Heisenbug bug
22 Feb 2016As stated in Wikipedia,
In computer programming jargon, a heisenbug is a software bug that seems to disappear or alter its behavior when one attempts to study it .
I recently came across one whilst developing a small program:
- when I tried to run this program from the console, it crashed with a segmentation fault
DEBUG - Tue Feb 16 12:39:29 2016 - creation of mesher
DEBUG - Tue Feb 16 12:39:29 2016 - mesher run
DEBUG - Tue Feb 16 12:39:29 2016 - run start reading mesh "/home/tcabel/Devel/tracesinria/Tests/Regr/SAT_HY_1.1/Result/Data_A/tmp_hydro_1.1"
INFO - Tue Feb 16 12:39:29 2016 - numTracesMesher : elem_type = 20
DEBUG - Tue Feb 16 12:39:29 2016 - mesh dimension : 2
INFO - Tue Feb 16 12:39:29 2016 - nb points = 2601 nb_cells = 2500 nb_faces_or_aretes = 5100
DEBUG - Tue Feb 16 12:39:29 2016 - vertexes and points creation
DEBUG - Tue Feb 16 12:39:29 2016 - cells creation
DEBUG - Tue Feb 16 12:39:29 2016 - mesh read finished, setting cells
Segmentation fault (core dumped)- when I tried to run the same program with the same arguments under gdb, it worked fine
DEBUG - Tue Feb 16 12:35:34 2016 - creation of mesher
DEBUG - Tue Feb 16 12:35:34 2016 - mesher run
DEBUG - Tue Feb 16 12:35:34 2016 - run start reading mesh "/home/tcabel/Devel/tracesinria/Tests/Regr/SAT_HY_1.1/Result/Data_A/tmp_hydro_1.1"
INFO - Tue Feb 16 12:35:34 2016 - numTracesMesher : elem_type = 20
DEBUG - Tue Feb 16 12:35:34 2016 - mesh dimension : 2
INFO - Tue Feb 16 12:35:34 2016 - nb points = 2601 nb_cells = 2500 nb_faces_or_aretes = 5100
DEBUG - Tue Feb 16 12:35:34 2016 - vertexes and points creation
DEBUG - Tue Feb 16 12:35:34 2016 - cells creation
DEBUG - Tue Feb 16 12:35:34 2016 - mesh read finished, setting cells
DEBUG - Tue Feb 16 12:35:34 2016 - finished setting cells
INFO - Tue Feb 16 12:35:34 2016 - Mesh read in "00:00:00.010"
DEBUG - Tue Feb 16 12:35:34 2016 - run mesher finisher
DEBUG - Tue Feb 16 12:35:34 2016 - creation of meshView
DEBUG - Tue Feb 16 12:35:34 2016 - meshView finished One way to debug this type of error is to dump a core file and use it to get the memory state from the crash. In order to get this core file, follow the below:
ulimit -c unlimited- relaunch the program which will now dump a core file when it crashes.
- relaunch gdb with this core file
gdb ./program core.XXX
In my case, it was an incorrect array index that was causing this error.
When you finish debugging, don’t forget to execute ulimit -c 0 to disable the dump of core files each time a program crashes.