On 13/10/2026 23:58, Harrison Booth wrote:
pg_upgrade can stall when localhost first reaches a refused IPv6
endpoint on Windows. Its aggregate select loop omits the exception
set, so PQconnectPoll does not process the failure and try IPv4. Libpq
already handles this in its single-socket helper.
The patch handles exceptional readiness in pg_upgrade's existing state
machine. Its Windows TAP test checks both successful-first IPv4 and
refused-first localhost fallback, skipping when resolver/refusal
preconditions are unavailable.
All seven assertions pass on MSVC ARM64, MSVC x64 and MinGW x64. The
x64 runs use emulation on the ARM64 host. Earlier copied-upgrade tests
from released 18.0 x64 and official 19rc1 ARM64 also preserve the
seeded data.
Is there any harm in checking for the exception set on other systems too?
@@ -344,7 +347,18 @@ select_loop(int maxFd, fd_set *input, fd_set *output)
*input = save_input;
*output = save_output;
+#ifdef WIN32
+ /* Winsock reports failed nonblocking connects as exceptions. */
+ exceptions = save_output;
+ i = select(maxFd + 1, input, output, &exceptions, NULL);
+ if (i > 0)
+ {
+ for (unsigned int j = 0; j < exceptions.fd_count; j++)
+ FD_SET(exceptions.fd_array[j], output);
+ }
+#else
i = select(maxFd + 1, input, output, NULL, NULL);
+#endif
Looks wrong to set merge the exception set with the writable set like
that. I think it'd be better to add an 'exceptions' argument to the
function.
As a side-note, I'm not convinced that saving the fdsets and looping
here on EINTR is really worth it, the caller would reconstruct the
fdsets and loop back here anyway if there's no work to do. But that's
not new with this patch.
- Heikki
