Windows 10 IoT Core Installer Blocked?

If you try to install Windows 10 IoT core from the installer chances are you wil get blocked with the following error.

Your administrator has blocked this application because it potentially poses 
a security risk to your computer."  and "Your security settings do not allow 
this application to be installed on your computer.

I ran into this recently when preparing a Raspberry Pi to run Windows 10 IoT Core. What gives? Well, that is due to a Windows Security Setting. The setting can be changed by editing the registry.  The registry key can be found at the following location

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\Security\TrustManager\PromptingLevel

The keys inside of this path contain one key named Internet that is set to Disabled. Change it to Enabled. Then you should be able to perform the installation and then change the key back.

Raspberry Pi Starter Kit

Available on Amazon for free at the time of this writing

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Getting Ready for the Holiday Season with Phillips Hue and a Raspberry Pi

The holiday season is upon us; by the end of this month I expect to start seeing my neighbors put out their fall decorations. By mid-October decorations for Halloween will show up. After Halloween the decorations roll back to fall themed only and then are changed to Christmas decorations right after new years. Two of these holidays tend to come with flashy displays and lights: Halloween and Christmas.

porch

I primarily use Phillips Hue lighting throughout my house and it is a perfect companion for festive displays. The color bulbs are adaptable to any color scheme and the newly released Edison-style bulbs add a warm glow to fall scenes.  The Phillips Hue lighting sets are programmable if you are using a hub. While the new light bulbs have Bluetooth support to directly be controlled by a phone there’s not public API for them (yet). For programming a hub is needed.

pumpkin

I’ve written on controlling the Phillips Hue lights before. Expanding on that I wanted to make a project that would let an IoT device trigger a scene according to some external event. I’ll use a motion sensor to trigger the relevant events.

 

But you could also use sound, change in temperature, lighting, or time as sources. I’ll be using a Raspberry Pi; it has network connectivity and can be easily interfaced to a number of devices.  I’m using the Raspberry Pi zero but about any Pi will do. Hue does have available a motion sensor ; if one only wishes to control lights based on motion a solution is available. But if one wishes to have other triggers or trigger other actions along with the lights a custom solution is needed.

20191005_160504.jpg

The Raspberry Pi 4 with a heat sink attached.

20191005_161532.jpg

Raspberry Pi Zero with a 4-port USB hub

All that I want to happen is for the the lighting pattern to change when a person is detected. I’ll use a passive infrared sensor for presence detection.  For Halloween I want a Hue light that is illuminating a jack-o-lantern to pulsate an orange color. When someone comes up knock on the door I want the light for the front door to go bright white. A few moments after a person is no longer there I want the system to go back to it’s previous pattern. But past a certain hour I don’t want this to continue; after 10:00pm the lights should extinguish. Simple enough, right?

 

20191005_155936.jpg

This is the passive infrared sensor that I used.

The physical build for this circuit is easy. The Passive Infrared Sensor (PIR) will get power from the VCC and ground pins of the Raspberry Pi. The signal line from the PIR can be connected to any of the GPIO pins. I’m going to use pin 3. The circuit will need to be put in an enclosure to protect it from rain or humidity in general. If your enclosure doesn’t already have a weather protected way to get power in your options are to either run the Pi off of a battery that is within the enclosure  (that means periodic recharging) or drill a hole for the wires yourself and apply a sealant.

There are a lot of languages that I could use for writing my program on the Pi. Python, Java, and C/C++ make the top of the list (in no specific order). For this project I’ve decided to go with Java. To interact with the pins in Java we will need to import classes from com.pi4j.io and com.pi4j.wiringpi. These are not standard libraries; they exists to provide an interface to the pins. To demonstrate reading a pin in Java here is a simple program that will print text in a look that reflects the pin state.

import com.pi4j.io.*;
import com.pi4j.wiringpi.Gpio;
import com.pi4j.wiringpi.GpioUtil;

public class PinTest {
   public static void main(String args[]) throws InterruptedException {   
      final GpioController gpio = GpioFactory.getInstance();
      Gpio.pinMode (3, Gpio.INPUT) ;          
      while(true) {
         if (Gpio.digitalRead(3) == 0){
               System.out.println(The Pin is ON");
         }else{
            System.out.println("The Pin is OFF");
         }
      }
   }
}

Phillips has an SDK for Java. You might see it present as an SDK for Android, but it works fine in other Java environments. A convenience from this is that a significant portion of the development can be done on your computer of choice. I did most of the development on a Mac and used git to transfer it to the Raspberry Pi when done.

