Squashed 'third_party/ctemplate/' content from commit 6742f62
Change-Id: I828e4e4c906f13ba19944d78a8a78652b62949af
git-subtree-dir: third_party/ctemplate
git-subtree-split: 6742f6233db12f545e90baa8f34f5c29c4eb396a
diff --git a/m4/ac_interlocked_exchange.m4 b/m4/ac_interlocked_exchange.m4
new file mode 100644
index 0000000..2de5007
--- /dev/null
+++ b/m4/ac_interlocked_exchange.m4
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+# Check whether InterlockedExchange() takes a LONG or a volatile LONG
+# as its first argument. InterlockedCompareExchange is a windows
+# function; obviously, this macro is useful only for cygwin and mingw,
+# and other systems that compile against the windows API.
+#
+# Apparently the interface for this function is a bit inconsistent.
+# Windows likes volatile LONG, but mingw and cygwin don't, at least
+# for the versions I'm using. But rather than try to guess who
+# supports what, let's just check at configure time. (Note: this
+# is an error in C++ but only a warning in C, so we test in the former.)
+#
+# This function returns 'yes' if the type does not need volatile,
+# and defines the symbol INTERLOCKED_EXCHANGE_NONVOLATILE. (This
+# is the expected case for mingw and cygwin). It returns 'no',
+# and defines no symbol, otherwise. (This is the expected case for
+# MSVC.) The return value was sset this way so that we don't need
+# to define any symbols on windows, which doesn't run configure.
+
+AC_DEFUN([AC_INTERLOCKED_EXCHANGE_NONVOLATILE],
+[
+AC_MSG_CHECKING(whether first argument to InterlockedExchange omits volatile)
+AC_CACHE_VAL(ac_cv_interlocked_exchange_nonvolatile,
+[AC_LANG_SAVE
+ AC_LANG_CPLUSPLUS
+ AC_TRY_COMPILE([#include <windows.h>],
+ [volatile LONG once; InterlockedExchange(&once, 1);],
+ ac_cv_interlocked_exchange_nonvolatile="no",
+ ac_cv_interlocked_exchange_nonvolatile="yes")
+ AC_LANG_RESTORE
+])
+if test "$ac_cv_interlocked_exchange_nonvolatile" = "yes"; then
+ AC_DEFINE(INTERLOCKED_EXCHANGE_NONVOLATILE, 1,
+ [define if first argument to InterlockedExchange is just LONG])
+fi
+AC_MSG_RESULT($ac_cv_interlocked_exchange_nonvolatile)
+])