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1 /* |
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2 * Copyright (c) 2018, Red Hat, Inc. All rights reserved. |
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3 * |
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4 * This code is free software; you can redistribute it and/or modify it |
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5 * under the terms of the GNU General Public License version 2 only, as |
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6 * published by the Free Software Foundation. |
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7 * |
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8 * This code is distributed in the hope that it will be useful, but WITHOUT |
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9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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11 * version 2 for more details (a copy is included in the LICENSE file that |
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12 * accompanied this code). |
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13 * |
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14 * You should have received a copy of the GNU General Public License version |
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15 * 2 along with this work; if not, write to the Free Software Foundation, |
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16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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17 * |
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18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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19 * or visit www.oracle.com if you need additional information or have any |
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20 * questions. |
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21 * |
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22 */ |
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23 |
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24 #include "precompiled.hpp" |
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25 |
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26 #include "gc/shenandoah/shenandoahHeap.hpp" |
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27 #include "gc/shenandoah/shenandoahUtils.hpp" |
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28 #include "gc/shenandoah/shenandoahEvacOOMHandler.hpp" |
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29 #include "gc/shenandoah/shenandoahThreadLocalData.hpp" |
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30 #include "runtime/orderAccess.hpp" |
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31 #include "runtime/os.hpp" |
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32 #include "runtime/thread.hpp" |
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33 |
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34 const jint ShenandoahEvacOOMHandler::OOM_MARKER_MASK = 0x80000000; |
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35 |
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36 ShenandoahEvacOOMHandler::ShenandoahEvacOOMHandler() : |
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37 _threads_in_evac(0) { |
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38 } |
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39 |
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40 void ShenandoahEvacOOMHandler::wait_for_no_evac_threads() { |
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41 while ((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) != 0) { |
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42 os::naked_short_sleep(1); |
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43 } |
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44 // At this point we are sure that no threads can evacuate anything. Raise |
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45 // the thread-local oom_during_evac flag to indicate that any attempt |
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46 // to evacuate should simply return the forwarding pointer instead (which is safe now). |
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47 ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), true); |
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48 } |
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49 |
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50 void ShenandoahEvacOOMHandler::enter_evacuation() { |
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51 jint threads_in_evac = OrderAccess::load_acquire(&_threads_in_evac); |
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52 |
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53 assert(!ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity"); |
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54 assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set"); |
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55 |
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56 if ((threads_in_evac & OOM_MARKER_MASK) != 0) { |
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57 wait_for_no_evac_threads(); |
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58 return; |
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59 } |
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60 |
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61 while (true) { |
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62 jint other = Atomic::cmpxchg(threads_in_evac + 1, &_threads_in_evac, threads_in_evac); |
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63 if (other == threads_in_evac) { |
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64 // Success: caller may safely enter evacuation |
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65 DEBUG_ONLY(ShenandoahThreadLocalData::set_evac_allowed(Thread::current(), true)); |
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66 return; |
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67 } else { |
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68 // Failure: |
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69 // - if offender has OOM_MARKER_MASK, then loop until no more threads in evac |
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70 // - otherwise re-try CAS |
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71 if ((other & OOM_MARKER_MASK) != 0) { |
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72 wait_for_no_evac_threads(); |
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73 return; |
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74 } |
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75 threads_in_evac = other; |
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76 } |
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77 } |
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78 } |
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79 |
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80 void ShenandoahEvacOOMHandler::leave_evacuation() { |
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81 if (!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current())) { |
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82 assert((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) > 0, "sanity"); |
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83 // NOTE: It's ok to simply decrement, even with mask set, because unmasked value is positive. |
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84 Atomic::dec(&_threads_in_evac); |
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85 } else { |
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86 // If we get here, the current thread has already gone through the |
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87 // OOM-during-evac protocol and has thus either never entered or successfully left |
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88 // the evacuation region. Simply flip its TL oom-during-evac flag back off. |
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89 ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), false); |
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90 } |
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91 DEBUG_ONLY(ShenandoahThreadLocalData::set_evac_allowed(Thread::current(), false)); |
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92 assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must be turned off"); |
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93 } |
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94 |
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95 void ShenandoahEvacOOMHandler::handle_out_of_memory_during_evacuation() { |
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96 assert(ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity"); |
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97 assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set"); |
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98 |
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99 jint threads_in_evac = OrderAccess::load_acquire(&_threads_in_evac); |
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100 while (true) { |
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101 jint other = Atomic::cmpxchg((threads_in_evac - 1) | OOM_MARKER_MASK, |
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102 &_threads_in_evac, threads_in_evac); |
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103 if (other == threads_in_evac) { |
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104 // Success: wait for other threads to get out of the protocol and return. |
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105 wait_for_no_evac_threads(); |
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106 return; |
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107 } else { |
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108 // Failure: try again with updated new value. |
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109 threads_in_evac = other; |
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110 } |
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111 } |
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112 } |
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113 |
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114 void ShenandoahEvacOOMHandler::clear() { |
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115 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint"); |
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116 assert((OrderAccess::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) == 0, "sanity"); |
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117 OrderAccess::release_store_fence<jint>(&_threads_in_evac, 0); |
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118 } |
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119 |
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120 ShenandoahEvacOOMScope::ShenandoahEvacOOMScope() { |
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121 ShenandoahHeap::heap()->enter_evacuation(); |
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122 } |
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123 |
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124 ShenandoahEvacOOMScope::~ShenandoahEvacOOMScope() { |
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125 ShenandoahHeap::heap()->leave_evacuation(); |
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126 } |
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127 |
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128 ShenandoahEvacOOMScopeLeaver::ShenandoahEvacOOMScopeLeaver() { |
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129 ShenandoahHeap::heap()->leave_evacuation(); |
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130 } |
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131 |
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132 ShenandoahEvacOOMScopeLeaver::~ShenandoahEvacOOMScopeLeaver() { |
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133 ShenandoahHeap::heap()->enter_evacuation(); |
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134 } |