no parallel threads with openMP

Question

My problem is that I get no parallelization with openMP.

My system: ubuntu 11.4 Intel(R) Core(TM) i5 CPU M 430 @ 2.27GHz

Compiler: g++ Version: 4.5.2 with flag -fopenmp

With this code I see that there is only one thread:

int nthreads, tid, procs, maxt, inpar, dynamic, nested;

// Start parallel region 
#pragma omp parallel private(nthreads, tid)   {

// Obtain thread number    
tid = omp_get_thread_num();

// Only master thread does this    
if (tid == 0) 
{
printf("Thread %d getting environment info...\n", tid);

// Get environment information 
procs = omp_get_num_procs();
nthreads = omp_get_num_threads();
maxt = omp_get_max_threads();
inpar = omp_in_parallel();
dynamic = omp_get_dynamic();
nested = omp_get_nested();

// Print environment information 
printf("Number of processors = %d\n", procs);
printf("Number of threads = %d\n", nthreads);
printf("Max threads = %d\n", maxt);
printf("In parallel? = %d\n", inpar);
printf("Dynamic threads enabled? = %d\n", dynamic);
printf("Nested parallelism supported? = %d\n", nested);  
}
}

because I see the following output:

Number of processors = 4
Number of threads = 1
Max threads = 4
In parallel? = 0
Dynamic threads enabled? = 0
Nested parallelism supported? = 0

What is the problem?

Can some one help, please?

Answer 1

Your code works for me on Ubuntu 11.04 with the g++ compiler version 4.5.2 however I had to change

#pragma omp parallel private(nthreads, tid)   {

to

#pragma omp parallel private(nthreads, tid)  
{

for it to compile successfully.

EDIT: If fixing the syntax doesn't work my next idea would be to ask what is the exact command that you are using to compile code?

Answer 2

#pragma omp parallel private(nthreads, tid)   {

is incorrect syntax, as noted by hrandjet

The pragma must end with a new line, so the { should be on the next line.

#pragma omp parallel private(nthreads, tid)   
{

This works for me on Windows XP.

Answer 3

Is the output prefaced by

Thread 0 getting environment info...

If not, the problem is as stated above - the open bracket ( { ) must be on a new line. To prove this further, try initializing

int tid = 1

and see if the output still shows up. If not, the #pragma is being ignored by your compiler (probably because of the bracket issue).