1 /*

     2  * Copyright (c) 2001, 2010, 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_implementation/g1/concurrentZFThread.hpp"

    27 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"

    28 #include "gc_implementation/g1/heapRegion.hpp"

    29 #include "memory/space.inline.hpp"

    30 #include "runtime/mutexLocker.hpp"

    31 #include "utilities/copy.hpp"

    32 

    33 // ======= Concurrent Zero-Fill Thread ========

    34 

    35 // The CM thread is created when the G1 garbage collector is used

    36 

    37 int ConcurrentZFThread::_region_allocs = 0;

    38 int ConcurrentZFThread::_sync_zfs = 0;

    39 int ConcurrentZFThread::_zf_waits = 0;

    40 int ConcurrentZFThread::_regions_filled = 0;

    41 

    42 ConcurrentZFThread::ConcurrentZFThread() :

    43   ConcurrentGCThread()

    44 {

    45   create_and_start();

    46 }

    47 

    48 void ConcurrentZFThread::wait_for_ZF_completed(HeapRegion* hr) {

    49   assert(ZF_mon->owned_by_self(), "Precondition.");

    50   note_zf_wait();

    51   while (hr->zero_fill_state() == HeapRegion::ZeroFilling) {

    52     ZF_mon->wait(Mutex::_no_safepoint_check_flag);

    53   }

    54 }

    55 

    56 void ConcurrentZFThread::processHeapRegion(HeapRegion* hr) {

    57   assert(!Universe::heap()->is_gc_active(),

    58          "This should not happen during GC.");

    59   assert(hr != NULL, "Precondition");

    60   // These are unlocked reads, but if this test is successful, then no

    61   // other thread will attempt this zero filling.  Only a GC thread can

    62   // modify the ZF state of a region whose state is zero-filling, and this

    63   // should only happen while the ZF thread is locking out GC.

    64   if (hr->zero_fill_state() == HeapRegion::ZeroFilling

    65       && hr->zero_filler() == Thread::current()) {

    66     assert(hr->top() == hr->bottom(), "better be empty!");

    67     assert(!hr->isHumongous(), "Only free regions on unclean list.");

    68     Copy::fill_to_words(hr->bottom(), hr->capacity()/HeapWordSize);

    69     note_region_filled();

    70   }

    71 }

    72 

    73 void ConcurrentZFThread::run() {

    74   initialize_in_thread();

    75   Thread* thr_self = Thread::current();

    76   _vtime_start = os::elapsedVTime();

    77   wait_for_universe_init();

    78 

    79   G1CollectedHeap* g1 = G1CollectedHeap::heap();

    80   _sts.join();

    81   while (!_should_terminate) {

    82     _sts.leave();

    83 

    84     {

    85       MutexLockerEx x(ZF_mon, Mutex::_no_safepoint_check_flag);

    86 

    87       // This local variable will hold a region being zero-filled.  This

    88       // region will neither be on the unclean or zero-filled lists, and

    89       // will not be available for allocation; thus, we might have an

    90       // allocation fail, causing a full GC, because of this, but this is a

    91       // price we will pay.  (In future, we might want to make the fact

    92       // that there's a region being zero-filled apparent to the G1 heap,

    93       // which could then wait for it in this extreme case...)

    94       HeapRegion* to_fill;

    95 

    96       while (!g1->should_zf()

    97              || (to_fill = g1->pop_unclean_region_list_locked()) == NULL)

    98         ZF_mon->wait(Mutex::_no_safepoint_check_flag);

    99       while (to_fill->zero_fill_state() == HeapRegion::ZeroFilling)

   100         ZF_mon->wait(Mutex::_no_safepoint_check_flag);

   101 

   102       // So now to_fill is non-NULL and is not ZeroFilling.  It might be

   103       // Allocated or ZeroFilled.  (The latter could happen if this thread

   104       // starts the zero-filling of a region, but a GC intervenes and

   105       // pushes new regions needing on the front of the filling on the

   106       // front of the list.)

   107 

   108       switch (to_fill->zero_fill_state()) {

   109       case HeapRegion::Allocated:

   110         to_fill = NULL;

   111         break;

   112 

   113       case HeapRegion::NotZeroFilled:

   114         to_fill->set_zero_fill_in_progress(thr_self);

   115 

   116         ZF_mon->unlock();

   117         _sts.join();

   118         processHeapRegion(to_fill);

   119         _sts.leave();

   120         ZF_mon->lock_without_safepoint_check();

   121 

   122         if (to_fill->zero_fill_state() == HeapRegion::ZeroFilling

   123             && to_fill->zero_filler() == thr_self) {

   124           to_fill->set_zero_fill_complete();

   125           (void)g1->put_free_region_on_list_locked(to_fill);

   126         }

   127         break;

   128 

   129       case HeapRegion::ZeroFilled:

   130         (void)g1->put_free_region_on_list_locked(to_fill);

   131         break;

   132 

   133       case HeapRegion::ZeroFilling:

   134         ShouldNotReachHere();

   135         break;

   136       }

   137     }

   138     _vtime_accum = (os::elapsedVTime() - _vtime_start);

   139     _sts.join();

   140   }

   141   _sts.leave();

   142 

   143   assert(_should_terminate, "just checking");

   144   terminate();

   145 }

   146 

   147 bool ConcurrentZFThread::offer_yield() {

   148   if (_sts.should_yield()) {

   149     _sts.yield("Concurrent ZF");

   150     return true;

   151   } else {

   152     return false;

   153   }

   154 }

   155 

   156 void ConcurrentZFThread::stop() {

   157   // it is ok to take late safepoints here, if needed

   158   MutexLockerEx mu(Terminator_lock);

   159   _should_terminate = true;

   160   while (!_has_terminated) {

   161     Terminator_lock->wait();

   162   }

   163 }

   164 

   165 void ConcurrentZFThread::print() const {

   166   print_on(tty);

   167 }

   168 

   169 void ConcurrentZFThread::print_on(outputStream* st) const {

   170   st->print("\"G1 Concurrent Zero-Fill Thread\" ");

   171   Thread::print_on(st);

   172   st->cr();

   173 }

   174 

   175 

   176 double ConcurrentZFThread::_vtime_accum;

   177 

   178 void ConcurrentZFThread::print_summary_info() {

   179   gclog_or_tty->print("\nConcurrent Zero-Filling:\n");

   180   gclog_or_tty->print("  Filled %d regions, used %5.2fs.\n",

   181                       _regions_filled,

   182                       vtime_accum());

   183   gclog_or_tty->print("  Of %d region allocs, %d (%5.2f%%) required sync ZF,\n",

   184                       _region_allocs, _sync_zfs,

   185                       (_region_allocs > 0 ?

   186                        (float)_sync_zfs/(float)_region_allocs*100.0 :

   187                        0.0));

   188   gclog_or_tty->print("     and %d (%5.2f%%) required a ZF wait.\n",

   189                       _zf_waits,

   190                       (_region_allocs > 0 ?

   191                        (float)_zf_waits/(float)_region_allocs*100.0 :

   192                        0.0));

   193 

   194 }