whose event loop terminates under it. An asynchronous resolver completes its promise from a response or from a scheduled timeout, and shutdown cancels the latter without running it, so the stage stayed pending for good. The listener goes on after the task is accepted, and comes off when the stage completes. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2 participants
Groundwork for expanding a contact-point hostname to every address it resolves to (next PR in the stack): nothing in the driver can ask Netty's configured resolver for all the addresses of a name, only for one, and only inside
Bootstrap.connect().ChannelFactory.resolveAll(SocketAddress)builds a bootstrap the wayconnect()does, runsNettyOptions.afterBootstrapInitializedon it, and asks the resolver that hook left installed, so a customAddressResolverGroupis honoured.AddressResolver#resolveAllresolves inline, and the default resolver blocks on the JDK lookup. A connect already pays that on an event loop, so this is parity, and the admin executor is left free.bootstrap.resolver(new DnsAddressResolverGroup(...))would otherwise mint a resolver, a socket and an empty DNS cache every time.connect().Verified:
ChannelFactoryResolveAllTest(15 cases), the thread, hook-count, hook-race and loop-termination cases proven red against the pre-change file; every existingChannelFactory*Testunmodified and green; fullcoreunit suite green (3983) on JDK 11. Not covered: no integration test — the caller in the next PR carries those.#1065 has merged, so this is one commit on
scylla-4.xnow. #1074 stacks on it.Refs: #890, #215
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