1 /*
   2  * Copyright (c) 2001, 2020, Oracle and/or its affiliates. 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 #include "gc/g1/g1BarrierSet.hpp"
  27 #include "gc/g1/g1ConcurrentRefine.hpp"
  28 #include "gc/g1/g1ConcurrentRefineThread.hpp"
  29 #include "gc/g1/g1DirtyCardQueue.hpp"
  30 #include "gc/shared/suspendibleThreadSet.hpp"
  31 #include "logging/log.hpp"
  32 #include "runtime/atomic.hpp"
  33 #include "runtime/thread.hpp"
  34 
  35 G1ConcurrentRefineThread::G1ConcurrentRefineThread(G1ConcurrentRefine* cr, uint worker_id) :
  36   ConcurrentGCThread(),
  37   _vtime_start(0.0),
  38   _vtime_accum(0.0),
  39   _total_refinement_time(),
  40   _total_refined_cards(0),
  41   _worker_id(worker_id),
  42   _notifier(new Semaphore(0)),
  43   _should_notify(true),
  44   _cr(cr)
  45 {
  46   // set name
  47   set_name("G1 Refine#%d", worker_id);
  48   create_and_start();
  49 }
  50 
  51 // _notifier and _should_notify form a single-reader / multi-writer
  52 // notification mechanism.  The thread is the single reader. The writers
  53 // are (other) threads that call activate() on the thread.
  54 
  55 void G1ConcurrentRefineThread::wait_for_completed_buffers() {
  56   assert(this == Thread::current(), "precondition");
  57   while (Atomic::load_acquire(&_should_notify)) {
  58     _notifier->wait();
  59   }
  60 }
  61 
  62 void G1ConcurrentRefineThread::activate() {
  63   assert(this != Thread::current(), "precondition");
  64   // Notify iff transitioning from needing activation to not.  This helps
  65   // keep the semaphore count bounded and minimizes the work done by
  66   // activators when the thread is already active.
  67   if (Atomic::load_acquire(&_should_notify) &&
  68       Atomic::cmpxchg(&_should_notify, true, false)) {
  69     _notifier->signal();
  70   }
  71 }
  72 
  73 // Called when no refinement work found for this thread.
  74 // Returns true if should deactivate.
  75 bool G1ConcurrentRefineThread::maybe_deactivate(bool more_work) {
  76   assert(this == Thread::current(), "precondition");
  77 
  78   if (more_work) {
  79     // Suppress unnecessary notifications.
  80     Atomic::release_store(&_should_notify, false);
  81     return false;
  82   } else if (Atomic::load_acquire(&_should_notify)) {
  83     // Deactivate if no notifications since enabled (see below).
  84     return true;
  85   } else {
  86     // Try for more refinement work with notifications enabled, to close
  87     // race; there could be a plethora of suppressed activation attempts
  88     // after we found no work but before we enable notifications here
  89     // (so there could be lots of work for this thread to do), followed
  90     // by a long time without activation after enabling notifications.
  91     // But first, clear any pending signals to prevent accumulation.
  92     while (_notifier->trywait()) {}
  93     Atomic::release_store(&_should_notify, true);
  94     return false;
  95   }
  96 }
  97 
  98 void G1ConcurrentRefineThread::run_service() {
  99   _vtime_start = os::elapsedVTime();
 100 
 101   while (!should_terminate()) {
 102     // Wait for work
 103     wait_for_completed_buffers();
 104     if (should_terminate()) {
 105       break;
 106     }
 107 
 108     log_debug(gc, refine)("Activated worker %d, on threshold: " SIZE_FORMAT ", current: " SIZE_FORMAT,
 109                           _worker_id, _cr->activation_threshold(_worker_id),
 110                           G1BarrierSet::dirty_card_queue_set().num_cards());
 111 
 112     size_t start_total_refined_cards = _total_refined_cards; // For logging.
 113 
 114     {
 115       SuspendibleThreadSetJoiner sts_join;
 116 
 117       while (!should_terminate()) {
 118         if (sts_join.should_yield()) {
 119           sts_join.yield();
 120           continue;             // Re-check for termination after yield delay.
 121         }
 122 
 123         Ticks start_time = Ticks::now();
 124         bool more_work = _cr->do_refinement_step(_worker_id, &_total_refined_cards);
 125         _total_refinement_time += (Ticks::now() - start_time);
 126 
 127         if (maybe_deactivate(more_work)) break;
 128       }
 129     }
 130 
 131     log_debug(gc, refine)("Deactivated worker %d, off threshold: " SIZE_FORMAT
 132                           ", current: " SIZE_FORMAT ", refined cards: "
 133                           SIZE_FORMAT ", total refined cards: " SIZE_FORMAT,
 134                           _worker_id, _cr->deactivation_threshold(_worker_id),
 135                           G1BarrierSet::dirty_card_queue_set().num_cards(),
 136                           _total_refined_cards - start_total_refined_cards,
 137                           _total_refined_cards);
 138 
 139     if (os::supports_vtime()) {
 140       _vtime_accum = (os::elapsedVTime() - _vtime_start);
 141     } else {
 142       _vtime_accum = 0.0;
 143     }
 144   }
 145 
 146   log_debug(gc, refine)("Stopping %d", _worker_id);
 147 }
 148 
 149 void G1ConcurrentRefineThread::stop_service() {
 150   activate();
 151 }