rt_die began with fflush(stdout) and ended with exit(134), and under a merged
flan dev both could hang. The flush waits on a 64K pipe whose reader is busy;
exit runs the atexit chain and the ELF destructors, which want the loader lock
a dlopening listener thread may be holding, and in that build the chain also
holds OCaml's shutdown. A bounds failure that hangs is worse than one that
kills the process, because nothing is printed and nothing exits.
So the flush every trap does first goes through rt_flush_out, which puts fd 1
into non-blocking mode and accepts a truncated tail, and rt_die takes _exit
and unlinks FLAN_DEV_SOCK by hand -- the same shape as die_now in
flan_agent.c, which argued all of this first and is quoted rather than
diverged from. On a terminal, a file, or a pipe with room, O_NONBLOCK changes
nothing, and the acceptance corpus diffs that output.
One consequence worth knowing: _exit skips ASan's exit-time leak report, so a
trapping program under @sanitize no longer reports leaks.
Joseph Ferano
0c0eadb424