1/* 2 * Copyright (c) 2009, 2012, 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. 18 * 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 21 * questions. 22 * 23 */ 24 25#ifndef SHARE_VM_UTILITIES_STACK_HPP 26#define SHARE_VM_UTILITIES_STACK_HPP 27 28#include "memory/allocation.hpp" 29#include "memory/allocation.inline.hpp" 30 31// Class Stack (below) grows and shrinks by linking together "segments" which 32// are allocated on demand. Segments are arrays of the element type (E) plus an 33// extra pointer-sized field to store the segment link. Recently emptied 34// segments are kept in a cache and reused. 35// 36// Notes/caveats: 37// 38// The size of an element must either evenly divide the size of a pointer or be 39// a multiple of the size of a pointer. 40// 41// Destructors are not called for elements popped off the stack, so element 42// types which rely on destructors for things like reference counting will not 43// work properly. 44// 45// Class Stack allocates segments from the C heap. However, two protected 46// virtual methods are used to alloc/free memory which subclasses can override: 47// 48// virtual void* alloc(size_t bytes); 49// virtual void free(void* addr, size_t bytes); 50// 51// The alloc() method must return storage aligned for any use. The 52// implementation in class Stack assumes that alloc() will terminate the process 53// if the allocation fails. 54 55template <class E, MEMFLAGS F> class StackIterator; 56 57// StackBase holds common data/methods that don't depend on the element type, 58// factored out to reduce template code duplication. 59template <MEMFLAGS F> class StackBase 60{ 61public: 62 size_t segment_size() const { return _seg_size; } // Elements per segment. 63 size_t max_size() const { return _max_size; } // Max elements allowed. 64 size_t max_cache_size() const { return _max_cache_size; } // Max segments 65 // allowed in cache. 66 67 size_t cache_size() const { return _cache_size; } // Segments in the cache. 68 69protected: 70 // The ctor arguments correspond to the like-named functions above. 71 // segment_size: number of items per segment 72 // max_cache_size: maxmium number of *segments* to cache 73 // max_size: maximum number of items allowed, rounded to a multiple of 74 // the segment size (0 == unlimited) 75 inline StackBase(size_t segment_size, size_t max_cache_size, size_t max_size); 76 77 // Round max_size to a multiple of the segment size. Treat 0 as unlimited. 78 static inline size_t adjust_max_size(size_t max_size, size_t seg_size); 79 80protected: 81 const size_t _seg_size; // Number of items per segment. 82 const size_t _max_size; // Maximum number of items allowed in the stack. 83 const size_t _max_cache_size; // Maximum number of segments to cache. 84 size_t _cur_seg_size; // Number of items in the current segment. 85 size_t _full_seg_size; // Number of items in already-filled segments. 86 size_t _cache_size; // Number of segments in the cache. 87}; 88 89#ifdef __GNUC__ 90#define inline 91#endif // __GNUC__ 92 93template <class E, MEMFLAGS F> 94class Stack: public StackBase<F> 95{ 96public: 97 friend class StackIterator<E, F>; 98 99 // Number of elements that fit in 4K bytes minus the size of two pointers 100 // (link field and malloc header). 101 static const size_t _default_segment_size = (4096 - 2 * sizeof(E*)) / sizeof(E); 102 static size_t default_segment_size() { return _default_segment_size; } 103 104 // segment_size: number of items per segment 105 // max_cache_size: maxmium number of *segments* to cache 106 // max_size: maximum number of items allowed, rounded to a multiple of 107 // the segment size (0 == unlimited) 108 inline Stack(size_t segment_size = _default_segment_size, 109 size_t max_cache_size = 4, size_t max_size = 0); 110 inline ~Stack() { clear(true); } 111 112 inline bool is_empty() const { return this->_cur_seg == NULL; } 113 inline bool is_full() const { return this->_full_seg_size >= this->max_size(); } 114 115 // Performance sensitive code should use is_empty() instead of size() == 0 and 116 // is_full() instead of size() == max_size(). Using a conditional here allows 117 // just one var to be updated when pushing/popping elements instead of two; 118 // _full_seg_size is updated only when pushing/popping segments. 119 inline size_t size() const { 120 return is_empty() ? 0 : this->_full_seg_size + this->_cur_seg_size; 121 } 122 123 inline void push(E elem); 124 inline E pop(); 125 126 // Clear everything from the stack, releasing the associated memory. If 127 // clear_cache is true, also release any cached segments. 128 void clear(bool clear_cache = false); 129 130protected: 131 // Each segment includes space for _seg_size elements followed by a link 132 // (pointer) to the previous segment; the space is allocated as a single block 133 // of size segment_bytes(). _seg_size is rounded up if necessary so the link 134 // is properly aligned. The C struct for the layout would be: 135 // 136 // struct segment { 137 // E elements[_seg_size]; 138 // E* link; 139 // }; 140 141 // Round up seg_size to keep the link field aligned. 142 static inline size_t adjust_segment_size(size_t seg_size); 143 144 // Methods for allocation size and getting/setting the link. 145 inline size_t link_offset() const; // Byte offset of link field. 146 inline size_t segment_bytes() const; // Segment size in bytes. 147 inline E** link_addr(E* seg) const; // Address of the link field. 148 inline E* get_link(E* seg) const; // Extract the link from seg. 149 inline E* set_link(E* new_seg, E* old_seg); // new_seg.link = old_seg. 150 151 virtual E* alloc(size_t bytes); 152 virtual void free(E* addr, size_t bytes); 153 154 void push_segment(); 155 void pop_segment(); 156 157 void free_segments(E* seg); // Free all segments in the list. 158 inline void reset(bool reset_cache); // Reset all data fields. 159 160 DEBUG_ONLY(void verify(bool at_empty_transition) const;) 161 DEBUG_ONLY(void zap_segment(E* seg, bool zap_link_field) const;) 162 163private: 164 E* _cur_seg; // Current segment. 165 E* _cache; // Segment cache to avoid ping-ponging. 166}; 167 168template <class E, MEMFLAGS F> class ResourceStack: public Stack<E, F>, public ResourceObj 169{ 170public: 171 // If this class becomes widely used, it may make sense to save the Thread 172 // and use it when allocating segments. 173// ResourceStack(size_t segment_size = Stack<E, F>::default_segment_size()): 174 ResourceStack(size_t segment_size): Stack<E, F>(segment_size, max_uintx) 175 { } 176 177 // Set the segment pointers to NULL so the parent dtor does not free them; 178 // that must be done by the ResourceMark code. 179 ~ResourceStack() { Stack<E, F>::reset(true); } 180 181protected: 182 virtual E* alloc(size_t bytes); 183 virtual void free(E* addr, size_t bytes); 184 185private: 186 void clear(bool clear_cache = false); 187}; 188 189template <class E, MEMFLAGS F> 190class StackIterator: public StackObj 191{ 192public: 193 StackIterator(Stack<E, F>& stack): _stack(stack) { sync(); } 194 195 Stack<E, F>& stack() const { return _stack; } 196 197 bool is_empty() const { return _cur_seg == NULL; } 198 199 E next() { return *next_addr(); } 200 E* next_addr(); 201 202 void sync(); // Sync the iterator's state to the stack's current state. 203 204private: 205 Stack<E, F>& _stack; 206 size_t _cur_seg_size; 207 E* _cur_seg; 208 size_t _full_seg_size; 209}; 210 211#ifdef __GNUC__ 212#undef inline 213#endif // __GNUC__ 214 215#endif // SHARE_VM_UTILITIES_STACK_HPP 216