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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@mail.gmail.com>
This commit is contained in:
Robert Haas 2016-09-20 12:04:41 -04:00
parent 45310221a9
commit 419113dfdc
1 changed files with 19 additions and 14 deletions
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33
src/backend/storage/ipc/dsm_impl.c
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@ -671,6 +671,7 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
{
DWORD size_high;
DWORD size_low;
DWORD errcode;
/* Shifts >= the width of the type are undefined. */
#ifdef _WIN64
@ -686,25 +687,29 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
size_high, /* Upper 32 bits of size */
size_low, /* Lower 32 bits of size */
name);
if (!hmap)
{
_dosmaperr(GetLastError());
ereport(elevel,
(errcode_for_dynamic_shared_memory(),
errmsg("could not create shared memory segment \"%s\": %m",
name)));
return false;
}
_dosmaperr(GetLastError());
if (errno == EEXIST)
errcode = GetLastError();
if (errcode == ERROR_ALREADY_EXISTS || errcode == ERROR_ACCESS_DENIED)
{
/*
* On Windows, when the segment already exists, a handle for the
* existing segment is returned. We must close it before
* returning. We don't do _dosmaperr here, so errno won't be
* modified.
* returning. However, if the existing segment is created by a
* service, then it returns ERROR_ACCESS_DENIED. We don't do
* _dosmaperr here, so errno won't be modified.
*/
CloseHandle(hmap);
if (hmap)
CloseHandle(hmap);
return false;
}
if (!hmap)
{
_dosmaperr(errcode);
ereport(elevel,
(errcode_for_dynamic_shared_memory(),
errmsg("could not create shared memory segment \"%s\": %m",
name)));
return false;
}
}