[libstdc++] do not destruct mutex_pool mutexes

On vxworks, after destroying the semaphore used to implement a mutex,
__gthread_mutex_lock fails and __gnu_cxx::__mutex::lock calls
__throw_concurrence_lock_error.  Nothing ensures the mutex_pool
mutexes survive init-once objects containing _Safe_sequence_base.  If
such an object completes construction before mutex_pool
initialization, it will be registered for atexit destruction after the
mutex_pool mutexes, so the _M_detach_all() call in the
_Safe_sequence_base dtor will use already-destructed mutexes, and
basic_string/requirements/citerators_cc fails calling terminate.

This patch fixes this problem by ensuring the mutex pool mutexes are
constructed on demand, on a statically-allocated buffer, but never
destructed.


for  libstdc++-v3/ChangeLog

	* src/c++11/shared_ptr.cc (__gnu_internal::get_mutex):
	Avoid destruction of the mutex pool.

1 files changed, 5 insertions, 1 deletions

diff --git a/libstdc++-v3/src/c++11/shared_ptr.cc b/libstdc++-v3/src/c++11/shared_ptr.cc
index bc70134..74e879e 100644
--- a/libstdc++-v3/src/c++11/shared_ptr.cc
+++ b/libstdc++-v3/src/c++11/shared_ptr.cc
@@ -36,7 +36,11 @@ namespace __gnu_internal _GLIBCXX_VISIBILITY(hidden)
   {
     // increase alignment to put each lock on a separate cache line
     struct alignas(64) M : __gnu_cxx::__mutex { };
-    static M m[mask + 1];
+    // Use a static buffer, so that the mutexes are not destructed
+    // before potential users (or at all)
+    static __attribute__ ((aligned(__alignof__(M))))
+      char buffer[(sizeof (M)) * (mask + 1)];
+    static M *m = new (buffer) M[mask + 1];
     return m[i];
   }
 }