1 /*
   2  * Copyright (c) 2018, 2020, 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/shenandoahEvacOOMHandler.inline.hpp"
  28 #include "gc/shenandoah/shenandoahUtils.hpp"
  29 #include "runtime/os.hpp"
  30 #include "runtime/thread.hpp"
  31 
  32 const jint ShenandoahEvacOOMHandler::OOM_MARKER_MASK = 0x80000000;
  33 
  34 ShenandoahEvacOOMHandler::ShenandoahEvacOOMHandler() :
  35   _threads_in_evac(0) {
  36 }
  37 
  38 void ShenandoahEvacOOMHandler::wait_for_no_evac_threads() {
  39   while ((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) != 0) {
  40     os::naked_short_sleep(1);
  41   }
  42   // At this point we are sure that no threads can evacuate anything. Raise
  43   // the thread-local oom_during_evac flag to indicate that any attempt
  44   // to evacuate should simply return the forwarding pointer instead (which is safe now).
  45   ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), true);
  46 }
  47 
  48 void ShenandoahEvacOOMHandler::register_thread(Thread* thr) {
  49   jint threads_in_evac = Atomic::load_acquire(&_threads_in_evac);
  50 
  51   assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
  52   while (true) {
  53     jint other = Atomic::cmpxchg(&_threads_in_evac, threads_in_evac, threads_in_evac + 1);
  54     if (other == threads_in_evac) {
  55       // Success: caller may safely enter evacuation
  56       return;
  57     } else {
  58       // Failure:
  59       //  - if offender has OOM_MARKER_MASK, then loop until no more threads in evac
  60       //  - otherwise re-try CAS
  61       if ((other & OOM_MARKER_MASK) != 0) {
  62         wait_for_no_evac_threads();
  63         return;
  64       }
  65       threads_in_evac = other;
  66     }
  67   }
  68 }
  69 
  70 void ShenandoahEvacOOMHandler::unregister_thread(Thread* thr) {
  71   if (!ShenandoahThreadLocalData::is_oom_during_evac(thr)) {
  72     assert((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) > 0, "sanity");
  73     // NOTE: It's ok to simply decrement, even with mask set, because unmasked value is positive.
  74     Atomic::dec(&_threads_in_evac);
  75   } else {
  76     // If we get here, the current thread has already gone through the
  77     // OOM-during-evac protocol and has thus either never entered or successfully left
  78     // the evacuation region. Simply flip its TL oom-during-evac flag back off.
  79     ShenandoahThreadLocalData::set_oom_during_evac(thr, false);
  80   }
  81   assert(!ShenandoahThreadLocalData::is_oom_during_evac(thr), "TL oom-during-evac must be turned off");
  82 }
  83 
  84 void ShenandoahEvacOOMHandler::handle_out_of_memory_during_evacuation() {
  85   assert(ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity");
  86   assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
  87 
  88   jint threads_in_evac = Atomic::load_acquire(&_threads_in_evac);
  89   while (true) {
  90     jint other = Atomic::cmpxchg(&_threads_in_evac, threads_in_evac, (threads_in_evac - 1) | OOM_MARKER_MASK);
  91     if (other == threads_in_evac) {
  92       // Success: wait for other threads to get out of the protocol and return.
  93       wait_for_no_evac_threads();
  94       return;
  95     } else {
  96       // Failure: try again with updated new value.
  97       threads_in_evac = other;
  98     }
  99   }
 100 }
 101 
 102 void ShenandoahEvacOOMHandler::clear() {
 103   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
 104   assert((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) == 0, "sanity");
 105   Atomic::release_store_fence(&_threads_in_evac, (jint)0);
 106 }