PC² Version 8.2 FAQ and Troubleshooting Guide

This page lists some of the common problems which users have reported encountering while trying to set up and use PC². It explains some reasons why the problems might occur, and provides suggestions for trying to eliminate them.

Click here to see the PC² Version 7.6 FAQ

• Question: Can you describe the fields for Edit Language? Can you provide samples?

• Answer: Below are descriptions of the fields, variable names, and samples.
  Field Names:
  • Display Name - name for language displayed for users
  • Compile Cmd Line - command to compile source file
  • Executable Filename - name of the resulting executable file (see examples below)
  • Program Execution Command Line - command line to execute executable
  Variables: (these are filled in by pc2 during run-time)
  Example input file name: hello.java
  • {:basename} - name of input file without directory and extension (hello)
  • {:mainfile} - name of file with extension (hello.java)

  
  Display Name: GNU C (gcc)
  Compile Cmd Line: gcc -lm -o {:basename} {:mainfile}
  Executable Filename: {:basename}
  Program Execution Command Line: {:basename}
  
  Display Name: GNU C++
  Compile Cmd Line: g++ -o {:basename} {:mainfile}
  Executable Filename: {:basename}
  Program Execution Command Line: {:basename}
  
  Display Name: Java
  Compile Cmd Line: javac {:mainfile}
  Executable Filename: {:basename}.class
  Program Execution Command Line: java {:basename}
  
  Display Name: Kylix Delphi
  Compile Cmd Line: dcc {:mainfile}
  Executable Filename: {:basename}
  Program Execution Command Line: {:basename}
  
  Display Name: Kylix C++
  Compile Cmd Line: bc++ -A  {:mainfile}
  Executable Filename: {:basename}
  Program Execution Command Line: {:basename}
  
  Display Name: Turbo Pascal (DOS)
  Compile Cmd Line: tpc {:mainfile}
  Executable Filename: {:basename}.exe
  Program Execution Command Line: {:basename}.exe
  

• Question: Sometimes when a PC² team executes a TEST run they get back no results in the team output window -- even though they can get the program to produce output by compiling it at the command line. Also I notice that in the command window there are error messages like "Bad File Descriptor" and "IOCollector Error" or other similar messages. We've also seen this happen on the PC² Judge when judging a submitted run. What might be causing this? (p.s. This seems to happen more often when running under Unix/Linux.)

• Answer:

  We have noticed that under certain conditions the Java virtual machine which is acting as the interface between PC² and the host OS does not accurately handle the connection between PC² and the external processes being used to execute the team program. In fact, this can also happen when executing the compiler command used to produce the team's executable program. The problem seems to occur more frequently under Unix/Linux simply because those OS's are faster in the way they handle spawning and handling of the I/O channels for processes.

  We are currently investigating this issue and seeking a permanent solution. Meanwhile, we have discovered that a workaround appears to be simply slowing the external processes down under Unix/Linux so that the JVM has time to keep up with the external OS process management operations.

  For example, we have successfully eliminated this problem in a large Regional Contest by defining each "compiler call" (language) in PC² so that instead of directly invoking the compiler, it invokes a short script (which we call "slowdown"), whose contents are simply:

  #!/bin/sh
  nice -19 $*
  

  We then define the compiler execution command (using the PC² Languages tab in the Administrator) to be (for example for gcc):

  slowdown gcc -o {:basename} {:mainfile}
  

  We do a similar thing to invoke the executable program:

  slowdown {:basename}
  

  What this does is simply execute the "slowdown" script, passing it the rest of the compile (or execute) command as arguments; the script in turn runs the "nice" command which again in turn runs the command (arguments), but at a low process priority. Note that the "slowdown" script must appear somewhere in the "path"; we typically put it in the PC² installation directory.

  We do note that one undesirable side effect of this two-level process structure (running a script to run the actual program) is that if the actual program hangs for any reason -- for example, a team submits a program with an infinite loop -- and then the Judge uses the "Terminate" button on the Execution Timer, what gets terminated is the external script process, not the actual team program program process running "niced". This means that the Judge will need to use "ps" and "kill" ("TaskManager" for Windows types) to remove the looping process. We are working on a fix for this side effect.

• Question: Why can't my PC² Clients connect to the PC² Server when I run the server on my Linux machine? (It works fine when the Server is running under Windows, even if the Clients are on Linux machines.)

• Answer:

  We have seen this happen when a Linux machine running the PC² Server has not been properly configured for a network environment. Specifically, Linux machines typically start up configured to report their "machine name" as "localhost". PC² queries the OS to obtain the machine name, and then maps this name to a corresponding IP address. The machine name "localhost" maps to the "loopback" IP address 127.0.0.1. This ends up being the IP address which the PC² Server broadcasts to the Clients as the address they should use for communication back to the Server -- which means the Clients will be unable to contact the Server because they will use their own local loopback channel.

