/*

 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

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#ifndef SHARE_GC_SHARED_OOPSTORAGE_HPP

#define SHARE_GC_SHARED_OOPSTORAGE_HPP

#include "memory/allocation.hpp"

#include "oops/oop.hpp"

#include "utilities/globalDefinitions.hpp"

#include "utilities/macros.hpp"

class Mutex;

class outputStream;

// OopStorage supports management of off-heap references to objects allocated

// in the Java heap.  An OopStorage object provides a set of Java object

// references (oop values), which clients refer to via oop* handles to the

// associated OopStorage entries.  Clients allocate entries to create a

// (possibly weak) reference to a Java object, use that reference, and release

// the reference when no longer needed.

//

// The garbage collector must know about all OopStorage objects and their

// reference strength.  OopStorage provides the garbage collector with support

// for iteration over all the allocated entries.

//

// There are several categories of interaction with an OopStorage object.

//

// (1) allocation and release of entries, by the mutator or the VM.

// (2) iteration by the garbage collector, possibly concurrent with mutator.

// (3) iteration by other, non-GC, tools (only at safepoints).

// (4) cleanup of unused internal storage, possibly concurrent with mutator.

//

// A goal of OopStorage is to make these interactions thread-safe, while

// minimizing potential lock contention issues within and between these

// categories.  In particular, support for concurrent iteration by the garbage

// collector, under certain restrictions, is required.  Further, it must not

// block nor be blocked by other operations for long periods.

//

// Internally, OopStorage is a set of Block objects, from which entries are

// allocated and released.  A block contains an oop[] and a bitmask indicating

// which entries are in use (have been allocated and not yet released).  New

// blocks are constructed and added to the storage object when an entry

// allocation request is made and there are no blocks with unused entries.

// Blocks may be removed and deleted when empty.

//

// There are two important (and somewhat intertwined) protocols governing

// concurrent access to a storage object.  These are the Concurrent Iteration

// Protocol and the Allocation Protocol.  See the ParState class for a

// discussion of concurrent iteration and the management of thread

// interactions for this protocol.  Similarly, see the allocate() function for

// a discussion of allocation.

class OopStorage : public CHeapObj<mtGC> {

public:

  OopStorage(const char* name, Mutex* allocate_mutex, Mutex* active_mutex);

  ~OopStorage();

  // These count and usage accessors are racy unless at a safepoint.

  // The number of allocated and not yet released entries.

  size_t allocation_count() const;

  // The number of blocks of entries.  Useful for sizing parallel iteration.

  size_t block_count() const;

  // The number of blocks with no allocated entries.  Useful for sizing

  // parallel iteration and scheduling block deletion.

  size_t empty_block_count() const;

  // Total number of blocks * memory allocation per block, plus

  // bookkeeping overhead, including this storage object.

  size_t total_memory_usage() const;

  enum EntryStatus {

    INVALID_ENTRY,

    UNALLOCATED_ENTRY,

    ALLOCATED_ENTRY

  };

  // Locks _allocate_mutex.

  // precondition: ptr != NULL.

  EntryStatus allocation_status(const oop* ptr) const;

  // Allocates and returns a new entry.  Returns NULL if memory allocation

  // failed.  Locks _allocate_mutex.

  // postcondition: *result == NULL.

  oop* allocate();

  // Deallocates ptr, after setting its value to NULL. Locks _allocate_mutex.

  // precondition: ptr is a valid allocated entry.

  // precondition: *ptr == NULL.

  void release(const oop* ptr);

  // Releases all the ptrs.  Possibly faster than individual calls to

  // release(oop*).  Best if ptrs is sorted by address.  Locks

  // _allocate_mutex.

  // precondition: All elements of ptrs are valid allocated entries.

  // precondition: *ptrs[i] == NULL, for i in [0,size).

  void release(const oop* const* ptrs, size_t size);

  // Applies f to each allocated entry's location.  f must be a function or

  // function object.  Assume p is either a const oop* or an oop*, depending

  // on whether the associated storage is const or non-const, respectively.

  // Then f(p) must be a valid expression.  The result of invoking f(p) must

  // be implicitly convertible to bool.  Iteration terminates and returns

  // false if any invocation of f returns false.  Otherwise, the result of

  // iteration is true.

  // precondition: at safepoint.

  // oops_do and weak_oops_do are wrappers around iterate_safepoint, providing

  // an adaptation layer allowing the use of existing is-alive closures and

  // OopClosures.  Assume p is either const oop* or oop*, depending on whether

  // the associated storage is const or non-const, respectively.  Then

  //

  // - closure->do_oop(p) must be a valid expression whose value is ignored.

  //

  // - is_alive->do_object_b(*p) must be a valid expression whose value is

  // convertible to bool.

