about send in rtems_timer_service_routine

[Daron Chabot]

Joel Sherrill wrote:
> Daron Chabot wrote:
>> Not having checked send(2) for blocking behavior, this is just a guess:
>>
>> The function, rtems_timer_service_routine( ), is called from an
>> interrupt context. Code called from an interrupt context *cannot*
>> perform operations that may block waiting for resources (i.e. send(2)).
>>
>> You could use an rtems_timer_server instead: this server runs in a
>> thread context which has no restrictions on the methods invoked from it.
>>
>> (see http://www.rtems.com/onlinedocs/releases/rtemsdocs-4.8.0/share/
>> rtems/html/c_user/c_user00116.html)
>>
>>   
> I wouldn't say no restrictions.  While in the timer server,
> dispatching is disabled so blocking is definitely not possible.
> So a blocking send() wouldn't block, it would continue executing
> like it didn't block causing havoc.
>
> There is another oddity.  By default, the task runs at priority 0
> which is not possible to set from user applications.  So changing
> the priority temporarily is impossible -- it can't be restored.
>
> See cpukit/rtems/src/timerserver.c.
>
>    _Thread_Disable_dispatch();
>      _Timer_Server_process_ticks_chain();
>      _Timer_Server_process_seconds_chain();
>
> Does it seem like the documentation is overstating how safe
> this is? 
No... the problems lie solely with this reader ;-)

The documentation is fine (might be made a little more explicit, though).
>From 
http://www.rtems.com/onlinedocs/releases/rtemsdocs-4.8.0/share/rtems/html/c_user/c_user00122.html:
    "...However, since the Timer Server task is non-preemptible, only 
directives allowed from an ISR can be called in the timer service routine."

> If so, then we need to either change the documentation
> or change the critical section management here. 

However, it does seem as though the "priority=0, 
Thread_Disable_dispatch()", makes a Timer-Server nearly as restricted as 
an ISR-context...

-- dc

>> -- dc
>>
>> On 20-Apr-08, at 2:16 AM, Ray wrote:
>>  
>>> Dear  powerain ,
>>> Maybe you should check this website first
>>> http://linuxmafia.com/faq/Essays/smart-questions.html
>>> here is a mandarin version
>>> http://www.linuxforum.net/doc/smartq-grand.html
>>>
>>> BTW, it seems to me that rtems_timer_service_routine=void if I read
>>> code correct
>>>
>>> Thanks & Best Regards!
>>>
>>> Ray, rayx.cn at gmail.com
>>> 2008-04-20
>>>
>>>
>>> =========================
>>> ----- Receiving the following content -----
>>> =========================
>>> From:  powerain
>>> Receiver:  rtems-users
>>> Time: 2008-04-20, 09:25:20
>>> Subject: about send in rtems_timer_service_routine
>>>
>>>
>>>
>>>
>>>    
>>>> hi everyone,
>>>> i send a package in a rtems_timer_service_routine using send
>>>> function by a socket.
>>>> but is does not work.
>>>> who tell me why.
>>>> thanks very much.
>>>>
>>>> 2008-04-20
>>>>
>>>>
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>>
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>
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