Bug 334826: use compiler's intrinsic atomic functions only when our ownNSPR_HEAD_20080127

PR_AtomicXXX functions are truly atomic, otherwise the macros and functions
can't be used interchangeably.  Add Nelson's suggested changes as a TODO
comment.
Modified files: pratom.h atomic.c

2 files changed, 22 insertions, 2 deletions

diff --git a/pr/include/pratom.h b/pr/include/pratom.h
index 2e4967c2..9389ee38 100644
--- a/pr/include/pratom.h
+++ b/pr/include/pratom.h
@@ -102,6 +102,13 @@ NSPR_API(PRInt32)	PR_AtomicAdd(PRInt32 *ptr, PRInt32 val);
 ** DESCRIPTION:
 **    Macro versions of the atomic operations.  They may be implemented
 **    as compiler intrinsics.
+**
+** IMPORTANT NOTE TO NSPR MAINTAINERS:
+**    Implement these macros with compiler intrinsics only on platforms
+**    where the PR_AtomicXXX functions are truly atomic (i.e., where the
+**    configuration macro _PR_HAVE_ATOMIC_OPS is defined).  Otherwise,
+**    the macros and functions won't be compatible and can't be used
+**    interchangeably.
 */
 #if defined(_WIN32) && (_MSC_VER >= 1310)
 
@@ -123,8 +130,13 @@ long __cdecl _InterlockedExchangeAdd(long volatile *Addend, long Value);
 #define PR_ATOMIC_ADD(ptr, val) (_InterlockedExchangeAdd(ptr, val) + (val))
 
 #elif ((__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 1)) && \
-    (defined(__i386__) || defined(__ia64__) || defined(__x86_64__) || \
-    defined(__powerpc__) || defined(__ppc__) || defined(__alpha))
+      ((defined(DARWIN) && \
+           (defined(__ppc__) || defined(__i386__))) || \
+       (defined(LINUX) && \
+           (defined(__i386__) || defined(__ia64__) || defined(__x86_64__) || \
+           (defined(__powerpc__) && !defined(__powerpc64__)) || \
+           defined(__alpha))))
+
 /*
  * Because the GCC manual warns that some processors may support
  * reduced functionality of __sync_lock_test_and_set, we test for the
diff --git a/pr/tests/atomic.c b/pr/tests/atomic.c
index 4b454fee..5970fe0c 100644
--- a/pr/tests/atomic.c
+++ b/pr/tests/atomic.c
@@ -39,6 +39,14 @@
 #include "prprf.h"
 #include "pratom.h"
 
+/*
+ * TODO: create a macro to generate the six lines of code that are repeated
+ * for every test.  Also rewrite the statement
+ *     result = result | ((EXPRESSION) ? 0 : 1);
+ * as
+ *     result |= !(EXPRESSION);
+ */
+
 PRIntn main(PRIntn argc, char **argv)
 {
     PRInt32 rv, oldval, test, result = 0;