The scaler is multi-threaded (monitor and demand threads); invoke() forked
and, in the child, logged, snprintf'd and setenv()'d before execl(), which
can deadlock on a lock another thread held at fork time and block the
caller in waitpid() forever.
run_script() now posix_spawn()s `sh <script> -f <in.json>`: stdout and
stderr go to the output file through file actions, the provider variables
(PRO_CONF_DIR, PRO_DATA_DIR, PRO_LOG_DIR, PROVIDER_NAME) are passed as the
child's envp (provider_env()), the child starts with an empty signal mask
and default dispositions, and waitpid() retries on EINTR.
The scaler unit suite (scaler/testsuite) was never built; it is now the
meson test "autoscaler test", linked with -Wl,--wrap=fork so it counts
fork() calls during a provider call.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Rongsong Shen
19052674bd
