pgsql: Retry DSM control segment creation if Windows indicates access d

Retry DSM control segment creation if Windows indicates access denied.

Otherwise, attempts to run multiple postmasters running on the same
machine may fail, because Windows sometimes returns ERROR_ACCESS_DENIED
rather than ERROR_ALREADY_EXISTS when there is an existing segment.

Hitting this bug is much more likely because of another defect not
fixed by this patch, namely that dsm_postmaster_startup() uses
random() which returns the same value every time. But that's not
a reason not to fix this.

Kyotaro Horiguchi and Amit Kapila, reviewed by Michael Paquier

Discussion: <CAA4eK1JyNdMeF-dgrpHozDecpDfsRZUtpCi+1AbtuEkfG3YooQ(at)mail(dot)gmail(dot)com>

Branch
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REL9_6_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/6bcd26c43c4f0ef718e984643338ddd5b207f9f9

Modified Files
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src/backend/storage/ipc/dsm_impl.c | 31 ++++++++++++++++++-------------
1 file changed, 18 insertions(+), 13 deletions(-)