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/g1YoungRemSetSamplingThread.hpp"
  29 #include "gc/g1/heapRegion.inline.hpp"
  30 #include "gc/g1/heapRegionRemSet.hpp"
  31 #include "gc/g1/suspendibleThreadSet.hpp"
  32 #include "runtime/mutexLocker.hpp"
  33 
  34 void G1YoungRemSetSamplingThread::run() {
  35   initialize_in_thread();
  36   wait_for_universe_init();
  37 
  38   run_service();
  39 
  40   terminate();
  41 }
  42 
  43 void G1YoungRemSetSamplingThread::stop() {
  44   // it is ok to take late safepoints here, if needed
  45   {
  46     MutexLockerEx mu(Terminator_lock);
  47     _should_terminate = true;
  48   }
  49 
  50   stop_service();
  51 
  52   {
  53     MutexLockerEx mu(Terminator_lock);
  54     while (!_has_terminated) {
  55       Terminator_lock->wait();
  56     }
  57   }
  58 }
  59 
  60 G1YoungRemSetSamplingThread::G1YoungRemSetSamplingThread() :
  61     ConcurrentGCThread(),
  62     _monitor(Mutex::nonleaf,
  63              "G1YoungRemSetSamplingThread monitor",
  64              true,
  65              Monitor::_safepoint_check_never) {
  66   set_name("G1 Young RemSet Sampling");
  67   create_and_start();
  68 }
  69 
  70 G1YoungRemSetSamplingThread::~G1YoungRemSetSamplingThread() {
  71   assert(!_monitor.is_locked(), "don't delete locked monitor");
  72 }
  73 
  74 void G1YoungRemSetSamplingThread::sleep_before_next_cycle() {
  75   MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);
  76   if (!_should_terminate) {
  77     intx waitms = G1ConcRefinementServiceIntervalMillis; // 300, really should be?
  78     _monitor.wait(Mutex::_no_safepoint_check_flag, waitms);
  79   }
  80 }
  81 
  82 void G1YoungRemSetSamplingThread::run_service() {
  83   double vtime_start = os::elapsedVTime();
  84 
  85   while (!_should_terminate) {
  86     sample_young_list_rs_lengths();
  87 
  88     if (os::supports_vtime()) {
  89       _vtime_accum = (os::elapsedVTime() - vtime_start);
  90     } else {
  91       _vtime_accum = 0.0;
  92     }
  93 
  94     sleep_before_next_cycle();
  95   }
  96 }
  97 
  98 void G1YoungRemSetSamplingThread::stop_service() {
  99   MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);
 100   _monitor.notify();
 101 }
 102 
 103 void G1YoungRemSetSamplingThread::sample_young_list_rs_lengths() {
 104   SuspendibleThreadSetJoiner sts;
 105   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 106   G1CollectorPolicy* g1p = g1h->g1_policy();
 107   if (g1p->adaptive_young_list_length()) {
 108     int regions_visited = 0;
 109     HeapRegion* hr = g1h->young_list()->first_region();
 110     size_t sampled_rs_lengths = 0;
 111 
 112     while (hr != NULL) {
 113       size_t rs_length = hr->rem_set()->occupied();
 114       sampled_rs_lengths += rs_length;
 115 
 116       // The current region may not yet have been added to the
 117       // incremental collection set (it gets added when it is
 118       // retired as the current allocation region).
 119       if (hr->in_collection_set()) {
 120         // Update the collection set policy information for this region
 121         g1p->update_incremental_cset_info(hr, rs_length);
 122       }
 123 
 124       ++regions_visited;
 125 
 126       // we try to yield every time we visit 10 regions
 127       if (regions_visited == 10) {
 128         if (sts.should_yield()) {
 129           sts.yield();
 130           // A gc may have occurred and our sampling data is stale and further
 131           // traversal of the young list is unsafe
 132           return;
 133         }
 134         regions_visited = 0;
 135       }
 136       hr = hr->get_next_young_region();
 137     }
 138     g1p->revise_young_list_target_length_if_necessary(sampled_rs_lengths);
 139   }
 140 }