1 /*
   2  * Copyright (c) 2015, 2016, 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/g1CollectedHeap.inline.hpp"
  27 #include "gc/g1/g1CollectorPolicy.hpp"
  28 #include "gc/g1/g1CollectionSet.hpp"
  29 #include "gc/g1/g1YoungRemSetSamplingThread.hpp"
  30 #include "gc/g1/heapRegion.inline.hpp"
  31 #include "gc/g1/heapRegionRemSet.hpp"
  32 #include "gc/g1/suspendibleThreadSet.hpp"
  33 #include "runtime/mutexLocker.hpp"
  34 
  35 void G1YoungRemSetSamplingThread::run() {
  36   initialize_in_thread();
  37   wait_for_universe_init();
  38 
  39   run_service();
  40 
  41   terminate();
  42 }
  43 
  44 void G1YoungRemSetSamplingThread::stop() {
  45   // it is ok to take late safepoints here, if needed
  46   {
  47     MutexLockerEx mu(Terminator_lock);
  48     _should_terminate = true;
  49   }
  50 
  51   stop_service();
  52 
  53   {
  54     MutexLockerEx mu(Terminator_lock);
  55     while (!_has_terminated) {
  56       Terminator_lock->wait();
  57     }
  58   }
  59 }
  60 
  61 G1YoungRemSetSamplingThread::G1YoungRemSetSamplingThread() :
  62     ConcurrentGCThread(),
  63     _monitor(Mutex::nonleaf,
  64              "G1YoungRemSetSamplingThread monitor",
  65              true,
  66              Monitor::_safepoint_check_never) {
  67   set_name("G1 Young RemSet Sampling");
  68   create_and_start();
  69 }
  70 
  71 void G1YoungRemSetSamplingThread::sleep_before_next_cycle() {
  72   MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);
  73   if (!_should_terminate) {
  74     uintx waitms = G1ConcRefinementServiceIntervalMillis; // 300, really should be?
  75     _monitor.wait(Mutex::_no_safepoint_check_flag, waitms);
  76   }
  77 }
  78 
  79 void G1YoungRemSetSamplingThread::run_service() {
  80   double vtime_start = os::elapsedVTime();
  81 
  82   while (!_should_terminate) {
  83     sample_young_list_rs_lengths();
  84 
  85     if (os::supports_vtime()) {
  86       _vtime_accum = (os::elapsedVTime() - vtime_start);
  87     } else {
  88       _vtime_accum = 0.0;
  89     }
  90 
  91     sleep_before_next_cycle();
  92   }
  93 }
  94 
  95 void G1YoungRemSetSamplingThread::stop_service() {
  96   MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);
  97   _monitor.notify();
  98 }
  99 
 100 void G1YoungRemSetSamplingThread::sample_young_list_rs_lengths() {
 101   SuspendibleThreadSetJoiner sts;
 102   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 103   G1CollectorPolicy* g1p = g1h->g1_policy();
 104   if (g1p->adaptive_young_list_length()) {
 105     int regions_visited = 0;
 106     HeapRegion* hr = g1h->young_list()->first_region();
 107     size_t sampled_rs_lengths = 0;
 108 
 109     while (hr != NULL) {
 110       size_t rs_length = hr->rem_set()->occupied();
 111       sampled_rs_lengths += rs_length;
 112 
 113       // The current region may not yet have been added to the
 114       // incremental collection set (it gets added when it is
 115       // retired as the current allocation region).
 116       if (hr->in_collection_set()) {
 117         // Update the collection set policy information for this region
 118         g1h->collection_set()->update_young_region_prediction(hr, rs_length);
 119       }
 120 
 121       ++regions_visited;
 122 
 123       // we try to yield every time we visit 10 regions
 124       if (regions_visited == 10) {
 125         if (sts.should_yield()) {
 126           sts.yield();
 127           // A gc may have occurred and our sampling data is stale and further
 128           // traversal of the young list is unsafe
 129           return;
 130         }
 131         regions_visited = 0;
 132       }
 133       hr = hr->get_next_young_region();
 134     }
 135     g1p->revise_young_list_target_length_if_necessary(sampled_rs_lengths);
 136   }
 137 }