Virtual Programming Laboratory
Frequently Asked Questions

http://www.npac.syr.edu/projects/VPL/

Question: My problem is that the FILE CONTENTS get truncated. What I do is the following:

1) I add some lines at the end of the file

2) save the file and close the editor window.

Then, if I edit the file again (or view it from the directory manager) the lines I just added are missing. In any case I renamed the file and the problem persists.

Answer: VPL text editor's original 8KB limit was increased, and it currently supports files of up to 64KB. Larger files are truncated. Be aware!


Question: I try to access VPL, but nothing shows up in the screen.

Answer: You should use Netscape 3.0 or some other browser that supports both Java and JavaScript. Otherwise, all or some things will not show up.


Question: Although the Lab window is closed, VPL says it is open, and rejects to open it. Sometime a similar situation happens for closed windows.

Answer: You should always use the supplied "open/close" buttons in order to open or close VPL windows. Otherwise, the state of the window may stay as locked and appears to be in an inconsistent state.


Question: I have just noticed that the problem with some files not being correctly displayed int he File Manager's "Current File View" is connected to "<" and ">" characters. E.g., lines like #include <xyz.h> have problems while lines like #include "xyz.h" are fine. Apart from that, the first line in my program that has a "<" is the first line to have a problem.

Answer: This problem will be fixed in future releases.


Question: What is the purpose of "style" directory.

Answer: You will find in the 'style' directory the file 'programming-tips'. It contains very valuable programming tips written by the man who co-authored the C bible.


Question: I just deleted a file from within VPL, and now the File Manager does not show ANY subdirectories in my account. I hope VPL hasn't deleted all my files :-)

Answer: A bug in the program has caused the files being not shown in the directory manager, although they are actually there. VPL does whatever you ask for. If you have deleted a file, you may try going into the cache of your browser (usually in ~/.netscape/cache) and see if a copy of it still exists in the cache.


Question:  I am getting "Error: Socket not connected" error.

Answer:  The server is probably dead, let us know, we will restart it.


Question: I am getting the following error when I try to use VPL:

Error: HTTPd/CGI: could not fork new process, errno is 35.

Answer: Sometimes run-away processes accumulate and make the system unusable. Let us know, so that we can clean up the system.


Question: It seems like running jobs using VPL takes more time than running jobs directly from my UNIX account.

Answer: Because the VPL copies the executable files to /scratch first in accordance with the system use policy, before starting the execution. You should, too, observe the same system policy :

/scratch is available for use for TEMPORARY files. Use it instead of /tmp and /var/tmp, and when doing IO intensive work.

WARNING: If you run an MPI based job, you MUST make that code local to each kestrel by copying it to the /scratch of each kestrel and run it there. If you VIOLATE this policy, YOU LOSE ACCESS TO THE KESTRELS.


Question: I am submitting jobs using VPL, yet getting the results takes much longer time than it used to take.

Answer: The problem apparently was too many processes got started but never terminated or it didn't terminate successfully so they just got hung. Those processes got killed and the lab got restarted so now it is OK.

Make sure you use the correct functions. Also make sure your job terminates successfully. First, check your code (the non-MPI part) to see if it is in a correct order, for example, no infinite loops, etc. You always need to terminate you MPI with MPI_Finalize() ...


Question: I have problems with the text editor. When I compile HPF programs it complains about extra characters at the end of each line in the source program although they are not part of my program.

Answer: The VPL editor is really not an editor in the class of emacs or vi. So when you edit a file and use for example the control commands of emacs to remove/add things, etc. after you save it you will get the file you want and you can view/print with no problem. But, when you did the "save" there was more than just the text that got saved; the editor will also stick a control-M "^M" at the end of every line in the file. Of course, when you compile you will get those weird error messages complaining about those control characters. Fortunately, they don't seem to have any effect on the object file so the program will run ok unless you have some other errors in it. So, the point is when you do the editing you will get more than what you asked for, unseen control characters, and the only way at the moment of avoiding this is to do the boring stuff by editing things off-line and doing cut and paste. The editor has some resemblance with the "script" command which makes a typescript of term session. After exiting the file will have "^M" all over it.


Question: I cannot remove or edit some of the files in my directories. For example, I cannot do anything with the files in the directories that contains program examples.

Answer: These files and examples are not physically present at each user's account but linked to one physical set that is not accessed by the users. So, before editing and saving those examples, FIRST copy them to different files and edit or do whatever you would like to do with those new files.


Question: Where can I find more examples on MPI?

Answer: You could check the Cornell Theory Center's MPI tutorials and lab exercises at http://www.tc.cornell.edu/Edu/Tutor/MPI/.


Question: What is the difference between fixed and free form programs?

Answer: Fixed form programs dictates certain constraints found on the formatting of older Fortran IV style. The first 6 columns are reserved for special use, programs start from the 7th column, and expand up to 72th column. Free form programs follow the formatting of Fortran 90 programs, basically no restrictions on placement of program.


For problems or more help, contact to dincer@npac.syr.edu.