1 /*
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  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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  24 
  25 #ifndef SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP
  26 #define SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP
  27 
  28 #include "gc/shared/oopStorage.hpp"
  29 #include "utilities/macros.hpp"
  30 
  31 //////////////////////////////////////////////////////////////////////////////
  32 // Support for parallel and optionally concurrent state iteration.
  33 //
  34 // Concurrent Iteration
  35 //
  36 // Iteration involves the _active_array (an ActiveArray), which contains all
  37 // of the blocks owned by a storage object.
  38 //
  39 // A concurrent ParState increments the associated storage's
  40 // _concurrent_iteration_count when the state is constructed, and
  41 // decrements it when the state is destroyed.  These assignments are made with
  42 // _active_mutex locked.  Meanwhile, empty block deletion is not done while
  43 // _concurrent_iteration_count is non-zero.  The counter check and the dependent
  44 // removal of a block from the _active_array is performed with _active_mutex
  45 // locked.  This prevents concurrent iteration and empty block deletion from
  46 // interfering with with each other.
  47 //
  48 // Both allocate() and delete_empty_blocks() lock the
  49 // _allocation_mutex while performing their respective list and array
  50 // manipulations, preventing them from interfering with each other.
  51 //
  52 // When allocate() creates a new block, it is added to the end of the
  53 // _active_array.  Then _active_array's _block_count is incremented to account
  54 // for the new block.  When concurrent iteration is started (by a parallel
  55 // worker thread calling the state's iterate() function), the current
  56 // _active_array and its _block_count are captured for use by the iteration,
  57 // with iteration processing all blocks in that array up to that block count.
  58 //
  59 // As a result, the sequence over which concurrent iteration operates is
  60 // stable.  However, once the iteration is started, later allocations may add
  61 // blocks to the end of the array that won't be examined by the iteration.
  62 // An allocation may even require expansion of the array, so the iteration is
  63 // no longer processing the current array, but rather the previous one.
  64 // And while the sequence is stable, concurrent allocate() and release()
  65 // operations may change the set of allocated entries in a block at any time
  66 // during the iteration.
  67 //
  68 // As a result, a concurrent iteration handler must accept that some
  69 // allocations and releases that occur after the iteration started will not be
  70 // seen by the iteration.  Further, some may overlap examination by the
  71 // iteration.  To help with this, allocate() and release() have an invariant
  72 // that an entry's value must be NULL when it is not in use.
  73 //
  74 // ParState<concurrent, is_const>
  75 //   concurrent must be true if iteration may be concurrent with the
  76 //   mutators.
  77 //
  78 //   is_const must be true if the iteration is over a constant storage
  79 //   object, false if the iteration may modify the storage object.
  80 //
  81 // ParState([const] OopStorage* storage)
  82 //   Construct an object for managing an iteration over storage.  For a
  83 //   concurrent ParState, empty block deletion for the associated storage
  84 //   is inhibited for the life of the ParState.
  85 //
  86 // template<typename F> void iterate(F f)
  87 //   Repeatedly claims a block from the associated storage that has
  88 //   not been processed by this iteration (possibly by other threads),
  89 //   and applies f to each entry in the claimed block. Assume p is of
  90 //   type const oop* or oop*, according to is_const. Then f(p) must be
  91 //   a valid expression whose value is ignored.  Concurrent uses must
  92 //   be prepared for an entry's value to change at any time, due to
  93 //   mutator activity.
  94 //
  95 // template<typename Closure> void oops_do(Closure* cl)
  96 //   Wrapper around iterate, providing an adaptation layer allowing
  97 //   the use of OopClosures and similar objects for iteration.  Assume
  98 //   p is of type const oop* or oop*, according to is_const.  Then
  99 //   cl->do_oop(p) must be a valid expression whose value is ignored.
 100 //   Concurrent uses must be prepared for the entry's value to change
 101 //   at any time, due to mutator activity.
 102 //
 103 // Optional operations, provided only if !concurrent && !is_const.
