Re: pg_listener entries deleted under heavy NOTIFY load only on Windows

I've completed my test for changes to the Windows implementation of
pgkill. I ran two clients constantly doing a pair of notifications,
with one client subscribing to those events. I ran the test for 90
hours. I found 760 cases where the CallNamedPipe function initially
failed, but succeeded after recalling. In all but one of those cases,
only a single retry was needed; the other case required two retries.

As Tom has pointed out, there is no principled way to determine the
correct number of times to retry. Therefore, I have set the maximum
number of retries to 2, which is the worst case found in a fairly long
stress test. This strikes me as a reasonable balance between failing
quickly in truly erroneous cases, while still avoiding transient
pseudo-failures.

A patch with this change is attached. It should be applied to the
8.3.5 version of src/port/kill.c

Steve