20191005_162433.jpg

The color Hue lighting can take on a variety of colors.

The overall execution loop of the program will check whether or not the trigger condition has occurred. If the trigger condition has occurred then the program will activate a scene. If not then it deactivates the scene. The program loop also contains some debouncing logic. Depending on the type of sensor used and the sensors characteristics a sensor could change states with ever cycle. I’ve chosen to only deactivate if a certain amount of time has passed since the last activation. For initial development instead of interfacing to an actual sensor I have a method that is returning a random Boolean value. When the code is moved to the Raspberry Pi this method will be updated to read the state of the actual sensor. The following will only deactivate after there have been 2 seconds with no activation event.

    boolean getActivationState() { 
        return random.nextBoolean();
    }

    void runLoop() throws InterruptedException{ 
        System.out.println("running");
        long lastActivation = System.currentTimeMillis();
        while(true) { 
            Thread.sleep(100);
            boolean isActivated = getActivationState();
            if(isActivated) {
                lastActivation = System.currentTimeMillis();
                activateScene();
            }
            else {
                long now = System.currentTimeMillis();
                if ((now - lastActivation)> 2000)
                    deactivateScene();
            }
        }
    }

Controlling the lights happens through the Hue SDK. Before activating the lights the Hue bridge must be discovered. While Hue makes a series of lights that have Bluetooth controllers built in and can be controlled without the Hue Bridge currently they only support APIs through the bridge. It is a required hardware component.

The SDK already contains functions for discovering the bridge. All that a developer needs to do is initiate a search and implement a callback object that will receive information on the bridges discovered. In the following I instantiate the Phillips Hue SDK object and register a listener.  If the program had been connected with a bridge before the IP address if that bridge is loaded and it reconnects to it. Otherwise the search is initiated. As the search occurs the earlier registered listener receives callbacks.

private void init() {
    this.loadSettings();
    System.out.println("Getting SDK instance");
    phHueSDK = PHHueSDK.create();
    System.out.println("Setting App Name");
    phHueSDK.setAppName("HolidayLights");
    phHueSDK.setDeviceName("RaspPi");
    System.out.println("SDK initialized");
    phHueSDK.getNotificationManager().registerSDKListener(listener);

    if(this.getLastIpAddress()  != null) {
        System.out.println("Connect to last access point");
        PHAccessPoint lastAccessPoint = new PHAccessPoint();
        lastAccessPoint.setIpAddress(getLastIpAddress());
        lastAccessPoint.setUsername(getUserName());
        if (!phHueSDK.isAccessPointConnected(lastAccessPoint)) {
            phHueSDK.connect(lastAccessPoint);
        }
    } else {
        System.out.println("Searching for access point");
        PHBridgeSearchManager sm = (PHBridgeSearchManager) phHueSDK.getSDKService(PHHueSDK.SEARCH_BRIDGE);
        // Start the UPNP Searching of local bridges.
        sm.search(true, true);
    }
}

The listener is of type PHSDKListener. I won’t show the full implementation here but will show some of the more relevant parts.

When the bridges are found they are returned as a list. I’ve only got one on my home network and so I connect to the first one seen. If you have more than one bridge you’ll need to implement your own logic for making a selection.

