CS 3733 Operating Systems, Recitation Session D

In this session you will run the UNIX Concurrent I/O Simulator.

• You can run this either from Linux or Windows.
  To run on our Linux machines:
  • Read this if running from VDI
  • Log on to your Linux Account.
  • Create a directory called recD under your CS 3733 directory.
  • Download this tar file to your recD directory.
  • Untar the files into the recD directory.
  • In the recD directory, execute runio
  • If all goes well you will have started the Unix Concurrent I/O Simulator.
  • If it does not run, try executing
    sh
    and trying runio again.
  To run from windows directly:
  • Download this zip file into a directory called RecD.
  • If you are using VDI, make sure this is on your V drive.
  • Unzip the contents to recD.
  • Run the simulator by double clicking on runio.bat
  • If asked to edit a file, you can use notepad.
• If all goes well you will have started the Unix Concurrent I/O Simulator.
• Click on the Quit button on the upper left part of the window.
• Edit the file ioconfig.
  One of the lines in this file starts with user.
  Replace New User on this line with your name.
• Execute runio again.
• Locate the button labeled Open Log and click on it.
  The button should now say Close Log.
  You have created a log file called logfile.html in the recD/logs directory.
• Find the Log Comment button and click on it.
  A Log Comments dialog will appear.
  Click on the Current Comment window and type some text. Then push the Log button and the Hide button.
• Find the Log Image button. Click on it. Wait for it to finish and click Close Log.
• You have put a log file in the recD/logs directory.
  You can see it by clicking on Show Local Log.
  The log file should have a heading containing your name.
  It should also contain the comment you entered and a picture of the simulator.
  
• Each time you open and close the log it creates files in the recD/logs direcrory.
  If you do it again, it will write over the files you previously created.
  To save these, rename the log directory. Be sure to create a new empty logs directory before running the simulalor again.
• Start the simulator again. Find the Choose Program button in the lower right corner. Click on it and choose Program 2. In this program an open is done followed by a fork. Step through the program using the Step button at the top of the rightmost buttons. When the program is done, the irst process should have abcd in its buffer and the second one should have efgh. Make sure you understand why this is the case.
• Now push the Reset button and open the log. After pushing the Step button 3 times, switch the active process to the child by pushing the Active button (between the Reset and Choose Program buttons. Now push the Step button until both processes have completed. The first process should have abgh and the second should have cdef. Understand what has happened. Use the Log Comment button to insert the comment:
  Program 2, Test 1. Then push the Log Image button. Close the log and exit the program. Change the name of the logs directory to program2test1. This will make sure it is not written over the next time you run the program.
  Create a new empty logs directory.
• Start the program again with Program 2. Think about where the context switches need to be in order for the first process to end up with cdef and the second process to end up with abgh. Open the log, choose program 2, step through the program to produce the desired output. Insert a comment into the log file:
  Program 2, Test 2: abgh and cdef
  and log the image. Close the log, exit the program and rename the logs directory program2test2. Make an empty logs directory.
• Start the program again with Program 2. Find the button labeled Atomic: read and IO statement. Click it twice until it says Atomic: none. Below it there is a slider. Move the slider all the way to the left. This will prevent automatic context switched.

  Now the read statements will be executed in three steps:

  1. First byte is read and put in the buffer
  2. Second byte is read and put in the buffer
  3. the total variable is updated.

  There are now a lot more possibilities of the values in the buffers depending on where the context switches take place. Figure out a sequence that will end up with the parent having acde and the child with bfgh. Make a log file as before, this time inserting the comment
  Program 2, Not atomic with acde and bfgh.
  Rename the log directory program2test3 and create a new logs directory.

• Run the simulator again, this time with Program 3. This program does a fork, and parent and child both open and write. The parent writes abcd and the child writes ABCD Step through he program without any context switches (except when the parent terminates) and understand what has happened.

  Now reset and run it again. Figure out a sequence of context switches that will leave the file with abCD after both processes have finished. Log the result as before. The comment should be:
  Program 3 with output abCD
  Rename the log directory program3test and make a new empty logs directory.

• Run the simulator again, this time with Program 4. This program opens a file before forking and writing. By setting atomic to none, run the program so that it produces the output: aABbcdCD. Log this again with the appropriate comment and change the name of the log directory to program4test.
• Experiment with the other versions of Program 3. Make sure you understand how they behave.
• Demonstrate to the TA that you have created a log files containing the required information.
  You should have links to the following:
  • Program 2, Test 1
  • Program 2, Test 2
  • Program 2, Not atomic
  • Program 3
  • Program 4