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.
Thread
A thread is a lightweight process that owns a stack and machine registers including program counter, but shares code and data with other threads within the same address space. If the underlying operating system recognizes a thread, it is known as kernel thread, otherwise it is known as user-thread. A context-switch between threads refers to suspending one thread’s execution and transferring control to another thread. Kernel threads typically have higher context switching costs than user-threads because of operating system overheads. The policy implemented by the underlying system for transferring control between threads is known as thread scheduling policy. Scheduling policy for kernel threads is determined by the operating system, and is often more inflexible than user-threads. Scheduling policy is said to be non-preemptive if a context-switch occurs only when the currently running thread willingly asks to be suspended, otherwise it is said to be preemptive. Jade threads are non-preemptive user-level threads.
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.

4.3. Jade

Every mainchare’s main is executed at startup.

4.3.1. threaded methods

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

4.3.2. readonly

class C {
    public static readonly CProxy_TheMain mainChare;
    public static int readonly aReadOnly;
}

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/

and follow the download link. Now one has to build Charm++ and Jade from source.

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.

charm/doc/jade Jade user documentation files
charm/src/langs/jade/ ANTLR parser files, Jade runtime library code
charm/java/charm/jade/ Jade java code
charm/java/bin/ Jade scripts
charm/pgms/jade/ Jade example programs and tests

After building Jade, files are installed in:

charm/include/ Jade runtime library header files
charm/lib/ Jade runtime library
charm/java/bin/ jade.jar file

4.6.2. Java packages

The way packages work in Java is as follows: There is a ROOT directory. Within the ROOT, a subdirectory is used which also gives the package name. Beneath the package directory all the .class files are stored. The ROOT directory should be placed in the java CLASSPATH.

For Jade, the ROOT is charm/java/charm/.

The Jade package name is jade, and is in charm/java/charm/jade. Within here, all the jade Java files are placed, they are compiled to .class files, and then jar’d up into the jade.jar file, which is placed in charm/java/bin for convenience.