@Override
public void onAccessPointsFound(List accessPoint) {
    System.out.println("Access point found");
    if (accessPoint != null && accessPoint.size() > 0) {
        System.out.println("Number of access points: "+new Integer(accessPoint.size()).toString());
        phHueSDK.getAccessPointsFound().clear();
        phHueSDK.getAccessPointsFound().addAll(accessPoint);      
        phHueSDK.connect(accessPoint.get(0));       
    }
}

When the connect attempt is made it is necessary to press the pairing button on the bridge. The console will print a message from the SDK saying this.  Once the bridge is connected I save an instance of the bridge and the a

 

 

        @Override
        public void onBridgeConnected(PHBridge b, String username) {
            HolidayController.this.bridge = b;
            isBridgeConnected = true;
            System.out.println("on bridge connected...");
            phHueSDK.setSelectedBridge(b);
            phHueSDK.enableHeartbeat(b, PHHueSDK.HB_INTERVAL);
            phHueSDK.getLastHeartbeat().put(b.getResourceCache().getBridgeConfiguration() .getIpAddress(), System.currentTimeMillis());
            setLastIpAddress(b.getResourceCache().getBridgeConfiguration().getIpAddress());
            setUserName(username);
        }

After the bridge connects the SDK will query the state of the lights on the system and update some objects representing the last known state of each light. The first time the cache is updated the program prints the name of each light and the light’s identity. This information is useful for selecting which lights will be controlled.  The light list is saved for the program to use.

        @Override
        public void onCacheUpdated(List<Integer> arg0, PHBridge bridge) {
            if(!isDeviceListPrinted) {
                PHBridgeResourcesCache rc = bridge.getResourceCache();
                List<PHLight> lightList = rc.getAllLights();
                HolidayController.this.lightList = lightList;
                ListIterator<PHLight> it = lightList.listIterator();
                while(it.hasNext()) {
                    PHLight l = it.next();
                    System.out.println(l.getIdentifier() + "    " + l.getName());
                }
                isDeviceListPrinted = true;
            }
        }
With that in place we now have enough information to change the state of the lights. To test things out I started with implementations of activateScene and deactivateScene that will just turn all the Hue lights on and off (don’t do this if you have other people in your dwelling that this would affect).
void activateScene() {
    ListIterator<PHLight> it = lightList.listIterator();
    while(it.hasNext()) {
        PHLight l = it.next();
        System.out.println(l.getIdentifier() + "    " + l.getName());
        PHLightState state = l.getLastKnownLightState();
        state.setOn(true);
        state.setBrightness(254);
        float[] xy = PHUtilities.calculateXYFromRGB(
            0xFF & ((int)color>> 0x10), 
            0xFF & ((int)color >> (long)0x08), 
            0xFF & (int)color, l.getModelNumber());
        l.setLastKnownLightState(state);
    
        bridge.updateLightState(l.getIdentifier(), state,  NOPListener);
    }
    isDeviceListPrinted = true;
}

void deactivateScene() {
    ListIterator<PHLight> it = lightList.listIterator();
    while(it.hasNext()) {
        PHLight l = it.next();
        System.out.println(l.getIdentifier() + "    " + l.getName());
        PHLightState state = l.getLastKnownLightState();
        state.setOn(false);
        //state.setBrightness(254);
        l.setLastKnownLightState(state);
    
        this.bridge.updateLightState(l.getIdentifier(), state,  NOPListener);
    }
    isDeviceListPrinted = true;
}
If the program is run at this point the lights will turn on and off somewhat randomly. Ultimately we don’t want it to control all the lights. Instead I want to be able to specify the lights that it is going to control. I’ve made a JSON file file that contains a couple of elements. One is the RGB color that I want to use in the form of an integer, the other is an array of numbers where each number is an ID for the light to be controlled. The RGB color is specified here as a base 10 number instead of the normal base 16 that you may see used for RGB codes. Unfortunately JSON doesn’t support hexadecimal numbers 🙁.
{
    "lights":[5, 7, 9],
    "color": 16711935
}
These values are read by the code. Before the code acts on any light it checks to see if its identifier is in this array before continuing. During activation if the identifier is in the array the light’s state is set to on, brightness is set to full, and the color is applied. The color must be converted to the right color space before being applied to the light; something that is done with a utility function that the SDK provides.
void activateScene() {
    System.out.println("activating scene");
    ListIterator<PHLight> it = lightList.listIterator();
    while(it.hasNext()) {
        PHLight l = it.next();
        if(isTargetLight(l.getIdentifier())) {
            System.out.println(l.getIdentifier() + "    " + l.getName());
            PHLightState state = l.getLastKnownLightState();
            state.setOn(true);
            state.setBrightness(254);
            float[] xy = PHUtilities.calculateXYFromRGB(
                0xFF & ((int)color>> 0x10), 
                0xFF & ((int)color >> (long)0x08), 
                0xFF & (int)color, l.getModelNumber()
            );
            state.setX(xy[0]);
            state.setY(xy[1]);
            l.setLastKnownLightState(state);        
            bridge.updateLightState(l.getIdentifier(), state,  NOPListener);
        }
    }
}

