Lab 1 - Introduction

Lab tasks

The tasks for today are:

• General information about labs and grading.

• Try a remote method invocation:

  • Example of Java RMI.
    • Download the example code.
    • Compile and run the example program.
  • Make a remote call to another computer.
  • Just try it - how it works will be explained in next labs.

• Try measuring the time it takes to do a remote call:

  • This will help you with the first task.
  • Run a program that makes remote calls and records the times.
  • View the data in a Python notebook.

• Check out a few code snippets:

  • We will use Java, C++, Python.
  • Might be useful when solving the tasks.

First remote method invocation

• Download and unzip the source codes.
• Navigate into directory First-Example.
• Run bash make.sh to comile the code.
• Run bash run-registry.sh an keep it running.
• Run bash run-server.sh localhost an keep it running.
• Run bash run-client.sh localhost.
• Observe the messages printed from both the client and server programs.

Remote method invocation over a network

• Log in to another computer in the labs
  • Hostnames are u2-X.ms.mff.cuni.cz, where X is a number between 0 an 25
  • You can also use computers in Rotunda u-plX.ms.mff.cuni.cz
• On that computer, run bash run-registry.sh an keep it running.
• Also on that computer, run bash run-server.sh HOSTNAME an keep it running.
• On the prevous computer, run bash run-client.sh HOSTNAME.
• Observe that the invocation happened over the network.

Measuring remote method invocation

In this part, you will run a program that makes multiple remote calls with increasingly large arguments. We should expect the call to take more time when larger arguments are used. Also, calls made over the network will be slower than on just localhost. We will use a Jupyter notebook to plot the data in a chart.

• Navigate into directory Measure-Remote-Call.
• Run bash make.sh to comile the code.
• Run bash run-registry.sh an keep it running.
• Run bash run-server.sh localhost an keep it running.
• Run bash run-client.sh localhost 10000 100 > data.csv.
  • If it takes too long, use lower size.
  • The first number is the size by which the size of the argument to the call increases every sample.
  • The second number is the number of samples.
• Check that data.csv contains measurement results.
• Run jupyter notebook to start a jupyter notebook server.
  • You may need to install python packages beforehand. On lab computers, use pip install --user bokeh
• Open the Jupyter notebook measurement.ipynb.
• Execute the code in the notebook
• Observe the chart showing the results.

Code examples

In these labs, you will have to write programs in Java an C++. Basic knowledge of these languages is sufficient, but to make it easier, here are some small tasks that may remind you of how a few particular features work in those languages. You may encounter similar problems when solving the tasks in the following labs.

Java reminder - equality

Identify the problem in the following code and fix it.

    public static void main(String[] args){
        if(args.length < 1){
            System.out.printf("No command given%n");
            return;
        }
        if(command == "generate")
            generate();
        else if(command == "analyze")
            generate();
        else
            System.out.printf("Unknown command %s%n", command);
    }

Java reminder - synchronization

Fix the following code, so that it works correctly when the methods increment and read are called form different threads.

class Data {
    private int counter;
    public void inc(){
        ++counter;
    }
    public int read(){
        return counter;
    }
}

C++ reminder - object lifetime

Identify the problem in the following code and fix it.

  class Data{
    string value;
  }
  class Component{
    Data* data;
    Component(Data* data): data(data){}
  }
  shared_ptr<Component> create_component(){
    Data data;
    return make_shared<Component>(&data);
  }

C++ reminder - map comparison

Implement the following function which checks whether two map collection contain the same elements (the same key-value pairs). (Hint: it might be easier than you expect).

  bool check_equal(
    std::map<string, string> mapA,
    std::map<string, string> mapB) {

  }

C++ reminder - polymorphism

Given the class hierarchy, implement the following function which prints the value from every object it receives.

(Hint: Either add virtual methods to the classes, or check the type using dynamic_cast.

  class Base {}
  class A: public Base { public: int value; }
  class B: public Base { public: string value; }
  class C: public Base { public: bool value; }

  void print(Base& object){

  }