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

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

*** 30,40 ****
  #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)
  {}
  
  void G1HotCardCache::initialize(G1RegionToSpaceMapper* card_counts_storage) {
    if (default_use_cache()) {
      _use_cache = true;
--- 30,40 ----
  #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), _cache_wrapped_around(false)
  {}
  
  void G1HotCardCache::initialize(G1RegionToSpaceMapper* card_counts_storage) {
    if (default_use_cache()) {
      _use_cache = true;
*** 46,55 ****
--- 46,57 ----
  
      // 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() {
*** 67,76 ****
--- 69,83 ----
      // 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