This document discusses support for debugging your Chapel program and a set of experimental flags and configuration constants to enable task monitoring and memory tracking.
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 gasnetrun_psm 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.
For certain tasking layers, Chapel supports a few experimental
capabilities 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
--task-tracking flag. These flags
add a fair amount of runtime overhead to task-parallel programs. The
flags are as follows:
-b, --blockreport When
<CTRL-C>is entered during a program executing under this flag, it will display a list of where tasks are blocked on a synchronization variable. Running with this flag will also cause the executable to attempt to automatically detect deadlock for single-locale executions. This is only supported with
-t, --taskreport When
<CTRL-C>is entered during a program executing under this flag, 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
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:
--memTrack turn on memory tracking and enable reporting --memStats call
printMemAllocStats()on normal termination
printMemAllocsByType()on normal termination
printMemAllocs()on normal termination
--memMax=int set maximum level of allocatable memory --memThreshold=int set minimum threshold for memory tracking --memLog=string file to contain all memory reporting --memLeaksLog=string if set, append final stats and leaks-by-type here