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Re: [cdt-dev] Timeouts for GDB/MI commands (Was: [DSF] Making Sequence more robust)

> -----Original Message-----
> From: cdt-dev-bounces@xxxxxxxxxxx 
> [mailto:cdt-dev-bounces@xxxxxxxxxxx] On Behalf Of Vladimir Prus
> Sent: Saturday, October 22, 2011 5:55 AM
> To: Pawel Piech; Mikhail Khodjaiants
> Cc: cdt-dev@xxxxxxxxxxx
> Subject: [cdt-dev] Timeouts for GDB/MI commands (Was: [DSF] 
> Making Sequence more robust)


I think it would be great to add some timer infrastructure
for commands sent to GDB.  Thanks for pushing this forward.
Please see below for some comments.

> On Thursday, October 20, 2011 21:40:17 Pawel Piech wrote:
> > > 2. While a general repository for outstanding RM's might 
> be a good idea,
> > > what would you say if we start small, and implement the 
> solution that
> > > would remember outstanding RequestMonitor instances for 
> some limited
> > > cases (for example, 'target *-remote' commands in 
> DSF-GDB, and then
> > > cancel those RequestMonitors after a timeout? This is somewhat
> > > orthogonal from the initial goal of catching lost RMs, but seems
> > > sufficiently related and immediately useful.
> > 
> > This is something that could be done at the service level, 
> where these 
> > commands are issued.  If we expect that the back-end may 
> never complete 
> > some commands then in those cases a timeout guard should even be 
> > required.  For example, we queue commands with the command 
> control, but 
> > we count on the process monitor to notify us if the back 
> end process 
> > dies.  At that point we complete any outstanding command in 
> queue with 
> > an error.  So our process monitor is the guard.
> We discussed this approach internally (turned out to be 
> faster), and Mikhail has proposed approach like this:
> 1. Add new interface:
>     interface IMIControlTimeoutPolicy {
>         void commandSend(CommandHandle);
>         void commandDone(CommandHandle);
>     }

ICommandListener has commandSent() and commandDone().
How about using 'sendCommand' and 'processCommandReply' to avoid
> 2. Add new method AbstractMIControl.createTimeoutPolicy 
> (returning null by default).
> Adjust the code so that when this method returns non-null, 
> the commandSend and commandDone
> methods of the result are called by TxThread/RxThread as appropriate.

Sure, that mostly makes that code easy to override.
The interesting part will be the code that handles the timers.

> 3. Make GDBControl.createTimeoutPolicy return a policy that 
> sets a timer whenever a command
> is sent, and if the command is not done within a timeout, 
> just calls GDBControl.shutdown.

I wonder if such a solution is sufficient?
Do we want to recover for a missing reply, or should it never
happen and we can indeed just abort?

A more flexible solution, which may be overkill as it may never
be triggered would be to allow for different behaviors
for different MI commands and different timeouts as well
(I think CDI has that already).

How about adding some methods to MICommand?  Something like:
  getTimeout() // Returns timeout value for this MICommand
  timeout(RequestMonitor)    // Called if the timer expires before 
                             // a reply has been received.  This method
                             // will decide what to do with the RM
We'd put in default implementation in MICommand, but it would be possible
to override them in individual commands, such as 'target *-remote'.

I'm imagining that the MICommand.timeout(RM) will deal with the RM
so that the service that sent the command can decided what to do
in that case.

But again, this may be overkill if we don't expect this to happen
often or at all.

Are you trying to address a specific scenario or a general safety


> Does this seem reasonable, on a high level? We should be able 
> to implement this fairly
> quickly.
> Thanks,
> -- 
> Vladimir Prus
> CodeSourcery / Mentor Graphics
> +7 (812) 677-68-40
> _______________________________________________
> cdt-dev mailing list
> cdt-dev@xxxxxxxxxxx

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