Processes

The following http://siber.cankaya.edu.tr/ParallelComputing/cfiles/code22.c program determines the sum the elements of an array A[1000], we also need http://siber.cankaya.edu.tr/ParallelComputing/cfiles/lockinit.c lockinit, http://siber.cankaya.edu.tr/ParallelComputing/cfiles/lock.c lock, http://siber.cankaya.edu.tr/ParallelComputing/cfiles/unlock.c unlock.

• The sequential structure is

  int sum, A[1000];
  sum = 0;
  for (i = 0, i < 1000; i++) sum += A[i];
  

• Division into two processes; in this method, we will divide the program into two parts, one doing the even $i$ and one doing the odd $i$. Running the two processes, $sum$ will need to be shared.
• For demonstration purpose; creating a library is also presented.
  • After creating the C source files, compile the files into object files.

    gcc -c -fPIC lock.c
    gcc -c -fPIC lockinit.c
    gcc -c -fPIC unlock.c
    

  • Static library
    • Create a static library called $libspin.a$. Then, create an index inside the library.

      ar rc libspin.a lock.o lockinit.o unlock.o
      ranlib libspin.a
      

    • When linking your program to the libraries, make sure you specify where the library can be found:

      gcc -o sumprocess  code22.c -L. -lspin
      

      The $-L.$ piece tells gcc to look in the current directory in addition to the other library directories for finding $libspina.a$.
  • Shared library
    • To create a shared library

      gcc -shared -fPIC -o libspin.so lock.o lockinit.o unlock.o
      

    • The $-fPIC$ option is to tell the compiler to create Position Independent Code (create libraries using relative addresses rather than absolute addresses because these libraries can be loaded multiple times)
    • To compile the actual program using the libraries

      gcc -o sumprocess1 code22.c -L. -lspin
      

  • Notice they are exactly the same as creating. Although, it is compiled in the same way, none of the actual library code is inserted into the executable, hence the dynamic/shared library.
  • Shared libraries dynamically access libraries at run-time thus the program needs to know where the shared library is stored.
  • The executable is much smaller than with static libraries. If it is a standard library that can be installed, there is no need to compile it into the executable at compile time!
• Analyse these codes, execute them and observe the outputs.