< prev index next > src/hotspot/share/gc/shared/oopStorageParState.hpp
8211718: Supporting multiple concurrent OopStorage iterators
#include "utilities/macros.hpp"
//////////////////////////////////////////////////////////////////////////////
// Support for parallel and optionally concurrent state iteration.
//
-// Parallel iteration is for the exclusive use of the GC. Other iteration
-// clients must use serial iteration.
-//
// Concurrent Iteration
//
// Iteration involves the _active_array (an ActiveArray), which contains all
// of the blocks owned by a storage object.
//
-// At most one concurrent ParState can exist at a time for a given storage
-// object.
-//
-// A concurrent ParState sets the associated storage's
-// _concurrent_iteration_active flag true when the state is constructed, and
-// sets it false when the state is destroyed. These assignments are made with
+// A concurrent ParState increments the associated storage's
+// _concurrent_iteration_active count when the state is constructed, and
+// decrements it when the state is destroyed. These assignments are made with
// _active_mutex locked. Meanwhile, empty block deletion is not done while
-// _concurrent_iteration_active is true. The flag check and the dependent
+// _concurrent_iteration_active is non-zero. The counter check and the dependent
// removal of a block from the _active_array is performed with _active_mutex
// locked. This prevents concurrent iteration and empty block deletion from
// interfering with with each other.
//
// Both allocate() and delete_empty_blocks_concurrent() lock the
// the start of a concurrent iteration over the _active_mutex. Since both are
// under GC control, that potential contention can be eliminated by never
// scheduling both operations to run at the same time.
//
// ParState<concurrent, is_const>
-// concurrent must be true if iteration is concurrent with the
-// mutator, false if iteration is at a safepoint.
+// concurrent must be true if iteration may be concurrent with the
+// mutators.
//
// is_const must be true if the iteration is over a constant storage
// object, false if the iteration may modify the storage object.
//
// ParState([const] OopStorage* storage)
// Construct an object for managing an iteration over storage. For a
// concurrent ParState, empty block deletion for the associated storage
-// is inhibited for the life of the ParState. There can be no more
-// than one live concurrent ParState at a time for a given storage object.
+// is inhibited for the life of the ParState.
//
// template<typename F> void iterate(F f)
// Repeatedly claims a block from the associated storage that has
// not been processed by this iteration (possibly by other threads),
// and applies f to each entry in the claimed block. Assume p is of
BasicParState(const BasicParState&);
BasicParState& operator=(const BasicParState&);
struct IterationData;
- void update_iteration_state(bool value);
+ void update_iteration_state(int value);
bool claim_next_segment(IterationData* data);
bool finish_iteration(const IterationData* data) const;
// Wrapper for iteration handler; ignore handler result and return true.
template<typename F> class AlwaysTrueFn;
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