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error #2660: thread locality is incompatible with a previous declaration of variable xxx

Hi,
I am using intel c++ compiler icpc version 12.1.0 and I get this compilation error when compiling the following code. Can someone point out why it occurs?.
I am pasting my sample .h and .cpp file here:
myheader.h:
---------------
extern int j;
#pragma omp threadprivate(j)
==============================
mycppfile.cpp
-----------------
#include
#include
#include "myheader.h"
using namespace std;
int j;
int
main(int argc, char *argv[])
{
#pragma omp parallel num_threads(2)
{
cout<<"Number of threads created is" << omp_get_num_threads() << endl;
cout<<"My thread ID is " << omp_get_thread_num() << endl;
j = j + 10;
cout << "j=" << j;
}
return(0);
}
Basically because of the OMP primitives I should see j=10 printed twice. If the OMP primitives are removed one thread should print j=10 and other j=20. It is working with gcc but icpc 12.1.0 throws the error.I was using icpc version 12.0.3 previously and did not come across this error.I am currently working with a large code base containing similar scenario.Can some one point whats wrong here.
Thanks,
karthik
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Employee
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Your application exiting before the values are printed. I have modified the code as below:

// mycppfile.cpp

#include

#include

#include "myheader.h"

using namespace std;

int j;

int

main(int argc, char *argv[])

{

#pragma omp parallel num_threads(2)

{

cout<<"Number of threads created is" << omp_get_num_threads() << endl;

cout<<"My thread ID is " << omp_get_thread_num() << endl;

j = j + 10;

cout << "j=" << j << endl;

}

cout.flush();

return(0);

}

$ icc -V

Intel C Intel 64 Compiler XE for applications running on Intel 64, Version 12.1.1.235 Build 20110824

Copyright (C) 1985-2011 Intel Corporation. All rights reserved.


$ icc -openmp mycppfile.cpp

$ ./a.out

Number of threads created is2

My thread ID is 0

j=10

Number of threads created is2

My thread ID is 1

j=10

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Hi Om Sachan,
Thanks for the modification of code. I really appreciate it. Also should'nt we be using intel's c++ compiler icpc for compiling the code and linking with the c++ libraries. I am experiencing the posted error while using icpc 12.1.0 and my large c++ code base uses STLs a lot and hence it needs to be linked with c++ library. Please let me know your comments.
Thanks,
karthik
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The icc driver is smart enough to recognize the .cpp extension on the file and compile as C++.

It's not that smart for some other file extensions so we still have icpc when you need it.
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Black Belt
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icpc includes -lstdc++ at link time (as well as including corresponding header search path in the compilation), finding that library in the g++ installation.
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>> oops, disregard the following, I did not pay attention to the contents of the header file

j isn't initialized.
Although this can, or should I say may be, initialized to zero using linker switch, the code does not assert the initialization. (IOW bad programming assumption).

Assuming you explicitly have int j=0; or by reliance on linker to initialize j to 0, then due to data race in your code you have three possible results:

ID0, ID1
10, 20 (ID0 beat ID1)
20, 10 (ID1 beat ID0)
10, 10 (ID0 and ID1 performed Read of j before either performed modify/write)

Also note that j not being volatile or atomic tends to cause issues where j becomes registerized.

Jim Dempsey
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Hi,
Thanks to all for their replies. I really appreciate it.
But the main issue is I do not want to link with stdc++ libraries provided by gcc/g++. This is because the current libstdc++ does not allow non POD(Plain Old Data) types like class objects in thread local storage. Hence I switched to icc/icpc.
So my issue is why does this error occurs when we compile with icc/icpc 12.1.0using only intel libraries. But icc/icpc 12.0.3 does not give this error for the same code.
Thanks,
karthik
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Black Belt
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Both 12.0 and 12.1 compilers link against the same libstdc++, if you haven't changed your active g++ installation.
Newer Intel compiler versions tend to become more stricter about source code issues, sometimes even giving erroneous indications. I think maybe you don't mean to focus on this libstdc++ question. If you build C++, for g++ compatibility, icpc and g++ make the same requirements about presence of the same STL headers and libraries. If you don't use them in your code or libraries, they have no effect.
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