Author: Miq

TANGO – Making equipment remotely controllable

Usually hardwareTango_logo vendors ship some end user application for Microsoft Windows and drivers for their hardware. Sometimes there are generic application like coriander for firewire cameras. While this is often enough most of these solutions are not remotely controllable. Some of our clients use multiple devices and equipment to conduct their experiments which must be orchestrated to achieve the desired results. This is where TANGO – an open source software (OSS) control system framework – comes into play.

Most of the time hardware also can be controlled using a standardized or proprietary protocol and/or a vendor library. TANGO makes it easy to expose the desired functionality of the hardware through a well-defined and explorable interface consisting of attributes and commands. Such an interface to hardware –  or a logical piece of equipment completely realised in software – is called a device in TANGO terms.

Devices are available over the (intra)net and can be controlled manually or using various scripting systems. Integrating your hardware as TANGO devices into the control system opens up a lot of possibilites in using and monitoring your equipment efficiently and comfortably using TANGO clients. There are a lot of bindings for TANGO devices if you do not want to program your own TANGO client in C++, Java or Python, for example LabVIEW, Matlab, IGOR pro, Panorama and WinCC OA.

So if you have the need to control several pieces of hardware at once have a look at the TANGO framework. It features

  • network transparency
  • platform-indepence (Windows, Linux, Mac OS X etc.) and -interoperability
  • cross-language support(C++, Java and Python)
  • a rich set of tools and frameworks

There is a vivid community around TANGO and many drivers for different types of equipment already exist as open source projects for different types of cameras, a plethora of motion controllers and so on. I will provide a deeper look at the concepts with code examples and guidelines building for TANGO devices in future posts.

Database Migration Categories

Most long-running projects need to manage changes to the database schema of the system and data migrations in some way. As the system evolves new datatypes/tables and properties/columns are added, some are removed and others are changed. Relationships between objects also change in unpredictable ways so that you have to deal with these changes in some way. Not all changes are equal in nature, so we handle them differently!

One tool we use to manage our database is liquibase. The units of change are called migrations and are logged in the database itself (table “databasemigrations”) so that you can actually see in which state the schema is. Our experience using such tools for several years is very positive because there is no manual work on the database of some production system needed and new installations automatically create the database schema matching the running software. There are however a few situations when you want to do things manually. So we identified three types of changes and defined how to handle them:

1. structural changes

Structural changes modify the database schema but no data. In some cases you have to care about the default values for not null columns. These changes are handled by database management/versioning tools. They are relevant for all instances and specific for each deployed version of the system. The changes are stored with the source code under version control. Most of the time they are needed when extending the functionality of the system and implementing new features. In SQL the typical commands are CREATE, DROP and ALTER.

2. data rule changes

Changes to the way how the data is stored we call data rule changes. Examples for this are changing the representation of an enum from integer to string or a relation from one-to-many to many-to-many. In such a case the schema and importantly existing data has to be changed. For these migrations you do not need explicit ids of an object in the database but you change all entries in the same way according to the new rules. The changes can be applied to each instance of the system that is update to the new database (and software) version. Like structural changes they are executed using the database migration tool and stored under version control. The typical SQL command after the involveld structural changes needed is UPDATE with an where clause and sometimes CASE WHEN statements.

3. data modifications

Sometimes you have to change individual data sets of one instance of a system. That may be because of a bug in the software or corrupted/wrong entries that cannot by fixed using the system itself, e.g. as super user. Here you fix the entries of one instance of the system manually or with a SQL script. You will usually name specific object ids of the database and perform these exact changes only on this instance. It may be necessary to perfom similar tasks on other instances using different object ids. Because of this one-time and instance-specific nature of the changes we do not use a migration tool but some kind of SQL shell. Such manual changes have to be performed with extra caution and need to be thoroughly documented, e.g. in your issue tracker and wiki. If possible use a non-destructive approach and make backups of the data before executing the changes. Typical SQL statements are UPDATE or DELETE containing ids or business keys.

