From 66198f447f45a87718b6457756976baa8defb2fd Mon Sep 17 00:00:00 2001
From: Jay Berkenbilt <ejb@ql.org>
Date: Fri, 10 Apr 2020 13:30:00 -0400
Subject: Use -latomic if needed with gcc

---
 configure.ac | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

(limited to 'configure.ac')

diff --git a/configure.ac b/configure.ac
index 9a887b90..a3c3d064 100644
--- a/configure.ac
+++ b/configure.ac
@@ -240,6 +240,32 @@ for i in 0 1; do
 done
 AC_LANG_POP
 
+AC_LANG_PUSH([C++])
+AC_MSG_CHECKING(whether to use -latomic)
+dnl On some platforms with some versions of gcc, you have to link with
+dnl -latomic in order for std::atomic to work. Passing --as-needed
+dnl prevents unnecessary linking with -latomic.
+oLDFLAGS="$LDFLAGS"
+LDFLAGS="$LDFLAGS -Wl,--as-needed -latomic"
+AC_LINK_IFELSE([AC_LANG_SOURCE(
+  [[#include <atomic>
+    int main()
+    {
+        static std::atomic<int> a{0};
+        a = a.fetch_add(1);
+        return 0;
+    }
+   ]])],
+   [qpdf_USE_ATOMIC=1],
+   [qpdf_USE_ATOMIC=0])
+if test "$qpdf_USE_ATOMIC" = "1"; then
+  AC_MSG_RESULT(yes)
+else
+  AC_MSG_RESULT(no)
+  LDFLAGS="$oLDFLAGS"
+fi
+AC_LANG_POP
+
 if test "x$qpdf_OS_SECURE_RANDOM" = "x1"; then
   OLIBS=$LIBS
   LIBS="$LIBS Advapi32.lib"
-- 
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