1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25#ifndef SHARE_UTILITIES_STACK_HPP
26#define SHARE_UTILITIES_STACK_HPP
27
28#include "memory/allocation.hpp"
29
30// Class Stack (below) grows and shrinks by linking together "segments" which
31// are allocated on demand. Segments are arrays of the element type (E) plus an
32// extra pointer-sized field to store the segment link. Recently emptied
33// segments are kept in a cache and reused.
34//
35// Notes/caveats:
36//
37// The size of an element must either evenly divide the size of a pointer or be
38// a multiple of the size of a pointer.
39//
40// Destructors are not called for elements popped off the stack, so element
41// types which rely on destructors for things like reference counting will not
42// work properly.
43//
44// Class Stack allocates segments from the C heap. However, two protected
45// virtual methods are used to alloc/free memory which subclasses can override:
46//
47// virtual void* alloc(size_t bytes);
48// virtual void free(void* addr, size_t bytes);
49//
50// The alloc() method must return storage aligned for any use. The
51// implementation in class Stack assumes that alloc() will terminate the process
52// if the allocation fails.
53
54template <class E, MEMFLAGS F> class StackIterator;
55
56// StackBase holds common data/methods that don't depend on the element type,
57// factored out to reduce template code duplication.
58template <MEMFLAGS F> class StackBase
59{
60public:
61 size_t segment_size() const { return _seg_size; } // Elements per segment.
62 size_t max_size() const { return _max_size; } // Max elements allowed.
63 size_t max_cache_size() const { return _max_cache_size; } // Max segments
64 // allowed in cache.
65
66 size_t cache_size() const { return _cache_size; } // Segments in the cache.
67
68protected:
69 // The ctor arguments correspond to the like-named functions above.
70 // segment_size: number of items per segment
71 // max_cache_size: maxmium number of *segments* to cache
72 // max_size: maximum number of items allowed, rounded to a multiple of
73 // the segment size (0 == unlimited)
74 inline StackBase(size_t segment_size, size_t max_cache_size, size_t max_size);
75
76 // Round max_size to a multiple of the segment size. Treat 0 as unlimited.
77 static inline size_t adjust_max_size(size_t max_size, size_t seg_size);
78
79protected:
80 const size_t _seg_size; // Number of items per segment.
81 const size_t _max_size; // Maximum number of items allowed in the stack.
82 const size_t _max_cache_size; // Maximum number of segments to cache.
83 size_t _cur_seg_size; // Number of items in the current segment.
84 size_t _full_seg_size; // Number of items in already-filled segments.
85 size_t _cache_size; // Number of segments in the cache.
86};
87
88#ifdef __GNUC__
89#define inline
90#endif // __GNUC__
91
92template <class E, MEMFLAGS F>
93class Stack: public StackBase<F>
94{
95public:
96 friend class StackIterator<E, F>;
97
98 // Number of elements that fit in 4K bytes minus the size of two pointers
99 // (link field and malloc header).
100 static const size_t _default_segment_size = (4096 - 2 * sizeof(E*)) / sizeof(E);
101 static size_t default_segment_size() { return _default_segment_size; }
102
103 // segment_size: number of items per segment
104 // max_cache_size: maxmium number of *segments* to cache
105 // max_size: maximum number of items allowed, rounded to a multiple of
106 // the segment size (0 == unlimited)
107 inline Stack(size_t segment_size = _default_segment_size,
108 size_t max_cache_size = 4, size_t max_size = 0);
109 inline ~Stack() { clear(true); }
110
111 inline bool is_empty() const { return this->_cur_seg == NULL; }
112 inline bool is_full() const { return this->_full_seg_size >= this->max_size(); }
113
114 // Performance sensitive code should use is_empty() instead of size() == 0 and
115 // is_full() instead of size() == max_size(). Using a conditional here allows
116 // just one var to be updated when pushing/popping elements instead of two;
117 // _full_seg_size is updated only when pushing/popping segments.
118 inline size_t size() const {
119 return is_empty() ? 0 : this->_full_seg_size + this->_cur_seg_size;
120 }
121
122 inline void push(E elem);
123 inline E pop();
124
125 // Clear everything from the stack, releasing the associated memory. If
126 // clear_cache is true, also release any cached segments.
127 void clear(bool clear_cache = false);
128
129protected:
130 // Each segment includes space for _seg_size elements followed by a link
131 // (pointer) to the previous segment; the space is allocated as a single block
132 // of size segment_bytes(). _seg_size is rounded up if necessary so the link
133 // is properly aligned. The C struct for the layout would be:
134 //
135 // struct segment {
136 // E elements[_seg_size];
137 // E* link;
138 // };
139
140 // Round up seg_size to keep the link field aligned.
141 static inline size_t adjust_segment_size(size_t seg_size);
142
143 // Methods for allocation size and getting/setting the link.
144 inline size_t link_offset() const; // Byte offset of link field.
145 inline size_t segment_bytes() const; // Segment size in bytes.
146 inline E** link_addr(E* seg) const; // Address of the link field.
147 inline E* get_link(E* seg) const; // Extract the link from seg.
148 inline E* set_link(E* new_seg, E* old_seg); // new_seg.link = old_seg.
149
150 virtual E* alloc(size_t bytes);
151 virtual void free(E* addr, size_t bytes);
152
153 void push_segment();
154 void pop_segment();
155
156 void free_segments(E* seg); // Free all segments in the list.
157 inline void reset(bool reset_cache); // Reset all data fields.
158
159 DEBUG_ONLY(void verify(bool at_empty_transition) const;)
160 DEBUG_ONLY(void zap_segment(E* seg, bool zap_link_field) const;)
161
162private:
163 E* _cur_seg; // Current segment.
164 E* _cache; // Segment cache to avoid ping-ponging.
165};
166
167template <class E, MEMFLAGS F> class ResourceStack: public Stack<E, F>, public ResourceObj
168{
169public:
170 // If this class becomes widely used, it may make sense to save the Thread
171 // and use it when allocating segments.
172// ResourceStack(size_t segment_size = Stack<E, F>::default_segment_size()):
173 ResourceStack(size_t segment_size): Stack<E, F>(segment_size, max_uintx)
174 { }
175
176 // Set the segment pointers to NULL so the parent dtor does not free them;
177 // that must be done by the ResourceMark code.
178 ~ResourceStack() { Stack<E, F>::reset(true); }
179
180protected:
181 virtual E* alloc(size_t bytes);
182 virtual void free(E* addr, size_t bytes);
183
184private:
185 void clear(bool clear_cache = false);
186};
187
188template <class E, MEMFLAGS F>
189class StackIterator: public StackObj
190{
191public:
192 StackIterator(Stack<E, F>& stack): _stack(stack) { sync(); }
193
194 Stack<E, F>& stack() const { return _stack; }
195
196 bool is_empty() const { return _cur_seg == NULL; }
197
198 E next() { return *next_addr(); }
199 E* next_addr();
200
201 void sync(); // Sync the iterator's state to the stack's current state.
202
203private:
204 Stack<E, F>& _stack;
205 size_t _cur_seg_size;
206 E* _cur_seg;
207 size_t _full_seg_size;
208};
209
210#ifdef __GNUC__
211#undef inline
212#endif // __GNUC__
213
214#endif // SHARE_UTILITIES_STACK_HPP
215