3. Charj

3.1. Introduction

Charj is a new programming language which incorporates syntax, semantic analysis, and optimization targeted at HPC code with its associated compiler.


52 Charj

With Charj, we aim to allow programmers to achieve the performance associated with carefully written, hand-optimized Charm++ applications, but with much less time and effort. If effect, we hope to combine the productivity that programmers experience when writing relatively simple, naive applications while enjoying performance that would normally require a much greater investment of time, effort, and expertise.

Charj compiler takes Charj codes as input and produces Charm++ interface (.ci) and C++ code (.C and .h) as an output.


53 Compilation process for Charj application

To make use of Charj;

  1. Build Charm++, then build Charj
  2. Write your Charj program
  3. Compile and run it!

3.2. Building, Compiling and Running

To write a program and compile with Charj:

  1. Go to: charm/src/langs/charj and “make” (Assuming Charm++ is already installed)

  2. Write your Charj code in a file with .cj extension. (SampleProgram.cj)

  3. Execute charjc script on the file SampleProgram.cj:
    $ charm/src/langs/charj/bin/charjc SampleProgram.cj
    For other compiler options, use help:
    $ charm/src/langs/bin/charjc -h
  4. After execution of charjc script, a folder named “SampleProgram.cj.gen” will be created in the directory of SampleProgram.cj. This folder will contain the emitted Charm++ files; SampleProgram.ci, SampleProgram.h SampleProgram.cc .

    * Example Charj programs can be found at charm/src/langs/charj/tests

3.3. Writing a Charj Program

3.3.1. General structure of a Charj program;

readonly Main@ mainProxy;   //readonly proxy type
readonly int value;         //readonly variable

public mainchare Main {
    public entry Main(CkArgMsg[~]@ m){...}  //Main constructor
    public entry void done(){...}               //entry method
    private int localMethod(int value){...}     //non-entry method
public chare_array [1d] SampleChareArray1d{...} //1d chare array
public chare_array [2d] SampleChareArray2d{...} //2d chare array

public class SampleObject{...}                  //sample class

public chare SampleChare {
    public entry SampleChare(){...}             //constructor
    public entry SampleChare(boolean flag){...} //constructor 2
    public entry void test(SampleObject obj){...}   //entry method

3.3.2. Chare creation and method calls:

SampleChare@ sp = new SampleChare@();
SampleChareArray1d@ sp1 = new SampleChareArray1d@(x_dim);
SampleChareArray2d@ sp2 = new SampleChareArray2d@(x_dim, y_dim);
sp2@test(int value);

3.3.3. Arrays:

Array<int> foo = new Array<int>([10]);  //1d array of integers of size 10
foo[i] = ...;
Array<double, 2> foo2 = new Array<double, 2>([s1, s2]); //2d array of size s1, s2
foo2[i, j] = ...;

3.3.4. SDAG statements:

These statements can be used inside of any entry method.

when receiveMsg(SampleObject obj) {...}

overlap{    //two overlapping when statements
    when receiveMsg1[i](int iter, SampleObject obj) {...}
    when receiveMsg2[i](int iter, int value) {...}

3.3.5. Extern statements:

If you want to use any other C++ function/feature, you have to define it as extern.

extern atoi;            //define in the beginning of the file
int x = atoi(y);        //use anywhere

3.3.6. Reduction statements:

Currently only plain reductions are supported.

contribute(CkCallback(CkReductionTarget(Main, done), mainProxy));

3.3.7. Some Charm++ statements that can be used in a Charj program: