[Developers] automatic notification of parameter steering requests

[Thomas Radke]

Hi,

making a parameter steerable during runtime currently requires a thorn 
writer to add extra logic to the code which periodically checks if the 
parameter has changed, and takes appropriate action in that case. It 
would be good if interested thorns could be notified automatically when 
a parameter gets steered.

I propose to add a new flesh function CCTK_ParameterSetNotify() to let 
thorns register a callback function which in turn is automatically 
invoked by CCTK_ParameterSet() whenever a parameter is being steered. 
Each callback function gets passed the triple of thorn name, parameter 
name, and (stringified) new parameter value as passed to 
CCTK_ParameterSet(), plus an optional callback data pointer defined by 
the user at registration time. When a callback function is registered 
with CCTK_ParameterSetNotify(), the calling routine may also pass an 
optional regular expression string for both a thorn name and a parameter 
name to match against in a parameter set notification; leave them empty 
or pass a NULL pointer to get notified about changes of _any_ parameter.
Registered notification callbacks would be invoked by 
CCTK_ParameterSet() only _after_ initial parameter setup from the 
parfile, and - in case of recovery - only _after_ all parameters have 
been restored from the checkpoint file. The callbacks are then invoked 
just _before_ the parameter is set to its new value so that they can 
still query its old value if necessary.

The C prototype would look like this:

   int CCTK_ParameterSetNotify (void (callback) (CCTK_POINTER cb_data,
                                                 CCTK_STRING  thorn,
                                                 CCTK_STRING  parameter,
                                                 CCTK_STRING  new_value),
                                CCTK_POINTER cb_data,
                                CCTK_STRING  thorn_regex,
                                CCTK_STRING  parameter_regex);

Comments, suggestions ?

-- 
Cheers, Thomas.