[Patch] Optimise unix/apr_atomic.c

[Colin Hirsch]

Hi,

this patch only makes one change in three places:

* Remove the redundant memory read from the CAS-based fallback
  implementations.

Regards, Colin


Index: atomic/unix/apr_atomic.c
===================================================================
--- atomic/unix/apr_atomic.c    (revision 472020)
+++ atomic/unix/apr_atomic.c    (working copy)
@@ -252,12 +252,13 @@
 #if defined(APR_OVERRIDE_ATOMIC_CAS32)
 apr_uint32_t apr_atomic_add32(volatile apr_uint32_t *mem, apr_uint32_t val)
 {
-    apr_uint32_t old_value, new_value;
+    apr_uint32_t old_value;
+    apr_uint32_t tmp_value = *mem;
     
     do {
-        old_value = *mem;
-        new_value = old_value + val;
-    } while (apr_atomic_cas32(mem, new_value, old_value) != old_value);
+        old_value = tmp_value;
+        tmp_value = apr_atomic_cas32(mem, old_value + val, old_value);
+    } while (tmp_value != old_value);
     return old_value;
 }
 #else
@@ -285,12 +286,13 @@
 #if defined(APR_OVERRIDE_ATOMIC_CAS32)
 void apr_atomic_sub32(volatile apr_uint32_t *mem, apr_uint32_t val)
 {
-    apr_uint32_t old_value, new_value;
+    apr_uint32_t old_value;
+    apr_uint32_t tmp_value = *mem;
     
     do {
-        old_value = *mem;
-        new_value = old_value - val;
-    } while (apr_atomic_cas32(mem, new_value, old_value) != old_value);
+        old_value = tmp_value;
+        tmp_value = apr_atomic_cas32(mem, old_value - val, old_value);
+    } while (tmp_value != old_value);
 }
 #else
 void apr_atomic_sub32(volatile apr_uint32_t *mem, apr_uint32_t val) 
@@ -334,12 +336,13 @@
 #if defined(APR_OVERRIDE_ATOMIC_CAS32)
 int apr_atomic_dec32(volatile apr_uint32_t *mem)
 {
-    apr_uint32_t old_value, new_value;
+    apr_uint32_t old_value;
+    apr_uint32_t tmp_value = *mem;
     
     do {
-        old_value = *mem;
-        new_value = old_value - 1;
-    } while (apr_atomic_cas32(mem, new_value, old_value) != old_value);
+        old_value = tmp_value;
+        tmp_value = apr_atomic_cas32(mem, old_value - 1, old_value);
+    } while (tmp_value != old_value);
     return old_value != 1;
 }
 #else