Don't trust CreateFileMapping() to clear the error code on success.

We must test GetLastError() even when CreateFileMapping() returns a
non-null handle.  If that value were left over from some previous system
call, we might be fooled into thinking the segment already existed.
Experimentation on Windows 7 suggests that CreateFileMapping() clears
the error code on success, but it is not documented to do so, so let's
not rely on that happening in all Windows releases.

Amit Kapila

Discussion: <20811.1474390987@sss.pgh.pa.us>

diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index ff72d045ea54b8d707cc257a389b2d3a03adef1e..8482cd86445e25657ca708b2879cd2515134892e 100644 (file)
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -681,6 +681,9 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
 #endif
        size_low = (DWORD) request_size;
 
+       /* CreateFileMapping might not clear the error code on success */
+       SetLastError(0);
+
        hmap = CreateFileMapping(INVALID_HANDLE_VALUE,  /* Use the pagefile */
                                 NULL,  /* Default security attrs */
                                 PAGE_READWRITE,        /* Memory is read/write */