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Commitc124e36

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Retry DSM control segment creation if Windows indicates access denied.
Otherwise, attempts to run multiple postmasters running on the samemachine may fail, because Windows sometimes returns ERROR_ACCESS_DENIEDrather than ERROR_ALREADY_EXISTS when there is an existing segment.Hitting this bug is much more likely because of another defect notfixed by this patch, namely that dsm_postmaster_startup() usesrandom() which returns the same value every time. But that's nota reason not to fix this.Kyotaro Horiguchi and Amit Kapila, reviewed by Michael PaquierDiscussion: <CAA4eK1JyNdMeF-dgrpHozDecpDfsRZUtpCi+1AbtuEkfG3YooQ@mail.gmail.com>
1 parentf0a86df commitc124e36

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‎src/backend/storage/ipc/dsm_impl.c

Lines changed: 18 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -671,6 +671,7 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
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{
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DWORDsize_high;
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DWORDsize_low;
674+
DWORDerrcode;
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675676
/* Shifts >= the width of the type are undefined. */
676677
#ifdef_WIN64
@@ -686,27 +687,31 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
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size_high,/* Upper 32 bits of size */
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size_low,/* Lower 32 bits of size */
688689
name);
690+
691+
errcode=GetLastError();
692+
if (errcode==ERROR_ALREADY_EXISTS||errcode==ERROR_ACCESS_DENIED)
693+
{
694+
/*
695+
* On Windows, when the segment already exists, a handle for the
696+
* existing segment is returned. We must close it before
697+
* returning. However, if the existing segment is created by a
698+
* service, then it returns ERROR_ACCESS_DENIED. We don't do
699+
* _dosmaperr here, so errno won't be modified.
700+
*/
701+
if (hmap)
702+
CloseHandle(hmap);
703+
return false;
704+
}
705+
689706
if (!hmap)
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{
691-
_dosmaperr(GetLastError());
708+
_dosmaperr(errcode);
692709
ereport(elevel,
693710
(errcode_for_dynamic_shared_memory(),
694711
errmsg("could not create shared memory segment \"%s\": %m",
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name)));
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return false;
697714
}
698-
_dosmaperr(GetLastError());
699-
if (errno==EEXIST)
700-
{
701-
/*
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* On Windows, when the segment already exists, a handle for the
703-
* existing segment is returned. We must close it before
704-
* returning. We don't do _dosmaperr here, so errno won't be
705-
* modified.
706-
*/
707-
CloseHandle(hmap);
708-
return false;
709-
}
710715
}
711716
else
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{

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