Conclusion

With categories and guidelines above developers can easily figure out how to deal with changes to the database. They can keep the software, database schema and customer data up-to-date, nice and clean over many years while improving and evolving the system and managing several instances running possibly different versions of the system.

Configuring your Java webapp

There are several ways to configure your Java Servlet-based webapp with values for deployment-specific things like the database connection or directories for data and logs. Let us take a look at the alternatives and their benefits and drawbacks.

web.xml

The deployment descriptor (web.xml) resides inside your WAR file. You can specify init parameters available using the ServletContext.
web.xml

<context-param>
    <param-name>LogDirectory</param-name>
    <param-value>/myapp/logs</param-value>
</context-param>

Accessing the parameter in your Servlet:

String logDirectory = getServletContext().getInitParameter("LogDirectory");
// do something with it

The nice thing about this solution is the self-containment of your packaged application. The price is building a customized web.xml/WAR for each deployment instance.

Environment variables

Another possibility is to pass environment variables to your servlet container at startup, e.g. using JAVA_OPTS in the case of Apache Tomcat.
tomcat.conf

...
JAVA_OPTS="-DLogDirectory=/myapp/logs"
...

They can be easily accessed using

    System.getProperty("LogDirectory");

This is very easy to employ but has several drawbacks:

  • you have to mess with the configuration of your servlet container/host to set the variables
  • they are valid for the whole servlet container, possibly interferring with other webapps or the container itself
  • the settings are harder to find than in one file that you deliver with your webapp
  • need of server restart to change the values

context.xml

Using context.xml and JNDI is our preferred way of configuring our webapps. You can ship a default context.xml in the META-INF directory of your WAR and easily configure resources and beans:

<Context>
    <Environment name="LogDirectory" value="/myapp/logs" type="java.lang.String" />
    <!-- Development DB -->
    <Resource name="jdbc/devdb" auth="Container" type="javax.sql.DataSource"
               maxActive="100" maxIdle="30" maxWait="-1"
               username="sa" password="" driverClassName="org.h2.Driver"
               url="jdbc:h2:mem:devDB;mode=Oracle"/>
</Context>

A context.xml outside of your WAR has to be copied in the context configuration directory of your servlet container, e.g.:

cp context.xml /etc/tomcat7/Catalina/localhost/myapp.xml

You can then access the configuration items using JNDI:

Context ctx = (Context) new InitialContext().lookup("java:comp/env");
String logDirectory = (String) ctx.lookup("LogDirectory");
// do something

You can of course use context-params and the ServletContext to retrieve simple String parameters stored in the context.xml instead of web.xml, too.

The name of the context file must match the name of the deployed application. That way we can deploy the same WAR on several target machines and configure the applications separately. The context.xml not only contains the JNDI datasources (which is very common) but also configuration parameters that may change for each target system.

Bit-fiddling is possible in Java

We have a service interface for Modbus devices that we can use remotely from Java. Modbus supports only very basic data types like single bits and 16-bit words. Our service interface provides the contents of a 16-bit input or holding register as a Java integer.

Often one 16-bit register is not enough to solve a problem in your domain, like representing a temperature as floating point number. A common solution is to combine two 16-bit registers and interpret their contents as a floating point number.

So the question is how to combine the bits of the two int values and convert them to a float in Java. There are at least two possiblities I want to show you.

The “old-fashioned” way includes bit-shifting and bit-wise operators which you actually can use in Java despite of the major flaw regarding primitive types: there are no unsigned data types; even byte is signed!

public static float floatFrom(int mostSignificat16Bits, int leastSignificant16Bits) {
    int bits = (mostSignificat16Bits << 16) | leastSignificant16Bits;
    return Float.intBitsToFloat(bits);
}

As seemingly more modern way is using java.nio.ByteBuffer:

public static float nioFloatFrom(int mostSignificat16Bits, int leastSignificant16Bits) {
    final ByteBuffer buf = ByteBuffer.allocate(4).putShort((short) mostSignificat16Bits).putShort((short) leastSignificant16Bits);
    buf.rewind(); // rewind to the beginning of the buffer, so it can be read!
    return buf.getFloat();
}

The second method seems superior when working with many values because you can fill the buffer conveniently in one phase and extract the float values conveniently by subsequent calls to getFloat().

