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

NOTE: WDB-GUI provides graphical representation of the Arena Profile. For more
information see“Arena Profiling Using WDB GUI” (page 84).
Leak Profiling
The leak profile feature in WDB conservatively identifies the blocks of memory that are
leaked in an application, and displays the stack trace that shows when the block was
allocated. All the leaks detected by WDB are definite physical leaks.
WDB uses a garbage collection algorithm to identify the blocks that are leaked. It identifies
the root-set of memory that are possible pointers to the heap. The initial root-set includes
the shared library data, the program/thread stacks, the registers, the thread specific
private data, the mmap regions, and the shared memory regions. The initial root-set
includes all data except the heap blocks.
The debugger considers suitably aligned words in the root-set as possible pointers to the
heap. The debugger performs a reachability analysis based on the root-set, and
determines the memory blocks that are reachable through possible pointers from the
root-set. The heap blocks that are not reachable through possible pointers from the root-set
are reported as leaks.
WDB is conservative in detecting the memory leaks. The memory leaks can be masked
if a datum in the root-set inadvertently holds a possible pointer to a heap block.
Table 7 lists the basic commands for leak profiling in WDB.
Table 7 Commands for Leak Profiling
DescriptionCommand
Controls WDB memory leak checkingset heap-check leaks <on/off>
Displays a leak report. It also lists information such
as the leaks, size of blocks, and number of instances.
info leaks
Writes the complete report output containing the leak
summary as well as the details to the specified file.
info leaks <filename>
Displays detailed information on the specified leak
including the allocation call stack
info leak <leaknumber>
Specifies the minimum leak size for stack trace
collection. The debugger continues to report leaks
that are smaller than <num> bytes, but it does not
provide the stack trace for the same. By default, num
is set to 0.
This command also enables you to reduce
performance degradation. See “Settings to Manage
Performance Degradation” (page 58)
set heap-check min-leak-size <num>
To view the leak profile, complete the following steps:
Memory-Debugging Features of WDB 27