From f34bf427b5270285225c613f81e3e056d505cfaa Mon Sep 17 00:00:00 2001
From: pliden <unknown>
Date: Tue, 20 May 2014 10:24:30 +0200
Subject: [PATCH] 8039042: G1: Phantom zeros in cardtable Reviewed-by:
 tschatzl, mgerdin

---
 .../gc_implementation/g1/g1SATBCardTableModRefBS.cpp   | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/share/vm/gc_implementation/g1/g1SATBCardTableModRefBS.cpp b/src/share/vm/gc_implementation/g1/g1SATBCardTableModRefBS.cpp
index 9f20a920b..7382be27f 100644
--- a/src/share/vm/gc_implementation/g1/g1SATBCardTableModRefBS.cpp
+++ b/src/share/vm/gc_implementation/g1/g1SATBCardTableModRefBS.cpp
@@ -95,7 +95,15 @@ void G1SATBCardTableModRefBS::g1_mark_as_young(const MemRegion& mr) {
   jbyte *const first = byte_for(mr.start());
   jbyte *const last = byte_after(mr.last());
 
-  memset(first, g1_young_gen, last - first);
+  // Below we may use an explicit loop instead of memset() because on
+  // certain platforms memset() can give concurrent readers phantom zeros.
+  if (UseMemSetInBOT) {
+    memset(first, g1_young_gen, last - first);
+  } else {
+    for (jbyte* i = first; i < last; i++) {
+      *i = g1_young_gen;
+    }
+  }
 }
 
 #ifndef PRODUCT
-- 
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