We'd like to use TimestampDifferenceMilliseconds with the stop_time
possibly being TIMESTAMP_INFINITY, but up to now it's disclaimed
responsibility for overflow cases. Define it to clamp its output to
the range [0, INT_MAX], handling overflow correctly. (INT_MAX rather
than LONG_MAX seems appropriate, because the function is already
described as being intended for calculating wait times for WaitLatch
et al, and that infrastructure only handles waits up to INT_MAX.
Also, this choice gets rid of cross-platform behavioral differences.)
Having done that, we can replace some ad-hoc code in walreceiver.c
with a simple call to TimestampDifferenceMilliseconds.
While at it, fix some buglets in existing callers of
TimestampDifferenceMilliseconds: basebackup_copy.c had not read the
memo about TimestampDifferenceMilliseconds never returning a negative
value, and postmaster.c had not read the memo about Min() and Max()
being macros with multiple-evaluation hazards. Neither of these
quite seem worth back-patching.
Patch by me; thanks to Nathan Bossart for review.
Discussion: https://postgr.es/m/3126727.1674759248@sss.pgh.pa.us
Tom Lane
Bruce Momjian
Robert Haas