Implement a more reliable detection scheme for os_unfair_lock.
The core issue here is the weak linking of the symbol, and in certain
environments--for instance, using the latest Xcode (8.1) with the latest
SDK (10.12)--os_unfair_lock may resolve even though you're compiling on
a host that doesn't support it (10.11).
We can use the availability macros to circumvent this problem, and
detect that we're not compiling for a target that is going to support
them and error out at compile time. The other alternative is to do a
runtime check, but that presents issues for cross-compiling.
diff --git a/configure.ac b/configure.ac
index 25dcc2c..2e3ef36 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1670,10 +1670,15 @@
JE_COMPILABLE([Darwin os_unfair_lock_*()], [
#include <os/lock.h>
+#include <AvailabilityMacros.h>
], [
+ #if MAC_OS_X_VERSION_MIN_REQUIRED < 101200
+ #error "os_unfair_lock is not supported"
+ #else
os_unfair_lock lock = OS_UNFAIR_LOCK_INIT;
os_unfair_lock_lock(&lock);
os_unfair_lock_unlock(&lock);
+ #endif
], [je_cv_os_unfair_lock])
if test "x${je_cv_os_unfair_lock}" = "xyes" ; then
AC_DEFINE([JEMALLOC_OS_UNFAIR_LOCK], [ ])
