1 /*
2 * Copyright (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
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23 */
24
25 #ifndef SHARE_VM_UTILITIES_STACK_HPP
26 #define SHARE_VM_UTILITIES_STACK_HPP
27
28 #include "memory/allocation.inline.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
54 template <class E> 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.
58 class StackBase
59 {
60 public:
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
68 protected:
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
79 protected:
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
92 template <class E>
93 class Stack: public StackBase
94 {
95 public:
96 friend class StackIterator<E>;
97
98 // segment_size: number of items per segment
99 // max_cache_size: maxmium number of *segments* to cache
100 // max_size: maximum number of items allowed, rounded to a multiple of
101 // the segment size (0 == unlimited)
102 inline Stack(size_t segment_size = default_segment_size(),
103 size_t max_cache_size = 4, size_t max_size = 0);
104 inline ~Stack() { clear(true); }
105
106 inline bool is_empty() const { return _cur_seg == NULL; }
107 inline bool is_full() const { return _full_seg_size >= max_size(); }
108
109 // Performance sensitive code should use is_empty() instead of size() == 0 and
110 // is_full() instead of size() == max_size(). Using a conditional here allows
111 // just one var to be updated when pushing/popping elements instead of two;
112 // _full_seg_size is updated only when pushing/popping segments.
113 inline size_t size() const {
114 return is_empty() ? 0 : _full_seg_size + _cur_seg_size;
115 }
116
117 inline void push(E elem);
118 inline E pop();
119
120 // Clear everything from the stack, releasing the associated memory. If
121 // clear_cache is true, also release any cached segments.
122 void clear(bool clear_cache = false);
123
124 static inline size_t default_segment_size();
125
126 protected:
127 // Each segment includes space for _seg_size elements followed by a link
128 // (pointer) to the previous segment; the space is allocated as a single block
129 // of size segment_bytes(). _seg_size is rounded up if necessary so the link
130 // is properly aligned. The C struct for the layout would be:
131 //
132 // struct segment {
133 // E elements[_seg_size];
134 // E* link;
135 // };
136
137 // Round up seg_size to keep the link field aligned.
138 static inline size_t adjust_segment_size(size_t seg_size);
139
140 // Methods for allocation size and getting/setting the link.
141 inline size_t link_offset() const; // Byte offset of link field.
142 inline size_t segment_bytes() const; // Segment size in bytes.
143 inline E** link_addr(E* seg) const; // Address of the link field.
144 inline E* get_link(E* seg) const; // Extract the link from seg.
145 inline E* set_link(E* new_seg, E* old_seg); // new_seg.link = old_seg.
146
147 virtual E* alloc(size_t bytes);
148 virtual void free(E* addr, size_t bytes);
149
150 void push_segment();
151 void pop_segment();
152
153 void free_segments(E* seg); // Free all segments in the list.
154 inline void reset(bool reset_cache); // Reset all data fields.
155
156 DEBUG_ONLY(void verify(bool at_empty_transition) const;)
157 DEBUG_ONLY(void zap_segment(E* seg, bool zap_link_field) const;)
158
159 private:
160 E* _cur_seg; // Current segment.
161 E* _cache; // Segment cache to avoid ping-ponging.
162 };
163
164 template <class E> class ResourceStack: public Stack<E>, public ResourceObj
165 {
166 public:
167 // If this class becomes widely used, it may make sense to save the Thread
168 // and use it when allocating segments.
169 ResourceStack(size_t segment_size = Stack<E>::default_segment_size()):
170 Stack<E>(segment_size, max_uintx)
171 { }
172
173 // Set the segment pointers to NULL so the parent dtor does not free them;
174 // that must be done by the ResourceMark code.
175 ~ResourceStack() { Stack<E>::reset(true); }
176
177 protected:
178 virtual E* alloc(size_t bytes);
179 virtual void free(E* addr, size_t bytes);
180
181 private:
182 void clear(bool clear_cache = false);
183 };
184
185 template <class E>
186 class StackIterator: public StackObj
187 {
188 public:
189 StackIterator(Stack<E>& stack): _stack(stack) { sync(); }
190
191 Stack<E>& stack() const { return _stack; }
192
193 bool is_empty() const { return _cur_seg == NULL; }
194
195 E next() { return *next_addr(); }
196 E* next_addr();
197
198 void sync(); // Sync the iterator's state to the stack's current state.
199
200 private:
201 Stack<E>& _stack;
202 size_t _cur_seg_size;
203 E* _cur_seg;
204 size_t _full_seg_size;
205 };
206
207 #ifdef __GNUC__
208 #undef inline
209 #endif // __GNUC__
210
211 #endif // SHARE_VM_UTILITIES_STACK_HPP