pgsql: Work around unfortunate getppid() behavior on BSD-ish systems.

Work around unfortunate getppid() behavior on BSD-ish systems.

On MacOS X, and apparently also on other BSD-derived systems, attaching
a debugger causes getppid() to return the pid of the debugging process
rather than the actual parent PID. As a result, debugging the
autovacuum launcher, startup process, or WAL sender on such systems
causes it to exit, because the previous coding of PostmasterIsAlive()
detects postmaster death by testing whether getppid() == PostmasterPid.

Work around that behavior by checking the return value of getppid()
more carefully. If it's PostmasterPid, the postmaster must be alive;
if it's 1, assume the postmaster is dead. If it's any other value,
assume we've been debugged and fall through to the less-reliable
kill() test.

Review by Tom Lane.

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=24ecde7742cd4d7c781e6890b07571fff42b25dc

Modified Files
--------------
src/backend/storage/ipc/pmsignal.c | 34 +++++++++++++++++++++-------------
1 files changed, 21 insertions(+), 13 deletions(-)