Re: [wildfly-dev] Wildfly start-up as service script depends on console log to determinate start result
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(a)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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