On Tue, 2014-08-26 at 07:18 -0600, Glenn Golden wrote:
> Here are some pre-questions that I'll need to understand before even starting
> to tackle the Wiki description of the runtime dirs and pid files:
>
> ============================================================================
> * --start:
> "Start PulseAudio if it is not running yet. This is different from
> starting PulseAudio without --start which would fail if PA is already
> running."
>
> Q1: What is the semantic distinction between those two sentences?
> Parsing straightforwardly seems to lead to this:
>
> If (--start option is specified on cmdline)
> {
> if (PA is not running)
> {
> Start PA;
> }
> else # PA is running
> {
> Don't start PA; # What exit code is supplied?
Zero.
> }
> }
>
> else # PA is not specfied on cmdline
> {
> if (PA running)
> {
> Don't start PA, and return nonzero exit code;
> }
> else # PA is not running
> {
> Start PA;
> }
> }
>
> But the outer if/else seem to have no distinction between them, other
> than (perhaps) the exit code supplied by the top clause may differ from
> the explicitly nonzero error code of the bottom clause. Is there any other
> difference?
No, the exit code is the only significant difference.
>
> Q2: In the above pseudocode, how are the tests for running-ness performed?
It's done by creating the pid file. pa_pid_file_create() returns -1, 0
or 1 depending on whether the creation failed due to an error (-1), the
creation succeeded (0) or the creation failed due to there being already
a daemon running (1).
> Q3: Related to Q2 and Q7 below: What if there are multiple PAs running,
> some of which may have been started with --use-pid-file=0?. Are these
> non-PIDfile-d PA's included in the notion of "running" as used in
> the above --start option description?
Gah, I wasn't aware of this silly option... No, the daemons started with
--use-pid-file=0 are invisible to the --start logic.
> ============================================================================
> * --kill:
> "Kill an already running PulseAudio daemon of the calling user.
> (Equivalent to sending a SIGTERM)."
>
> Q4: (Ok, this not really a question but an obsevation): The same ambiguity
> issue exists here as for --check, i.e regarding which PA daemon is being
> referred to, and what "calling user" might mean. Whatever way I wind up
> solving the doc issue for --check will have to be applied here as well.
True.
> ============================================================================
> * --daemonize[=BOOL]
> "Daemonize after startup, i.e. detach from the terminal."
>
> Q5: Is there any interaction between this option and the creation (or not)
> of a PID file? I.e., if --daemonize=0, does it still create a pid file?
>
> Please tell me the answer to the latter question is "yes", otherwise
> I'm going to have to start drinking heavily because it will roughly
> quadruple the complexity of what I need to describe in the Wiki writeup.
>
> (So you should feel free to lie to me about it and say "yes", lol...)
The answer is "yes", and I don't lie, I promise :)
> ============================================================================
> * --use-pid-file=[BOOL]
> "Create a PID file. If this options is disabled it is possible to run
> multiple sound servers per user."
>
> Q6: Suppose one or more PA daemons have been started with --use-pid-file=0
> (hence there are no pid files corresponding to these daemon processes.)
> In this case, is it possible to use --kill or --check to refer to such
> daemon process(es)? [Quick experiments seem to indicate answer is "no"]
The answer is indeed "no".
> Q7: Same as Q7, but w.r.t. "--start" option: How is the "--start" pseudocode
> in Q1 affected by the possible presence of running PA daemon(s) that have
> no associated PID file(s)?
Daemons without pid files are invisible to the --start logic.
--
Tanu
