1 /*
2 * Copyright (c) 2001, 2019, 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_MEMORY_FREELIST_HPP
26 #define SHARE_MEMORY_FREELIST_HPP
27
28 // A class for maintaining a free list of Chunk's. The FreeList
29 // maintains a the structure of the list (head, tail, etc.) plus
30 // statistics for allocations from the list. The links between items
31 // are not part of FreeList. The statistics are
32 // used to make decisions about coalescing Chunk's when they
33 // are swept during collection.
34 //
35 // See the corresponding .cpp file for a description of the specifics
36 // for that implementation.
37
38 class Mutex;
39
40 template <class Chunk_t>
41 class FreeList {
42 friend class VMStructs;
43
44 private:
45 Chunk_t* _head; // Head of list of free chunks
46 Chunk_t* _tail; // Tail of list of free chunks
47 size_t _size; // Size in Heap words of each chunk
48 ssize_t _count; // Number of entries in list
49
50 protected:
51
52 #ifdef ASSERT
53 Mutex* _protecting_lock;
54 void assert_proper_lock_protection_work() const;
55 #endif
56
57 // Asserts false if the protecting lock (if any) is not held.
58 void assert_proper_lock_protection() const {
59 DEBUG_ONLY(assert_proper_lock_protection_work());
60 }
61
62 void increment_count() {
63 _count++;
64 }
65
66 void decrement_count() {
67 _count--;
68 assert(_count >= 0, "Count should not be negative");
69 }
70
71 public:
72 // Constructor
73 // Construct a list without any entries.
74 FreeList();
75
76 // Do initialization
77 void initialize();
78
79 // Reset the head, tail, and count of a free list.
80 void reset();
81
82 // Declare the current free list to be protected by the given lock.
83 #ifdef ASSERT
84 Mutex* protecting_lock() const { return _protecting_lock; }
85 void set_protecting_lock(Mutex* v) {
86 _protecting_lock = v;
87 }
88 #endif
89
90 // Accessors.
91 Chunk_t* head() const {
92 assert_proper_lock_protection();
93 return _head;
94 }
95 void set_head(Chunk_t* v) {
96 assert_proper_lock_protection();
97 _head = v;
98 assert(!_head || _head->size() == _size, "bad chunk size");
99 }
100 // Set the head of the list and set the prev field of non-null
101 // values to NULL.
102 void link_head(Chunk_t* v);
103
104 Chunk_t* tail() const {
105 assert_proper_lock_protection();
106 return _tail;
107 }
108 void set_tail(Chunk_t* v) {
109 assert_proper_lock_protection();
110 _tail = v;
111 assert(!_tail || _tail->size() == _size, "bad chunk size");
112 }
113 // Set the tail of the list and set the next field of non-null
114 // values to NULL.
115 void link_tail(Chunk_t* v) {
116 assert_proper_lock_protection();
117 set_tail(v);
118 if (v != NULL) {
119 v->clear_next();
120 }
121 }
122
123 // No locking checks in read-accessors: lock-free reads (only) are benign.
124 // Readers are expected to have the lock if they are doing work that
125 // requires atomicity guarantees in sections of code.
126 size_t size() const {
127 return _size;
128 }
129 void set_size(size_t v) {
130 assert_proper_lock_protection();
131 _size = v;
132 }
133 ssize_t count() const { return _count; }
134 void set_count(ssize_t v) { _count = v;}
135
136 size_t get_better_size() { return size(); }
137
138 size_t returned_bytes() const { ShouldNotReachHere(); return 0; }
139 void set_returned_bytes(size_t v) {}
140 void increment_returned_bytes_by(size_t v) {}
141
142 // Unlink head of list and return it. Returns NULL if
143 // the list is empty.
144 Chunk_t* get_chunk_at_head();
145
146 // Remove the first "n" or "count", whichever is smaller, chunks from the
147 // list, setting "fl", which is required to be empty, to point to them.
148 void getFirstNChunksFromList(size_t n, FreeList<Chunk_t>* fl);
149
150 // Unlink this chunk from it's free list
151 void remove_chunk(Chunk_t* fc);
152
153 // Add this chunk to this free list.
154 void return_chunk_at_head(Chunk_t* fc);
155 void return_chunk_at_tail(Chunk_t* fc);
156
157 // Similar to returnChunk* but also records some diagnostic
158 // information.
159 void return_chunk_at_head(Chunk_t* fc, bool record_return);
160 void return_chunk_at_tail(Chunk_t* fc, bool record_return);
161
162 // Prepend "fl" (whose size is required to be the same as that of "this")
163 // to the front of "this" list.
164 void prepend(FreeList<Chunk_t>* fl);
165
166 // Verify that the chunk is in the list.
167 // found. Return NULL if "fc" is not found.
168 bool verify_chunk_in_free_list(Chunk_t* fc) const;
169
170 // Printing support
171 static void print_labels_on(outputStream* st, const char* c);
172 void print_on(outputStream* st, const char* c = NULL) const;
173 };
174
175 #endif // SHARE_MEMORY_FREELIST_HPP