src/hotspot/share/gc/g1/g1HotCardCache.cpp

rev 56673 : imported patch 8227739-merge-scan-rs-update-rs-cost

@@ -30,11 +30,11 @@
 #include "runtime/atomic.hpp"
 
 G1HotCardCache::G1HotCardCache(G1CollectedHeap *g1h):
   _g1h(g1h), _use_cache(false), _card_counts(g1h),
   _hot_cache(NULL), _hot_cache_size(0), _hot_cache_par_chunk_size(0),
-  _hot_cache_idx(0), _hot_cache_par_claimed_idx(0)
+  _hot_cache_idx(0), _hot_cache_par_claimed_idx(0), _cache_wrapped_around(false)
 {}
 
 void G1HotCardCache::initialize(G1RegionToSpaceMapper* card_counts_storage) {
   if (default_use_cache()) {
     _use_cache = true;

@@ -46,10 +46,12 @@
 
     // For refining the cards in the hot cache in parallel
     _hot_cache_par_chunk_size = ClaimChunkSize;
     _hot_cache_par_claimed_idx = 0;
 
+    _cache_wrapped_around = false;
+
     _card_counts.initialize(card_counts_storage);
   }
 }
 
 G1HotCardCache::~G1HotCardCache() {

@@ -67,10 +69,15 @@
     // return it for immediate refining.
     return card_ptr;
   }
   // Otherwise, the card is hot.
   size_t index = Atomic::add(1u, &_hot_cache_idx) - 1;
+  // This does not need an atomic update. Racing threads may at most write the
+  // same value.
+  if (index == _hot_cache_size) {
+    _cache_wrapped_around = true;
+  }
   size_t masked_index = index & (_hot_cache_size - 1);
   CardValue* current_ptr = _hot_cache[masked_index];
 
   // Try to store the new card pointer into the cache. Compare-and-swap to guard
   // against the unlikely event of a race resulting in another card pointer to