Conclusion

Even if it is not one of Java’s strengths you actually can work on the bit- and byte-level and perform low level tasks. Do not let the lack of unsigned data types scare you; signedness is irrelevant for the bits in memory.

Documentation for your project: what and how

Writing documentation is seldom fun for developers and much useless documentation is written. I want to provide some guidelines helping to focus your project documentation efforts on useful stuff instead of following a set of dogmatic rules to plainly fulfill requirements.

Code Documentation

Probably written many times before but nevertheless often neglected:

  • Avoid untouched documentation templates, e.g. // This is a getter for A. They only clutter the code hurting developers instead of providing value.
  • Do not document every class, method, file etc. blindly. Focus on all API classes et al. to be used by other (external) developers.
  • Do not document what the code does, it should speak for itself. Rather explain why a certain algorithm or data structure is used. Try to communicate design decisions.
  • Check comments everytime you touch documented code and update them if necessary. Outdated documentation hurts more than its worth so if docs exists keep them up-to-date.

Project Documentation

This kind of documentation usually provides more value than many javadoc/doxygen generated pages. Nowadays, many people use a wiki software for project documentation. I encourage you to use a powerful wiki like Confluence because it provides rich formatting options and templating allowing for visually pleasing and expressive documentation. As such it may be even printed (to PDF) and handed out to your customers.

  • Putting parts like Installation into the code repository and integrating them into the wiki often serves administrators, managers (visibility!) and developers. See my older post “centralized project documentation” for some other ideas.
  • Wikis allow for easy editing and document sharing and are version controlled. All this facilitates reviews and updates of the documents.
  • Document prerequisites and external dependencies explicitly. They may be hard to find in configuration files but are of good use to people running your project.
  • Improve  searches in the wiki by providing tags and other metadata to help your future me and others finding the information they are looking for.
  • Provide consistent examples or even templates for common documentation tasks to encourage others and help them getting their project documentation started.

Conclusion

Good documentation is a real asset and can provide much value if you keep your efforts focused on the important stuff. Complex workflows and draconic rules will hinder documentation efforts wheres open collaboration and valuable documentation will motivate bringing more of it into existence.

Look into the past, become more agile: egoless programming

Agile software development methods like extreme programming and Scrum have been around for almost 20 years now. Many think of them as “the right way” or some kind of “holy grail”. So it is no wonder that many companies try to hop on the agile train to improve quality and efficiency of their software development.

Why is it that I hear of failures in adopting/switching to agile most of the time?

In my experience there are two main reasons why implementing agile methods does not work as expected:

  1. It is the management deciding to change the development process, not the developers. After a short while many aspects – especially using rigid methods like Scrum – do not seem to fit the organisation and therefore are changed. This leads to process implementations like ScrumBut
  2. Many developers do not have the mindset for the interactive, open and collaborative work style required by agile methods. Too often developers try to secure their job by isolating themselves and their solutions. Or they are doing stuff the way they are used to for many years not willing to learn, change and improve. Communication is hard, especially for programming nerds…

What can be done about it?

I would suggest trying to slowly change the culture in the company based on concepts from the 1970’s: egoless programming. In essence you have to let developers become more open and collaborative by internalising the Ten Commandments of Egoless Programming:

  1. Understand and accept that you will make mistakes.
  2. You are not your code.
  3. No matter how much “karate” you know, someone else will always know more.
  4. Don’t rewrite code without consultation.
  5. Treat people who know less than you with respect, deference, and patience.
  6. The only constant in the world is change.
  7. The only true authority stems from knowledge, not from position.
  8. Fight for what you believe, but gracefully accept defeat.
  9. Don’t be “the guy in the room.”
  10. Critique code instead of people—be kind to the coder, not to the code.

There is a PDF version of the commandments with some amplifying sentenctes from Builder.com published on techrepublic in 2002. If you manage to create a development culture based on these values you are more than half-way down the agile road and can try to implement one of the popular agile methods – or your own!