void deactivateScene() {
    System.out.println("deactivating");
    ListIterator<PHLight> it = lightList.listIterator();
    while(it.hasNext()) {
        PHLight l = it.next();
        if(isTargetLight(l.getIdentifier())) {
        System.out.println(l.getIdentifier() + "    " + l.getName());
        PHLightState state = l.getLastKnownLightState();
        state.setOn(false);
        l.setLastKnownLightState(state);
    
        this.bridge.updateLightState(l.getIdentifier(), state,  NOPListener);
        }
    }
}
The last steps needed to make the device work as intended are to update the getActivationState() function to read the actual state of the motion sensor instead of a random value and wiring the motion sensor to a Raspberry Pi. From hereon the code is only going to work on a Raspberry Pi since the libraries for reading the pins are only applicable to this device. It is possible to dynamically load class libraries and use them as needed for the specific platform on which code is running. But information on doing that is beyond the scope of what I wish to discuss here.
I’m declaring a GpioController variable at the class level and am instantiating it in the constructor. I also set the mode of the IO pin that I’ll be using to  input.
    GpioController gpio;
    
    HolidayController() {
        gpio = GpioFactory.getInstance();
        Gpio.pinMode (3, Gpio.INPUT) ; 
        //....
     }
The getActivationState() implementation only needs to contain a single line.
boolean getActivationState() { 
   return Gpio.digitalRead(3);
}
With that change it will now work. If the Raspberry Pi is placed in a position where the motion sensor has a view of the space of interest then it will control the lights. If you are using one of the earlier Raspberry Pis (anything before the Raspberry Pi 4) you should be able to also power the Pi off of a portable phone charger; there are many that will make sufficient batteries for the Pi. The Raspberry Pi 4 has higher energy requirements and you may run into more challenges finding a portable power supply that works.
Why use the Pi at all for this? Because there is a lot of room to expand. Such as using the video capabilities of the pi to power a display or controlling other devices. Controlling the lights is a start. I’ll be revisiting this project for add-ons in the future.
If you want to start on something similar yourself the following (affiliate) links will take you to the products on Amazon.
Parts Lists

Developing for older Samsung TVs

If you already have a Samsung TV and want to start developing for it chances are you don’t have the latest and greatest model. But when you install the Tizen development tools they only target 2 operating system versions; the latest version that is out now and the version that is yet to be released in a year or so. Your TV is too old! So what can you do?

If you check the Tizen development forums the suggestion is to install an older version of the development tools. But that’s no fun! And it is possible to develop for the older TVs with the newer tools. Go ahead and install the latest versions of the Tizen development Studio first. While that is installing you will need to download an older version of the Extensions for TV. You can find them at this site. As you scroll through the available versions you will see that if you attempt to get a version older than the 3.0 version you can’t download it. Download the 3.1 or 4.0 extensions. Don’t worry, the  extensions also contain the components needed for TV’s running the 2.3 and 2.4 Tizen version.

tizen extension for tizen sdk

After Tizen Development Studio is installed open the package manager. In the upper right corner of the package manager is a gear icon. Select it.

 

packagemaker

Expand the “Extensions SDK” area of the window to see the extensions installed and click on the + button to add an extension. A window opens asking for a URL. Leave the URL blank and click on the three dots next to it. You’ll now be asked to navigate to a local archive of the extension you with to add. Navigate to the file that you downloaded earlier and select it.  The package manager will take a few moments to install the extension.

