Write a function to initialize persistent data

Write a function to check whether a graph of cities and distances exists in the data cache. If the graph does not exist, create it from an Excel^® spreadsheet that contains the distance data and write it to the cache. Because only one MATLAB Production Server worker at a time can perform this write operation, use a synchronization lock to ensure that data initialization happens only once.

Connect to the cache that stores the distance data or create it if it does not exist using mps.cache.connect. Acquire a lock on a mutex using mps.sync.mutex for the duration of the write operation. Release the lock once the data is written to the cache.

Initialize the distance data using the loadDistanceData function.

function tf = loadDistanceData(connectionName, cacheName)
    c = mps.cache.connect(cacheName,'Connection',connectionName);    
    tries = 0;

    while isKey(c,'Distances') == false && tries < 6
        lk = mps.sync.mutex('DistanceData','Connection',connectionName);       
        if acquire(lk,10)
            if isKey(c,'Distances') == false
                g = initDistanceData('Distances.xlsx');
                c.Distances = g;
            end
            release(lk);
        end
        tries = tries + 1;
    end   
    tf = isKey(c,'Distances');
end

Write functions to read persistent data

Write a function to read the distance data graph from the data cache. Because reading data from the cache is an idempotent operation, you do not need to use synchronization locks. Connect to the cache using mps.cache.connect and then retrieve the graph.

Read the graph from the cache and convert it into a cell array using the listDestinations function.

Calculate the shortest possible route using the findRoute function. Use the nearest neighbor algorithm, by starting at a given city and repeatedly visiting the next nearest city until all cities have been visited.

function destinations = listDestinations()
    c = mps.cache.connect('TravelingSalesman','Connection','ScratchPad');   
    if loadDistanceData('ScratchPad','TravelingSalesman') == false
        error('Failed to load distance data. Cannot continue.');
    end
    
    g = c.Distances;
    destinations = table2array(g.Nodes);
end

function [route,distance] = findRoute(start,destinations)
    c = mps.cache.connect('TravelingSalesman','Connection','ScratchPad');    
    if loadDistanceData('ScratchPad','TravelingSalesman') == false
        error('Failed to load distance data. Cannot continue.');
    end
        
    g = c.Distances;    
    route = {start};
    distance = 0;
    current = start;
    
    while ~isempty(destinations)
        minDistance = Inf;
        nextSegment = {};        
        for n = 1:numel(destinations)
            [p,d] = shortestpath(g,current,destinations{n});
            if d < minDistance
                nextSegment = p(2:end);
                minDistance = d;
            end
        end

        current = nextSegment{end};
        distance = distance + minDistance;
        destinations = setdiff(destinations,current);        
        route = [ route nextSegment ];
    end
end

Write a function to modify persistent data

Write a function to add a new city. Adding a city modifies the graph stored in the data cache. Because this operation requires writing to the cache, use the mps.sync.mutex function described in Step 1 for locking. After adding a city, check that the graph is still complete by confirming that the distance between every pair of cities is known.

Add a city using the addDestination function. Adding a city adds a new graph node name along with new edges connecting this node to all existing nodes in the graph. The weights of the newly added edges are given by the vector distances. destinations is a cell array of character vectors that has the names of other cities in the graph.

function count = addDestination(name, destinations, distances)  
    count = 0;
    c = mps.cache.connect('TravelingSalesman','Connection','ScratchPad');   
    if loadDistanceData('ScratchPad','TravelingSalesman') == false
        error('Failed to load distance data. Cannot continue.');
    end
    
    lk = mps.sync.mutex('DistanceData','Connection','ScratchPad');  
    if acquire(lk,10)
        g = c.Distances;      
        newDestinations = setdiff(g.Nodes.Name, destinations);       
        if ~isempty(newDestinations)
            error('MPS:Example:TSP:MissingDestinations', ...
                  'Add distances for missing destinations: %s', ...
                strjoin(newDestinations,', '));
        end
        
        src = repmat({name},1,numel(destinations));
        g = addedge(g, src, destinations, distances);
        c.Distances = g;
        release(lk);
        count = numnodes(g);
    end   
end

Write a MATLAB app to call route-finding functions

Write a MATLAB app that wraps the functions described in Steps 2 and 3 in their respective proxy functions. The app allows you to specify a host and a port. For testing, invoke the local version of the route-finding functions when the host is blank and the port has the value 0. For the deployment workflow, invoke the deployed functions on the server running on the specified host and port. Use the webwrite (MATLAB) function to send HTTP POST requests to the server.

For more information on how to write an app, see Create and Run a Simple App Using App Designer (MATLAB).

Write the proxy functions findRouteProxy, addDestinationProxy, and listDestinationProxy for the findRoute, addDestination, and listDestination functions, respectively.

function destinations = listDestinationsProxy(app)
    if isempty(app.HostEditField.Value) && ...
            app.PortEditField.Value <= 0
        destinations = listDestinations();
        return;
    end
        
    listDestinations_OPTIONS = weboptions('MediaType','application/json','Timeout',60,'ContentType','raw');
    listDestinations_HOST = app.HostEditField.Value;
    listDestinations_PORT = app.PortEditField.Value;
    noInputJSON = '{ "rhs": [], "nargout": 1 }';
    destinations_JSON = webwrite(sprintf('http://%s:%d/TravelingSalesman/listDestinations', ...
        listDestinations_HOST,listDestinations_PORT), noInputJSON, listDestinations_OPTIONS);
    if iscolumn(destinations_JSON), destinations_JSON = destinations_JSON'; end
    destinations_RESPONSE = mps.json.decoderesponse(destinations_JSON);
    if isstruct(destinations_RESPONSE)
        error(destinations_RESPONSE.id,destinations_RESPONSE.message);
    else
        if nargout > 0, destinations = destinations_RESPONSE{1}; end
    end        
end

