Pthread Wrapper for Fortran

Question

I am newbie to both Fortran and C++, working on a task to couple two programs written in Fortran and C++.

I am trying to create a pthread(detached) wrapper and call it from my Fortran subroutine and pass a cpp function to it. I wrote some code by following this link Calling a subroutine in FORTRAN without blocking the main program.

I get run time error like below, when i execute it.

Program received signal SIGSEGV: Segmentation fault - invalid memory reference.

Backtrace for this error:

I compiled using the following commands

gfortran-mp-4.7 -c pthread_mod.f90 
g++-mp-4.7 -c -std=c++11 pcmodel.cpp 
gfortran-mp-4.7 -c  mainFort.F
gfortran-mp-4.7 pthreads_module.o pcmodel.o mainFort.o -o test -lstdc++

Here is the minimal code where i can reproduce the error.

Pthreads_interface.h

extern "C" void pthread_create_opaque(pthread_t *threadptr, void *(**procptr)(void *), int *comerr){
  //   creates a new thread using an opaque pointer to the pthread_t structure
   pthread_attr_t  attr;
   pthread_attr_init(&attr);
   pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
   *comerr = pthread_create(threadptr, &attr, (*procptr), NULL);
}

pthreads_module.f90

module pthreads_module
implicit none
 interface

   subroutine pthread_create_opaque (threadptr, procptr, comerr) bind(C,name="pthread_create_opaque")
        USE ISO_C_BINDING
        type(c_ptr) :: threadptr
        type(c_funptr),value :: procptr
        integer(c_int),intent(out) :: comerr
   end subroutine

   subroutine PCModel () bind (c,name="PCModel_")
         USE ISO_C_BINDING
   end subroutine PCModel

  end interface
 end module pthreads_module

mainFort.F

program test
 call BCL00
end program test

  SUBROUTINE BCL00
  use pthreads_module
  USE ISO_C_BINDING
  implicit none
  type(c_ptr) :: threadptr
  integer :: comerr
  call pthread_create_opaque(threadptr,
 &          c_funloc(PCModel),comerr)

  END

where PCModelis the C++ function to be executed by pthread.

pcmodel.cpp

 #include <iostream>
 #include "pthreads_interface.h"
 using namespace std;

 void PCModel(){
      cout<<"PCModel is called"<<endl;
 }

 extern "C" void PCModel_(){
  PCModel();
 }

Ideally both my Fortran and C++ code should run in parallel, once the fortran code triggers the thread to start the C++ function(PCModel)

It would be great, if some one could check the code and help me out.

Answer 1

In Pthreads_interface.h I changed the way procptr is passed from (*procptr) to procptr

extern "C" void pthread_create_opaque(pthread_t *threadptr, void *(*procptr)(void *), int *comerr){
 //   creates a new thread using an opaque pointer to the pthread_t structure
 pthread_attr_t  attr;
 pthread_attr_init(&attr);
 pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
 *comerr = pthread_create(threadptr, &attr, procptr, NULL);
}

Now it runs without Segmentation fault and main program continues without waiting for the thread.