 104 // These are not provided when is_const, because the storage object
 105 // may be modified by the iteration infrastructure, even if the
 106 // provided closure doesn't modify the storage object.  These are not
 107 // provided when concurrent because any pre-filtering behavior by the
 108 // iteration infrastructure is inappropriate for concurrent iteration;
 109 // modifications of the storage by the mutator could result in the
 110 // pre-filtering being applied (successfully or not) to objects that
 111 // are unrelated to what the closure finds in the entry.
 112 //
 113 // template<typename Closure> void weak_oops_do(Closure* cl)
 114 // template<typename IsAliveClosure, typename Closure>
 115 // void weak_oops_do(IsAliveClosure* is_alive, Closure* cl)
 116 //   Wrappers around iterate, providing an adaptation layer allowing
 117 //   the use of is-alive closures and OopClosures for iteration.
 118 //   Assume p is of type oop*.  Then
 119 //
 120 //   - cl->do_oop(p) must be a valid expression whose value is ignored.
 121 //
 122 //   - is_alive->do_object_b(*p) must be a valid expression whose value
 123 //   is convertible to bool.
 124 //
 125 //   If *p == NULL then neither is_alive nor cl will be invoked for p.
 126 //   If is_alive->do_object_b(*p) is false, then cl will not be
 127 //   invoked on p.
 128 
 129 class OopStorage::BasicParState {
 130   const OopStorage* _storage;
 131   ActiveArray* _active_array;
 132   size_t _block_count;
 133   volatile size_t _next_block;
 134   uint _estimated_thread_count;
 135   bool _concurrent;
 136 
 137   NONCOPYABLE(BasicParState);
 138 
 139   struct IterationData;
 140 
 141   void update_concurrent_iteration_count(int value);
 142   bool claim_next_segment(IterationData* data);
 143   bool finish_iteration(const IterationData* data) const;
 144 
 145   // Wrapper for iteration handler; ignore handler result and return true.
 146   template<typename F> class AlwaysTrueFn;
 147 
 148 public:
 149   BasicParState(const OopStorage* storage,
 150                 uint estimated_thread_count,
 151                 bool concurrent);
 152   ~BasicParState();
 153 
 154   const OopStorage* storage() const { return _storage; }
 155 
 156   template<bool is_const, typename F> void iterate(F f);
 157 
 158   static uint default_estimated_thread_count(bool concurrent);
 159 };
 160 
 161 template<bool concurrent, bool is_const>
 162 class OopStorage::ParState {
 163   BasicParState _basic_state;
 164 
 165   typedef typename Conditional<is_const,
 166                                const OopStorage*,
 167                                OopStorage*>::type StoragePtr;
 168 
 169 public:
 170   ParState(StoragePtr storage,
 171            uint estimated_thread_count = BasicParState::default_estimated_thread_count(concurrent)) :
 172     _basic_state(storage, estimated_thread_count, concurrent)
 173   {}
 174 
 175   const OopStorage* storage() const { return _basic_state.storage(); }
 176   template<typename F> void iterate(F f);
 177   template<typename Closure> void oops_do(Closure* cl);
 178 };
 179 
 180 template<>
 181 class OopStorage::ParState<false, false> {
 182   BasicParState _basic_state;
 183 
 184 public:
 185   ParState(OopStorage* storage,
 186            uint estimated_thread_count = BasicParState::default_estimated_thread_count(false)) :
 187     _basic_state(storage, estimated_thread_count, false)
 188   {}
 189 
 190   const OopStorage* storage() const { return _basic_state.storage(); }
 191   template<typename F> void iterate(F f);
 192   template<typename Closure> void oops_do(Closure* cl);
 193   template<typename Closure> void weak_oops_do(Closure* cl);
 194   template<typename IsAliveClosure, typename Closure>
 195   void weak_oops_do(IsAliveClosure* is_alive, Closure* cl);
 196 };
 197 
 198 #endif // SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP