• CnC-Python Find Primes Example
Skip to end of metadata
Go to start of metadata

First, we need to define the CnC graph:


The CnC graph states that oddNums is a Tag Collection with strings as the tags.
Currently, strings are the only supported tag types in CnC-Python.

Next, we define the Item Collection primes which has strings as tags and integer as its values. These types are defined in the format tagType->itemType before the name of the Item Collection.

We define the implementation language of the Step in the Step prescription as in (python compute). In CnC-Python, python is the only allowable value. In future releases we plan to expan this value to include other languages such as C, C++, Fortran, Matlab, etc.

env is a special keyword representing the environment and in this example we define the environment will put string tags into the oddNums Tag Collection and read the results from the primes Item Collection.

After defining the CnC graph, we need to run this file using the CnC-Python translator using the following command:
cnc_t FindPrimes.cnc

Running the command will generate the following directories: hj-cnc-api, sidl, java-client, py-lib, user-code, and hj-main. In short, these are what the directories represent:

Directory Name



Wrapper classes for the HJ-CnC runtime used by Babel while generating SIDL server/client code


SIDL files used by the program. This includes the SIDL file for the runtime wrapper classes as well as the Step and Item Collections for the current program


The java client generated from the SIDL files used by the HJ program to call into the python implementation


The generated python files that are invoked from the HJ program


This is the only directory the user should need to edit. It will contain template files for the python Steps as well as an application class to attach start and end event handlers. The even handlers are used to place values from the environment into Item Collections and read results back from Item Collections.


The generated HJ files that manages code to make native invocations into the python implementations using the Babel runtime. The user launches the CnC-Python program using a generated script that invokes the generated HJ main class.

Back to the example, once the translator completes running there should be the following files in the user-code directory:




Rename both files to userFindPrimesApp.py and userComputeStep.py. The userFindPrimesApp.py provides the onStart and onEnd functions. The function signatures are determined by detecting the environment interactions in the CnC graph. The onStart function also provides access to any command line arguments used while launching the program. The userComputeStep.py file provides the file the user needs to edit to provide the Step implementation. A Step needs to implement the createAwaitsList and compute functions. The createAwaitsList function allows the user to specify the input data dependences on Item Collections. Once these dependences have been satisfied the compute function will be invoked.

Below are simple implementations for the two python files:




Please refer to the Partition-String example to see an example of how to implement the createAwaitsList function.

Running this program with an input of 100 should produce the following output:

  • No labels