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 /*

  * Copyright (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved.

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

  *

  * This code is free software; you can redistribute it and/or modify it

  * 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.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

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  */

 #ifndef SHARE_VM_UTILITIES_STACK_HPP

 #define SHARE_VM_UTILITIES_STACK_HPP

 #include "memory/allocation.inline.hpp"

 // Class Stack (below) grows and shrinks by linking together "segments" which

 // are allocated on demand.  Segments are arrays of the element type (E) plus an

 // extra pointer-sized field to store the segment link.  Recently emptied

 // segments are kept in a cache and reused.

 //

 // Notes/caveats:

 //

 // The size of an element must either evenly divide the size of a pointer or be

 // a multiple of the size of a pointer.

 //

 // Destructors are not called for elements popped off the stack, so element

 // types which rely on destructors for things like reference counting will not

 // work properly.

 //

 // Class Stack allocates segments from the C heap.  However, two protected

 // virtual methods are used to alloc/free memory which subclasses can override:

 //

 //      virtual void* alloc(size_t bytes);

 //      virtual void  free(void* addr, size_t bytes);

 //

 // The alloc() method must return storage aligned for any use.  The

 // implementation in class Stack assumes that alloc() will terminate the process

 // if the allocation fails.

 template <class E> class StackIterator;

 // StackBase holds common data/methods that don't depend on the element type,

 // factored out to reduce template code duplication.

 class StackBase

 {

 public:

   size_t segment_size()   const { return _seg_size; } // Elements per segment.

   size_t max_size()       const { return _max_size; } // Max elements allowed.

   size_t max_cache_size() const { return _max_cache_size; } // Max segments

                                                             // allowed in cache.

   size_t cache_size() const { return _cache_size; }   // Segments in the cache.

 protected:

   // The ctor arguments correspond to the like-named functions above.

   // segment_size:    number of items per segment

   // max_cache_size:  maxmium number of *segments* to cache

   // max_size:        maximum number of items allowed, rounded to a multiple of

   //                  the segment size (0 == unlimited)

   inline StackBase(size_t segment_size, size_t max_cache_size, size_t max_size);

   // Round max_size to a multiple of the segment size.  Treat 0 as unlimited.

   static inline size_t adjust_max_size(size_t max_size, size_t seg_size);

 protected:

   const size_t _seg_size;       // Number of items per segment.

   const size_t _max_size;       // Maximum number of items allowed in the stack.

   const size_t _max_cache_size; // Maximum number of segments to cache.

   size_t       _cur_seg_size;   // Number of items in the current segment.

   size_t       _full_seg_size;  // Number of items in already-filled segments.

   size_t       _cache_size;     // Number of segments in the cache.

 };

 #ifdef __GNUC__

 #define inline

 #endif // __GNUC__

 template <class E>

 class Stack:  public StackBase

 {

 public:

   friend class StackIterator<E>;

   // segment_size:    number of items per segment

   // max_cache_size:  maxmium number of *segments* to cache

   // max_size:        maximum number of items allowed, rounded to a multiple of

   //                  the segment size (0 == unlimited)

   inline Stack(size_t segment_size = default_segment_size(),

                size_t max_cache_size = 4, size_t max_size = 0);

   inline ~Stack() { clear(true); }

   inline bool is_empty() const { return _cur_seg == NULL; }

   inline bool is_full()  const { return _full_seg_size >= max_size(); }

   // Performance sensitive code should use is_empty() instead of size() == 0 and

   // is_full() instead of size() == max_size().  Using a conditional here allows

   // just one var to be updated when pushing/popping elements instead of two;

   // _full_seg_size is updated only when pushing/popping segments.

   inline size_t size() const {

     return is_empty() ? 0 : _full_seg_size + _cur_seg_size;

   }

   inline void push(E elem);

   inline E    pop();

   // Clear everything from the stack, releasing the associated memory.  If

   // clear_cache is true, also release any cached segments.

   void clear(bool clear_cache = false);

   static inline size_t default_segment_size();

 protected:

   // Each segment includes space for _seg_size elements followed by a link

   // (pointer) to the previous segment; the space is allocated as a single block

   // of size segment_bytes().  _seg_size is rounded up if necessary so the link

   // is properly aligned.  The C struct for the layout would be:

   //

   // struct segment {

   //   E     elements[_seg_size];

   //   E*    link;

   // };

   // Round up seg_size to keep the link field aligned.

   static inline size_t adjust_segment_size(size_t seg_size);

   // Methods for allocation size and getting/setting the link.

   inline size_t link_offset() const;              // Byte offset of link field.

   inline size_t segment_bytes() const;            // Segment size in bytes.

   inline E**    link_addr(E* seg) const;          // Address of the link field.

   inline E*     get_link(E* seg) const;           // Extract the link from seg.

   inline E*     set_link(E* new_seg, E* old_seg); // new_seg.link = old_seg.

   virtual E*    alloc(size_t bytes);

   virtual void  free(E* addr, size_t bytes);

   void push_segment();

   void pop_segment();

   void free_segments(E* seg);          // Free all segments in the list.

   inline void reset(bool reset_cache); // Reset all data fields.

   DEBUG_ONLY(void verify(bool at_empty_transition) const;)

   DEBUG_ONLY(void zap_segment(E* seg, bool zap_link_field) const;)

 private:

   E* _cur_seg;    // Current segment.

   E* _cache;      // Segment cache to avoid ping-ponging.

 };

 template <class E> class ResourceStack:  public Stack<E>, public ResourceObj

 {

 public:

   // If this class becomes widely used, it may make sense to save the Thread

   // and use it when allocating segments.

   ResourceStack(size_t segment_size = Stack<E>::default_segment_size()):

     Stack<E>(segment_size, max_uintx)

     { }

   // Set the segment pointers to NULL so the parent dtor does not free them;

   // that must be done by the ResourceMark code.

   ~ResourceStack() { Stack<E>::reset(true); }

 protected:

   virtual E*   alloc(size_t bytes);

   virtual void free(E* addr, size_t bytes);

 private:

   void clear(bool clear_cache = false);

 };

 template <class E>

 class StackIterator: public StackObj

 {

 public:

   StackIterator(Stack<E>& stack): _stack(stack) { sync(); }

   Stack<E>& stack() const { return _stack; }

   bool is_empty() const { return _cur_seg == NULL; }

   E  next() { return *next_addr(); }

   E* next_addr();

   void sync(); // Sync the iterator's state to the stack's current state.

 private:

   Stack<E>& _stack;

   size_t    _cur_seg_size;

   E*        _cur_seg;

   size_t    _full_seg_size;

 };

 #ifdef __GNUC__

 #undef inline

 #endif // __GNUC__

 #endif // SHARE_VM_UTILITIES_STACK_HPP