• Status: Accepted
• Date: 2026-09-14

Context

Copying the mutable logger registry under a read lock on every log call made the normal dispatch path pay synchronization and allocation costs. Logger registry mutations and reconfiguration are infrequent compared with logging.

Decision

Publish an immutable copy-on-write strategy-list snapshot on registry changes. The hot path reads it with an atomic shared_ptr load. Mutable enabled and single_mode state is atomic. The per-strategy execution mutex remains around formatter/backend invocation because custom formatters and backends do not have a universal concurrent-invocation contract.

Consequences

Normal dispatch avoids the registry mutex and temporary vector copy while preserving safe lifetime and mutation semantics. A future lock-elision path requires an explicit capability contract and separate regression coverage; a benchmark sink alone is not evidence that arbitrary backends are thread-safe.