Watchpoints

NextGen TotalView for HPC User Guide : PART II Debugging Tools and Tasks : Chapter 5 Setting and Managing Action Points (Breakpoints) : Watchpoints

Watchpoints

TotalView can monitor the changes that occur to memory locations with a special type of action point called a watchpoint. Watchpoints are most frequently used to find a statement in your program that is writing to inappropriate places. This can occur, for example, when processes share memory, and more than one process writes to the same location. It can also occur when your program writes off the end of an array or when your program has a dangling pointer.

Topics in this section are:

• "Creating Watchpoints"

• "Modifying Watchpoints"

• "Watching Memory"

• "Triggering Watchpoints"

• "Using Watchpoint Expressions"

• "Using Watchpoints on Different Architectures"

TotalView watchpoints are called modify watchpoints because TotalView triggers a watchpoint only when your program modifies a memory location. If a program writes a value into a location that is the same as that which is already stored, TotalView doesn’t trigger the watchpoint because the location’s value did not change.

For example, if location 0x10000 has a value of 0, and your program writes a value of 0 to this location, TotalView doesn’t trigger the watchpoint, even though your program wrote data to the memory location. See "Triggering Watchpoints" for more details on when watchpoints trigger.

NOTE >> This discussion describes how to create and modify watchpoints using the UI. To set a watchpoint with the CLI see "Watchpoints".