Debugging Dynamic Memory Usage Errors Using HP WDB (5900-1474; WDB 6.2; January 2011)

Monitoring Changes in Data Segment Space Allocation (High Water Mark Feature)
The high water mark feature records the number of times the break value changes which
is the number of times the heap grows.
The high water mark feature monitors changes in the program break value. This value
points to the end of the heap (which is also the end of the data segment). When memory
is allocated using malloc() in excess of the available heap memory, the brk() call
extends the heap. This changes the break value. Most implementations of malloc()
do not decrease the heap size when the memory is freed. The break value is indicative
of the memory consumption by the program.
Table 10 lists the commands that support the high water mark feature.
Table 10 Commands Supporting High Water-Mark Feature
DescriptionCommand
Displays the number of times that the break value
has been changed for the current run at the instant,
the command is issued
info heap high-mem
Stops when break value has moved the specified
number, <X_number>, of times
set heap-check high-mem-count
<X_number>
NOTE: This feature assumes that an application has a deterministic memory allocation
pattern from one run to another.
The info heap high-mem command displays the maximum number of times the break
value changes for a given run. The set heap-check high-mem-count <X_number>
stops program execution when the break value moves a specified number <X_number>
of times, and transfers execution control to the user. Both these commands display the
size and call site of the last memory allocation that extended the high water mark.
This feature also enables you to analyze the memory-usage in an application and check
if the memory-usage is critical or close to triggering an out-of-memory error.Example 10
(page 43) illustrates the high water mark feature.
42