Search⌘ K
AI Features
Home
Courses
Learn C Programming

Compiler-assisted threading with OpenMP

Understand how OpenMP enables compiler-assisted threading in C by using directives to create parallel regions, manage private and shared variables, and parallelize loops efficiently. Learn key concepts like critical sections and reduction to safely handle shared data in multithreaded programs.

We'll cover the following...

OpenMP is an API that implements a multithreaded, shared memory form of parallelism. It uses a set of compiler directives (statements that we add to our C code) that are incorporated at compile-time to generate a multithreaded version of our code.

We can think of pthreads (from the previous lesson) as doing multithreaded programming ‘by hand’ and OpenMP as a slightly more automated, higher-level API to make our program multithreaded. OpenMP takes care of many of the low-level details that we would normally have to implement ourselves, if we were using pthreads from the ground up.

Blueprint of an OpenMP program

Here is the general code structure of an OpenMP program with omp.h included at the top:

C
#include <omp.h>
main ()  {
int var1, var2, var3;
Serial code 
      .
      .
      .
Beginning of parallel section. Fork a team of threads.
Specify variable scoping 
#pragma omp parallel private(var1, var2) shared(var3)
  {
  Parallel section executed by all threads 
        .
        .
        .
  All threads join master thread and disband 
  }  
Resume serial code 
      .
      .
      .
}

The syntax #pragma omp parallel is called the parallel directive and the block of code that follows it (enclosed within curly brackets { and }) is called the parallel region. ...