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Daniel Hilst
c62434d22d
Both places that fork the install monitor repeat the same careful sequence: record the
attempt, block SIGCHLD, fork, unblock, and on failure record the exit so the next attempt
backs off. Two of those steps are ordering requirements rather than steps -- the attempt
must be recorded before the fork, because the child can die and be reaped before fork()
returns, and SIGCHLD must be blocked across the fork and the assignment, or the reaper
compares the dead child against a stale pid and misses it. Neither is apparent from
reading the code, and both were got wrong at least once while writing it. Leaving them
open-coded means the next caller -- $pid_UDP has the same never-respawned shape -- gets to
rediscover them.
Move the sequence into xCAT::RespawnUtils::supervise(), which takes the child body as a
block and the rest as named arguments:
($mon_respawn, $pid_MON) = supervise {
...the child...
} state => $mon_respawn, pid => $pid_MON, now => time();
The (&@) prototype is what allows the leading block, and it applies to a fully qualified
call, so no Exporter machinery is needed. It does require the module to be loaded with
`use` rather than `require`: under `require` the sub is unknown when the call is compiled,
the block is then read as a bare block and its value arrives as the first argument, which
fails at runtime rather than at compile time. Both call sites and the test use `use`, and
the constraint is written down next to the sub. Passing a live pid is a no-op, so a caller
that forgets to check does not end up with two children.
The module gains its first impure function, which is why it sits under its own heading with
the pure ones stated to be pure above it: those return new state and touch nothing, which is
what keeps them testable on a made-up clock and safe inside a signal handler. supervise()
forks, so it is tested by the fork-and-port case instead, which now drives it rather than
its own copy of the same sequence. POSIX and xCAT::Utils are required inside supervise()
rather than at the top, so loading the module for the pure functions still pulls in nothing.
xcatd loses $mon_chldmask and its :signal_h import along with the duplication.
Verified on a live MN: the startup fork goes through supervise() and produces a monitor
holding xcatiport, and two consecutive kills are recovered in 5s then 10s -- the backoff --
with the port reclaimed and the SSL listener holding its pid throughout.
Signed-off-by: Daniel Hilst <392820+dhilst@users.noreply.github.com>