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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - NONDETERMINIZM: It seems, ThreadSanitizer does not understand OpenMP's critical section in C++"
href="https://bugs.llvm.org/show_bug.cgi?id=32840">32840</a>
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</tr>
<tr>
<th>Summary</th>
<td>NONDETERMINIZM: It seems, ThreadSanitizer does not understand OpenMP's critical section in C++
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>lebedev.ri@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Example one: (good)
#include <stdio.h>
int main() {
#ifdef _OPENMP
#pragma omp parallel num_threads(2)
#endif
#ifdef _OPENMP
#pragma omp critical(io)
#endif
{
printf("thread\n");
}
return 0;
}
$ clang-5.0 openmp-critical.c -fsanitize=thread
$ ./a.out
thread
As you can see, TSan does not complain, and there were only one print.
Let's enable OpenMP.
$ clang-5.0 openmp-critical.c -fsanitize=thread -fopenmp
$ ./a.out
thread
thread
As you can see, TSan does not complain, and there were two prints.
Now, let's check C++.
Example two (bad):
#include <cstdio>
#include <iostream>
int main() {
#ifdef _OPENMP
#pragma omp parallel num_threads(2)
#endif
#ifdef _OPENMP
#pragma omp critical(io)
#endif
{
std::cout << "thread\n";
}
return 0;
}
$ clang++-5.0 openmp-critical.cpp -fsanitize=thread
$ ./a.out
thread
Again all fine. Let's enable OpenMP.
$ clang++-5.0 openmp-critical.cpp -fsanitize=thread -fopenmp
$ ./a.out
==================
WARNING: ThreadSanitizer: data race (pid=30729)
Atomic read of size 1 at 0x7b6800000b00 by main thread:
#0 pthread_mutex_lock <null> (a.out+0x432067)
#1 <null> <null> (libomp.so.5+0x477a2)
#2 __libc_start_main <null> (libc.so.6+0x202b0)
Previous write of size 1 at 0x7b6800000b00 by thread T2:
#0 pthread_mutex_init <null> (a.out+0x42ae0a)
#1 <null> <null> (libomp.so.5+0x44c51)
Location is heap block of size 1440 at 0x7b6800000600 allocated by main
thread:
#0 malloc <null> (a.out+0x4296dd)
#1 getenv <null> (libomp.so.5+0x18202)
#2 __libc_start_main <null> (libc.so.6+0x202b0)
Thread T2 (tid=30732, running) created by main thread at:
#0 pthread_create <null> (a.out+0x42ab26)
#1 <null> <null> (libomp.so.5+0x458bb)
#2 __libc_start_main <null> (libc.so.6+0x202b0)
SUMMARY: ThreadSanitizer: data race (/tmp/a.out+0x432067) in pthread_mutex_lock
==================
thread
thread
ThreadSanitizer: reported 1 warnings
I'd expect that it should not complain.
And now the weirdest part: it only happens if the system is not in idle, i.e.
if there are some other computational/compilation processes running!</pre>
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