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>

diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index 419c48e5ffd3687db12244fbc35d4f96745277ec..9cc9c5d2c299509880f0e01a8f3dd4ef43717e52 100644 (file)
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -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
@@ -686,27 +687,31 @@ 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);
+
+               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.  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.
+                        */
+                       if (hmap)
+                               CloseHandle(hmap);
+                       return false;
+               }
+
                if (!hmap)
                {
-                       _dosmaperr(GetLastError());
+                       _dosmaperr(errcode);
                        ereport(elevel,
                                        (errcode_for_dynamic_shared_memory(),
                                  errmsg("could not create shared memory segment \"%s\": %m",
                                                 name)));
                        return false;
                }
-               _dosmaperr(GetLastError());
-               if (errno == EEXIST)
-               {
-                       /*
-                        * 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.
-                        */
-                       CloseHandle(hmap);
-                       return false;
-               }
        }
        else
        {