Possible data race while reading 2 files - c++

Question

I am trying to read the contents of the same file using 2 different threads in C++. Helgrind complains of a possible data race. Since reading the contents of the file does not change the state of the file, I do not understand why Helgrind is reporting a problem.
Below is Helgrind's message:
Possible data race during write of size 8 at 0x6647828 by thread #3
==10434== Locks held: none
==10434== at 0x4C2C387: free (vg_replace_malloc.c:537)
==10434== by 0x58E61B6: fclose##GLIBC_2.2.5 (iofclose.c:84)
==10434== by 0x50D454D: std::\__basic_file\<char\>::close() (basic_file.cc:277)
==10434== by 0x510F6CD: std::basic_filebuf\<char, std::char_traits\<char\> \>::close() (fstream.tcc:166)
==10434== by 0x510F9B4: \~basic_filebuf (fstream:220)
==10434== by 0x510F9B4: std::basic_ifstream\<char, std::char_traits\<char\> \>::\~basic_ifstream() (fstream:499)
==10434== by 0x401286: fn(void\*) (in a.out)
==10434== by 0x4C30EEE: mythread_wrapper (hg_intercepts.c:387)
==10434== by 0x4E43EA4: start_thread (pthread_create.c:307)
==10434== by 0x597696C: clone (clone.S:111)
==10434==
==10434== This conflicts with a previous write of size 8 by thread #2
==10434== Locks held: none
==10434== at 0x58F437F: \_IO_un_link (genops.c:81)
==10434== by 0x58E61DC: fclose##GLIBC_2.2.5 (iofclose.c:54)
==10434== by 0x50D454D: std::\__basic_file\<char\>::close() (basic_file.cc:277)
==10434== by 0x510F6CD: std::basic_filebuf\<char, std::char_traits\<char\> \>::close() (fstream.tcc:166)
==10434== by 0x510F9B4: \~basic_filebuf (fstream:220)
==10434== by 0x510F9B4: std::basic_ifstream\<char, std::char_traits\<char\> \>::\~basic_ifstream() (fstream:499)
==10434== by 0x401286: fn(void\*) (in a.out)
==10434== by 0x4C30EEE: mythread_wrapper (hg_intercepts.c:387)
==10434== by 0x4E43EA4: start_thread (pthread_create.c:307)
Below is the code to reproduce the above issue:
#include <fstream>
#include <iostream>
#include <stdio.h>
using namespace std;
void* fn(void* parameter) {
ifstream inputFile("sample", ios::in);
while (!inputFile.eof()) {
string line;
getline(inputFile, line);
}
return NULL;
}
int main() {
pthread_t t1, t2;
pthread_create(&t1, NULL, fn, NULL);
pthread_create(&t2, NULL, fn, NULL);
pthread_join(t1, NULL);
pthread_join(t2, NULL);
}
I tried to find out if reading a file changes the state of the file but I could not find any possible explanation. I am expecting that there is no data race when reading a file paralelly.