Fixing Matlab's actxserver

Matlab’s built-in actxserver function provides access to COM/DCOM server applications on Microsoft Windows platforms. This enables us, for example, to open a Microsoft Office document programmatically, and modify it from within Matlab. This in turn can be used, for example, to prepare professional PDF reports, relying on Office’s ability to save documents in PDF format. Alternately, we could programmatically update cell formatting (colors, fonts, borders etc.) and embed images and graphs in an Excel workbook – something that the standard xlswrite cannot do (my officedoc utility does this, using the same COM interface).
Note: For some reason, COM servers are called an ActiveX server in Matlab, although the term ActiveX is normally used for clients (i.e., controls), for which we have the actxcontrol* set of built-in functions.
Today I will focus on two changes that I made to Matlab’s built-in actxserver function:

Reusing an active server (no pun intended…)

By default, actxserver starts a new instance of the specified COM server whenever it is called. Sometimes this is indeed useful. However, I find that in the vast majority of cases, I actually want to reuse an existing server instance if it is currently running. For example, it is much faster and more memory-efficient to open an Excel workbook file in an existing Excel process, than to open it in a new dedicated process.
In R2007a, Matlab introduced the actxGetRunningServer function. Unfortunately, it did not see fit to set it as the default behavior for actxserver, nor even as an optional additional parameter (although MathWorks *did* change the actxserver function in that very same release, to accept a custom interface parameter). Users need to change their programs to first call actxGetRunningServer, check whether it works or fails, and then call actxserver if it fails (meaning that a server process is not currently running and a new one needs to be started):

% Try to reuse an existing COM server instance if possible
try
    hServer = actxGetRunningServer('excel.application');
    % no crash so probably succeeded to connect to a running server
catch
    % Never mind - continue normally to start the COM server and connect to it
    hServer = actxserver('excel.application');
end

This is downright silly, I must say.

Moreover, all the existing user and Matlab code that uses actxserver will continue to start a new server instance rather than reuse existing ones. For example, the widely-used xlsread and xlswrite functions.
Instead of fixing Matlab’s installed actxserver.m file, which could be problematic when deploying applications to end-users, I created a copy of actxserver.m somewhere in my user folders that is high on the Matlab path. This way I can modify the file and bundle it with any application that I send to clients. The change to this file is simply to add a variant of the code above at the very top of the actxserver.m file, as follows (the new lines are highlighted):

function h = actxserver(progID, varargin)
%ACTXSERVER Creates a COM Automation server.
...
% Copyright 2006-2007 The MathWorks, Inc.
% $Revision: 1.8.6.12 $ $Date: 2011/08/13 17:30:50 $
error(nargchk(1, 5, nargin, 'struct'));
% Yair 17/5/2009: Try to reuse an existing COM server instance if possible
try
    h = actxGetRunningServer(progID);    return;  % no crash so probably succeeded - returncatch    % Never mind - continue normally to start the COM server and connect to itendmachinename = '';interface = 'IDispatch';...

This simple change means that all exiting code, including Matlab’s built-in xlsread and xlswrite functions, now try to reuse a running COM server process if possible, starting a new one only if this fails. The code is fault-tolerant in that it also works on old Matlab releases where the actxGetRunningServer is not available.

Fix of the progID

The %matlabroot%/toolbox/matlab/winfun/private/newprogid.m function, a private function used by actxserver, normalizes COM program identifiers (progIDs), which is the string used to locate the COM server. Unfortunately, until R2011a (or specifically, when this was fixed by some MathWorker on June 10, 2010), this function had a bug that caused the normalization to fail. In order to correct this, I simply added the fixed function to the bottom of my modified actxserver.m file:

% Taken from: [matlabroot '\toolbox\matlab\winfun\private\newprogid.m']
function convertedProgID = newprogid(progID)
% Copyright 1984-2004 The MathWorks, Inc.
% $Revision: 1.1.8.5 $ $Date: 2004/04/15 00:07:00 $
convertedProgID = lower(progID);  % Yair: in the new version (after 2010/06/10) this line is missing i.e. case-sensitive progID
convertedProgID = regexprep(convertedProgID, '_', '__');  % Yair 17/5/2009: was progId - probably a bug
convertedProgID = regexprep(convertedProgID, '-', '___');
convertedProgID = regexprep(convertedProgID, '\.', '_');
convertedProgID = regexprep(convertedProgID, ' ', '____');
convertedProgID = regexprep(convertedProgID, '&', '_____');

Note that when MathWorks fixed %matlabroot%/toolbox/matlab/winfun/private/newprogid.m in 2010, they removed the conversion of progID to lower-case, making it case-sensitive. In my modified version above, I have kept the older conversion to lowercase for case-insensitivity.

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