Posix Threads: In a vector addition program assume a, b and c are vectors (arrays of doubles), and that n is the number of elements in the vectors. Assume that a,b,c and n are global variables and the program should compute c = a + b. Assume that chunksize = ceiling(numThreads) is a global integer and that each thread calls addMyVec to add its assigned portion (chunk) of the vector. (a) Write a main function to create numThreads threads and execute the function "addMy Vec (b) Write a loop that would be at the end of main to wait on all the threads to be finished and then call writeVector(c) to write out the result. (c) What element and functions are used to control and ensure atomic (one at a time) access to a global variable that is shared amongst several threads