Can a child process detect postmaster death when in pg_usleep?

Hi,

In my dev system(Ubuntu) when the postmaster is killed with SIGKILL,
SIGPWR is being sent to its child processes (backends/any other bg
process). If a child process is waiting with pg_usleep, it looks like
it is not detecting the postmaster's death and it doesn't exit
immediately but stays forever until it gets killed explicitly. For
this experiment, I did 2 things to simulate the scenario i.e. a
backend waiting in pg_usleep and killing the postmaster. 1) I wrote a
wait function that uses pg_usleep and called it in a backend. This
backend doesn't exit on postmaster death. 2) I set PostAuthDelay to
100 seconds and started the postmaster. Then, the "auotvacuum
launcher" process still stays around (as it has pg_usleep in its main
function), even after postmaster death.

Questions:
1) Is it really harmful to use pg_usleep in a postmaster child process
as it doesn't let the child process detect postmaster death?

2) Can pg_usleep() always detect signals? I see the caution in the
pg_usleep function definition in pgsleep.c, saying the signal handling
is platform dependent. We have code blocks like below in the code. Do
we actually process interrupts before going to sleep with pg_usleep()?
while/for loop
{
......
......
CHECK_FOR_INTERRUPTS();
pg_usleep();
}
and
if (PostAuthDelay)
pg_usleep();

3) Is it intentional to use pg_usleep in some places in the code? If
yes, what are they? At least, I see one place where it's intentional
in the wait_pid function which is used while running the regression
tests.

4) Are there any places where we need to replace pg_usleep with
WaitLatch/equivalent of pg_sleep to detect the postmaster death
properly?

Correct me if I'm missing something or if my observation/understanding
of the pg_usleep() is wrong.

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com