3.1 Record Replay

The Record Replay feature is independant of the charmdebug application. It is a mechanism used to detect bugs that happen only once in a while depending on the order in which messages are processed. The program in consideration is first run in a record mode which produces a trace. When the program is run in replay mode it uses a previous trace got from a record run to ensure that messages are processed in the same order as the recorded run. The idea is to make use of a message-sequence number and a theorem says that the serial numbers will be the same if the messages are processed in the same order. [#!rashmithesis!#]

-tracemode recordreplay

To enable the required tracing for record and replay, a CHARM++ program is linked with the option ``-tracemode recordreplay'' and run with the ``+record'' option, which records messages in order in a file for each processor. The same execution order can be replayed using the ``+replay'' runtime option; which can be used at the same time as the other debugging tools in CHARM++.

Note! If your CHARM++ is built with CMK_OPTIMIZE on, all tracing will be disabled. So, use an unoptimized CHARM++ to do your debugging.