[GitHub] [arrow] bkietz commented on a change in pull request #7493: ARROW-9183: [C++] Fix build with clang & old libstdc++.

[GitBox <gi...@apache.org>]

bkietz commented on a change in pull request #7493:
URL: https://github.com/apache/arrow/pull/7493#discussion_r442924149



##########
File path: cpp/src/arrow/util/atomic_shared_ptr.h
##########
@@ -24,7 +24,9 @@
 namespace arrow {
 namespace internal {
 
-#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ < 5
+// https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html#abi.versioning
+// https://gcc.gnu.org/develop.html#timeline
+#if defined(__GLIBCXX__) && __GLIBCXX__ < 20150422
 
 // atomic shared_ptr operations only appeared in gcc 5,
 // emulate them with unsafe ops on gcc 4.x.

Review comment:
       ```suggestion
   #if defined(__GLIBCXX__) && __GLIBCXX__ < 20150422
   
   // Atomic shared_ptr operations only appeared in gcc 5's libstdc++,
   // emulate them with unsafe ops if unavailable.
   // 
   // The libstdc++ version is a the encoded release date of gcc 5, see
   // https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html#abi.versioning.__GLIBCXX__
   ```




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