1 /*
2 * Copyright (c) 2018, Red Hat, Inc. All rights reserved.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #include "precompiled.hpp"
25
26 #include "gc/shenandoah/shenandoahHeap.hpp"
27 #include "gc/shenandoah/shenandoahUtils.hpp"
28 #include "gc/shenandoah/shenandoahEvacOOMHandler.hpp"
29 #include "gc/shenandoah/shenandoahThreadLocalData.hpp"
30 #include "runtime/orderAccess.hpp"
31 #include "runtime/os.hpp"
32 #include "runtime/thread.hpp"
33
34 const jint ShenandoahEvacOOMHandler::OOM_MARKER_MASK = 0x80000000;
35
36 ShenandoahEvacOOMHandler::ShenandoahEvacOOMHandler() :
37 _threads_in_evac(0) {
38 }
39
40 void ShenandoahEvacOOMHandler::wait_for_no_evac_threads() {
41 while ((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) != 0) {
42 os::naked_short_sleep(1);
43 }
44 // At this point we are sure that no threads can evacuate anything. Raise
45 // the thread-local oom_during_evac flag to indicate that any attempt
46 // to evacuate should simply return the forwarding pointer instead (which is safe now).
47 ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), true);
48 }
49
50 void ShenandoahEvacOOMHandler::enter_evacuation() {
51 jint threads_in_evac = OrderAccess::load_acquire(&_threads_in_evac);
52
53 assert(!ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity");
54 assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
55
56 if ((threads_in_evac & OOM_MARKER_MASK) != 0) {
57 wait_for_no_evac_threads();
58 return;
59 }
60
61 while (true) {
62 jint other = Atomic::cmpxchg(threads_in_evac + 1, &_threads_in_evac, threads_in_evac);
63 if (other == threads_in_evac) {
64 // Success: caller may safely enter evacuation
65 DEBUG_ONLY(ShenandoahThreadLocalData::set_evac_allowed(Thread::current(), true));
66 return;
67 } else {
68 // Failure:
69 // - if offender has OOM_MARKER_MASK, then loop until no more threads in evac
70 // - otherwise re-try CAS
71 if ((other & OOM_MARKER_MASK) != 0) {
72 wait_for_no_evac_threads();
73 return;
74 }
75 threads_in_evac = other;
76 }
77 }
78 }
79
80 void ShenandoahEvacOOMHandler::leave_evacuation() {
81 if (!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current())) {
82 assert((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) > 0, "sanity");
83 // NOTE: It's ok to simply decrement, even with mask set, because unmasked value is positive.
84 Atomic::dec(&_threads_in_evac);
85 } else {
86 // If we get here, the current thread has already gone through the
87 // OOM-during-evac protocol and has thus either never entered or successfully left
88 // the evacuation region. Simply flip its TL oom-during-evac flag back off.
89 ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), false);
90 }
91 DEBUG_ONLY(ShenandoahThreadLocalData::set_evac_allowed(Thread::current(), false));
92 assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must be turned off");
93 }
94
95 void ShenandoahEvacOOMHandler::handle_out_of_memory_during_evacuation() {
96 assert(ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity");
97 assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
98
99 jint threads_in_evac = OrderAccess::load_acquire(&_threads_in_evac);
100 while (true) {
101 jint other = Atomic::cmpxchg((threads_in_evac - 1) | OOM_MARKER_MASK,
102 &_threads_in_evac, threads_in_evac);
103 if (other == threads_in_evac) {
104 // Success: wait for other threads to get out of the protocol and return.
105 wait_for_no_evac_threads();
106 return;
107 } else {
108 // Failure: try again with updated new value.
109 threads_in_evac = other;
110 }
111 }
112 }
113
114 void ShenandoahEvacOOMHandler::clear() {
115 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
116 assert((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) == 0, "sanity");
117 OrderAccess::release_store_fence<jint>(&_threads_in_evac, 0);
118 }
119
120 ShenandoahEvacOOMScope::ShenandoahEvacOOMScope() {
121 ShenandoahHeap::heap()->enter_evacuation();
122 }
123
124 ShenandoahEvacOOMScope::~ShenandoahEvacOOMScope() {
125 ShenandoahHeap::heap()->leave_evacuation();
126 }