1 /*
2 * Copyright (c) 2001, 2009, 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 "incls/_precompiled.incl"
26 #include "incls/_concurrentZFThread.cpp.incl"
27
28 // ======= Concurrent Zero-Fill Thread ========
29
30 // The CM thread is created when the G1 garbage collector is used
31
32 int ConcurrentZFThread::_region_allocs = 0;
33 int ConcurrentZFThread::_sync_zfs = 0;
34 int ConcurrentZFThread::_zf_waits = 0;
35 int ConcurrentZFThread::_regions_filled = 0;
36
37 ConcurrentZFThread::ConcurrentZFThread() :
38 ConcurrentGCThread()
39 {
40 create_and_start();
41 }
42
43 void ConcurrentZFThread::wait_for_ZF_completed(HeapRegion* hr) {
44 assert(ZF_mon->owned_by_self(), "Precondition.");
45 note_zf_wait();
46 while (hr->zero_fill_state() == HeapRegion::ZeroFilling) {
47 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
48 }
49 }
50
51 void ConcurrentZFThread::processHeapRegion(HeapRegion* hr) {
52 assert(!Universe::heap()->is_gc_active(),
53 "This should not happen during GC.");
54 assert(hr != NULL, "Precondition");
55 // These are unlocked reads, but if this test is successful, then no
56 // other thread will attempt this zero filling. Only a GC thread can
57 // modify the ZF state of a region whose state is zero-filling, and this
58 // should only happen while the ZF thread is locking out GC.
59 if (hr->zero_fill_state() == HeapRegion::ZeroFilling
60 && hr->zero_filler() == Thread::current()) {
61 assert(hr->top() == hr->bottom(), "better be empty!");
62 assert(!hr->isHumongous(), "Only free regions on unclean list.");
63 Copy::fill_to_words(hr->bottom(), hr->capacity()/HeapWordSize);
64 note_region_filled();
65 }
66 }
67
68 void ConcurrentZFThread::run() {
69 initialize_in_thread();
70 Thread* thr_self = Thread::current();
71 _vtime_start = os::elapsedVTime();
72 wait_for_universe_init();
73
74 G1CollectedHeap* g1 = G1CollectedHeap::heap();
75 _sts.join();
76 while (!_should_terminate) {
77 _sts.leave();
78
79 {
80 MutexLockerEx x(ZF_mon, Mutex::_no_safepoint_check_flag);
81
82 // This local variable will hold a region being zero-filled. This
83 // region will neither be on the unclean or zero-filled lists, and
84 // will not be available for allocation; thus, we might have an
85 // allocation fail, causing a full GC, because of this, but this is a
86 // price we will pay. (In future, we might want to make the fact
87 // that there's a region being zero-filled apparent to the G1 heap,
88 // which could then wait for it in this extreme case...)
89 HeapRegion* to_fill;
90
91 while (!g1->should_zf()
92 || (to_fill = g1->pop_unclean_region_list_locked()) == NULL)
93 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
94 while (to_fill->zero_fill_state() == HeapRegion::ZeroFilling)
95 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
96
97 // So now to_fill is non-NULL and is not ZeroFilling. It might be
98 // Allocated or ZeroFilled. (The latter could happen if this thread
99 // starts the zero-filling of a region, but a GC intervenes and
100 // pushes new regions needing on the front of the filling on the
101 // front of the list.)
102
103 switch (to_fill->zero_fill_state()) {
104 case HeapRegion::Allocated:
105 to_fill = NULL;
106 break;
107
108 case HeapRegion::NotZeroFilled:
109 to_fill->set_zero_fill_in_progress(thr_self);
110
111 ZF_mon->unlock();
112 _sts.join();
113 processHeapRegion(to_fill);
114 _sts.leave();
115 ZF_mon->lock_without_safepoint_check();
116
117 if (to_fill->zero_fill_state() == HeapRegion::ZeroFilling
118 && to_fill->zero_filler() == thr_self) {
119 to_fill->set_zero_fill_complete();
120 (void)g1->put_free_region_on_list_locked(to_fill);
121 }
122 break;
123
124 case HeapRegion::ZeroFilled:
125 (void)g1->put_free_region_on_list_locked(to_fill);
126 break;
127
128 case HeapRegion::ZeroFilling:
129 ShouldNotReachHere();
130 break;
131 }
132 }
133 _vtime_accum = (os::elapsedVTime() - _vtime_start);
134 _sts.join();
135 }
136 _sts.leave();
137
138 assert(_should_terminate, "just checking");
139 terminate();
140 }
141
142 bool ConcurrentZFThread::offer_yield() {
143 if (_sts.should_yield()) {
144 _sts.yield("Concurrent ZF");
145 return true;
146 } else {
147 return false;
148 }
149 }
150
151 void ConcurrentZFThread::stop() {
152 // it is ok to take late safepoints here, if needed
153 MutexLockerEx mu(Terminator_lock);
154 _should_terminate = true;
155 while (!_has_terminated) {
156 Terminator_lock->wait();
157 }
158 }
159
160 void ConcurrentZFThread::print() const {
161 print_on(tty);
162 }
163
164 void ConcurrentZFThread::print_on(outputStream* st) const {
165 st->print("\"G1 Concurrent Zero-Fill Thread\" ");
166 Thread::print_on(st);
167 st->cr();
168 }
169
170
171 double ConcurrentZFThread::_vtime_accum;
172
173 void ConcurrentZFThread::print_summary_info() {
174 gclog_or_tty->print("\nConcurrent Zero-Filling:\n");
175 gclog_or_tty->print(" Filled %d regions, used %5.2fs.\n",
176 _regions_filled,
177 vtime_accum());
178 gclog_or_tty->print(" Of %d region allocs, %d (%5.2f%%) required sync ZF,\n",
179 _region_allocs, _sync_zfs,
180 (_region_allocs > 0 ?
181 (float)_sync_zfs/(float)_region_allocs*100.0 :
182 0.0));
183 gclog_or_tty->print(" and %d (%5.2f%%) required a ZF wait.\n",
184 _zf_waits,
185 (_region_allocs > 0 ?
186 (float)_zf_waits/(float)_region_allocs*100.0 :
187 0.0));
188
189 }