CS414 Programming Project 1

In the first project, your task is to write a non-preemptive, user-level threads package. Many operating systems provide an implementation of threads at user-level because they allow concurrency with a very low overhead, without requiring a call to the kernel to switch between threads. Windows NT does not provide a user-level threads package, only kernel threads.

We have provided you with some skeletal code that creates an environment on top of NT that closely resembles the environment on top of raw hardware shortly after booting. We use NT to provide us with a virtual processor and memory. NT also bootstraps our kernel; that is, it loads it into memory and starts executing it at its entry point. Your task is to build high-level abstractions on top of this environment in the same way that NT builds its abstractions on top of the hardware.

Special announcement! There is an incompatibility between the version of machineprimitives_x86.c and the new C compiler included with Visual Studio .NET.

This manifests itself when you do the following: context switch from thread A to B, and then context switch back to A, and will cause minithreads to crash (return address is outside the program). This problem only occurs if you're using Visual Studio .NET; earlier versions of Visual Studio will not have this problem. To fix it, download machineprimitives_x86_dotnet.c and rename it to "machineprimitives_x86.c", replacing the old version. Everything will now work.

Special announcement! Some special steps are required to get minithreads to work on the machines in Rhodes Hall 453, since they run a different version of Visual Studio (the .NET version).

If you have tried compiling minithreads using Visual Studio .NET, you'll probably have discovered that the instructions we've given you don't work. The problem is that Visual Studio .NET puts its libraries in a different place from the earlier version, which breaks the linking stage of building minithreads. Here's some revised instructions:

1. In the Build Properties dialog, put "nmake /F Makefile" as the "build command".
2. Modify "Makefile" as follows:
   1. Replace 'VISUALSTUDIO = c:\Program Files\Microsoft Visual Studio' with
      'VISUALSTUDIO = c:\Program Files\Microsoft Visual Studio .NET'
   2. In the LFLAGS declaration, replace '/LIBPATH:$SYSLIBPATH' with
      /LIBPATH:"$(VISUALSTUDIO)\VC7\lib\\" /LIBPATH:"$(VISUALSTUDIO)\VC7\PlatformSDK\lib\\"
      (i.e. two /LIBPATHs, one after the other).
3. Everything should now work.

n.b. The original instructions will work fine if you're using an earlier version of Visual Studio.

Project Organisation

• To start off, you will have to write some generic FIFO (first-in, first-out) enqueue and dequeue operations on an unbounded queue. We will be relying on this queue implementation throughout the rest of the course, so it's important that the implementation be efficient. Specifically, enqueue and dequeue operations should both work in O(1) time.
• You need to define and implement thread control blocks, and the functions that operate on them. We suggest you start with minithread_create and minithread_yield, and go on to implement the scheduler. Once you have those two working, you can come back to implement the rest of the functionality.
• You need to implement a scheduler. For this assignment, all you need is a first-come, first-served scheduler. You can assume that your threads will voluntarily give up the CPU, which means that your test programs should make occasional calls to minithread_yield().
• You need to implement semaphores in order to be able to synchronize multiple threads.

Finally, you need to demonstrate your threads package by implementing a solution to the "food services" problem. This is actually an instance of the better-known multiple-producer, multiple-consumer problem. There are N cooks (each a separate minithread) who constantly produce burgers. We'll assume for debugging purposes that each burger has a unique id assigned to it at the time it is created. The cooks place their burgers on a stack (at the front of the queue you built earlier in this assignment). There are M hungry students (each a separate minithread) who constantly grab burgers from the stack and eat them. Each time a student eats a burger, she prints a message containing the id of the burger she just ate. Ensure, for health and sanity reasons, that a given burger is consumed at most once by at most one student.

How to Get Started

• Download the code here: minithreads1.zip
• Open Microsoft Visual Studio C++.
• Select "New" from the File menu to create a new project. Choose to create a new Makefile, enter "minithreads" for the project name, and whatever location you want, and click "Ok".
• In the dialog box, replace "minithreads.mak" with "Makefile" in the "Command line" text box and click "Finish".
• Unzip the minithreads.zip file in the directory for your project.
• Click on the "FileView" tab to get the list of the files. Go to the "Source Files" folder and right-click to get "Add Files to Folder", then select all the .c files. Do the same in the "Header Files" folder, and add all the .h files.
• ONLY DO THIS STEP IF YOU ARE NOT WORKING IN THE UNDERGRADUATE LAB. If the computer you are using does not have Visual Studio installed in the usual place (c:\Program Files\Microsoft Visual Studio), then change the line
  VISUALSTUDIO = c:\Program Files\Microsoft Visual Studio
  in "Makefile" to point to the correct location.
• Select "Build minithreads.exe" from the "Build" menu. It should compile and link with a bunch of warnings. If you execute minithreads.exe, it will terminate immediately.

If you decide not to use the integrated development environment (Visual Studio), you can use any other editor you like and compile the code from the command line. To compile the code from the command line, go to the directory where you unpacked the project and type make to compile the project incrementally (will detect which files have been modified and recompile them).

Three small test programs, test1.c, test2.c, and test3.c, are included in the minithreads1.zip file. They test spawning a thread, spawning multiple threads, and ping-ponging between threads. They should be useful when you are implementing minithreads. Two larger test programs, buffer.c, a bounded buffer, and sieve.c, a sieve for finding primes, are more complicated. Ideally, you should test your Minithreads implementation against these.

If you have problems with the project or questions, please send mail to the instructors or come to office hours.

How to Test Your Code

It's crucial that systems code be correct and robust. You must test your code with reasonable and unreasonable test cases, and ensure that it behaves correctly. Note that you should maintain some separation between the Minithread package and minithread applications. Most importantly, your minithread applications should not contain any dependencies on the scheduling algorithm or on the lack of preemption.

To facilitate testing, we provided you with some test programs. It's a good idea to start with these, and develop your own tests as you need them. The simplest test cases are test1.c, test2.c and test3.c, which test single thread creation, multiple thread creation, and ping-pong between two threads. buffer.c provides a bounded buffer implementation. A producer and consumer keep producing values and consuming them across a buffer of finite length. sieve.c is a Sieve of Eratosthenes for concurrently searching for primes. It has a single thread on one end, injecting the numbers 1, 2, 3, 4, 5, 6, 7, 8, ... into a pipe. For each prime p, there is a thread in the middle of the pipe that consumes a number from the pipe if that number is divisible by p. Otherwise, it passes the value on to the next thread in the pipe. At the very end, there is a thread that prints the values that emerge from the pipe. Note that this assembly will only print out prime numbers, because the threads in the pipe will consume all non-primes.

Since we will soon make the threads package preemptive, all code you write should be properly synchronized. That is, everything should work no matter where in the application thread you place a minithread_yield. Consequently, it's a good idea to test your code with minithread_yield() calls inserted at random locations throughout the application code (note that we don't expect the system code in minithread.c or synch.c to be yield-safe for this project -- just the applications).

Do not forget to check for memory leaks. Your threads package should not run out of memory when large numbers of threads are created and destroyed.

Submitting your project

For this project you have to submit the source of all the files you modify (at least minithread.c, queue.c, synch.c) and the NT executable for the multi-producer, multi-consumer problem. Also submit the Makefile with the MAIN symbol set to the name of your producer-consumer program.