  To check whether your Linux machine running the PC² Server has this problem, type the command "hostname" (or "/bin/hostname") at a command prompt. If this returns "localhost", your OS is not properly configured for network operations.

  One way to fix this problem on most machines is to edit the file /etc/sysconfig/network and change the HOSTNAME entry to a host name which resolves to a non-local IP address, and then reboot the machine.

  Another approach is to use the "hostname" command, run as root, to set the hostname to either a specific non-local IP address or to a hostname which resolves to a non-local IP address. One user with this problem wound up changing the hostname before starting PC², via a command line like:

   hostname $(ifconfig eth0 | grep inet | sed 's/.*r:\|  B.*//g')
  

  or (depending on your shell)

   hostname `ifconfig eth0 | grep inet | sed 's/.*r:\|  B.*//g'`
  

  which is basically getting the address from the eth0 interface and setting the hostname to that value.

  In any case, be sure to coordinate such actions with your local network administrator.

• Question: How can I run a "Practice Contest" during which contestants get to login and use the system to see how it works, and then "restart" a real contest?

• Answer: The current release of PC² does not have such a function integrated into it (although it is on the list for a near-future release). However, it is relatively simple to run a practice contest followed by a real contest. The following steps describe how to do this.
  1. Start a PC² Server, then an Admin Client.
  2. Configure the "real" contest using the Admin (put in the names of the real contest problems, etc., as well as create the Team/Judge/Scoreboard/Admin accounts and so forth as described in the Admin Guide).
  3. Log off the Admin (shut it down).
  4. Shutdown all PC² programs (i.e. kill all Clients and then the Server).
  5. Go into the PC² installation directory.
  6. Copy the db/ and r_db/ directory hierarchies somewhere safe, outside of the PC². This gives you a clean, initialized copy of the PC² contest database, but with no runs in it.
  7. Restart the Server, then an Admin Client.
  8. In the Admin, delete any "real" contest information which you do not want contestants to see ahead of time (such as the problem names). Note: the V8.2 code distribution contains a batch file named "reset.bat" which can be used in a Windows environment to perform most of the necessary deletion functions. However, paths and other such information vary between installations and "reset.bat" does not take this into account. Use it as a *guide* to the functions which must be done to "reset" a PC² installation to a clean initial state.
  9. In the Admin, add the "practice" contest information. For example, you might have only one "Problem" in a practice contest, with its own data set.
  10. Start Team and Judge Clients as necessary.
  11. Run the practice contest.
  12. After the practice is over, shutdown all PC² programs.
  13. Remove (delete) the db/ and r_db directories from the PC² installation directory (or rename them or move them somewhere safe). Again, "reset.bat" can be used as a guide to the necessary resetting operations.
  14. Copy the original db/ and r_db/ directories from the safe place where they were saved back into the PC² installation directory. This gives you a cleanly "reset" contest, with all the orginal configuration items but none of the runs from the practice.
  15. Start real contest (Server, then Clients).

• Question: What does it mean when the system generates the message "NoClassDefFound" and won't run ?

• Answer: This is a Java error message meaning that it could not find one of the "classes" (programs) required to run the system. The missing classes could either be PC² modules or Java system modules. There are a number of possible causes for this error. Here are some things you can try:
  • Verify that the PC² system was unzipped "including subdirectories" and "with case-sensitivity". PC² uses many Java "packages", which must be stored in the proper subdirectories beneath the PC² installation directory. Make sure the program which was used to "unzip" the distribution properly created and maintained the hierarchical directory structure and the "case" of filenames in the system.
  • Verify that the CLASSPATH environment variable includes the Java/lib and PC² installation directories.

• Question: I would like to be able to change the format of the Scoreboard -- I want to be able to put the data into a Web Page for example. Is there a way to get to the Scoreboard data in text form or something like that?

• Answer: Yes; something like that. When you run a PC² Scoreboard module, it generates a simple ranking display in its own format. You can't change that.

  However, the Scoreboard module ALSO automatically generates a collection of HTML files showing contest standings and submission data in several different formats. These HTML files are updated and placed in a directory name "html" under the $PC2HOME directory (PC² installation directory) each time there is a change in the contest standings state (roughly, each time a submission is judged). This updating is done automatically, on the fly as the state changes.

  There are currently FIVE different HTML files generated:

  • full.html -- a full listing of all (active) teams by name, ranked by number of problems solved and then by "penalty points"
  • fullnums.html -- same as above, except also includes the PC² "Team Number"
  • sumatt.html -- a summary page showing, for each team and problem, how many submissions the team has made on that problem and whether or not they have solved the problem
  • sumtime.html -- same as above, except that instead of simply displaying "Y" or "N" if the team has (or has not) solved the problem, displays the contest-relative TIME (in minutes) at which the teams solved the problem (or shows "--" if the problem hasn't been solved)
  • final.html -- a standings page formatted in the style used by the ACM International Collegiate Programming Contest World Finals

  You can therefore get to the "text data" from the scoreboard by picking it out of the HTML files, if that's what you want. However, since the generated files are full valid HTML, you can simply use them as-is.

