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

[cacao.git] / src / threads / lock.cpp

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 */