# 4. Jade Language¶

## 4.1. Introduction¶

This manual describes Jade, which is a parallel programming language developed over Charm++ and Java. Charm++ is a C++-based parallel programming library developed by Prof. L. V. Kalé and his students over the last 10 years at University of Illinois.

We first describe our philosophy behind this work (why we do what we do). Later we give a brief introduction to Charm++ and rationale for Jade. We describe Jade in detail. Appendices contain the details of installing Jade, building and running Jade programs.

### 4.1.2. Terminology¶

Module
A module refers to a named container which is the top-level construct in a program.
Object
An object is just a blob of memory on which certain computations can be performed. The memory is referred to as an object’s state, and the set of computations that can be performed on the object is called the interface of the object.

## 4.2. Charm++¶

Charm++ is an object-oriented parallel programming library for C++. It differs from traditional message passing programming libraries (such as MPI) in that Charm++ is “message-driven”. Message-driven parallel programs do not block the processor waiting for a message to be received. Instead, each message carries with itself a computation that the processor performs on arrival of that message. The underlying runtime system of Charm++ is called Converse, which implements a “scheduler” that chooses which message to schedule next (message-scheduling in Charm++ involves locating the object for which the message is intended, and executing the computation specified in the incoming message on that object). A parallel object in Charm++ is a C++ object on which a certain computations can be asked to performed from remote processors.

Charm++ programs exhibit latency tolerance since the scheduler always picks up the next available message rather than waiting for a particular message to arrive. They also tend to be modular, because of their object-based nature. Most importantly, Charm++ programs can be dynamically load balanced, because the messages are directed at objects and not at processors; thus allowing the runtime system to migrate the objects from heavily loaded processors to lightly loaded processors. It is this feature of Charm++ that we utilize for Jade.

Since many CSE applications are originally written using MPI, one would have to do a complete rewrite if they were to be converted to Charm++ to take advantage of dynamic load balancing. This is indeed impractical. However, Converse - the runtime system of Charm++ - came to our rescue here, since it supports interoperability between different parallel programming paradigms such as parallel objects and threads. Using this feature, we developed Jade, an implementation of a significant subset of MPI-1.1 standard over Charm++. Jade is described in the next section.

Every mainchare’s main is executed at startup.

### 4.3.1. threaded methods¶

class C {
public threaded void start(CProxy_CacheGroup cg) { ... }
}

class C {
public static readonly CProxy_TheMain mainChare;
}

The readonly variable can be accessed as C.aReadOnly.

Must be initialized in the main of a mainchare. Value at the end of main is propagated to all processors. Then execution begins.

### 4.3.3. msa¶

arr1.enroll();
int a = arr1[10]; // get
arr1[10] = 122; // set
arr1[10] += 2;  // accumulate
arr1.sync();    // sync

## 4.4. Installing Jade¶

Jade is included in the source distribution of Charm++. To get the latest sources from PPL, visit: http://charm.cs.uiuc.edu/

The build script for Charm++ is called build. The syntax for this script is:

$build <target> <version> <opts> For building Jade(which also includes building Charm++ and other libraries needed by Jade), specify <target> to be jade. And <opts> are command line options passed to the charmc compile script. Common compile time options such as -g, -O, -Ipath, -Lpath, -llib are accepted. To build a debugging version of Jade, use the option: -g. To build a production version of Jade, use the options: -O -DCMK_OPTIMIZE=1. <version> depends on the machine, operating system, and the underlying communication library one wants to use for running Jade programs. See the charm/README file for details on picking the proper version. Following is an example of how to build Jade under linux and ethernet environment, with debugging info produced:$ build jade netlrts-linux-x86_64 -g

## 4.5. Compiling and Running Jade Programs¶

### 4.5.1. Compiling Jade Programs¶

Charm++ provides a cross-platform compile-and-link script called charmc to compile C, C++, Fortran, Charm++ and Jade programs. This script resides in the bin subdirectory in the Charm++ installation directory. The main purpose of this script is to deal with the differences of various compiler names and command-line options across various machines on which Charm++ runs.

In spite of the platform-neutral syntax of charmc, one may have to specify some platform-specific options for compiling and building Jade codes. Fortunately, if charmc does not recognize any particular options on its command line, it promptly passes it to all the individual compilers and linkers it invokes to compile the program.

You can use charmc to build your Jade program the same way as other compilers like cc. To build an Jade program, the command line option -language jade should be specified. All the command line flags that you would use for other compilers can be used with charmc the same way. For example:

$charmc -language jade -c pgm.java -O3$ charmc -language jade -o pgm pgm.o -lm -O3

### 4.5.2. Running¶

The Charm++ distribution contains a script called charmrun that makes the job of running Jade programs portable and easier across all parallel machines supported by Charm++. When compiling a Jade program, charmc copies charmrun to the directory where the Jade program is built. charmrun takes a command line parameter specifying the number of processors to run on, and the name of the program followed by Jade options (such as TBD) and the program arguments. A typical invocation of Jade program pgm with charmrun is:

\$ charmrun pgm +p16 +vp32 +tcharm_stacksize 3276800

Here, the Jade program pgm is run on 16 physical processors with 32 chunks (which will be mapped 2 per processor initially), where each user-level thread associated with a chunk has the stack size of 3,276,800 bytes.

## 4.6. Jade Developer documentation¶

### 4.6.1. Files¶

Jade source files are spread out across several directories of the Charm++ CVS tree.