Hands-on; Shared Memory II; Synchronization Primitives

1. A threaded http://siber.cankaya.edu.tr/ozdogan/ParallelComputing/cfiles/code47.c program for computing the value of $\pi$,
   • The method is used here is based on generating random numbers in a unit length square and counting the number of points that fall within the largest circle inscribed in the square.
   • Since the area of the circle ($\pi r^2$) is equal to $\pi/4$, and the area of the square is $1 \times 1$, the fraction of random points that fall in the circle should approach $\pi/4$.
   • A simple threaded strategy for generating the value of $\pi$ assigns a fixed number of points to each thread.
   • Each thread generates these random points and keeps track of the number of points that land in the circle locally.
   • After all threads finish execution, their counts are combined to compute the value of $\pi$ (by calculating the fraction over all threads and multiplying by 4).
   Vary the number of sample points and threads, then observe the outcome.

2. A threaded http://siber.cankaya.edu.tr/ozdogan/ParallelComputing/cfiles/code23.c program that determines the sum with the use of mutex variables;
   • Increase the number of the threads and change the size of array.
   • Observe if the all the threads have the partial sum all the time. Why not?
3. A threaded http://siber.cankaya.edu.tr/ozdogan/ParallelComputing/cfiles/code48.c program that performs a dot product with the use of mutex variables; (http://siber.cankaya.edu.tr/ozdogan/ParallelComputing/cfiles/code49.c sequential version)
   • First study the sequential version.
   • The main data is made available to all threads through a globally accessible structure.
   • Each thread works on a different part of the data.
   • The main thread waits for all the threads to complete their computations, and then it prints the resulting sum.
4. This http://siber.cankaya.edu.tr/ozdogan/ParallelComputing/cfiles/code50.c program demonstrates the use of condition variables.
   • The main routine creates three threads.
   • Two of the threads perform work and update a ``count'' variable.
   • The third thread waits until the count variable reaches a specified value.