Use thread-safe reference counting if supported by the compiler.

This makes use of __atomic or __sync builtin compiler functions to make
json_decref and json_incref thread-safe.

Issue #387

1 files changed, 10 insertions, 2 deletions

diff --git a/configure.ac b/configure.ac
index d1c4faf..fa0f005 100644
--- a/configure.ac
+++ b/configure.ac
@@ -38,25 +38,33 @@ AC_CHECK_FUNCS([close getpid gettimeofday localeconv open read sched_yield strto
 AC_MSG_CHECKING([for gcc __sync builtins])
 have_sync_builtins=no
 AC_TRY_LINK(
-  [], [unsigned long val; __sync_bool_compare_and_swap(&val, 0, 1);],
+  [], [unsigned long val; __sync_bool_compare_and_swap(&val, 0, 1); __sync_add_and_fetch(&val, 1); __sync_sub_and_fetch(&val, 1);],
   [have_sync_builtins=yes],
 )
 if test "x$have_sync_builtins" = "xyes"; then
   AC_DEFINE([HAVE_SYNC_BUILTINS], [1],
     [Define to 1 if gcc's __sync builtins are available])
+  json_have_sync_builtins=1
+else
+  json_have_sync_builtins=0
 fi
+AC_SUBST([json_have_sync_builtins])
 AC_MSG_RESULT([$have_sync_builtins])
 
 AC_MSG_CHECKING([for gcc __atomic builtins])
 have_atomic_builtins=no
 AC_TRY_LINK(
-  [], [char l; unsigned long v; __atomic_test_and_set(&l, __ATOMIC_RELAXED); __atomic_store_n(&v, 1, __ATOMIC_RELEASE); __atomic_load_n(&v, __ATOMIC_ACQUIRE);],
+  [], [char l; unsigned long v; __atomic_test_and_set(&l, __ATOMIC_RELAXED); __atomic_store_n(&v, 1, __ATOMIC_RELEASE); __atomic_load_n(&v, __ATOMIC_ACQUIRE); __atomic_add_fetch(&v, 1, __ATOMIC_ACQUIRE); __atomic_sub_fetch(&v, 1, __ATOMIC_RELEASE);],
   [have_atomic_builtins=yes],
 )
 if test "x$have_atomic_builtins" = "xyes"; then
   AC_DEFINE([HAVE_ATOMIC_BUILTINS], [1],
     [Define to 1 if gcc's __atomic builtins are available])
+  json_have_atomic_builtins=1
+else
+  json_have_atomic_builtins=0
 fi
+AC_SUBST([json_have_atomic_builtins])
 AC_MSG_RESULT([$have_atomic_builtins])
 
 case "$ac_cv_type_long_long_int$ac_cv_func_strtoll" in