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_GC_CMS_FREECHUNK_HPP |
|
26 #define SHARE_GC_CMS_FREECHUNK_HPP |
|
27 |
|
28 #include "memory/memRegion.hpp" |
|
29 #include "oops/markWord.hpp" |
|
30 #include "runtime/mutex.hpp" |
|
31 #include "runtime/orderAccess.hpp" |
|
32 #include "utilities/debug.hpp" |
|
33 #include "utilities/globalDefinitions.hpp" |
|
34 #include "utilities/ostream.hpp" |
|
35 |
|
36 // |
|
37 // Free block maintenance for Concurrent Mark Sweep Generation |
|
38 // |
|
39 // The main data structure for free blocks are |
|
40 // . an indexed array of small free blocks, and |
|
41 // . a dictionary of large free blocks |
|
42 // |
|
43 |
|
44 // No virtuals in FreeChunk (don't want any vtables). |
|
45 |
|
46 // A FreeChunk is merely a chunk that can be in a doubly linked list |
|
47 // and has a size field. NOTE: FreeChunks are distinguished from allocated |
|
48 // objects in two ways (by the sweeper), depending on whether the VM is 32 or |
|
49 // 64 bits. |
|
50 // In 32 bits or 64 bits without CompressedOops, the second word (prev) has the |
|
51 // LSB set to indicate a free chunk; allocated objects' klass() pointers |
|
52 // don't have their LSB set. The corresponding bit in the CMSBitMap is |
|
53 // set when the chunk is allocated. There are also blocks that "look free" |
|
54 // but are not part of the free list and should not be coalesced into larger |
|
55 // free blocks. These free blocks have their two LSB's set. |
|
56 |
|
57 class FreeChunk { |
|
58 friend class VMStructs; |
|
59 // For 64 bit compressed oops, the markWord encodes both the size and the |
|
60 // indication that this is a FreeChunk and not an object. |
|
61 volatile size_t _size; |
|
62 FreeChunk* _prev; |
|
63 FreeChunk* _next; |
|
64 |
|
65 markWord mark() const volatile { return markWord((uintptr_t)_size); } |
|
66 void set_mark(markWord m) { _size = (size_t)m.value(); } |
|
67 |
|
68 public: |
|
69 NOT_PRODUCT(static const size_t header_size();) |
|
70 |
|
71 // Returns "true" if the address indicates that the block represents |
|
72 // a free chunk. |
|
73 static bool indicatesFreeChunk(const HeapWord* addr) { |
|
74 // Force volatile read from addr because value might change between |
|
75 // calls. We really want the read of _mark and _prev from this pointer |
|
76 // to be volatile but making the fields volatile causes all sorts of |
|
77 // compilation errors. |
|
78 return ((volatile FreeChunk*)addr)->is_free(); |
|
79 } |
|
80 |
|
81 bool is_free() const volatile { |
|
82 LP64_ONLY(if (UseCompressedOops) return mark().is_cms_free_chunk(); else) |
|
83 return (((intptr_t)_prev) & 0x1) == 0x1; |
|
84 } |
|
85 bool cantCoalesce() const { |
|
86 assert(is_free(), "can't get coalesce bit on not free"); |
|
87 return (((intptr_t)_prev) & 0x2) == 0x2; |
|
88 } |
|
89 void dontCoalesce() { |
|
90 // the block should be free |
|
91 assert(is_free(), "Should look like a free block"); |
|
92 _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2); |
|
93 } |
|
94 FreeChunk* prev() const { |
|
95 return (FreeChunk*)(((intptr_t)_prev) & ~(0x3)); |
|
96 } |
|
97 |
|
98 debug_only(void* prev_addr() const { return (void*)&_prev; }) |
|
99 debug_only(void* next_addr() const { return (void*)&_next; }) |
|
100 debug_only(void* size_addr() const { return (void*)&_size; }) |
|
101 |
|
102 size_t size() const volatile { |
|
103 LP64_ONLY(if (UseCompressedOops) return mark().get_size(); else ) |
|
104 return _size; |
|
105 } |
|
106 void set_size(size_t sz) { |
|
107 LP64_ONLY(if (UseCompressedOops) set_mark(markWord::set_size_and_free(sz)); else ) |
|
108 _size = sz; |
|
109 } |
|
110 |
|
111 FreeChunk* next() const { return _next; } |
|
112 |
|
113 void link_after(FreeChunk* ptr) { |
|
114 link_next(ptr); |
|
115 if (ptr != NULL) ptr->link_prev(this); |
|
116 } |
|
117 void link_next(FreeChunk* ptr) { _next = ptr; } |
|
118 void link_prev(FreeChunk* ptr) { |
|
119 LP64_ONLY(if (UseCompressedOops) _prev = ptr; else) |
|
120 _prev = (FreeChunk*)((intptr_t)ptr | 0x1); |
|
121 } |
|
122 void clear_next() { _next = NULL; } |
|
123 void markNotFree() { |
|
124 // Set _prev (klass) to null before (if) clearing the mark word below |
|
125 _prev = NULL; |
|
126 #ifdef _LP64 |
|
127 if (UseCompressedOops) { |
|
128 OrderAccess::storestore(); |
|
129 set_mark(markWord::prototype()); |
|
130 } |
|
131 #endif |
|
132 assert(!is_free(), "Error"); |
|
133 } |
|
134 |
|
135 // Return the address past the end of this chunk |
|
136 uintptr_t* end() const { return ((uintptr_t*) this) + size(); } |
|
137 |
|
138 // debugging |
|
139 void verify() const PRODUCT_RETURN; |
|
140 void verifyList() const PRODUCT_RETURN; |
|
141 void mangleAllocated(size_t size) PRODUCT_RETURN; |
|
142 void mangleFreed(size_t size) PRODUCT_RETURN; |
|
143 |
|
144 void print_on(outputStream* st); |
|
145 }; |
|
146 |
|
147 extern size_t MinChunkSize; |
|
148 |
|
149 |
|
150 #endif // SHARE_GC_CMS_FREECHUNK_HPP |
|