batchCancel

fn batchCancel(userdata: ?*anyopaque, b: *Io.Batch) void {
    const t: *Threaded = @ptrCast(@alignCast(userdata));
    if (is_windows) {
        if (b.pending.head == .none) return;
        waitForApcOrAlert();
        var index = b.pending.head;
        while (index != .none) {
            const pending = &b.storage[index.toIndex()].pending;
            const operation_userdata: *WindowsBatchOperationUserdata = .fromErased(&pending.userdata);
            var cancel_iosb: windows.IO_STATUS_BLOCK = undefined;
            _ = windows.ntdll.NtCancelIoFileEx(operation_userdata.file, &operation_userdata.iosb, &cancel_iosb);
            index = pending.node.next;
        }
        while (b.pending.head != .none) waitForApcOrAlert();
    } else if (b.userdata) |batch_userdata| {
        const poll_storage: [*]posix.pollfd = @ptrCast(@alignCast(batch_userdata));
        t.allocator.free(poll_storage[0..b.storage.len]);
        b.userdata = null;
    }
}