From: Stefan Ring <stefan@complang.tuwien.ac.at>
Date: Mon, 21 Sep 2009 18:39:19 +0000 (+0200)
Subject: * src/threads/lock.cpp: Slight memory barrier clarification.
X-Git-Url: http://wien.tomnetworks.com/gitweb/?p=cacao.git;a=commitdiff_plain;h=7393753e3a67c410b8741ed130422bdfbdc90f69

* 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 a26c7879b..140905e2b 100644
--- 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 a3a91be15..29c0603ea 100644
--- 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 787eba2d3..80ac34246 100644
--- 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 */