How can I pass data to the MATLAB oncleanup function? - matlab

Question

I have a compiled matlab program that automatically tunes machine parameters. At the end of a tuning cycle I need to reistate some original settings. Sometime unexpected errors occur and sometimes the user can see that tuning algorithm is not working properly so should be terminated (with control-C).
If a predictable error occurs, I can reinstate parameters with a try catch block. However, if an unexpected error occurs or the user invokes control-C, the program exits without passing though the catch clause and the machine is left in an undefined state.
I know I can register a cleanup function that will run as my working functions finish, either normally, via an predictable or unpredictable error, or control-C event. Ideally, the the clean up function would do nothing and pass control to the top level to clean up if a predictable error occurs. If a control-C event or an unpredictable error occurs, clean up function should warn the user that the program failed so they clean up manually.
To do this, I need to make the fact of a predicted or not-predicted termination (i.e. control-C) known to the clean up function at run time. I know that the cleanup function takes a copy of parameter values when it is registered, and that these cannot be changed at run time, so passing in a parameter cannot work. What I believe should work is nesting the cleanup function within my working function so local variables in the enclosing function are available to the clean up function. This however does not work.
My question is: can anyone see a way to make just a single boolean available to a clean function so it can select between normal and abnormal clean up?
Here is some contrived example code that I believe should work.
function do_tuning
% Set this false to cause a warning messages for control-C or MATLAB coding errors.
normalTermination = false;
oc = onCleanup(#() my_clean_up());
tuningError = tuning_function()
if tuningError
% Set this true to suppress the warning message if a predictable error occurs.
normalTermination = true;
error('tuningError')
end
% Set this true to suppress the warning message if the function runs to completion.
normalTermination = true;
function my_clean_up
if ~normalTermination
disp('Warning: clean up failed. Please clean up manually');
end
end
end
Running real code following this pattern causes the error:
Undefined function or variable "normalTermination".

Answer 1

The onCleanup object calls the function from outside the workspace of the do_tuning function so using a nested function will not help...
Infact the documetation states:
Your cleanup routine should never rely on variables that are defined outside of that routine
[edit - based on comments] A better solution would be to change the problem and have all cleaning up done within the my_clean_up function, which may require it to determine if what needs doing (or to have generic behaviour which can always be applied)
If we disregard this warning and solve the question...
Passing varables between workspaces is easiest with global variables so for the example code above.
Firstly define the variable as global before initially setting it to false (otherwise the variable may be overwritten)
function do_tuning
%# snip
global normalTermination
normalTermination = false;
%# snip
Secondly define the variable as global in the my_clean_up callback function before using it to retrieve the value
function my_clean_up
global normalTermination
if ~normalTermination
%# snip
Warning as ever with global variables this is susceptible to the value of the global variable being edited elsewhere at the wrong time.

Answer 2

Here is a modification of my example that behaves as I want, using the global suggested by #RTL.
function do_tuning
global normalTermination;
% Set this false to cause a warning messages for control-C or MATLAB coding errors.
normalTermination = false;
oc = onCleanup(#() my_clean_up());
tuningError = tuning_function()
if tuningError
% Set this true to suppress the warning message if a predictable error occurs.
normalTermination = true;
error('tuningError')
end
% Set this true to suppress the warning message if the function runs to completion.
normalTermination = true;
function my_clean_up
if ~normalTermination
disp('Warning: clean up failed. Please clean up manually');
else
disp('Normal termination, you can relax.');
end
end
end

Answer 3

A more elegant solution can be achieved by modifying the onCleanup code. You could easily add a property or method to cancel the normal behaviour. Example:
classdef onCleanupCancel < handle
properties
active = true;
end
properties(SetAccess = 'private', GetAccess = 'public', Transient)
task = #nop;
end
methods
function h = onCleanupCancel(functionHandle)
h.task = functionHandle;
end
function delete(h)
if h.active
h.task();
end
end
end
end
function nop
end
At the last line of your function set the active of the onCleanupCancel object to false...