Centralized project documentation

Project documentation is one thing developers do not like to think about but it is necessary for others to use the software. There are several approaches to project documentation where it is either stored in the source code repository and/or some kind of project web page, e.g. in a wiki. It is often hard for different groups of people to find the documentation they need and to maintain it. I want to show an approach to store and maintain the documentation in one place and integrate it in several other locations.

The project documentation (not API documentation, generated by tools like javadoc or Doxygen) should be version controlled and close to the source code. So a directory in the project source tree seems to be a good place. That way the developers or ducumenters can keep it up-to-date with the current source code version. For others it may be hard to access the docs hidden somewhere in the source tree. So we need to integrate them into other tools to become easily accessible by all the people who need them.

Documentation format

We start with markdown as the documentation format because it is easily read and written using a normal text editor. It can be converted to HTML, PDF and other common document formats. The markdown files reside in a directory next to the source tree, named documentation for example. With pegdown there is a nice java library allowing integration of markdown support in your projects.

Integration in your wiki

Often you want to have your project documentation available on a web page, usually a wiki. With confluence you can directly embed markdown files from an URL in your project page using a plugin. This allows you to enrich the general project documentation in the source tree with your organisation specific documentation. The documentation becomes more widely accessible and searchable. The link can be served by a source code browser like gitweb: http://myrepo/git/?p=MyProject.git;a=blob_plain;f=README.md;hb=HEAD and is alsways up-to-date.

Integration in jenkins

Jenkins has a plugin to use markdown as description format. Combined with the project description setter plugin you can use a file from your workspace to display the job description. Short usage instructions or other notes and links can be maintained in the source tree and show up on the jenkins job page.

Integration in Github or Gitlab

Project hosting platforms like Github or your own repository manager, e.g. gitlab also can display markdown-formatted content from your source tree as the project description yielding a basic project page more or less for free.

Conclusion

Using markdown as a basis for your project documentation is a very flexible approach. It stays usable without any tool support and can be integrated and used in various ways using a plethora of tools and converters. Especially if you plan to open source a project it should contain useful documentation in such a widely understood format distributed with your source code.

CMake as a project model

One thing I actually like about Maven is its attempt to create a project model, conventions and a basic project structure. It allows easy integration IDEs, build servers and so on. For projects in C/C++ I find CMake an attractive way to specify the project model.

Despite its name CMake is not really a build system but more of a cross-platform project description with an integrated build system generator. Cross-platform means not only operating system (OS) here but development environment in general. CMake thus can generate project files for MS Visual Studio 20xx, Eclipse CDT, Code::Blocks, KDevelop and the like. QtCreator can even import a CMake-based project natively which brings you up to speed in almost no time.

CMake allows you organise your project in modules and manage your external dependencies. It does not impose as strict rules as Maven does and lacks an own artifact repository infrastructure but you can use the CMake package definitions or pkg-config information many projects provide.

Packaging and deployment with CPack allows you to deliver releases of your project the way your user would expect it: Depending on the target platform you can package your software as a Windows installer executable (using NSIS), several options for Mac OS X (like Package Maker or Bundle) and the popular DEB and RPM package formats for Linux Distributions.

Conclusion

CMake is more than just another build system. It is a flexible tool to define your project and integrate it with your favorite development tools. It can support the whole project lifecyle from initial creation and normal development to deployment and delivery of your software to the user.

Integrating googletest in CMake-based projects and Jenkins

In my – admittedly limited – perception unit testing in C++ projects does not seem as widespread as in Java or the dynamic languages like Ruby or Python. Therefore I would like to show how easy it can be to integrate unit testing in a CMake-based project and a continuous integration (CI) server. I will briefly cover why we picked googletest, adding unit testing to the build process and publishing the results.

Why we chose googletest

There are a plethora of unit testing frameworks for C++ making it difficult to choose the right one for your needs. Here are our reasons for googletest:

  • Easy publishing of result because of JUnit-compatible XML output. Many other frameworks need either a Jenkins-plugin or a XSLT-script to make that work.
  • Moderate compiler requirements and cross-platform support. This rules out xUnit++ and to a certain degree boost.test because they need quite modern compilers.
  • Easy to use and integrate. Since our projects use CMake as a build system googletest really shines here. CppUnit fails because of its verbose syntax and manual test registration.
  • No external dependencies. It is recommended to put googletest into your source tree and build it together with your project. This kind of self-containment is really what we love. With many of the other frameworks it is not as easy, CxxTest even requiring a Perl interpreter.

