[jboss-as7-dev] Important note for MSC Service authors

[Brian Stansberry]

On 4/13/11 4:01 PM, David M. Lloyd wrote:
> That method will use the same thread pool as the MSC service threads, so
> using that method for blocking stuff doesn't actually help.
>

Thanks. That's what I figured.

Please see

https://github.com/bstansberry/jboss-msc/commit/e45fb05f2114a7261c45918eeadc77b244c025e5

> Also worth noting is that all of these rules also apply to listener methods.
>
> The execute() method is, however, good for parallelizing
> computation-heavy start/stop tasks, and also for running (non-blocking)
> tasks at runtime.
>
> Note that the problem isn't the task duration, it's the fact that an
> external factor (meaning, other than available CPU) then takes control
> of the state machine execution.
>
> On 04/13/2011 03:48 PM, Brian Stansberry wrote:
>> Is use of LifecycleContext.execute(Runnable) recommended? For anyone
>> doing as you say and using LifecycleContext.asynchronous() and
>> complete(), using that execute() method is going to be a path of least
>> resistance.
>>
>> On 4/13/11 2:55 PM, David M. Lloyd wrote:
>>> When writing MSC service implementations, your start() and stop()
>>> methods must never block.  This means these methods must not:
>>>
>>> - Establish or use network connections
>>> - Wait for network connections
>>> - Sleep
>>> - Wait on a condition
>>> - Wait on a count down latch
>>> - Call any method which may do any of the above
>>> - Wait for termination of a thread pool or other service
>>> - Wait for another service to change state!
>>>
>>> If your service start/stop involves any of these tasks, you must use the
>>> asynchronous start/stop mechanism (context.asynchronous()) and do one of
>>> the following:
>>>
>>> - Initiate your task in start()/stop(), and utilize a callback (NIO,
>>> ThreadPoolExecutor.terminated(), etc.) to call context.complete() when
>>> your start/stop completes instead of blocking
>>> - Delegate your blocking task to a thread pool (Executor) which calls
>>> context.complete() when done
>>> - Use proper dependencies instead of explicitly waiting for services in
>>> your start/stop
>>>
>>> Failure to do so can cause startup delays and can even lock up the MSC
>>> state machine!  If you are unsure what the best approach is for your
>>> problem, ping me in #jboss-as7 or #jboss-msc and I'll help you out.
>>>
>>
>>
>
>


-- 
Brian Stansberry
Principal Software Engineer
JBoss by Red Hat