Debugging begins by entering a dload or
dattach command. If you use the
dload command, you must use the
drun (or perhaps
drerun if there’s a starter program) command to start the program executing. These three commands work at the process level and you can’t use them to start individual threads. (This is also true for the
dkill command.)
To advance program execution, you enter a command that causes one or more threads to execute instructions. The commands are applied to a P/T set. (P/T sets are discussed in
Chapter 2, “About Threads, Processes, and Groups” and
Chapter 13, “Using Groups, Processes, and Threads”.) Because the set doesn’t have to include all processes and threads, you can cause some processes to be executed while holding others back. You can also advance program execution by increments,
stepping the program forward, and you can define the size of the increment. For example,
dnext 3 executes the next three statements, and then pauses what you’ve been stepping.
Typically, debugging a program means that you have the program run, and then you stop it and examine its state. In this sense, a debugger can be thought of as a tool that lets you alter a program’s state in a controlled way, and debugging is the process of stopping a process to examine its state. However, the term
stop has a slightly different meaning in a multi-process, multi-threaded program. In these programs,
stopping means that the CLI holds one or more threads at a location until you enter a command that tells them to start executing again. Other threads, however, may continue executing.