.. _readme-debugging: ========================= Debugging Chapel Programs ========================= 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. .. contents:: -------------- 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 ``-g`` flag. When using almost any launcher, you can launch ``gdb`` by setting the environment variable ``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 launchers:: amudprun aprun gasnetrun_ibv gasnetrun_mpi gasnetrun_ofi gasnetrun_psm mpirun4ofi pbs-aprun smp The default terminal emulator program is ``xterm``, but by setting the environment variable ``CHPL_COMM_DBG_TERM=urxvt`` you can force use of ``urxvt`` instead. Whichever terminal emulator is used must be in your ``PATH`` 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 ``gdb``. 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 ``x`` would be code generated as ``x_chpl``. This munging can be controlled using the ``--[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 using ``p`` *name*\ ``_chpl`` (or ``p`` *name*\ ``_chpl`` in cases where the compiler has further renamed the variable). If the ``--no-munge-user-idents`` flag is used, ``p`` *name* or ``p`` *name*\ ```` 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. ------------------------ Flags for Tracking Tasks ------------------------ 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 ```` 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 ``CHPL_TASKS=fifo``. -t, --taskreport When ```` 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 ``CHPL_TASKS=fifo``. ------------------------------------------- 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 :chpl:mod:`Memory`. A brief synopsis of these configuration constants is as follows: --memTrack turn on memory tracking and enable reporting --memStats call ``printMemAllocStats()`` on normal termination --memLeaksByType call ``printMemAllocsByType()`` on normal termination --memLeaks call ``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