Add CancelAndDrainContextWatcherHandler#2537
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Replace the racy 100ms sleep added in 93a5797 with a deterministic single-";" drain that absorbs any pending SQLSTATE 57014 (query_canceled) before the connection is reused. Key changes: - Add CancelAndDrainContextWatcherHandler implementing ctxwatch.Handler. HandleUnwatchAfterCancel sends exactly one ";" after a successful cancel, sufficient because PostgreSQL's QueryCancelPending is a single flag, not a queue. - Add mutex-guarded three-state cancel machine (idle/inFlight/sent) on CancelRequest. This prevents double-send from concurrent callers (ctxwatch, asyncClose, direct user code) which would produce multiple 57014 responses that a single drain cannot reconcile. - Fix data race on pid and secretKey in CancelRequest by grouping both into a backendKeyData struct behind atomic.Pointer. - Extract cancel protocol constants (cancelRequestCode, negotiateSSLCode, packet field offsets) from magic numbers, referencing CancelRequestPacket in src/include/libpq/pqcomm.h. AI: Claude Code (Anthropic) used for drafting and code generation.
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Replace the racy 100ms sleep added in 93a5797 with a deterministic single-";" drain that absorbs any pending SQLSTATE
57014(query_canceled) before the connection is reused.Key changes:
Add
CancelAndDrainContextWatcherHandlerimplementingctxwatch.Handler.HandleUnwatchAfterCancelsends exactly one";"after a successful cancel: sufficient because PostgreSQL'sQueryCancelPendingis a single flag, not a queue.Add mutex-guarded three-state cancel machine (idle/inFlight/sent) on
CancelRequest. This prevents double-send from concurrent callers (ctxwatch,asyncClose, direct user code) which would produce multiple57014responses that a single drain cannot reconcile.Fix data race on pid and secretKey in
CancelRequestby grouping both into abackendKeyDatastruct behindatomic.Pointer.Extract cancel protocol constants (
cancelRequestCode,negotiateSSLCode, packet field offsets) from magic numbers, referencingCancelRequestPacketinsrc/include/libpq/pqcomm.h.AI disclosure
Per the contributing guidelines: Claude Code (Anthropic, Opus 4.6) was used for drafting and code generation. I understand the code, traced the protocol flows through the PostgreSQL source, and can answer questions about the change directly.
Fixes: #2534