* src/threads/lock.cpp: Slight memory barrier clarification.

* src/vm/jit/i386/arch.h: Define CAS_PROVIDES_FULL_BARRIER.
* src/vm/jit/x86_64/arch.h: Likewise.

diff --git a/src/threads/lock.cpp b/src/threads/lock.cpp
index a26c7879b9643bc0e5dba9533d209b88925ce56c..140905e2b6625ae6b6bf497ff41947e8bbf494e0 100644 (file)
--- a/src/threads/lock.cpp
+++ b/src/threads/lock.cpp
@@ -864,9 +864,15 @@ retry:
 
        if (result == true) {
                // Success, we locked it.
-               // NOTE: The Java Memory Model requires an instruction barrier
-               // here (because of the CAS above).
+               // NOTE: The Java Memory Model requires a memory barrier here.
+#if defined(CAS_PROVIDES_FULL_BARRIER) && CAS_PROVIDES_FULL_BARRIER
+               // On some architectures, the CAS (hidden in the
+               // lockword->lock call above), already provides this barrier,
+               // so we only need to inform the compiler.
                Atomic::instruction_barrier();
+#else
+               Atomic::memory_barrier();
+#endif
                return true;
        }
 
@@ -972,7 +978,7 @@ bool lock_monitor_exit(java_handle_t* o)
                // Memory barrier for Java Memory Model.
                Atomic::write_memory_barrier();
                lockword->unlock();
-               // Memory barrier for thin locking.
+               // Memory barrier for FLC bit testing.
                Atomic::memory_barrier();
 
                /* check if there has been a flat lock contention on this object */

diff --git a/src/vm/jit/i386/arch.h b/src/vm/jit/i386/arch.h
index a3a91be153706d0abfdc8589163cdc47c6fecefd..29c0603eab8a8d1ec2590f6a781fe83798ed6307 100644 (file)
--- a/src/vm/jit/i386/arch.h
+++ b/src/vm/jit/i386/arch.h
@@ -149,6 +149,10 @@
 
 #define USES_NEW_SUBTYPE                 1
 
+/* memory barriers ************************************************************/
+
+#define CAS_PROVIDES_FULL_BARRIER        1
+
 #endif /* _ARCH_H */
 
 

diff --git a/src/vm/jit/x86_64/arch.h b/src/vm/jit/x86_64/arch.h
index 787eba2d30dc97d9f87c0a5180ddabf922047c4c..80ac34246003c2bf23ac998e5450249c9dd45f9e 100644 (file)
--- a/src/vm/jit/x86_64/arch.h
+++ b/src/vm/jit/x86_64/arch.h
@@ -1,9 +1,7 @@
 /* src/vm/jit/x86_64/arch.h - architecture defines for x86_64
 
-   Copyright (C) 1996-2005, 2006, 2007 R. Grafl, A. Krall, C. Kruegel,
-   C. Oates, R. Obermaisser, M. Platter, M. Probst, S. Ring,
-   E. Steiner, C. Thalinger, D. Thuernbeck, P. Tomsich, C. Ullrich,
-   J. Wenninger, Institut f. Computersprachen - TU Wien
+   Copyright (C) 1996-2008, 2009
+   CACAOVM - Verein zur Foerderung der freien virtuellen Maschine CACAO
 
    This file is part of CACAO.
 
@@ -124,6 +122,10 @@
 
 #define USES_NEW_SUBTYPE                 1
 
+/* memory barriers ************************************************************/
+
+#define CAS_PROVIDES_FULL_BARRIER        1
+
 #endif /* _ARCH_H */