+#if I_THREADSAFE
+/* We must use preexistent global mutexes or we will never be able to destroy
+ * them. */
+# if I_HAS_PERL(5, 9, 3)
+# define I_LOADED_LOCK MUTEX_LOCK(&PL_my_ctx_mutex)
+# define I_LOADED_UNLOCK MUTEX_UNLOCK(&PL_my_ctx_mutex)
+# else
+# define I_LOADED_LOCK OP_REFCNT_LOCK
+# define I_LOADED_UNLOCK OP_REFCNT_UNLOCK
+# endif
+#else
+# define I_LOADED_LOCK NOOP
+# define I_LOADED_UNLOCK NOOP
+#endif
+
+#if defined(OP_CHECK_MUTEX_LOCK) && defined(OP_CHECK_MUTEX_UNLOCK)
+# define I_CHECK_LOCK OP_CHECK_MUTEX_LOCK
+# define I_CHECK_UNLOCK OP_CHECK_MUTEX_UNLOCK
+#elif I_HAS_PERL(5, 9, 3)
+# define I_CHECK_LOCK OP_REFCNT_LOCK
+# define I_CHECK_UNLOCK OP_REFCNT_UNLOCK
+#else
+/* Before perl 5.9.3, indirect_ck_*() calls are already protected by the
+ * I_LOADED mutex, which falls back to the OP_REFCNT mutex. Make sure we don't
+ * lock it twice. */
+# define I_CHECK_LOCK NOOP
+# define I_CHECK_UNLOCK NOOP
+#endif
+
+typedef OP *(*indirect_ck_t)(pTHX_ OP *);
+
+#ifdef wrap_op_checker
+
+# define indirect_ck_replace(T, NC, OCP) wrap_op_checker((T), (NC), (OCP))
+
+#else
+
+static void indirect_ck_replace(pTHX_ OPCODE type, indirect_ck_t new_ck, indirect_ck_t *old_ck_p) {
+#define indirect_ck_replace(T, NC, OCP) indirect_ck_replace(aTHX_ (T), (NC), (OCP))
+ I_CHECK_LOCK;
+ if (!*old_ck_p) {
+ *old_ck_p = PL_check[type];
+ PL_check[type] = new_ck;
+ }
+ I_CHECK_UNLOCK;
+}
+
+#endif
+
+static void indirect_ck_restore(pTHX_ OPCODE type, indirect_ck_t *old_ck_p) {
+#define indirect_ck_restore(T, OCP) indirect_ck_restore(aTHX_ (T), (OCP))
+ I_CHECK_LOCK;
+ if (*old_ck_p) {
+ PL_check[type] = *old_ck_p;
+ *old_ck_p = 0;
+ }
+ I_CHECK_UNLOCK;
+}
+