Tue, 13 Apr 2010 13:52:10 -0700
6858496: Clear all SoftReferences before an out-of-memory due to GC overhead limit.
Summary: Ensure a full GC that clears SoftReferences before throwing an out-of-memory
Reviewed-by: ysr, jcoomes
1 /*
2 * Copyright 2002-2008 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
25 # include "incls/_precompiled.incl"
26 # include "incls/_spaceDecorator.cpp.incl"
28 // Catch-all file for utility classes
30 #ifndef PRODUCT
32 // Returns true is the location q matches the mangling
33 // pattern.
34 bool SpaceMangler::is_mangled(HeapWord* q) {
35 // This test loses precision but is good enough
36 return badHeapWord == (max_juint & (uintptr_t) q->value());
37 }
40 void SpaceMangler::set_top_for_allocations(HeapWord* v) {
41 if (v < end()) {
42 assert(!CheckZapUnusedHeapArea || is_mangled(v),
43 "The high water mark is not mangled");
44 }
45 _top_for_allocations = v;
46 }
48 // Mangle only the unused space that has not previously
49 // been mangled and that has not been allocated since being
50 // mangled.
51 void SpaceMangler::mangle_unused_area() {
52 assert(ZapUnusedHeapArea, "Mangling should not be in use");
53 // Mangle between top and the high water mark. Safeguard
54 // against the space changing since top_for_allocations was
55 // set.
56 HeapWord* mangled_end = MIN2(top_for_allocations(), end());
57 if (top() < mangled_end) {
58 MemRegion mangle_mr(top(), mangled_end);
59 SpaceMangler::mangle_region(mangle_mr);
60 // Light weight check of mangling.
61 check_mangled_unused_area(end());
62 }
63 // Complete check of unused area which is functional when
64 // DEBUG_MANGLING is defined.
65 check_mangled_unused_area_complete();
66 }
68 // A complete mangle is expected in the
69 // exceptional case where top_for_allocations is not
70 // properly tracking the high water mark for mangling.
71 // This can be the case when to-space is being used for
72 // scratch space during a mark-sweep-compact. See
73 // contribute_scratch() and PSMarkSweep::allocate_stacks().
74 void SpaceMangler::mangle_unused_area_complete() {
75 assert(ZapUnusedHeapArea, "Mangling should not be in use");
76 MemRegion mangle_mr(top(), end());
77 SpaceMangler::mangle_region(mangle_mr);
78 }
80 // Simply mangle the MemRegion mr.
81 void SpaceMangler::mangle_region(MemRegion mr) {
82 assert(ZapUnusedHeapArea, "Mangling should not be in use");
83 #ifdef ASSERT
84 if(TraceZapUnusedHeapArea) {
85 gclog_or_tty->print("Mangling [0x%x to 0x%x)", mr.start(), mr.end());
86 }
87 Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord);
88 if(TraceZapUnusedHeapArea) {
89 gclog_or_tty->print_cr(" done");
90 }
91 #endif
92 }
94 // Check that top, top_for_allocations and the last
95 // word of the space are mangled. In a tight memory
96 // situation even this light weight mangling could
97 // cause paging by touching the end of the space.
98 void SpaceMangler::check_mangled_unused_area(HeapWord* limit) {
99 if (CheckZapUnusedHeapArea) {
100 // This method can be called while the spaces are
101 // being reshaped so skip the test if the end of the
102 // space is beyond the specified limit;
103 if (end() > limit) return;
105 assert(top() == end() ||
106 (is_mangled(top())), "Top not mangled");
107 assert((top_for_allocations() < top()) ||
108 (top_for_allocations() >= end()) ||
109 (is_mangled(top_for_allocations())),
110 "Older unused not mangled");
111 assert(top() == end() ||
112 (is_mangled(end() - 1)), "End not properly mangled");
113 // Only does checking when DEBUG_MANGLING is defined.
114 check_mangled_unused_area_complete();
115 }
116 }
118 #undef DEBUG_MANGLING
119 // This should only be used while debugging the mangling
120 // because of the high cost of checking the completeness.
121 void SpaceMangler::check_mangled_unused_area_complete() {
122 if (CheckZapUnusedHeapArea) {
123 assert(ZapUnusedHeapArea, "Not mangling unused area");
124 #ifdef DEBUG_MANGLING
125 HeapWord* q = top();
126 HeapWord* limit = end();
128 bool passed = true;
129 while (q < limit) {
130 if (!is_mangled(q)) {
131 passed = false;
132 break;
133 }
134 q++;
135 }
136 assert(passed, "Mangling is not complete");
137 #endif
138 }
139 }
140 #undef DEBUG_MANGLING
141 #endif // not PRODUCT