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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - thread_local variables not constructed/destructed on Windows"
href="https://llvm.org/bugs/show_bug.cgi?id=30347">30347</a>
</td>
</tr>
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<th>Summary</th>
<td>thread_local variables not constructed/destructed on Windows
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.9
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++11
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>ryan.prichard@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>On Windows, C++11 thread_local variables aren't constructed (or destructed)
unless the program links with some other MSVC object file that also uses
thread_local variables.
Example:
#include <stdio.h>
struct MyLocal {
MyLocal() { printf("constructed\n"); }
~MyLocal() { printf("destructed\n"); }
void method() { printf("invoked\n"); }
};
thread_local MyLocal mylocal;
int main() {
mylocal.method();
}
The program should print:
constructed
invoked
destructed
Instead, it only prints "invoked". I'm using Clang 3.9 in a "VS2015 x64"
command window:
>"c:\Program Files\LLVM\bin\clang.exe" test.cc -o test.exe
>.\test
invoked
AFAICT, MSVC 2013 does not support thread_local variables. They were added in
MSVC 2015, which correctly calls the constructors.
I examined the object files produced by MSVC 2015. I noticed that it includes
one of these arguments in the .drectve section:
/include:___dyn_tls_init@12 [for 32-bit x86]
/include:__dyn_tls_init [for 64-bit x64]
My example code starts working if I add a pragma to the source:
#pragma comment(linker, "/include:___dyn_tls_init@12") [for 32-bit x86]
#pragma comment(linker, "/include:__dyn_tls_init") [for 64-bit x64]
Presumably Clang should also output this directive?
My specific toolchain versions:
clang version 3.9.0 (branches/release_39)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: c:\Program Files\LLVM\bin
Visual Studio 2015 Update 3
Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24213.1 for x64
Copyright (C) Microsoft Corporation. All rights reserved.</pre>
</div>
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