1. Debugging Support for Charm++
Rashmi Jyothi
11/19/2003
Parallel Programming Laboratory

2. Support in Charm: Overview
Ability to freeze/unfreeze the program
Set/remove breakpoints
View contents of array elements, messages in queues, readonlies, registration tables
Attach processes on specified number of processor elements to a sequential debugger during program execution
Basic record/replay functionality
11/19/2003
Parallel Programming Laboratory

3. Parallel Programming Laboratory
Debugger: Approach
Uses the CCS module in Charm
The program to be debugged is the parallel
server while the debugger is the client
Parallel Debugger
Charm++ program
ccs_set_break_point
ccs_debug_startgdb .
11/19/2003
Parallel Programming Laboratory

4. Debugger: Approach (contd)
CpdList allows to retrieve the contents of the chare table, messages in queues etc of a running program .
Ccs handler written which returns the pupped data for a particular CpdList, to the client
Lists registered to retrieve items in chare table, entry table, CmiLocalQueue, CsdSchedQueue etc
At time of initialization, pup function to be used for each of the CpdLists registered.
PUP::toText & PUP::sizerText used to return displayable strings
11/19/2003
Parallel Programming Laboratory

5. Parallel Programming Laboratory
Record Replay
This mechanism is useful to find bugs that occur due to the order in messages are processed
Program linked with –tracemode recordreplay
<srcpe env-size sequence no> written to a file for each pe when +record runtime option used
+replay reruns the program with the same message ordering sequence.
Tested for cases not using migration.
11/19/2003
Parallel Programming Laboratory

6. Parallel Programming Laboratory
Thank you
11/19/2003
Parallel Programming Laboratory