1 Introduction

The primary goal of the parallel debugger is to provide an integrated debugging environment which allows the programmer to examine the changing state of the parallel program during the course of its execution.

The CHARM++ debugging system has a number of useful features for CHARM++ programmers. The system includes a Java GUI client program which runs on the programmer's desktop, and a CHARM++ parallel program which acts as a server. The client and server need not be on the same machine, and communicate over the network using a secure protocol described in http://charm.cs.uiuc.edu/manuals/html/converse/5_CONVERSE_Client_Server_In.html

The system provides the following features:

• Provides a means to easily access and view the major programmer visible entities, including array elements and messages in queues, across the parallel machine during program execution. Objects and messages are extracted as raw data, and interpreted by the debugger, as explained in .

• Provides an interface to set and remove breakpoints on remote entry points, which capture the major programmer-visible control flows in a CHARM++ program.

• Provides the ability to freeze and unfreeze the execution of selected processors of the parallel program, which allows a consistent snapshot by preventing things from changing as they are examined.

• Provides a way to attach a sequential debugger to a specific subset of processes of the parallel program during execution, which keeps a manageable number of sequential debugger windows open. Currently these windows are opened independently of the GUI interface, while in the future they will be transformed into an integrated view.

The debugging client provides these features via extensive support built into the CHARM++ runtime.