title: C++ 11 threads with clang
body: <p>I wanted to learn use of C++11 threads to speed up compilation of my language (yes I'm building a compiler :x). The first sample I tried threw several errors with clang (3.3 SVN). It compiled fine under GCC (4.6.3).</p>
  
  <p>I downloaded clang and libc++ from llvm.org's SVN. clang was compiled with GCC (4.6.3) and libc++ was compiled with clang. Both makefiles were generated with CMake.</p>
  
  <p>For clang I followed this guide: <a href="http://llvm.org/docs/GettingStarted.html#checkout" rel="nofollow">http://llvm.org/docs/GettingStarted.html#checkout</a></p>
  
  <p>For libc++ I followed this guide: <a href="http://libcxx.llvm.org/" rel="nofollow">http://libcxx.llvm.org/</a></p>
  
  <p>The piece of code I want to compile (<code>foobar.cpp</code>):</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;thread&gt;
  
  using namespace std;
  
  int main(void) {
      thread t1([](void)-&gt;void {
          cout &lt;&lt; "foobar" &lt;&lt; endl;
      });
  }
  </code></pre>
  
  <p>It compiles fine with <code>clang --std=c++0x -stdlib=libc++ -lpthread foobar.cpp</code> but I get a lot of linker errors:</p>
  
