feat(logging): zero-allocation format->dispatch path (LogRecord view)#795
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feat(logging): zero-allocation format->dispatch path (LogRecord view)#795kamcheungting-db wants to merge 1 commit into
kamcheungting-db wants to merge 1 commit into
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Sinks now receive a non-owning `LogRecord` { level, string_view message,
source_location, span<const LogAttribute> } instead of an owned `LogMessage&&`.
The macros/function-style Log() format into a reused per-thread `FormatBuffer()`
(std::format_to + clear-keeps-capacity), so logging does no heap allocation after
the buffer warms up. `LogMessage`/`Builder` stay as the owned/retained type and
convert implicitly to `LogRecord`, so `logger->Log(builder.Build())` is unchanged.
Synchronous sinks (Cerr/Spd/Noop) read the view directly; retaining sinks
(test CapturingLogger) deep-copy into an owned LogMessage. Adds a dedicated
logging_zero_alloc_test (global operator-new counter + negative control) proving
the path is allocation-free. CerrLogger's own line rendering and
ICEBERG_LOG_RUNTIME_FMT still allocate (documented; out of this change's scope).
Co-authored-by: Isaac
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Makes the logging format → dispatch path allocation-free, addressing the zero-allocation request on #725. Builds on the merged logging blocks (#722/#723/#724).
What changed
LogRecord({ level, std::string_view message, std::source_location, std::span<const LogAttribute> }) instead of an ownedLogMessage&&. The views are valid only for the duration of theLog()call.Log()/FormatAndEmitformat into a reused per-threadFormatBuffer()viastd::format_to(clear()keeps capacity), so logging performs no heap allocation after the buffer warms up.std::format_towith astd::format_stringkeeps compile-time format-string checking.LogMessage/Builderstay as the owned/retained type and convert implicitly toLogRecord, sologger->Log(builder.Build())is unchanged.CerrLogger, no-op) read the view directly with no allocation; retaining sinks (the testCapturingLogger) deep-copy into an ownedLogMessage, so existing assertions are unaffected.Why now: every production sink consumes the record synchronously, so the owned-
std::stringmodel wasn't buying anything in practice — better to change the interface before external adoption.Tests: new
logging_zero_alloc_test(its own binary; globaloperator newcounter + a negative control proving the probe works) asserts the format→dispatch path does 0 heap allocations after warmup. Existing logging tests pass unchanged; ASan/TSan clean.Out of scope (documented):
CerrLogger's own rendered-linestd::formatandICEBERG_LOG_RUNTIME_FMT(vformat) still allocate.The open macro/spdlog/registry PRs (#725/#726/#737) will be rebased onto this interface once it lands.
This pull request and its description were written by Isaac.