Debugging Chapel Programs¶
This document discusses support for debugging your Chapel program and a set of experimental settings to enable task monitoring and memory tracking.
Running in gdb¶
The compiler-generated executable has a
--gdb flag that can be used
to launch the program within a
gdb session. For best results, make
sure that your program has been compiled using the chpl compiler’s
When using almost any launcher, you can launch
gdb by setting the
CHPL_COMM_USE_GDB when running the program.
This will open up a separate terminal emulator window for each locale,
each running the debugger on that locale’s program instance. On the Mac
OS X (darwin) platform, you can launch
lldb instead, by setting the
CHPL_COMM_USE_LLDB environment variable. This works in all of these
amudprun aprun gasnetrun_ibv gasnetrun_mpi gasnetrun_ofi mpirun4ofi pbs-aprun smp
The default terminal emulator program is
but by setting the environment variable
you can force use of
Whichever terminal emulator is used must be in your
on the compute node or an error will result.
Note that it is the user’s responsibility to make sure things are set up
so the terminal emulator run in the target environment can open its
display window in the launch environment.
The utility of this feature depends greatly on your familiarity with
the Chapel generated code. However, if your program is crashing or
running into a runtime error, you can often determine where that is
taking place by looking at a stack trace within
When debugging Chapel, it is useful to know that in generating its code,
the Chapel compiler renames user identifiers. By default, the Chapel
compiler munges all user identifiers, such that a variable named
would be code generated as
x_chpl. This munging can be controlled
--[no-]munge-user-idents flag (see the
chpl man page
for more information). In some cases, additional munging may be
required or applied that cannot be turned off.
The net effect of this is that Chapel variables can often be inspected
_chpl<TAB> in cases
where the compiler has further renamed the variable). If the
--no-munge-user-idents flag is used,
p name or
<TAB> should work in most cases.
Over time, we plan to improve our ability to debug the generated C code for a Chapel program. If you find yourself debugging the generated code a lot and need help or have requests for better support, please let us know so that we can prioritize accordingly.
Tracking and Reporting on Tasks¶
For certain tasking layers, Chapel supports an experimental
capability for tracking the status of tasks, primarily designed for
use in a single-locale execution. To enable this capability, your
program must be compiled with the
The feature itself is enabled at execution time by setting the boolean
CHPL_RT_ENABLE_TASK_REPORTING to any of the
values “1”, “yes”, or “true”. If this is done, then when
is entered while a program is executing, a list of pending and executing
tasks will be printed to the console, giving an indication of which
tasks are at which source locations. This is only supported with
Note that task tracking adds a fair amount of runtime overhead to task-parallel programs.
Configuration Constants for Tracking Memory¶
Chapel supports a number of configuration constants related to dynamic memory allocation for the compiler-generated executable, currently designed for use primarily by the development team to track memory usage in tests. Please note that our generated code currently contains memory leaks, so you should not be surprised if your program requires more memory than it seems it should.
For full information on these configuration constants consult
A brief synopsis of these configuration constants is as follows:
turn on memory tracking and enable reporting
printMemAllocStats()on normal termination
printMemAllocsByType()on normal termination
printMemAllocs()on normal termination
set maximum level of allocatable memory
set minimum threshold for memory tracking
file to contain all memory reporting
if set, append final stats and leaks-by-type here