1/*
2 * Copyright (c) 2001, 2015, 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.
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23 */
24
25#ifndef SHARE_VM_MEMORY_FREELIST_HPP
26#define SHARE_VM_MEMORY_FREELIST_HPP
27
28#include "gc/cms/allocationStats.hpp"
29
30class CompactibleFreeListSpace;
31
32// A class for maintaining a free list of Chunk's.  The FreeList
33// maintains a the structure of the list (head, tail, etc.) plus
34// statistics for allocations from the list.  The links between items
35// are not part of FreeList.  The statistics are
36// used to make decisions about coalescing Chunk's when they
37// are swept during collection.
38//
39// See the corresponding .cpp file for a description of the specifics
40// for that implementation.
41
42class Mutex;
43
44template <class Chunk_t>
45class FreeList VALUE_OBJ_CLASS_SPEC {
46  friend class CompactibleFreeListSpace;
47  friend class VMStructs;
48
49 private:
50  Chunk_t*      _head;          // Head of list of free chunks
51  Chunk_t*      _tail;          // Tail of list of free chunks
52  size_t        _size;          // Size in Heap words of each chunk
53  ssize_t       _count;         // Number of entries in list
54
55 protected:
56
57#ifdef ASSERT
58  Mutex*        _protecting_lock;
59  void assert_proper_lock_protection_work() const;
60#endif
61
62  // Asserts false if the protecting lock (if any) is not held.
63  void assert_proper_lock_protection() const {
64    DEBUG_ONLY(assert_proper_lock_protection_work());
65  }
66
67  void increment_count()    {
68    _count++;
69  }
70
71  void decrement_count() {
72    _count--;
73    assert(_count >= 0, "Count should not be negative");
74  }
75
76 public:
77  // Constructor
78  // Construct a list without any entries.
79  FreeList();
80
81  // Do initialization
82  void initialize();
83
84  // Reset the head, tail, and count of a free list.
85  void reset();
86
87  // Declare the current free list to be protected by the given lock.
88#ifdef ASSERT
89  Mutex* protecting_lock() const { return _protecting_lock; }
90  void set_protecting_lock(Mutex* v) {
91    _protecting_lock = v;
92  }
93#endif
94
95  // Accessors.
96  Chunk_t* head() const {
97    assert_proper_lock_protection();
98    return _head;
99  }
100  void set_head(Chunk_t* v) {
101    assert_proper_lock_protection();
102    _head = v;
103    assert(!_head || _head->size() == _size, "bad chunk size");
104  }
105  // Set the head of the list and set the prev field of non-null
106  // values to NULL.
107  void link_head(Chunk_t* v);
108
109  Chunk_t* tail() const {
110    assert_proper_lock_protection();
111    return _tail;
112  }
113  void set_tail(Chunk_t* v) {
114    assert_proper_lock_protection();
115    _tail = v;
116    assert(!_tail || _tail->size() == _size, "bad chunk size");
117  }
118  // Set the tail of the list and set the next field of non-null
119  // values to NULL.
120  void link_tail(Chunk_t* v) {
121    assert_proper_lock_protection();
122    set_tail(v);
123    if (v != NULL) {
124      v->clear_next();
125    }
126  }
127
128  // No locking checks in read-accessors: lock-free reads (only) are benign.
129  // Readers are expected to have the lock if they are doing work that
130  // requires atomicity guarantees in sections of code.
131  size_t size() const {
132    return _size;
133  }
134  void set_size(size_t v) {
135    assert_proper_lock_protection();
136    _size = v;
137  }
138  ssize_t count() const { return _count; }
139  void set_count(ssize_t v) { _count = v;}
140
141  size_t get_better_size() { return size(); }
142
143  size_t returned_bytes() const { ShouldNotReachHere(); return 0; }
144  void set_returned_bytes(size_t v) {}
145  void increment_returned_bytes_by(size_t v) {}
146
147  // Unlink head of list and return it.  Returns NULL if
148  // the list is empty.
149  Chunk_t* get_chunk_at_head();
150
151  // Remove the first "n" or "count", whichever is smaller, chunks from the
152  // list, setting "fl", which is required to be empty, to point to them.
153  void getFirstNChunksFromList(size_t n, FreeList<Chunk_t>* fl);
154
155  // Unlink this chunk from it's free list
156  void remove_chunk(Chunk_t* fc);
157
158  // Add this chunk to this free list.
159  void return_chunk_at_head(Chunk_t* fc);
160  void return_chunk_at_tail(Chunk_t* fc);
161
162  // Similar to returnChunk* but also records some diagnostic
163  // information.
164  void return_chunk_at_head(Chunk_t* fc, bool record_return);
165  void return_chunk_at_tail(Chunk_t* fc, bool record_return);
166
167  // Prepend "fl" (whose size is required to be the same as that of "this")
168  // to the front of "this" list.
169  void prepend(FreeList<Chunk_t>* fl);
170
171  // Verify that the chunk is in the list.
172  // found.  Return NULL if "fc" is not found.
173  bool verify_chunk_in_free_list(Chunk_t* fc) const;
174
175  // Printing support
176  static void print_labels_on(outputStream* st, const char* c);
177  void print_on(outputStream* st, const char* c = NULL) const;
178};
179
180#endif // SHARE_VM_MEMORY_FREELIST_HPP
181