Integrating googletest into CMake project

  1. Putting googletest into your source tree
  2. Adding googletest to your toplevel CMakeLists.txt to build it as part of your project: 
    add_subdirectory(gtest-1.7.0)
  3. Adding the directory with your (future) tests to your toplevel CMakeLists.txt: 
    add_subdirectory(test)
  4. Creating a CMakeLists.txt for the test executables: 
    include_directories(${gtest_SOURCE_DIR}/include)
set(test_sources
# files containing the actual tests
)
add_executable(sample_tests ${test_sources})
target_link_libraries(sample_tests gtest_main)
  5. Implementing the actual tests like so (@see examples): 
    #include "gtest/gtest.h"

TEST(SampleTest, AssertionTrue) {
    ASSERT_EQ(1, 1);
}

Integrating test execution and result publishing in Jenkins

  1. Additional build step with shell execution containing something like: 
    cd build_dir && test/sample_tests --gtest_output="xml:testresults.xml"
  2. Activate “Publish JUnit test results” post-build action.

Conclusion

The setup of a unit testing environment for a C++ project is easier than many developers think. Using CMake, googletest and Jenkins makes it very similar to unit testing in Java projects.

How to use partial mocks in real life

Partial mocks are an advanced feature of modern mocking libraries like mockito. Partial mocks retain the original code of a class only stubbing the methods you specify. If you build your system largely from scratch you most likely will not need to use them. Sometimes there is no easy way around them when working with dependencies not designed for testability. Let us look at an example:

/**
 * Evil dependency we cannot change
 */
public final class CarvedInStone {

    public CarvedInStone() {
        // may do unwanted things
    }

    public int thisHasSideEffects(int i) {
        return 31337;
    }

    // many more methods
}

public class ClassUnderTest {

    public Result computeSomethingInteresting() {
        // some interesting stuff
        int intermediateResult = new CarvedInStone().thisHasSideEffects(42);
        // more interesting code
        return new Result(intermediateResult * 1337);
    }
}

We want to test the computeSomethingInteresting() method of our ClassUnderTest. Unfortunately we cannot replace CarvedInStone, because it is final and does not implement an interface containing the methods of interest. With a small refactoring and partial mocks we can still test almost the complete class:

public class ClassUnderTest {
    public int computeSomethingInteresting() {
        // some interesting stuff
        int intermediateResult = intermediateResultsFromCarvedInStone(42);
        // more interesting code
        return intermediateResult * 1337;
    }

    protected int intermediateResultsFromCarvedInStone(int input) {
        return new CarvedInStone().thisHasSideEffects(input);
    }
}

We refactored our dependency into a protected method we can use to stub out with our partial mocking to be tested like this:

public class ClassUnderTestTest {
    @Test
    public void interestingComputation() throws Exception {
        ClassUnderTest cut = spy(new ClassUnderTest());
        doReturn(1234).when(cut).intermediateResultsFromCarvedInStone(42);
        assertEquals(1649858, cut.computeSomethingInteresting());
    }
}

Caveat: Do not use the usual when-thenReturn-style:

when(cut.intermediateResultsFromCarvedInStone(42)).thenReturn(1234);

with partial mocks because the real method will get called once!

So the only untested code is a simple delegation. Measures like that refactoring and partial mocking generally serve as a first step and not the destination.

Where to go from here

To go the whole way we would encapsulate all unmockable dependencies into wrapper objects providing the functionality we need here and inject them into our ClassUnderTest. Then we can replace our wrapper(s) easily using regular mocking.

Doing all this can be a lot of work and/or risk depending on the situation so the depicted process serves as an low risk intermediate step for getting as much important code under test as possible.

Note that the wrappers themselves stay largely untestable like our protected delegating method.