UXBoot

This is not part of the toolkit

UXBoot is test scaffolding. No shipped code imports it, and a real application must never call it.

It is documented so that anyone who finds it in the source knows what it is for and why using it would be a mistake.

#import "UXBoot.xc"       // tests only; not reachable through #use <UXKit>

The problem it exists for

On the board, init(1) runs the boot scripts off the SD card, and one of them starts gemd with &.

Under qemu the SD card is not mounted. /bin/sh is missing, init runs no scripts, and nothing starts the window server. libGEM then hard-exits with “no window server”. That is correct: there is no single-process mode, and pretending otherwise would be worse than the error.

A test running under qemu therefore has to start gemd itself. That is all this class does.

Why an application must never do this

Starting the window server from a client is the “the desktop is not the server” mistake in miniature.

An application is a client. It connects to a service that something else is responsible for running. An application that starts its own server has taken the role of the system, and when two applications run, the second finds a server it did not start and does not own.

The file exists in one place, is imported by nothing that ships, and says so in its first line. The scaffolding is allowed to exist because this containment stops it from leaking.

What it does

static bool ensureWindowServer(void)

1. Try to connect to the gem service. If it is already up (as on the board), return immediately. The common case costs one connect.
2. Otherwise sys_spawn("/bin/gemd").
3. Wait for it to register, retrying with a sleep, for up to 5 seconds.

The sleep is required

A server has a plane to open, a theme to load and a service to bind. A tight retry loop on a failing connect does not yield enough time for that to finish, and gives up before gemd is ready. Sleeping between tries makes startup reliable. Without it, the failure looks like “the window server does not work” when the cause is asking too early.

Returns false if the spawn failed or the server never registered, so a test can report “no window server” instead of proceeding into a crash.

See also

• UXGemDriver: the backend that needs the server this starts
• UXApplication: what a real application starts instead