function [route,distance] = findRouteProxy(app,start,destinations)
    if isempty(app.HostEditField.Value) && ...
            app.PortEditField.Value <= 0
        [route,distance] = findRoute(start,destinations);
        return;
    end  
    findRoute_OPTIONS = weboptions('MediaType','application/json','Timeout',60,'ContentType','raw');
    findRoute_HOST = app.HostEditField.Value;
    findRoute_PORT = app.PortEditField.Value;
    start_destinations_DATA = {};
    if nargin > 0, start_destinations_DATA = [ start_destinations_DATA { start } ]; end
    if nargin > 1, start_destinations_DATA = [ start_destinations_DATA { destinations } ]; end
    route_distance_JSON = webwrite(sprintf('http://%s:%d/TravelingSalesman/findRoute', ...
            findRoute_HOST,findRoute_PORT), ...
            mps.json.encoderequest(start_destinations_DATA,'nargout',nargout), findRoute_OPTIONS);
    if iscolumn(route_distance_JSON), route_distance_JSON = route_distance_JSON'; end
    route_distance_RESPONSE = mps.json.decoderesponse(route_distance_JSON);
    if isstruct(route_distance_RESPONSE)
        error(route_distance_RESPONSE.id,route_distance_RESPONSE.message);
    else
        if nargout > 0, route = route_distance_RESPONSE{1}; end
        if nargout > 1, distance = route_distance_RESPONSE{2}; end
    end
end

function count = addDestinationProxy(app, name, destinations,distances)
    if isempty(app.HostEditField.Value) && ...
            app.PortEditField.Value <= 0
        count = addDestination(name, destinations,distances);
        return;
    end
                    
    addDestination_OPTIONS = weboptions('MediaType','application/json','Timeout',60,'ContentType','raw');
    addDestination_HOST = app.HostEditField.Value;
    addDestination_PORT = app.PortEditField.Value;
    name_destinations_distances_DATA = {};
    if nargin > 0, name_destinations_distances_DATA = [ name_destinations_distances_DATA { name } ]; end
    if nargin > 1, name_destinations_distances_DATA = [ name_destinations_distances_DATA { destinations } ]; end
    if nargin > 2, name_destinations_distances_DATA = [ name_destinations_distances_DATA { distances } ]; end
    count_JSON = webwrite(sprintf('http://%s:%d/TravelingSalesman/addDestination', ...
        addDestination_HOST,addDestination_PORT), ...
        mps.json.encoderequest(name_destinations_distances_DATA,'nargout',nargout), addDestination_OPTIONS);
    if iscolumn(count_JSON), count_JSON = count_JSON'; end
    count_RESPONSE = mps.json.decoderesponse(count_JSON);
    if isstruct(count_RESPONSE)
        error(count_RESPONSE.id,count_RESPONSE.message);
    else
        if nargout > 0, count = count_RESPONSE{1}; end
    end
end

Create an mps.cache.Controller object for a local persistence service that uses the Redis™ persistence provider.

>> ctrl = mps.cache.control('ScratchPad', 'Redis', 'Port', 8675);

When active, this controller enables a connection named ScratchPad. Connection names link caches to storage locations in persistence services. The mps.cache.connect function requires connection names to create data caches. The MATLAB Production Server administrator sets connection names in the cache configuration file mps_cache_config. For details, see Configure Server to Use Redis. By using the same connection names in MATLAB desktop sessions, you enable your code to move from development through testing to production without change.

Start the persistence service using start.

>> start(ctrl);

Start the TravelingSalesman route-finding app that uses the persistence service.

>> TravelingSalesman

The app starts with default values for Host and Port.

Click Load Cities to load the list of cities. Use the Start menu to set a starting location and the >> and << buttons to select and clear cities to visit. Click Compute Path to display a route that visits all the cities.

When you close the app, stop the persistence service using stop. Stopping a persistence service will delete the data stored by that service.

>> stop(ctrl);

Create a MATLAB Production Server instance

Create a server from the system command line using mps-new. For more information, see Create Server Instance Using Command Line. If you have not already set up your server environment, see mps-setup for more information.

Create a new server server_1 located in the folder tmp.

mps-new /tmp/server_1

Alternatively, use the MATLAB Production Server dashboard to create a server. For more information, see Set Up and Log In to MATLAB Production Server Dashboard.

Create a persistence service connection

The deployable archive requires a persistence service connection named ScratchPad. Use the dashboard to create the ScratchPad connection or copy the file mps_cache_config from the example directory to the config directory of your server instance. If you already have an mps_cache_config file in your config directory, edit it to add the ScratchPad connection as specified in the example mps_cache_config.

Create a deployable archive with the Production Server Compiler App and deploy it to the server

Start the server instance

Start the server from the system command line using mps-start.

mps-start -C /tmp/server_1

Start the persistence service

Start the persistence service from the system command line using mps-cache.

mps-cache start -C /tmp/server_1 --connection ScratchPad

Test the app

Start the TravelingSalesman route-finding app that uses the persistence service.

>> TravelingSalesman

The app starts with empty values for Host and Port. Refer to the server configuration file main_config located at server_name/config to get the host and port values for your MATLAB Production Server instance. For this example, find the config file at /tmp/server_1/config. Enter the host and port values in the app.

Click Load Cities to load the list of cities. Use the Start menu to set a starting location and the >> and << buttons to select and clear cities to visit. Click Compute Path to display a route that visits all the cities.