Ctrl-C killed meowc and left every compiler it had spawned running, still
holding CPU and still about to write into the build directory. There were no
signal handlers at all.
SIGINT and SIGTERM now cancel the same way a build failure does, and the run
returns cleanly so the cache is still written and the exit status is 130. A
second signal falls through to the default handler, so an unresponsive child
cannot trap the user.
Signalling a single pid was not enough: a compiler driver spawns its own
children, and those were reparented to init and survived. Each action is now
placed in its own process group with setsid, and cancellation signals the group,
which also makes the existing failure path reach grandchildren. Unix.wait is
retried on EINTR so a signal arriving mid-wait is not fatal.
Only new spawns were held back after a failure, so every action already running
was allowed to finish even though its output would be discarded. The scheduler
now sends SIGTERM to the remaining children on the first failure, and reports
them separately rather than counting a process it killed as a failure of its
own. Partial outputs are removed and their cache entries dropped, so the next
run starts clean.
Under -k the existing behaviour is kept, since keeping going is the point.
On a graph with three six-second generators alongside one translation unit that
fails immediately, -j4 now returns in 0.12 s rather than 6.03 s.
The default job limit read /proc/cpuinfo and silently fell back to four
anywhere that file is absent, so macOS and the BSDs ran at a fraction of the
available parallelism. Falls back to getconf _NPROCESSORS_ONLN before the
constant.
milner