1 /*
2 * Copyright (c) 2001, 2010, 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 #include "precompiled.hpp"
26 #include "gc_implementation/g1/concurrentZFThread.hpp"
27 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
28 #include "gc_implementation/g1/heapRegion.hpp"
29 #include "memory/space.inline.hpp"
30 #include "runtime/mutexLocker.hpp"
31 #include "utilities/copy.hpp"
32
33 // ======= Concurrent Zero-Fill Thread ========
34
35 // The CM thread is created when the G1 garbage collector is used
36
37 int ConcurrentZFThread::_region_allocs = 0;
38 int ConcurrentZFThread::_sync_zfs = 0;
39 int ConcurrentZFThread::_zf_waits = 0;
40 int ConcurrentZFThread::_regions_filled = 0;
41
42 ConcurrentZFThread::ConcurrentZFThread() :
43 ConcurrentGCThread()
44 {
45 create_and_start();
46 }
47
48 void ConcurrentZFThread::wait_for_ZF_completed(HeapRegion* hr) {
49 assert(ZF_mon->owned_by_self(), "Precondition.");
50 note_zf_wait();
51 while (hr->zero_fill_state() == HeapRegion::ZeroFilling) {
52 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
53 }
54 }
55
56 void ConcurrentZFThread::processHeapRegion(HeapRegion* hr) {
57 assert(!Universe::heap()->is_gc_active(),
58 "This should not happen during GC.");
59 assert(hr != NULL, "Precondition");
60 // These are unlocked reads, but if this test is successful, then no
61 // other thread will attempt this zero filling. Only a GC thread can
62 // modify the ZF state of a region whose state is zero-filling, and this
63 // should only happen while the ZF thread is locking out GC.
64 if (hr->zero_fill_state() == HeapRegion::ZeroFilling
65 && hr->zero_filler() == Thread::current()) {
66 assert(hr->top() == hr->bottom(), "better be empty!");
67 assert(!hr->isHumongous(), "Only free regions on unclean list.");
68 Copy::fill_to_words(hr->bottom(), hr->capacity()/HeapWordSize);
69 note_region_filled();
70 }
71 }
72
73 void ConcurrentZFThread::run() {
74 initialize_in_thread();
75 Thread* thr_self = Thread::current();
76 _vtime_start = os::elapsedVTime();
77 wait_for_universe_init();
78
79 G1CollectedHeap* g1 = G1CollectedHeap::heap();
80 _sts.join();
81 while (!_should_terminate) {
82 _sts.leave();
83
84 {
85 MutexLockerEx x(ZF_mon, Mutex::_no_safepoint_check_flag);
86
87 // This local variable will hold a region being zero-filled. This
88 // region will neither be on the unclean or zero-filled lists, and
89 // will not be available for allocation; thus, we might have an
90 // allocation fail, causing a full GC, because of this, but this is a
91 // price we will pay. (In future, we might want to make the fact
92 // that there's a region being zero-filled apparent to the G1 heap,
93 // which could then wait for it in this extreme case...)
94 HeapRegion* to_fill;
95
96 while (!g1->should_zf()
97 || (to_fill = g1->pop_unclean_region_list_locked()) == NULL)
98 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
99 while (to_fill->zero_fill_state() == HeapRegion::ZeroFilling)
100 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
101
102 // So now to_fill is non-NULL and is not ZeroFilling. It might be
103 // Allocated or ZeroFilled. (The latter could happen if this thread
104 // starts the zero-filling of a region, but a GC intervenes and
105 // pushes new regions needing on the front of the filling on the
106 // front of the list.)
107
108 switch (to_fill->zero_fill_state()) {
109 case HeapRegion::Allocated:
110 to_fill = NULL;
111 break;
112
113 case HeapRegion::NotZeroFilled:
114 to_fill->set_zero_fill_in_progress(thr_self);
115
116 ZF_mon->unlock();
117 _sts.join();
118 processHeapRegion(to_fill);
119 _sts.leave();
120 ZF_mon->lock_without_safepoint_check();
121
122 if (to_fill->zero_fill_state() == HeapRegion::ZeroFilling
123 && to_fill->zero_filler() == thr_self) {
124 to_fill->set_zero_fill_complete();
125 (void)g1->put_free_region_on_list_locked(to_fill);
126 }
127 break;
128
129 case HeapRegion::ZeroFilled:
130 (void)g1->put_free_region_on_list_locked(to_fill);
131 break;
132
133 case HeapRegion::ZeroFilling:
134 ShouldNotReachHere();
135 break;
136 }
137 }
138 _vtime_accum = (os::elapsedVTime() - _vtime_start);
139 _sts.join();
140 }
141 _sts.leave();
142
143 assert(_should_terminate, "just checking");
144 terminate();
145 }
146
147 bool ConcurrentZFThread::offer_yield() {
148 if (_sts.should_yield()) {
149 _sts.yield("Concurrent ZF");
150 return true;
151 } else {
152 return false;
153 }
154 }
155
156 void ConcurrentZFThread::stop() {
157 // it is ok to take late safepoints here, if needed
158 MutexLockerEx mu(Terminator_lock);
159 _should_terminate = true;
160 while (!_has_terminated) {
161 Terminator_lock->wait();
162 }
163 }
164
165 void ConcurrentZFThread::print() const {
166 print_on(tty);
167 }
168
169 void ConcurrentZFThread::print_on(outputStream* st) const {
170 st->print("\"G1 Concurrent Zero-Fill Thread\" ");
171 Thread::print_on(st);
172 st->cr();
173 }
174
175
176 double ConcurrentZFThread::_vtime_accum;
177
178 void ConcurrentZFThread::print_summary_info() {
179 gclog_or_tty->print("\nConcurrent Zero-Filling:\n");
180 gclog_or_tty->print(" Filled %d regions, used %5.2fs.\n",
181 _regions_filled,
182 vtime_accum());
183 gclog_or_tty->print(" Of %d region allocs, %d (%5.2f%%) required sync ZF,\n",
184 _region_allocs, _sync_zfs,
185 (_region_allocs > 0 ?
186 (float)_sync_zfs/(float)_region_allocs*100.0 :
187 0.0));
188 gclog_or_tty->print(" and %d (%5.2f%%) required a ZF wait.\n",
189 _zf_waits,
190 (_region_allocs > 0 ?
191 (float)_zf_waits/(float)_region_allocs*100.0 :
192 0.0));
193
194 }