[wildfly-dev] Wildfly start-up as service script depends on console log to determinate start result

[David M. Lloyd]

This is yet another good use case for an idea I proposed at the last 
couple developer meeting: the idea of configurable "availability" 
services, where you add a configuration which says "when these 
components and/or configured services are available, perform this 
action" where the action might be to notify a load balancer, perform a 
notification to humans, or even drop a file to the filesystem (which 
would be directly useful to this use case).

Note (in case someone thinks this is a great idea and runs out to 
implement it right away) that when I say "configured services" I do not 
mean MSC service names; more like management capabilities where you have 
a constrained namespace and each subsystem can contribute services to 
this category.

Also note that Java 9 adds limited support for signalling unrelated 
processes, though at the moment on UNIX the signals are basically 
limited to TERM and KILL.

On 06/12/2015 07:06 AM, Jason T. Greene wrote:
>
>> On Jun 10, 2015, at 11:46 AM, Brian Stansberry <brian.stansberry at redhat.com> wrote:
>>
>> So, what purpose is this fulfilling?
>>
>> 2) How does other software solve this problem? If it's solving a valid
>> problem, it seems like there would be a typical solution.
>
> The classic UNIX solution is that the daemon forks and returns, dropping a PID file of its child to disk, after it is done initializing and exits with an error code when there is a problem.
>
> Systemd added other approaches, where a daemon can signal systemd directly, or it can use dbus to send a message.
>
> The former can't be done efficiently in Java because it doesn't have a pure fork(), only an exec. Although it would be possible to emulate with an exec with an unacceptable hit to boot time. The latter options are too Linux specific.
>
> I think the best solution would be for us to add a signaling mechanism specifically for this purpose. We could use sun.misc.Signal (potentially an issue on Java 9), or we could exec the kill command to signal a process.
>
> We could also use a specially status file (e.g standalone.sh --start-status-file=blah) for a script to monitor.
>
> Thoughts?
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