  <pre><code>/tmp/foobar-59W5DR.o: In function `main':
  foobar.cpp:(.text+0x21): undefined reference to `std::__1::thread::~thread()'
  /tmp/foobar-59W5DR.o: In function `_ZNSt3__16threadC2IZ4mainE3$_0JEvEEOT_DpOT0_':
  foobar.cpp:(.text+0x5c): undefined reference to `operator new(unsigned long)'
  foobar.cpp:(.text+0x186): undefined reference to `operator delete(void*)'
  foobar.cpp:(.text+0x19b): undefined reference to `std::__1::__throw_system_error(int, char const*)'
  /tmp/foobar-59W5DR.o: In function `_ZNSt3__114__thread_proxyINS_5tupleIJZ4mainE3$_0EEEEEPvS4_':
  foobar.cpp:(.text+0x200): undefined reference to `std::__1::__thread_local_data()'
  foobar.cpp:(.text+0x211): undefined reference to `operator new(unsigned long)'
  foobar.cpp:(.text+0x23b): undefined reference to `std::__1::__thread_struct::__thread_struct()'
  foobar.cpp:(.text+0x31b): undefined reference to `operator delete(void*)'
  /tmp/foobar-59W5DR.o: In function `_ZNSt3__110unique_ptrINS_5tupleIJZ4mainE3$_0EEENS_14default_deleteIS3_EEED2Ev':
  foobar.cpp:(.text+0x3dd): undefined reference to `operator delete(void*)'
  /tmp/foobar-59W5DR.o: In function `main::$_0::operator()() const':
  foobar.cpp:(.text+0x3fc): undefined reference to `std::__1::cout'
  /tmp/foobar-59W5DR.o: In function `_ZNSt3__110unique_ptrINS_5tupleIJZ4mainE3$_0EEENS_14default_deleteIS3_EEEC2EPS3_':
  foobar.cpp:(.text+0x4e9): undefined reference to `std::terminate()'
  /tmp/foobar-59W5DR.o: In function `std::__1::__thread_specific_ptr&lt;std::__1::__thread_struct&gt;::reset(std::__1::__thread_struct*)':
  foobar.cpp:(.text._ZNSt3__121__thread_specific_ptrINS_15__thread_structEE5resetEPS1_[_ZNSt3__121__thread_specific_ptrINS_15__thread_structEE5resetEPS1_]+0x57): undefined reference to `std::__1::__thread_struct::~__thread_struct()'
  foobar.cpp:(.text._ZNSt3__121__thread_specific_ptrINS_15__thread_structEE5resetEPS1_[_ZNSt3__121__thread_specific_ptrINS_15__thread_structEE5resetEPS1_]+0x60): undefined reference to `operator delete(void*)'
  /tmp/foobar-59W5DR.o: In function `std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;&amp; std::__1::operator&lt;&lt; &lt;std::__1::char_traits&lt;char&gt; &gt;(std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;&amp;, char const*)':
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x28): undefined reference to `std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;::sentry::sentry(std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;&amp;)'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x1ec): undefined reference to `std::__1::ios_base::getloc() const'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x1fe): undefined reference to `std::__1::ctype&lt;char&gt;::id'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x206): undefined reference to `std::__1::locale::use_facet(std::__1::locale::id&amp;) const'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x272): undefined reference to `std::__1::locale::~locale()'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x294): undefined reference to `std::__1::locale::~locale()'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x378): undefined reference to `std::__1::ios_base::clear(unsigned int)'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x3d0): undefined reference to `std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;::sentry::~sentry()'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x3dc): undefined reference to `__cxa_begin_catch'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x3f9): undefined reference to `std::__1::ios_base::__set_badbit_and_consider_rethrow()'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x403): undefined reference to `__cxa_end_catch'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x424): undefined reference to `std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;::sentry::~sentry()'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x43d): undefined reference to `__cxa_end_catch'
  foobar.cpp:(.text._ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc[_ZNSt3__1lsINS_11char_traitsIcEEEERNS_13basic_ostreamIcT_EES6_PKc]+0x466): undefined reference to `std::terminate()'
  /tmp/foobar-59W5DR.o: In function `std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;&amp; std::__1::endl&lt;char, std::__1::char_traits&lt;char&gt; &gt;(std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;&amp;)':
  foobar.cpp:(.text._ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_[_ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_]+0x38): undefined reference to `std::__1::ios_base::getloc() const'
  foobar.cpp:(.text._ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_[_ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_]+0x49): undefined reference to `std::__1::ctype&lt;char&gt;::id'
  foobar.cpp:(.text._ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_[_ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_]+0x55): undefined reference to `std::__1::locale::use_facet(std::__1::locale::id&amp;) const'
  foobar.cpp:(.text._ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_[_ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_]+0xac): undefined reference to `std::__1::locale::~locale()'
  foobar.cpp:(.text._ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_[_ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_]+0xbe): undefined reference to `std::__1::locale::~locale()'
  foobar.cpp:(.text._ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_[_ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_]+0xcd): undefined reference to `std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;::put(char)'
  foobar.cpp:(.text._ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_[_ZNSt3__14endlIcNS_11char_traitsIcEEEERNS_13basic_ostreamIT_T0_EES7_]+0xdd): undefined reference to `std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;::flush()'
  /tmp/foobar-59W5DR.o: In function `std::__1::ostreambuf_iterator&lt;char, std::__1::char_traits&lt;char&gt; &gt; std::__1::__pad_and_output&lt;char, std::__1::char_traits&lt;char&gt; &gt;(std::__1::ostreambuf_iterator&lt;char, std::__1::char_traits&lt;char&gt; &gt;, char const*, char const*, char const*, std::__1::ios_base&amp;, char)':
  foobar.cpp:(.text._ZNSt3__116__pad_and_outputIcNS_11char_traitsIcEEEENS_19ostreambuf_iteratorIT_T0_EES6_PKS4_S8_S8_RNS_8ios_baseES4_[_ZNSt3__116__pad_and_outputIcNS_11char_traitsIcEEEENS_19ostreambuf_iteratorIT_T0_EES6_PKS4_S8_S8_RNS_8ios_baseES4_]+0x215): undefined reference to `std::__1::basic_string&lt;char, std::__1::char_traits&lt;char&gt;, std::__1::allocator&lt;char&gt; &gt;::__init(unsigned long, char)'
  foobar.cpp:(.text._ZNSt3__116__pad_and_outputIcNS_11char_traitsIcEEEENS_19ostreambuf_iteratorIT_T0_EES6_PKS4_S8_S8_RNS_8ios_baseES4_[_ZNSt3__116__pad_and_outputIcNS_11char_traitsIcEEEENS_19ostreambuf_iteratorIT_T0_EES6_PKS4_S8_S8_RNS_8ios_baseES4_]+0x389): undefined reference to `std::__1::basic_string&lt;char, std::__1::char_traits&lt;char&gt;, std::__1::allocator&lt;char&gt; &gt;::~basic_string()'
  foobar.cpp:(.text._ZNSt3__116__pad_and_outputIcNS_11char_traitsIcEEEENS_19ostreambuf_iteratorIT_T0_EES6_PKS4_S8_S8_RNS_8ios_baseES4_[_ZNSt3__116__pad_and_outputIcNS_11char_traitsIcEEEENS_19ostreambuf_iteratorIT_T0_EES6_PKS4_S8_S8_RNS_8ios_baseES4_]+0x3a4): undefined reference to `std::__1::basic_string&lt;char, std::__1::char_traits&lt;char&gt;, std::__1::allocator&lt;char&gt; &gt;::~basic_string()'
  /tmp/foobar-59W5DR.o:(.eh_frame+0x47): undefined reference to `__gxx_personality_v0'
  clang-3: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>Here are the standard search directories under the two standard libraries.
  As result of 'clang -Wp,-v -x c++ - -fsyntax-only' I got this:</p>
  
  <p>I tried <code>clang --std=c++11 -stdlib=libc++ -llibc++ -lpthread -o foobar foobar.cpp</code> but the linker failed again, it does not find libc++. Do I fail on linking to libc++ or is it something more difficult?</p>