MATLAB: Debug code invoked by timer

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Debugging code, which is invoked by a timer, is more of a challenge than it should be. The other day I expressed my frustration in What frustrates you about MATLAB?. Now, I'll try to be more constructive.
Wanted: Tips, tricks and tools to help me debug more efficiently. (Below, I present some of mine.)
My code: I have a code that is invoked by a timer on a regular basis. The code consist of a dozen classes and a handful of functions. Both objects and some functions have state. Below, I have included some small functions to illustrate my problems.
My development environment: R2012a (64bit) on Windows 7. I use a unit testing framework with a graphical interface and write some code in debug mode. The framework is based on MUNIT, by Brad Phelan.
Some problems:
  • Matlab's error messages are very generic and include neither function name nor line number
  • "Cannot clear classes". The old state must be cleared before each test. I often restart the unit testing tool to be able to clear old state.
  • Break-points are cleared by clear all and I often forget to reset them before executing the code.
Some examples:
The function, invoked_by_timer, as value of TimerFcn illustrates the error message of Matlab.
    >> debug_invoked_by_timer()
    Error while evaluating TimerFcn for timer 'my_timer' 
    Index exceeds matrix dimensions.
The function, invoked_by_timer_catch, as value of TimerFcn illustrates that it is possible to improve the error message. Daniels comment to my frustration triggered me to do this experiment.
    >> debug_invoked_by_timer()
    Error while evaluating TimerFcn for timer 'my_timer' 
    Error: Index exceeds matrix dimensions.
    In invoked_by_timer.index_out_of_bounds (line: 7)
    In invoked_by_timer.invoked_by_timer (line: 2)
    In invoked_by_timer_catch.invoked_by_timer_catch (line: 3)
    In timercb.timercb (line: 31)
    In timercb.timercb (line: 14)
    In wait.wait (line: 51)
    In debug_invoked_by_timer.debug_invoked_by_timer (line: 17)
TraceHistory is a singleton, which keeps its state after debug_invoked_by_timer has finished. It displays which functions have been called.
    >> log = TraceHistory.Instance;
    >> disp(log)
    --- tracer4m ---
    invoked_by_timer_catch
        invoked_by_timer
            index_out_of_bounds
( log.clearHistory and log.setup can be done outside the function, debug_invoked_by_timer).
where
    function    debug_invoked_by_timer()
        log = TraceHistory.Instance;
        log.clearHistory            
        log.setup( {'h:\m\PiaX\Experiments\debug\timer\invoked_by_timer.m'} )  
        %        
        tmr = timer('Name'      , 'my_timer'        ...
            ,   'TimerFcn'      , @invoked_by_timer_catch ...
    ...     ,   'TimerFcn'      , @invoked_by_timer ...
            ,   'BusyMode'      , 'drop'            ...
            ,   'ExecutionMode' , 'fixedRate'       ...
            ,   'Period'        ,  1                ...
            ,   'StartDelay'    ,  1                ...     
            ,   'TasksToExecute',  1           ...
            ); 
        start( tmr )
        wait ( tmr )
    end
and
    function    invoked_by_timer_catch( tmr, evnt )
        try
            invoked_by_timer( tmr, evnt ) 
        catch me
            str = exception2str( me );
            error( str )
        end
    end
and
    function    invoked_by_timer( tmr, evnt )
        index_out_of_bounds()
        variable_not_used( tmr, evnt ) 
    end
    function    index_out_of_bounds()
        a = 17;    
        b = a(2);
        variable_not_used( a, b ) 
    end
and
    function    str = exception2str( me )       
        str = sprintf( 'Error: %s\n', me.message );  
        for s = transpose( me.stack )
           str = [ str, hyperlink_row_( s ) ];   %#ok<AGROW>
        end
    end
    function    str = hyperlink_row_( s )
        [ ~, filename ] = fileparts( s.file );
         str = sprintf                                                      ...
            (   [ 'In <matlab:matlab.desktop.editor.openAndGoToLine'...
                , '(''%s'',%i);">%s.%s (line: %i)</a>\n' ]                  ...
            ,   s.file, s.line, filename, s.name, s.line                    );
    end
and
    function    variable_not_used( varargin )       
    %variable_not_used - helps keep the code analyzer box green  
    end
Persistent break-point: The function, dbs, sets a break-point on the following line. I found it useful.
    function dbs
    % dbs provides a persistent break-point; debug, dbstop
    %    

    %   Based on the FEX contribution kdb 
    %   By Romesh Abeysuriya 15-11-12
    %    
        stk = dbstack('-completenames');
        dbstop( 'in', stk(2).file, 'at', num2str( stk(2).line+1 ) )
    end
.
(Why do I use the timer in the first place? A while-loop with a computed pause would most likely have been good enough and easier to work with.)
See also: href = "http://www.mathworks.se/matlabcentral/answers/73322-can-t-find-where-the-warning-msg-is-from Can't find where the warning msg is from

Best Answer

My solution, that I alluded to in the original thread, looks almost identical to your invoke_by_timer_cacth, except I use the getReport method of the MException class instead. I also have defined a generic callback wrapper that I use for all callbacks that includes the try-catch.
The clear classes and clear all issues are separate and I have no insights.
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