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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Race condition in steady_clock::now for _LIBCPP_WIN32API"
href="https://bugs.llvm.org/show_bug.cgi?id=41323">41323</a>
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<th>Summary</th>
<td>Race condition in steady_clock::now for _LIBCPP_WIN32API
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>ivafanas@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>Method implementation is:
```
steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
static LARGE_INTEGER freq;
static BOOL initialized = FALSE;
if (!initialized)
initialized = QueryPerformanceFrequency(&freq); // always succceeds
LARGE_INTEGER counter;
QueryPerformanceCounter(&counter);
return time_point(duration(counter.QuadPart * nano::den / freq.QuadPart));
}
```
And seems like there is a race condition on `freq` and `initialized` variables
if `steady_clock::now` has never been called before new threads creation.
Possible fixes are:
1. use thread local storage for `freq` and `initialized`, but there might be
some problems on Windows XP:
<a href="https://reverseengineering.stackexchange.com/questions/14171/thread-local-storage-access-on-windows-xp">https://reverseengineering.stackexchange.com/questions/14171/thread-local-storage-access-on-windows-xp</a>
2. use `std::call_once` guard, but it is slightly slower than thread local due
to atomic access.</pre>
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