getCngDevice

fn getCngDevice(t: *Threaded) Io.RandomSecureError!windows.HANDLE {
    {
        mutexLock(&t.mutex);
        defer mutexUnlock(&t.mutex);
        if (t.random_file.handle) |handle| return handle;
    }

    var fresh_handle: windows.HANDLE = undefined;
    var io_status_block: windows.IO_STATUS_BLOCK = undefined;
    var syscall: Syscall = try .start();
    while (true) switch (windows.ntdll.NtOpenFile(
        &fresh_handle,
        .{
            .STANDARD = .{ .SYNCHRONIZE = true },
            .SPECIFIC = .{ .FILE = .{ .READ_DATA = true } },
        },
        &.{ .ObjectName = @constCast(&windows.UNICODE_STRING.init(
            &.{ '\\', 'D', 'e', 'v', 'i', 'c', 'e', '\\', 'C', 'N', 'G' },
        )) },
        &io_status_block,
        .VALID_FLAGS,
        .{ .IO = .SYNCHRONOUS_NONALERT },
    )) {
        .SUCCESS => {
            syscall.finish();
            mutexLock(&t.mutex); // Another thread might have won the race.
            defer mutexUnlock(&t.mutex);
            if (t.random_file.handle) |prev_handle| {
                windows.CloseHandle(fresh_handle);
                return prev_handle;
            } else {
                t.random_file.handle = fresh_handle;
                return fresh_handle;
            }
        },
        .CANCELLED => {
            try syscall.checkCancel();
            continue;
        },
        .OBJECT_NAME_NOT_FOUND => return syscall.fail(error.EntropyUnavailable), // Observed on wine 10.0
        else => return syscall.fail(error.EntropyUnavailable),
    };
}