feat(logging): add Logger interface and default logger (2/6)#723
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feat(logging): add Logger interface and default logger (2/6)#723kamcheungting-db wants to merge 3 commits into
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Re-add spdlog as a build dependency to serve as the foundation for the logging system. Adapted to current structure: spdlog joins the core iceberg lib interface lists (roaring has since moved to iceberg_data). Co-authored-by: Isaac
This is the first of six small PRs that together add a logging system to iceberg-cpp. It introduces LogLevel, the severity scale everything else builds on: trace, debug, info, warn, error, critical, fatal, plus an `off` sentinel for turning logging off entirely. Levels are ordered from most to least verbose, so deciding whether something should be logged is a plain `level >= threshold` comparison. Two helpers come with it: ToString to print a level, and LogLevelFromString to parse one (case-insensitive, returning a Result for unrecognized input). Both follow the same shape as CounterUnit in metrics/counter.h. There is no implementation behind the header yet, so this PR only adds the header, wires the new src/iceberg/logging directory into the build, and adds a test covering the round-trip, ordering, and parsing. Co-authored-by: Isaac
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Second of the logging stack. This defines what a logger is and where the rest of the code finds one, with no concrete backend yet. Logger is a small abstract interface: ShouldLog to test a level, Log to emit an already-formatted record, SetLevel/level, Flush, and a shared no-op instance. Records are passed as LogMessage, which owns its formatted text (so a sink may safely hold onto it) and carries the source location plus a reserved slot for structured key/values we may add later. The interface spells out two rules for implementations: never call back into logging from inside Log/Flush, and keep level() a true lower bound for ShouldLog. There is also one default logger per process, designed to be cheap to reach on the logging path: a lock-free atomic level check drops disabled messages outright, and when a message does need logging the current logger comes from a thread-local cache that only refreshes when the default actually changes, so the steady state has no lock or reference-count traffic. SetDefaultLogger and SetDefaultLevel swap it safely under a mutex. The seed default is the no-op logger; CerrLogger and the spdlog backend arrive in later PRs. Also adds the build-generated, .cc-only config header used later to pick the backend, and tests for the interface and the default-logger lifecycle. Co-authored-by: Isaac
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What
Second of the logging stack.
Adds the abstract Logger interface (ShouldLog/Log/SetLevel/level/Flush/Noop), the owned LogMessage record (formatted text + source location + reserved attributes), and the process-wide default logger: a lock-free atomic level gate for the disabled path and a thread-local generation cache for the enabled path (no lock/refcount in steady state), swapped under a mutex via SetDefaultLogger/SetDefaultLevel. Seed default is the no-op logger; CerrLogger and spdlog come in later PRs.
Also adds the .cc-only generated config.h used later for backend selection.
Testing
compiled and run with clang++ -std=c++23 -stdlib=libc++ (clang 18) — Noop singleton, seed default, set/get, generation-cache swaps, gate seeding,
SetDefaultLevel sync, and nullptr→Noop all pass.
Full ctest/spdlog-ON build needs a C++23 toolchain + network (gtest/spdlog) in CI.