When you attempt to create a new project and look at the TV templates available there’s only the 4.0 and 5.0 projects. What gives? The missing project templates can be found under the Custom projects. Select “TV-Samsung v3.0.” Even if you have a TV running Tizen 2.3 this opeion will work. When you click the next button you’ll see the familiar project templates.

Listing Applications on a Tizen Device

In a Tizen project I was working on I found that Tizen Web alone wasn’t enough to help me accomplish my goal. For some of the functionality that I needed a native application would be needed (more on that in another blog post). Rather than completely write the application in native code I was going to use HTML for the UI and a native service for other functionality. This is a Tizen Hybrid application.

The Tizen documentation wasn’t quite clear to me on what identifier to use when trying to launch a service packaged with an HTML application. It mentions using the App ID. This didn’t work for me. I only figured out the right name to use when I tried listing all of the applications and services on the device.

Getting a list of the applications and services is done through tizen.application.getAppsInfo. This function takes as a parameter a callback. The call back is given a list of the applications installed on the device. For my purposes I was only interested in the id member of the objects that were passed back.

  

tizen.application.getAppsInfo(
    function onListInstalledApps(applications) {
        console.log("List of Applications:");
        applications.forEach(
          function(app) {
    		console.log(`  app.id: ${app.id}`);
        });
    });

Once I saw the output of this it was easy to identify the problem I encountered with launching the service.

Screen Shot 2019-05-24 at 10.38.17 AM
Output of app listing code

According to the Tizen documentation when launching a service the ID string used is composed of the package ID and the app ID of the service. The package ID can be found in the confix.xml for the web application.  In the following you can see the package ID is “IVFd9Or08P”.

Screen Shot 2019-05-24 at 4.34.54 PM

The app ID can be found in then tizen-manifest.xml for the service project.

Screen Shot 2019-05-24 at 4.37.53 PM

The app ID here is “org.sample.service.” If you look in the output from the code sample for listing installed applications you will see that the service shows up as IVFd9Or08P.testservice. It is using the entry from the “exec” field instead of the appid field. I’m not sure why the documentation points to the appid only. But I’m happy to have figured out this problem.

 

Using a Game Pad in the Browser

GameController

I was thinking about a video game from my childhood and how easy it would be to rebuild the game now.  Having decided to do this I had to decide what platform to target. I chose to make it a browser application. While the game could be played with a keyboard or mouse I wanted to use a game pad to play it the way it was meant to be played.

Game pads can be used in HTML. I’ve not seen many applications that actually take advantage of this, but as game streaming becomes more popular this is likely to change.  Let’s start with one of the simplest things we can do: detect what game pads are present. I’m going to share all of my code in TypeScript. TypeScript is basically JavaScript with type information added. It compiles down to JavaScript. The advantage of using it here is that you will know the data types of a variable or parameter instead of needing to analyze the code and make inferences.

Detecting a Game Pad

To start we want to ensure that our browser supports the game pad API. To do this just check whether or not the getGamepads function exist on the navigator object.

var isGamepadSupported:boolean = (navigator.getGamepads != null);

There are two ways that we can detect the presence of game pads. We can listen for the events that are fired when a controller is connected or disconnected, or we can just poll for their presence. Here’s a code sample that does just that. The TypeScript elements are highlighted in blue.

function handleGamePadConnected(e:GamepadEvent) {
     console.log('A game pad was connected', e);
}
function handleGamePadDisconnected(e:GamepadEvent) {
     console.log('A game pad was disconnected', e);
}
window.addEventListener("gamepadconnected", handleGamePadConnected);
window.addEventListener("gamepaddisconnected", handleGamePadDisconnected);

If we run this code within a page we can see the code get triggered by ensuring the browser has focus (a browser without focus will not receive game pad events). Connecting and disconnecting a controller (if USB) or turning a controller on and off (for Bluetooth) will cause the event to trigger. On some controllers you may have to press a button for it to fully connect.  The event passed to the handlers has a field named game pad that contains all of the data for the game pad being used. The other way to get this information is to try to read the game pad state Calling navigator.getGamepads() will return information on all the game pads connected to the system. A word of warning though, the value returned is an array that has some null elements in it. If you iterate through the array don’t assume that because you are reading a valid index that there is actually an object there.

