Tests that call ForkReap or send signals to their own process now
re-exec as isolated subprocesses. This prevents ForkReap's
syscall.ForkExec and process-directed signals from interfering
with the parent test binary or other tests running in parallel.
Also:
- Wait for the reaper goroutine to fully exit between subtests
to prevent overlapping reapers from competing on Wait4(-1).
- Register signal handlers synchronously before spawning the
forwarding goroutine so no signal is lost between ForkExec
and the handler being ready.
Mathias Fredriksson
efe114119f