  For example, when we run a contest under PC² (as if there was some other way...) we never run more than ONE Scoreboard module for the entire contest (even if it is a multi-site contest spread over multiple continents). Once we have one Scoreboard module running, we build an external "master" HMTL file containing references to the PC² directory HTML files (for example, we insert the various PC² HTML files into frames in the master page, along with things like a header frame showing the contest title and graphics and so forth). We then write a script (batch file) to copy the master page to some publicly published location at regular intervals (e.g. once per minute).

  We then tell people who want to see the "scoreboard" (for example, Teams, Judges, Spectators) to simply point their favorite browser to the "public" location. The PC² Scoreboard will update the PC² HTML files whenever the standings change; the script will copy the updated HTML files to the public location at the frequency we specify.

  This approach also makes it easy to "freeze" the (public) scoreboard at some point near the end of the contest, if that's what is desired: simply kill the script which is doing the copying (but not the PC² Scoreboard module itself). The internal scoreboard will continue to update, while the public HTML scoreboard will "freeze" at the last displayed form.

• Question: If the PC² Server is shut down or dies for some reason, is it necessary for Clients (Teams, Judges, etc.) to log back in?

• Answer: In the current version of PC², Yes. Although the state of the contest (runs submitted, problem names, etc.) is retained between executions of the Server, the state of remote connections is not retained.

  Note also that if the reverse happens -- e.g. a Client gets killed or shut down improperly without executing a "log out" operation -- the system will think the Client is still "logged in" and will not allow the Client to reconnect when it starts back up -- it considers it a "duplicate login". To fix this, simply use the "Force Logout" function in the Admin to make the system drop the login connection to the dead Client, then have the Client log back in normally. The same is true if a Server dies in a multi-site contest; before the Server can "reconnect" to the system, it must be "forced off" by the Administrator. (We're working on improving this aspect of the system...)

• Question: Is there a way to prepare PC² "Account Information" (such as Team Names and Passwords) ahead of time and then load them into the system?

• Answer: Yes. PC² versions 7.4 and higher allow you to create account information ahead of time in a file and then "import" the file into the system. The file is loaded with the "Import" button on the Administrator. Imported values overwrite any values that were in the system previously. The format of the import file is as follows.

  File lines starting with ! or # in the first column are ignored. Each non-comment line has FOUR fields, separated by a pipe (|). The fields are:

  	Account_number
  	Display_name
  	Active  (either "true" or "false")
  	Password
  

  For example:

  1|Number 1|true|pass1
  2|Team Number 2||pass33
  

  Note: a blank "active" field is considered false (so the example above will cause team 2 to become inactive). True and false are not case sensitive.

• Question: I am the Contest Administrator for a Regional Contest which is using the ACM International Collegiate Programming Contest (ACM/ICPC) on-line Registration system for contestants. Is there a way to download and import team registration information from the ICPC site into PC²?

• Answer: Yes. To do this, login to the ACM/ICPC website using your Regional Contest Director's account. There is a button there to download a "zip" file to PC². Once you have downloaded this file, unzip it in a directory of your choice. Then on the PC² Administrator, go to the "Accounts" screen and click the "Import ICPC Data" button. This will ask you to navigate to the unzip directory and select one of the downloaded files. Once you do this, PC² will read the rest of the files automatically and load the ICPC data (such as the team names).
  Note: it is important to create PC² Accounts BEFORE importing ICPC data. The import function assigns imported account information to PC² accounts in the order in which the accounts are encountered in the import data files.

• Question: I have heard that PC² can automatically generate printed messages and/or automatically send email messages when a team correctly solves a problem. We'd like to use this function to tell our Contest Runners to take a balloon to the team. How do we get PC² to print/send balloon messages/e-mails ?

• Answer: Click here to see the Balloon e-mail in PC² Web Page.

• Question: What if my problem is not covered in the above list? Can you still help me?
  (Creating a .zip file for support)

• Answer: Well, we'll be happy to try (please keep in mind that this is a totally volunteer project on our part). The first thing we ask is that you make the effort to read the Administrator's Guide and see if you can find out from there what is going on. The Admin Guide is available on our web page, and it comes packaged with the system when you download it. If that doesn't do it....
  • Each of the PC² modules generates entries in a "log" file. The log file names correspond to the module -- team.log, judge.log, etc. Look through the log files and see if there are any obvious error messages -- this will frequently give you a clue as to what is happening.

  • If you still can't figure out what is happening, send us an email message ( pc2@ecs.csus.edu ) describing the problem and we'll see what we can do to help. Please include a zip file containing a complete copy of your PC² installation as an attachment to the email. To generate such a file, go to the PC² installation directory and type the command "java pc2.ZipPC2" ; this will create a .zip file of the system. (If the problem relates to multiple modules on multiple machines, please send a zip for each module).