This might sound weird at first, but imagine you are playing a four player game and player 2 decides to turn off his controller and leave. Rather than assign a new index to players 3 and 4 their controller indices will stay the same and the second element in the array will be null. To get the state of all of the game pads attached to the system use the following.

var controllerStates:Array<Gamepad> = navigator.getGamepads();

When I call this method I always receive an array with up to 4 elements in it, most of which are null.  If this function is being called in the game loop from one call to another one can see what controllers are present . Keep in mind that the object returned here is the state of the game pad, but it is not a reference to the game pad itself. If you hold onto the object it will not update as the state of the controller changes.

There are two properties on the GamePad object of most interest to us; the buttons property has the state of the buttons and the axes property contains the state of each axis for each directional control on the game pad.

Axes

A D-pad input on a controller has two axes that can range from -1 to 1. There will be a vertical axis with three possible values and a horizontal axis with three possible values. While one might expect the neutral position of the controller to be zero I’ve found that even with my digital controllers the neutral value is near-zero but not quite zero.  There is a range for which we could receive a non-zero value that we would need to treat as zero.

For the analog sticks the general range of values returned will also be between -1 and 1 for each axis, but there are values between this range that could also be returned depending on how far the directional stick has been used. When the stick isn’t being touched the axis will return a value that is near zero. Like the digital input there is a near zero range that should be treated as zero. Note that the controller interface may return more axes than actually exists on the controller.

Buttons

The buttons element of a GamePad object has a list of buttons. The collection may return more objects than there are physical buttons on the controller; these non-existing buttons will not change state. The GameButton Interface has three attributes.

  • pressed – will be true if the button is pressed, false otherwise.
  • touched – for controllers that can detect touch this attribute will be true if the button is touched, false otherwise
  • value – a value between 0 and 1 that tells how far the button is pressed or how hard it is pressed.

Even if you have a controller that doesn’t support touch or analog input the touched and values buttons will still update. If a button is pressed it can be inferred that it is being touched and the touched attribute updates accordingly. For a digital button the value attribute will only be 0 or 1 and no value between.

interface GamepadButton {
     readonly pressed:boolean;
     readonly touched:button;
     readonly value:number;
}

Other Attributes

There are some other attributes that can be found on the game pad that I haven’t discussed here. There GamePad object has an index attribute that will identify its own index in the array.  There is a string id field that gives a name identifying the controller. There is also a timestamp attribute that indicates the time at which a Gamepad object was grabbed.

interface GamePad {
     readonly id:String;
     readonly index:number;
     readonly connected:boolean;
     readonly timestamp:long;
     readonly mapping:GamepadMappingType;
     readonly axes:Array<number>;
     readonly buttons:Array<GamepadButton>;
}

 

Code Sample

This code sample here will read the states of up to 4 controllers and show their states on the screen. I’m using images to present the code here as I have found that WordPress will sometimes unescape HTML code and render it as HTML instead of text. But you download the code sample directly to view it.

 

gamePadHTMLCode

 

The file main.js here was compiled from a typescript file, main.ts. Execution in mail.ts starts after the document is loaded. The first method executed is named start. It adds some handlers for the game pad being connected or disconnected.  These handlers only print the event out to the console. We are more interested in what is running within the interval. In the interval the states of all of the game pads is retrieved and then we call a function (updateController) to display them on the screen.

 

startFunction

Update Controller will find the HTML block to which a specific controller index is assigned and get the represented button state and axes states updated. The functions updateAxes and updateButtons take care of the details of these. There are several other HTML elements needed for this that were not declared in the page. Instead they are being created as they are needed.

