Category Archives: C++

cpp, c++

RxCpp 2

RxCpp 2 and API

The last article on rxcpp was based on a now obsolete version of RxCpp. The key contributor to the library, Kirk Shoop, has kindly provided a rewrite based on the newer, 2.0 API of the library: see the pull request, upon which this article is based.

Since the first article, the project has been enriched with somewhat more readable GIVEN/WHEN/THEN-style tests using Catch [1. i.e. create.cpp].

Still Ticking: Scheduler and Coordination in RxCpp 2

The previous articles give examples of managing periodic events, such as ticker ticks and measurements in c++. The following example creates an event loop that will be used for coordinated output of various events to the console:

auto scheduler = rxcpp::schedulers::make_same_worker(

auto coordination = rxcpp::identity_one_worker(scheduler);

One such sequence of events is some kind of measurement [2. Observe the convergence of the API towards the C# version.]

auto measure = rxcpp::observable<>::interval(
        // when to start + std::chrono::milliseconds(250),
        // measurement frequency
    // take Hz values instead of a counter
    .map([&FM](int) { return FM.Hz(); });

auto measure_subscription = measure
    .subscribe([](int val) {
        std::cout << val << std::endl;

Why didn’t it tick?

If this code were the end of the main program, there wouldn’t be any observable ticks, as all the objects would be destroyed before the first scheduled event. To see the code in action, we shall wait for some condition that will change when we’re done. This step is not necessary if there’s a GUI toolkit event loop that keeps objects alive, but it has to be simulated for a console example.

To demonstrate the subscription change and wait for some time, we’ll wait twice for an atomic variable to become zero:

std::atomic<long> pending(2);


// after all subscriptions defined
while (pending) {
    sleep(1000); // wait for ticker and measure to finish

Tick and Stop

The other ticker will have another period, will only tick 10 times, and then decrement the pending counter:

auto ticker = rxcpp::observable<>::interval( + std::chrono::milliseconds(500),

    .subscribe([](int val) {
        std::cout << "tick " << val << std::endl;
        --pending; // take completed the ticker

Now, we can schedule the termination of the measurement (decrement pending) subscription halfway through the 10-tick run. This scheduling is done on the same scheduler that is running all the subscriptions:

scheduler.create_worker().schedule( + std::chrono::seconds(2), 
    [&](const rxcpp::schedulers::schedulable&) {
        std::cout << "Canceling measurement ..." << std::endl;
        measure_subscription.unsubscribe(); // cancel measurement
        --pending; // signal measurement canceled

The result:

tick 1
tick 2
tick 3
Canceling measurement ...
tick 4
tick 5
tick 6
tick 7
tick 8
tick 9
tick 10

Thanks, Kirk & other library contributors!

Code @ github

Next: deterministic testing of concurrent behavior

Presenting at TU-Munich: testing on c++ projects, Thursday, March 26, 2015 7:00 PM

Expecting Thank you to all for a superb heated debate! next week

“no excuses for not testing on c++ projects”

Thursday, March 26, 2015
7:00 PM


If only all test were comprehensible…

SCENARIO("acquiring wisdom") {

  GIVEN("an oracle") { 
    oracle gus;
    WHEN("I ask it to speak") {
      auto answer = gus.speak();

      THEN("wisdom is apparent") {
        CHECK( answer != "bla" );
[1. Catch]

→ The code can be found @github, including the presentation slides.

ris – a lightweight cross-platform resource compiler for c++ projects

Why a resource compiler in the 21st century?

Starting a c++ project that will potentially need static string resources (i.e. Lua scripts) makes one search for an easy way to embed large strings in an executable. There are many ways of including static resources, but there seems to be no simple but robust, platform-independent way [1.]. For fast prototyping and one-shot projects, I’d like to have lightweight, minimum-configuration and install solution to the problem of embedding binary resources without having to use a large framework.

Premake, my favourite light-weight meta-build system contains a number of Lua scripts in its binary. These are embedded using a Lua script into a simple array of C-string constants. This is the simplicity that in my view should be strived for. ris is an attempt to do something similar for general c++ projects with a possibility of embedding binary blobs.

ris – cross-platform resource compiler for c++

The project (ris@github) is in its infancy, but seems already to be usable. Here’s a preview:

Defining and compiling resources

ris <path_to>/<resources>.json

with an input file as this self-explaining one:

    "namespace" : "test",
    "header" : "acceptance_test/resource.h",
    "source" : "acceptance_test/resource.cpp",
    "resources" : [
            "name" : "string_test",
            "source_type" : "string",
            "source" : "plain text"
            "name" : "binary_file_test",
            "source_type" : "file",
            "source" : "test.bin"

will generate two c++11 files to include in your project, enabling easy resource retrieval:

std::string res = test::Resource::string_test();


std::string res = test::Resource::Get("string_test");

Update 30.07.2015: now resources can be defined more concisely in YAML. A minimal resource definition in YAML looks like the following:

header: "res.h"
source: "res.cpp"

    compression: "LZ4F"
    name: "some_text"
    source: "some text"
    source_type: "string"

Enumerating the resources

Resource keys in the compiled resource can be enumerated passing a callable to GetKeys:

std::vector<std::string> keys;
test::Resource::GetKeys([&keys](char const* key){


Using an optional compression library bundle, adding a compression property to a resource description enables transparent (de)compression:

"compression" : "LZ4HC"


updated 24.11.2014:
ris now uses text resources generated and bootstrapped by its own early version. The goal is to make The code generator is customizable. The default template can be seen in template.json, and the generated header in template.h. The generation sequence can be seen in ris.cpp.

Using the second parameter to ris, it’s possible to override strings in the generator template. See an example below.


updated 27.11.2014:
One such customization is available in template_cpp03.json, where the C++11 constructs are replaced with generateable C++03 constructs.

To generate the resources using the C++03 template:

ris my_template.json template_cpp03.json

Why C++?

Such code generator as ris could most probably be developed more rapidly using any other programming language with a huge framework and a ton of libraries behind them. My personal preference for certain kinds of small projects lies in the area of self-contained single-binary/single-file executables or libraries, such as Lua. Lua is the primary motivation for this project, as it is itself a compact library for building flexible and extensible prototypes and tools. ris can act as a bootstrapping component to embed resources for building specialized shell-scripting replacements, i.e. for massive scripted file operations.


There is a number of paths this project can take from here. Features, such as robustness, performance or flexibility could all be addressed, but most probably ris will be shaped by its usage or absence of such.