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

[Carlo de Wolf]

On 06/12/2015 02:57 PM, David M. Lloyd wrote:
> 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.

Wouldn't implementing a MSC service with dependencies be just the quick 
fix that covers the use case? :-)

Carlo

>
> 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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