In updateAxes if the needed element doesn’t exists I create it and then I show the value of the axis.

gamepadUpdateAxes

 

The function updateButtons does pretty much the same thing. Only instead of a single element it is updating three.

gamePadUpdateButtons.png

Do you have a game controller and want to try things out? I’ve got it loaded on a web page that you can try. Get your computer and controller paired. Then see the demo run at http://j2i.net/apps/gamePadStatus/

 

 

Keeping an Application Alive

I recently was working on a project in which, among other things, there needed to be a process that would restart the application should it ever be terminated for no reason. This isn’t unusual for kiosk applications where the only UI that the user will be able to get to is a single application running on the system. This isn’t an unusual need and something for which we had a utility that could do this; we generally refer to these as “Kiosk Application Monitors.”  But I decided not to use it. Why not? Because when developing it is a pain to deal with an app that isn’t easily killed. If I manually terminated the application it would almost immediately restart; this was a behaviour that was by design. When I really wanted the application to terminate and stay that way things were more challenging. This had to be done from the task manager and the task manager wasn’t easily accessible since the KIOSK app ran as always on top. To see the task manager I would first have to kill the app. But if the app were killed it would just restart.

Not wanting to deal with the difficulty of this I made a new a Kiosk Application Monitor (hereon referred to as KAM). While I would generally prefer to make utilities in C# I used C for this; I was going to be using Win32 APIs and it is easier to have direct access to them instead of  writing P/Invoking declarations for them.

The key difference in this KAM and the other ones that we had used was that this KAM could be terminated through keystrokes. It adds a keyboard hook that receives every keystroke that a user makes no matter what application.

Termination on Detecting Safe Word

I’ve got a variable named SafeWord that contains the word that when typed will kill all of the child processes and shut down the KAM. To better insulate the app from an accidental activation I’ve mandated that the escape key be pressed before the safe word and the enter key be pressed immediately after the safe word.  The keyboard hook receives the virtual key codes for the keys pressed. The code for escape (0x1b) and enter (0x0d) are both used directly within the source code.   Any other key press will be will be ignored until the escape key has been pressed, and will be checked for a match to the safe word. At the first mismatch the procedure will stop comparing until the escape key is pressed again. When the enter key is pressed the routine checks if the end of the safe word has been reached. If it has then the user has typed the same word; the routine to terminate the child processes is called.

keyboardHook

They keyboard routine is a small part in what this does, but a real time saver for me.

Allowing Only One Instance

I didn’t want more than one instance of this program ever running on the same machine. The way I managed that is pretty usual for Win32 programs; I used a named event to ensure there is a single instance. Named events are shared across programs. After creating one (with CreateEvent ) calling the GetLastError() function afterwords indicates whether or not this is the only instance of an application that has access to the event or if another program already has an instance of an event by the same name. When another instance has already created one GetLastError returns ERROR_ALREADY_EXISTS.

SingleInstance

Process Description and Start-Up

Moving from the ancillary functionality to the core functionality, I decided to use JSON for specifying information on the processes that should be started and watched. The C++ libraries do no intrinsically support JSON data handling. I used a third party library for this. The data in the JSON is used to populate a structure that gives very basic information on the process to be monitored.

Structure

Most of these values are passed directly to the Win32 function CreateFunction. Ignore is there so that I could disable a process without completely removing it from my configuration file. For each process that I’m going to start I create a new thread to monitor it.

CreateThreads

Most of the code within the CreateWatchedProcess function will run within an infinite loop. The process is created and information about it is populated into a PROCESS_INFORMATION variable (which I have named pi). The value of interest for the KAM is pi.hProcess. This is the process handle. The wait functions in the Win32 API can accept handles processes. In the case of WaitForSingleObject passing a process handle will block the calling thread until the process terminates.  There is nothing that my program has to do for detecting the termination of the process. When the next line after WaitForSingleObject executes we know the process has been terminated. The only question is if it was terminated because there was a request for the KAM to shut down or if this were an unexpected .

processLoop

How Did it Perform

In testing things worked fine. I’d intentionally put a bug in the program of interest that would cause it to crash and the KAM restarted it. The app I was using it with also remembered it’s state and could restore the UI to what it was before. From the perspective of the user the screen flashed but was otherwise normal. When I tried the same utility in the production environment I’m happy to say that its full functionality was not exercised; the program it was monitoring never crashed.

I’ve found the program to be useful and see some opportunities to increase it’s utility. I plan to make updates to it to support things such as starting processes in a specific order, monitoring the message pump of another process to detect lock conditions, and allowing the utility to accept or transmit process information over a network connection.