CMSC 421, Spring 2006 Principles of Operating Systems Section 0101 Specific Materials Section 0201 Specific Materials

Projects

This page will be updated during the semester.

1. Project 1
2. Project 2
3. Project 3

Notes/Changes:

• Extension Granted: The first project due date is: March 5, Sunday, 2006, 9 PM.
• Page 1 of handout, second to last line at bottom of page: It should be: 120 = 2^3 * 15, not 24 = ...

• Example code (this was taught in Section 0101 but can be useful to both sections) is available at: Directory.

• Posted on Feb 17, 2006: In searching for prime numbers, you can use the PND threads to search from 1 through N, instead of 1 through sqrt(N).

• Posted on Feb 17, 2006: On lower half of page 3: Under What to Do: it should read: generate a random number of maker processes (not 'threads') and a random number of student processes (not 'threads').

• Posted on Feb 19, 2006: shmget, shmat, and shmdt have some interesting "features" that can vary across systems. For instance, there may be a limit on how many shmget you can use per program. If you surpass that limit it gives you a -1.
  
  This means it is not reliable to have 1 shmget for each shelf. It is recommended to have one shared memory segment that stores all the needed shared information.
  
  Also, please be sure to explicitly remove shared memory segments and semaphores before your program exits. The system has a limit on the number of these and they do not necessarily get deleted on process termination. If you are getting "bus error" messages, this is a possible cause.

  The program should end after 10 iterations of sleeping and making states (per maker) and 10 iterations of hungry and studying states (per student).

• Besides the ITE 240 Lab, please visit OIT Computer Labs to locate other OIT laboratories. In this list, ENGR* 021 and 021a and Library Basement machines appear to have dual boot Win2K/Linux machines.

Notes/Changes:

• Updated: April 23, 2006: Question: During swapping out of a process from MM to VM, should the pages be copied explicitly from MM to VM and be copied back? Answer: This choice is left to the implementor.
• Updated: April 23, 2006: Suggested Sample Output File: This is a suggested format/text - if you have already written up a different format, that is acceptable too.
  This version removes some errors in an earlier version posted on April 20, 2006.

• When process(es) have to be swapped out from main memory to accomodate a swapin request, swap out the Least Recently Run process, followed by the next Least Recently Run process, etc.

  For example, if pids 4, 3, 6, 5, 8 were run (in that order), then 4 will be swapped out first, followed by 3, etc.

• Please read the Blackboard questions and responses first, before posting a query or sending an email.

• If program executable size is larger than main memory size, then the program will not be loaded: Print an error message to that effect.

• Virtual memory, as used in this project, is "secondary memory" as defined on Page 322 (Ch. 9). This will be typically a partition of the system's hard drive (e.g. swap on Linux systems: Look at /etc/fstab for swap partition entry). For our project, we can simulate this as an array. The swap space is a holding place for processes that are not in main memory. In this project, we are only dealing with increasing the number of processes (i.e. level of multi-programming) that are currently active in the system. We are *not* dealing with demand paging and the related per process virtual memory concepts described in Chapter 9. For a process to execute in this project, ALL its pages must be in main memory.

Posted on May 16, 2006: You can submit by 11.55 PM EDT May 16, 2006 to be eligible for 10% Extra Credit. This gives you two hours and fifty-five minutes more than the earlier deadline.

Posted on May 8, 2006:

1. Due to many student requests, the project submission date is extended to 11.45 PM EDT, May 21, Sunday. This applies to BOTH sections.
2. Projects (completed with all needed components) submitted by May 16, 9PM EDT will receive an Extra Credit of 10% (of the grade the project receives). For example, if you received 80/100 on Project 3, then your recorded grade will 88/100.
3. If you submit by May 16th 9pm, but submit a revised version after that, the LATER version will be graded and you will not be eligible for the 10% extra credit.
4. Given that the deadline is during finals week, use appropriate time management practices to ensure that you do not sacrifice performance in other courses' finals.

Project 3 clarifications:

• Posted April 26: All file related commands must return an error message when invoked on a file that has not been opened using the 'open' command.
• Posted April 26: Maximum string length in 'write' command will be 256 bytes.
• Posted: May 4, 2006:
  1. Reserve first 25% of the blocks for directory info. If you have finished implementing the project with different allocation, then inform the instructors asap and there is no need to change your implementation.

  2. Disk size will be between 2000 and 4000 blocks during testing.

  3. If two consecutive commands such as:
     

     > seekread /file1.c 10
     > seekread /file1.c 10
     

     
     are issued, the read pointer will point to the byte at position 10 after second command too. That is, seekread always uses absolute byte position.
     
     The same applies to seekwrite command.

  4. After read command, the readpointer moves forward by the number of bytes read (and for boundary condition, will point to past the last byte of the file). Example: File length is 600 bytes (0 .. 599 are byte position values) and current readpointer is 500:
     

      read /file1.c 100
     

     will set readpointer, after reading the 100 bytes to position 600.

  5. After write command, the writepointer moves forward by the number of bytes written. Note that 'write' can overwrite existing bytes.

• Posted on May 6, 2006: On page 5, the example for write should be:

  
  COMMAND: write /file1.c ABCDEFGHIJKLMNO; RESULT: File written and
  length is: 25 bytes 
  
  

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