  //

  // For weak_oops_do, if *p == NULL then neither is_alive nor closure will be

  // invoked for p.  If is_alive->do_object_b(*p) is false, then closure will

  // not be invoked on p, and *p will be set to NULL.

  template<typename IsAliveClosure, typename Closure>

#if INCLUDE_ALL_GCS

  // Parallel iteration is for the exclusive use of the GC.

  // Other clients must use serial iteration.

  template<bool concurrent, bool is_const> class ParState;

#endif // INCLUDE_ALL_GCS

  // Block cleanup functions are for the exclusive use of the GC.

  // Both stop deleting if there is an in-progress concurrent iteration.

  // Concurrent deletion locks both the allocate_mutex and the active_mutex.

  void delete_empty_blocks_safepoint(size_t retain = 1);

  void delete_empty_blocks_concurrent(size_t retain = 1);

  // Debugging and logging support.

  const char* name() const;

  void print_on(outputStream* st) const PRODUCT_RETURN;

  // Provides access to storage internals, for unit testing.

  // Declare, but not define, the public class OopStorage::TestAccess.

  // That class is defined as part of the unit-test. It "exports" the needed

  // private types by providing public typedefs for them.

  class TestAccess;

  // xlC on AIX can't compile test_oopStorage.cpp with following private

  // classes. C++03 introduced access for nested classes with DR45, but xlC

  // version 12 rejects it.

NOT_AIX( private: )

  class BlockEntry VALUE_OBJ_CLASS_SPEC {

    friend class BlockList;

    // Members are mutable, and we deal exclusively with pointers to

    // const, to make const blocks easier to use; a block being const

    // doesn't prevent modifying its list state.

    mutable const Block* _prev;

    mutable const Block* _next;

    // Noncopyable.

    BlockEntry(const BlockEntry&);

    BlockEntry& operator=(const BlockEntry&);

  public:

    BlockEntry();

    ~BlockEntry();

  };

  class BlockList VALUE_OBJ_CLASS_SPEC {

    const Block* _head;

    const Block* _tail;

    const BlockEntry& (*_get_entry)(const Block& block);

    // Noncopyable.

    BlockList(const BlockList&);

    BlockList& operator=(const BlockList&);

  public:

    BlockList(const BlockEntry& (*get_entry)(const Block& block));

    ~BlockList();

    Block* head();

    const Block* chead() const;

    const Block* ctail() const;

    Block* prev(Block& block);

    Block* next(Block& block);

    const Block* prev(const Block& block) const;

    const Block* next(const Block& block) const;

    void push_front(const Block& block);

    void push_back(const Block& block);

    void unlink(const Block& block);

  };

private:

  const char* _name;

  BlockList _active_list;

  BlockList _allocate_list;

  Block* volatile _active_head;

  Mutex* _allocate_mutex;

  Mutex* _active_mutex;

  // Counts are volatile for racy unlocked accesses.

  volatile size_t _allocation_count;

  volatile size_t _block_count;

  volatile size_t _empty_block_count;

  // mutable because this gets set even for const iteration.

  mutable bool _concurrent_iteration_active;

  Block* find_block_or_null(const oop* ptr) const;

  bool is_valid_block_locked_or_safepoint(const Block* block) const;

  EntryStatus allocation_status_validating_block(const Block* block, const oop* ptr) const;

  void check_release(const Block* block, const oop* ptr) const NOT_DEBUG_RETURN;

  void release_from_block(Block& block, uintx release_bitmask);

  void delete_empty_block(const Block& block);

  static void assert_at_safepoint() NOT_DEBUG_RETURN;

  template<typename F, typename Storage>

  static bool iterate_impl(F f, Storage* storage);

#if INCLUDE_ALL_GCS

  // Implementation support for parallel iteration

  class BasicParState;

#endif // INCLUDE_ALL_GCS

  // Wrapper for OopClosure-style function, so it can be used with

  // iterate.  Assume p is of type oop*.  Then cl->do_oop(p) must be a

  // valid expression whose value may be ignored.

  template<typename Closure> class OopFn;

  template<typename Closure> static OopFn<Closure> oop_fn(Closure* cl);

  // Wrapper for BoolObjectClosure + iteration handler pair, so they

  // can be used with iterate.

  template<typename IsAlive, typename F> class IfAliveFn;

  template<typename IsAlive, typename F>

  static IfAliveFn<IsAlive, F> if_alive_fn(IsAlive* is_alive, F f);

  // Wrapper for iteration handler, automatically skipping NULL entries.

  template<typename F> class SkipNullFn;

  template<typename F> static SkipNullFn<F> skip_null_fn(F f);

};

#endif // include guard