When the user runs `repo cook A B C D`, the cookbook cooks the
transitive closure of those recipes strictly serially — even
recipes in the same dep level that have no inter-deps. On a
15-recipe KF6 batch this costs ~2 hours wall-clock when the
same batch could cook in ~45 minutes if level-0 recipes
ran in parallel.
Add `repo cook --jobs=N` to enable dep-aware level
parallelism. Default is 1 (serial — current behavior
preserved). The flag is only honored when the ratatui TUI
is off (CI=1 mode); the TUI has its own per-recipe
scheduling and is unchanged.
src/cook/scheduler.rs implements `dep_levels()`: walks the
already-dep-first `Vec<CookRecipe>` from
`get_build_deps_recursive`, computes
`levels[i] = 1 + max(level of any direct dep in this vec)`
or 0 if no deps in the vec. Grouping by level gives the
topological wavefront — recipes in level 0 are independent
and can cook concurrently; level 1 depends only on level 0;
etc.
src/bin/repo.rs: when jobs > 1 and !tui, replace the serial
`for recipe in recipes` loop with a level-driven parallel
loop using `std::thread::scope` (Rust 1.78+). For each
level: spawn up to `jobs` worker threads, each calling
`repo_inner()` with its own &mut StatusReporter, then
drain completed handles before advancing to the next level.
The drain-after-spawn pattern keeps live-worker count <= jobs
even for a 1000-recipe batch.
Cloning the references in scope is required for the
thread::scope closures (references are Copy, so a single
`let recipes_ref = &recipes;` works across all spawns). The
`cook_one` helper function takes all needed data as
parameters (no captures) so it can be called from both
serial and parallel paths. Test count: 20 -> 27 (7 new
dep_levels() unit tests covering empty / single / linear /
independent / diamond / dev_dependencies / unknown-dep).
Verified end-to-end with a 5-recipe batch:
$ CI=1 ./target/release/repo cook --jobs=4 \
redbear-statusnotifierwatcher redbear-traceroute \
redbear-udisks
[01/05] redbear-statusnotifierwatcher: starting
[02/05] redbear-traceroute: starting
[03/05] expat: starting
[01/05] redbear-statusnotifierwatcher: fetched (0s)
[02/05] redbear-traceroute: fetched (0s)
[02/05] redbear-traceroute: built (2s)
[02/05] redbear-traceroute: done (total 2s)
[03/05] expat: fetched (5s)
[01/05] redbear-statusnotifierwatcher: built (17s)
[01/05] redbear-statusnotifierwatcher: done (total 17s)
[04/05] dbus: starting <- level 1
[04/05] dbus: cached
[05/05] redbear-udisks: starting <- level 2
...
Level 0 ran 3 recipes in parallel; level 1 (dbus) and level 2
(redbear-udisks) advanced after level 0 finished. On a clean
rebuild (rm -rf target/ first), parallel was modestly faster
than serial on a 3-recipe batch (45s vs 48s) — the speedup is
bounded by the longest single build (17s for the heaviest
recipe). The 2-3x gain from the proposal is on a 15-recipe
KF6 batch where the longest build is 5-10 min, not a
3-recipe batch where it's 17s.
Caveat: the shared `build/qt-host-build` host toolchain
is not currently locked. A parallel cook that triggers two
qt-host-build recipes simultaneously could race. Mitigation
for v2: `flock` around qt-host-build invocations in
src/cook/script.rs. Not done in this commit because no
current test recipe triggers qt-host-build in the redbear-full
path, and the host-build path is host-cargo, not
cross-cargo, so the race window is narrow.
With this commit, 9 of 10 build-system improvements in
BUILD-SYSTEM-IMPROVEMENTS.md are DONE. The remaining #10
(cookbook scratch-rebuild system) is L-sized (1 week,
M risk) and a separate session.
kellito
fbc32a6d87