rev 59438 : 8245823: Shenandoah: inline/optimize ShenandoahEvacOOMScope

   1 /*
   2  * Copyright (c) 2018, 2019, Red Hat, Inc. 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 
  27 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  28 #include "gc/shenandoah/shenandoahUtils.hpp"
  29 #include "gc/shenandoah/shenandoahEvacOOMHandler.hpp"
  30 #include "gc/shenandoah/shenandoahThreadLocalData.hpp"
  31 #include "runtime/atomic.hpp"
  32 #include "runtime/os.hpp"
  33 #include "runtime/thread.hpp"
  34 
  35 const jint ShenandoahEvacOOMHandler::OOM_MARKER_MASK = 0x80000000;
  36 
  37 ShenandoahEvacOOMHandler::ShenandoahEvacOOMHandler() :
  38   _threads_in_evac(0) {
  39 }
  40 
  41 void ShenandoahEvacOOMHandler::wait_for_no_evac_threads() {
  42   while ((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) != 0) {
  43     os::naked_short_sleep(1);
  44   }
  45   // At this point we are sure that no threads can evacuate anything. Raise
  46   // the thread-local oom_during_evac flag to indicate that any attempt
  47   // to evacuate should simply return the forwarding pointer instead (which is safe now).
  48   ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), true);
  49 }
  50 
  51 void ShenandoahEvacOOMHandler::enter_evacuation() {
  52   jint threads_in_evac = Atomic::load_acquire(&_threads_in_evac);
  53 
  54   Thread* const thr = Thread::current();
  55   uint8_t level = ShenandoahThreadLocalData::push_evac_oom_scope(thr);
  56   if ((threads_in_evac & OOM_MARKER_MASK) != 0) {
  57     wait_for_no_evac_threads();
  58     return;
  59   }
  60 
  61   // Nesting case, this thread already registered
  62   if (level > 0) {
  63      return;
  64   }
  65 
  66   assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
  67   while (true) {
  68     jint other = Atomic::cmpxchg(&_threads_in_evac, threads_in_evac, threads_in_evac + 1);
  69     if (other == threads_in_evac) {
  70       // Success: caller may safely enter evacuation
  71       return;
  72     } else {
  73       // Failure:
  74       //  - if offender has OOM_MARKER_MASK, then loop until no more threads in evac
  75       //  - otherwise re-try CAS
  76       if ((other & OOM_MARKER_MASK) != 0) {
  77         wait_for_no_evac_threads();
  78         return;
  79       }
  80       threads_in_evac = other;
  81     }
  82   }
  83 }
  84 
  85 void ShenandoahEvacOOMHandler::leave_evacuation() {
  86   Thread* const thr = Thread::current();
  87   uint8_t level = ShenandoahThreadLocalData::pop_evac_oom_scope(thr);
  88   // Not top level, just return
  89   if (level > 1) {
  90     return;
  91   }
  92 
  93   if (!ShenandoahThreadLocalData::is_oom_during_evac(thr)) {
  94     assert((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) > 0, "sanity");
  95     // NOTE: It's ok to simply decrement, even with mask set, because unmasked value is positive.
  96     Atomic::dec(&_threads_in_evac);
  97   } else {
  98     // If we get here, the current thread has already gone through the
  99     // OOM-during-evac protocol and has thus either never entered or successfully left
 100     // the evacuation region. Simply flip its TL oom-during-evac flag back off.
 101     ShenandoahThreadLocalData::set_oom_during_evac(thr, false);
 102   }
 103   assert(!ShenandoahThreadLocalData::is_oom_during_evac(thr), "TL oom-during-evac must be turned off");
 104 }
 105 
 106 void ShenandoahEvacOOMHandler::handle_out_of_memory_during_evacuation() {
 107   assert(ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity");
 108   assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
 109 
 110   jint threads_in_evac = Atomic::load_acquire(&_threads_in_evac);
 111   while (true) {
 112     jint other = Atomic::cmpxchg(&_threads_in_evac, threads_in_evac, (threads_in_evac - 1) | OOM_MARKER_MASK);
 113     if (other == threads_in_evac) {
 114       // Success: wait for other threads to get out of the protocol and return.
 115       wait_for_no_evac_threads();
 116       return;
 117     } else {
 118       // Failure: try again with updated new value.
 119       threads_in_evac = other;
 120     }
 121   }
 122 }
 123 
 124 void ShenandoahEvacOOMHandler::clear() {
 125   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
 126   assert((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) == 0, "sanity");
 127   Atomic::release_store_fence(&_threads_in_evac, (jint)0);
 128 }
 129 
 130 ShenandoahEvacOOMScope::ShenandoahEvacOOMScope() {
 131   ShenandoahHeap::heap()->enter_evacuation();
 132 }
 133 
 134 ShenandoahEvacOOMScope::~ShenandoahEvacOOMScope() {
 135   ShenandoahHeap::heap()->leave_evacuation();
 136 }
--- EOF ---