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 7122c4abe000368b7827c2fa963d068eba9f4db0..dbac7bdac086b513275ae81719cda0b1b04f23f2 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 */