PR libstdc++/71312 Increase alignment of pooled mutexes

	PR libstdc++/71312
	* src/c++11/shared_ptr.cc (get_mutex): Align pool mutexes to 64 bytes.

From-SVN: r270649

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index a5482bb..2168a79 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,8 @@
 2019-04-29  Jonathan Wakely  <jwakely@redhat.com>
 
+       PR libstdc++/71312
+       * src/c++11/shared_ptr.cc (get_mutex): Align pool mutexes to 64 bytes.
+
        * include/bits/stl_bvector.h (vector<bool>::empty()): Add nodiscard
        attribute.
 

diff --git a/libstdc++-v3/src/c++11/shared_ptr.cc b/libstdc++-v3/src/c++11/shared_ptr.cc
index 1f1323e..a4e833b 100644 (file)
--- a/libstdc++-v3/src/c++11/shared_ptr.cc
+++ b/libstdc++-v3/src/c++11/shared_ptr.cc
@@ -34,7 +34,9 @@ namespace __gnu_internal _GLIBCXX_VISIBILITY(hidden)
   __gnu_cxx::__mutex&
   get_mutex(unsigned char i)
   {
-    static __gnu_cxx::__mutex m[mask + 1];
+    // increase alignment to put each lock on a separate cache line
+    struct alignas(64) M : __gnu_cxx::__mutex { };
+    static M m[mask + 1];
     return m[i];
   }
 }