Replace x86 membarriers with GCC built-ins

This patch replaces the x86 asm memory barriers with
mostly platform-independent GCC built-ins. Beware though:
I've once seen __sync_synchronize() fail to generate
a barrier on MacOS X (Darwin)---maybe it could happen
again on another platform.

2 files changed, 22 insertions, 7 deletions

diff --git a/include/atomic.h b/include/atomic.h
new file mode 100644
index 0000000..ec5c09c
--- /dev/null
+++ b/include/atomic.h
@@ -0,0 +1,13 @@
+// Copyright (c) 2014, Glenn Elliott
+// All rights reserved.
+
+#pragma once
+
+static inline void __sync_pause()
+{
+#if (ARCH == x86_64) || (ARCH == i386) || (ARCH == i686)
+        asm volatile("pause": : :"memory");
+#else
+        __sync_synchronize();
+#endif
+}
diff --git a/include/ticketlock.h b/include/ticketlock.h
index 17e5000..4c1035c 100644
--- a/include/ticketlock.h
+++ b/include/ticketlock.h
@@ -13,6 +13,8 @@
 #include "litmus.h"
 #endif
 
+#include "atomic.h"
+
 #if ULONG_MAX == 0xffffffffffffffffUL
 typedef unsigned long long ticketdata_t;
 typedef uint32_t ticketid_t;
@@ -45,8 +47,8 @@ static inline void __tl_lock(ticketlock_t* t)
         ticketlock_t updated = { __sync_fetch_and_add(&t->data, TL_INC) };
         if(updated.next != updated.owner)
                 while(updated.next != t->owner)
-                        asm volatile("pause": : :"memory");
-        asm volatile("mfence": : :"memory");
+                        __sync_pause();
+        __sync_synchronize();
 }
 
 static inline void tl_lock(ticketlock_t* t)
@@ -56,7 +58,7 @@ static inline void tl_lock(ticketlock_t* t)
 
 static inline void __tl_unlock(ticketlock_t* t)
 {
-        asm volatile("mfence": : :"memory");
+        __sync_synchronize();
         __sync_fetch_and_add(&t->owner, (ticketid_t)1);
 }
 
@@ -95,9 +97,9 @@ static inline void tl_lock_np(ticketlock_t* t, unsigned long* flags)
         asm volatile("cli": : :"memory");
 #elif defined(PGM_NP_LITMUS)
         /* start non-preemption */
-        asm volatile("mfence": : :"memory");
+        __sync_synchronize();
         enter_np();
-        asm volatile("mfence": : :"memory");
+        __sync_synchronize();
 #endif
 
         __tl_lock(t);
@@ -112,9 +114,9 @@ static inline void tl_unlock_np(ticketlock_t* t, unsigned long flags)
         restore_flags(flags);
 #elif defined(PGM_NP_LITMUS)
         /* end non-preemption */
-        asm volatile("mfence": : :"memory");
+        __sync_synchronize();
         exit_np();
-        asm volatile("mfence": : :"memory");
+        __sync_synchronize();
 #endif
 }
 #endif