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 } 127 128 ShenandoahEvacOOMScopeLeaver::ShenandoahEvacOOMScopeLeaver() { 129 ShenandoahHeap::heap()->leave_evacuation(); 130 } 131 132 ShenandoahEvacOOMScopeLeaver::~ShenandoahEvacOOMScopeLeaver() { 133 ShenandoahHeap::heap()->enter_evacuation(); 134 }