CODEWITHSUNDEEP
shellocamlexecutable
charelf
charelf

Reputation: 3825

Ocaml execution of program not producing new output after some time

I have 3 ocaml modules, the last one of the tree does the actual computation and uses functions defined in the other 2.

The basic idea of the program is to have a port as initial state, which contains boats, and moving those boats until we reach either a winning situation or no more moves are possible. The actual code is not really a problem here. It is probably not very efficient, but finds a solution... except when it does not.

While the program takes a few seconds for complex situations, in some cases, when I add a bit more complexity, it takes forever to find a solutions.

When I execute the program like this:

$ ocamlc -o test.exe port.ml moves.ml solver.ml
$ ./test.exe > file

The resulting file is really huge, but its size stops increasing after some time.. It seems to me that after a while the program stops running but without terminating, no Stackoverflow or out of memory error is thrown. The program simply does not continue the execution. In other words, the command

$ ./test.exe > file

is still executed, but no more new lines are added to the file. If I log to the shell itself and not a file, I get the same result: no new lines keep getting added after some time.

What could this be?

The main function (that is responsible for finding a solution) uses a Depth-First-Search algorithm, and contains a lot of List operations, such as List.fold, List.map, List.iter, List.partition, List.filter. I was thinking that maybe these functions have problems dealing with huge lists of complex types at some moment, but again, no error is thrown, the execution just stops.

I explained this very vaguely, but I really don't understand the problem here. I don't know whether the problem has to do with my shell (Ubuntu subsystem on windows) running out of memory, or ocaml List functions being limited at some point... If you have any suggestions, feel free to comment

Upvotes: 0

Views: 234

Answers (1)

ivg
ivg

Reputation: 35270

To debug such cases you should use diagnostic utilities provided by your operating system and the OCaml infrastructure itself.

First of all, you shall look into the state of your process. You can use top or htop utilities if you're running a Unix machine. Otherwise, you can use the task manager.

If the process is running out of the physical memory, it could be swapped by the operating system. In that case, all memory operations will turn into hard drive reads and writes. Therefore, garbage collecting a heap stored in a hard drive will take some time. If this was the case, then you can use a memory profiler to identify the crux of the problem.

If the process is constantly running without a change in the memory footprint, then it looks like that you either hit a bug in your code, i.e., an infinite loop, or that some of your algorithms have exponential complexity, as Konstantin has mentioned in the comment. Use a debugging output or tracing to identify the location where the program stalled.

Finally, if your program is in the sleeping state, then it could be a deadlock. For example, if you're reading and writing to the same file, this can end up in a race condition. In general, if your program is multithreaded or operates multiple processes, there are lots of possibilities to induce a race condition.

Upvotes: 1

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