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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - leak in std/thread/futures/futures.shared_future/get.pass.cpp"
href="http://llvm.org/bugs/show_bug.cgi?id=22606">22606</a>
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<th>Summary</th>
<td>leak in std/thread/futures/futures.shared_future/get.pass.cpp
</td>
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<th>Product</th>
<td>libc++
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</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>
<tr>
<th>Component</th>
<td>All Bugs
</td>
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<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>earthdok@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>eric@efcs.ca, kcc@google.com, llvmbugs@cs.uiuc.edu, mclow.lists@gmail.com, samsonov@google.com
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
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<pre>Created <span class=""><a href="attachment.cgi?id=13879" name="attach_13879" title="reproducer">attachment 13879</a> <a href="attachment.cgi?id=13879&action=edit" title="reproducer">[details]</a></span>
reproducer
LeakSanitizer reports a flaky leak of __thread_struct + __thread_struct_impl in
this test:
<a href="http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-ubuntu-asan/builds/175/steps/test.libcxx/logs/libc%2B%2B%3A%3Aget.pass.cpp">http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-ubuntu-asan/builds/175/steps/test.libcxx/logs/libc%2B%2B%3A%3Aget.pass.cpp</a>
I've attached a reduced test case. To build:
../build/bin/clang++ -std=c++11 -nostdinc++
-I../llvm/projects/libcxx/test/support -include
../llvm/projects/libcxx/test/support/nasty_macros.hpp
-I../llvm/projects/libcxx/include -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
-D__STDC_CONSTANT_MACROS -nodefaultlibs -Llib/
-Wl,-rpath,/usr/local/google/home/earthdok/san/build-libcxx/lib -lc++ -lc++abi
-lgcc_eh -lc -lm -lpthread -lrt -lgcc_s -ldl -fsanitize=address -g
-fno-omit-frame-pointer repro.cpp
After adding some logging output, I believe that this is *not* an LSan issue.
Normally __thread_struct is allocated here:
#0 0x4c1e6b in operator new(unsigned long) _asan_rtl_:35
#1 0x4cee23 in void* std::__1::__thread_proxy<std::__1::tuple<void
(*)(std::__1::promise<void>), std::__1::promise<void> > >(void*)
/usr/local/google/home/earthdok/san/build-libcxx/../llvm/projects/libcxx/include/thread:346:33
#2 0x4ab00e in __asan::AsanThread::ThreadStart(unsigned long,
__sanitizer::atomic_uintptr_t*) _asan_rtl_:25
and deleted from a TSD destructor here:
#0 0x4c24eb in operator delete(void*) _asan_rtl_:3
#1 0x7fbaca476ad5 in
std::__1::__thread_specific_ptr<std::__1::__thread_struct>::__at_thread_exit(void*)
/usr/local/google/home/earthdok/san/llvm/projects/libcxx/include/thread:146:5
#2 0x7fbac95a5f81 in __nptl_deallocate_tsd
/build/buildd/eglibc-2.19/nptl/pthread_create.c:158:0
However, in those cases when there is a leak, the TSD destructor call doesn't
happen. Looks like there's a race between the global __thread_specific_ptr
destructor which runs on the main thread and calls pthread_key_delete(), and
the TSD destructor. If the pthread_key_delete() call happens first, the TSD
destructor is not run.
Now, we can probably work around this in LSan, but I'm not convinced this is
good behavior on part of libc++. Another option would be to hold
__thread_struct in a special kind of __thread_specific_ptr which wouldn't call
pthread_key_delete() on destruction.</pre>
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