c - maximum number of variables in private() clause in OpenMP -

i want know whether there limitation on number of variables can defined in private() clause in openmp.

i have code has 4 loops lot of variables. outermost loop can parallelized using pragma. inner loop can parallelized using pragma. using 1 pragma @ time. (either outermost or innermost) of course, using pragma in innermost loop not advisable because overhead of thread creation because of 3 loops above it. put pragma correctness test purposes.

#pragma omp parallel private(var1,var2,...i,k,l) for(j = ...)  {     int var1;    int var2;      (i = ... )     {         ...         for(k = ...  )         {              ...             for(l = ... )             {              ...              ...             }          }      } } 

or

for(j = ...)  {     int var1;    int var2;      (i = ... )     {         ...         for(k = ...  )         {              ...             #pragma omp parallel private(var3,var4)             for(l = ... )             {              int var3;              int var4;             }          }      } } 

correctness test fails outermost loop. compared inner loop, private variables list outermost loop 29 while inner pragma contains 21 variables in private variable list.

i compare c version openmp version, print values in array , sort , compare.

your problem has nothing number of variable names, allowed in private clause. rather first example syntactically incorrect.

#pragma omp parallel private(var1,var2,...i,k,l) for(j = ...)  {     int var1;    int var2;    ... } 

both var1 , var2 undeclared @ point parallel for directive , clauses parsed. don't have (and cannot) specify sharing class. belong inner scope , therefore have predetermined sharing class private. §2.9.1.1 openmp specification v3.1:

certain variables , objects have predetermined data-sharing attributes follows:

• variables automatic storage duration declared in scope inside construct private.

variables predetermined data-sharing attributes may not listed in data-sharing attribute clauses, except cases listed below.

it advisable use c99 features if possible , declare loop variables in scope referenced, e.g.:

#pragma omp parallel private(...) (int j = ...)  {     int var1;    int var2;     (int = ... )    {       ...       (int k = ... )       {           ...          (int l = ... )          {             ...             ...          }       }    } } 

in case no variable (i, j, k, l, var1, var2) list should appear in private clause.