1 /*

     2  * Copyright (c) 2014, 2015, 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 "classfile/javaClasses.inline.hpp"

    27 #include "gc/g1/g1CollectedHeap.hpp"

    28 #include "gc/g1/g1StringDedup.hpp"

    29 #include "gc/g1/g1StringDedupQueue.hpp"

    30 #include "gc/shared/gcLocker.hpp"

    31 #include "oops/oop.inline.hpp"

    32 #include "runtime/atomic.inline.hpp"

    33 #include "runtime/mutexLocker.hpp"

    34 #include "utilities/stack.inline.hpp"

    35 

    36 G1StringDedupQueue* G1StringDedupQueue::_queue = NULL;

    37 const size_t        G1StringDedupQueue::_max_size = 1000000; // Max number of elements per queue

    38 const size_t        G1StringDedupQueue::_max_cache_size = 0; // Max cache size per queue

    39 

    40 G1StringDedupQueue::G1StringDedupQueue() :

    41   _cursor(0),

    42   _cancel(false),

    43   _empty(true),

    44   _dropped(0) {

    45   _nqueues = MAX2(ParallelGCThreads, (size_t)1);

    46   _queues = NEW_C_HEAP_ARRAY(G1StringDedupWorkerQueue, _nqueues, mtGC);

    47   for (size_t i = 0; i < _nqueues; i++) {

    48     new (_queues + i) G1StringDedupWorkerQueue(G1StringDedupWorkerQueue::default_segment_size(), _max_cache_size, _max_size);

    49   }

    50 }

    51 

    52 G1StringDedupQueue::~G1StringDedupQueue() {

    53   ShouldNotReachHere();

    54 }

    55 

    56 void G1StringDedupQueue::create() {

    57   assert(_queue == NULL, "One string deduplication queue allowed");

    58   _queue = new G1StringDedupQueue();

    59 }

    60 

    61 void G1StringDedupQueue::wait() {

    62   MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);

    63   while (_queue->_empty && !_queue->_cancel) {

    64     ml.wait(Mutex::_no_safepoint_check_flag);

    65   }

    66 }

    67 

    68 void G1StringDedupQueue::cancel_wait() {

    69   MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);

    70   _queue->_cancel = true;

    71   ml.notify();

    72 }

    73 

    74 void G1StringDedupQueue::push(uint worker_id, oop java_string) {

    75   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");

    76   assert(worker_id < _queue->_nqueues, "Invalid queue");

    77 

    78   // Push and notify waiter

    79   G1StringDedupWorkerQueue& worker_queue = _queue->_queues[worker_id];

    80   if (!worker_queue.is_full()) {

    81     worker_queue.push(java_string);

    82     if (_queue->_empty) {

    83       MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);

    84       if (_queue->_empty) {

    85         // Mark non-empty and notify waiter

    86         _queue->_empty = false;

    87         ml.notify();

    88       }

    89     }

    90   } else {

    91     // Queue is full, drop the string and update the statistics

    92     Atomic::inc_ptr(&_queue->_dropped);

    93   }

    94 }

    95 

    96 oop G1StringDedupQueue::pop() {

    97   assert(!SafepointSynchronize::is_at_safepoint(), "Must not be at safepoint");

    98   No_Safepoint_Verifier nsv;

    99 

   100   // Try all queues before giving up

   101   for (size_t tries = 0; tries < _queue->_nqueues; tries++) {

   102     // The cursor indicates where we left of last time

   103     G1StringDedupWorkerQueue* queue = &_queue->_queues[_queue->_cursor];

   104     while (!queue->is_empty()) {

   105       oop obj = queue->pop();

   106       // The oop we pop can be NULL if it was marked

   107       // dead. Just ignore those and pop the next oop.

   108       if (obj != NULL) {

   109         return obj;

   110       }

   111     }

   112 

   113     // Try next queue

   114     _queue->_cursor = (_queue->_cursor + 1) % _queue->_nqueues;

   115   }

   116 

   117   // Mark empty

   118   _queue->_empty = true;

   119 

   120   return NULL;

   121 }

   122 

   123 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl) {

   124   // A worker thread first claims a queue, which ensures exclusive

   125   // access to that queue, then continues to process it.

   126   for (;;) {

   127     // Grab next queue to scan

   128     size_t queue = cl->claim_queue();

   129     if (queue >= _queue->_nqueues) {

   130       // End of queues

   131       break;

   132     }

   133 

   134     // Scan the queue

   135     unlink_or_oops_do(cl, queue);

   136   }

   137 }

   138 

   139 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) {

   140   assert(queue < _queue->_nqueues, "Invalid queue");

   141   StackIterator<oop, mtGC> iter(_queue->_queues[queue]);

   142   while (!iter.is_empty()) {

   143     oop* p = iter.next_addr();

   144     if (*p != NULL) {

   145       if (cl->is_alive(*p)) {

   146         cl->keep_alive(p);

   147       } else {

   148         // Clear dead reference

   149         *p = NULL;

   150       }

   151     }

   152   }

   153 }

   154 

   155 void G1StringDedupQueue::print_statistics(outputStream* st) {

   156   st->print_cr(

   157     "   [Queue]\n"

   158     "      [Dropped: "UINTX_FORMAT"]", _queue->_dropped);

   159 }

   160 

   161 void G1StringDedupQueue::verify() {

   162   for (size_t i = 0; i < _queue->_nqueues; i++) {

   163     StackIterator<oop, mtGC> iter(_queue->_queues[i]);

   164     while (!iter.is_empty()) {

   165       oop obj = iter.next();

   166       if (obj != NULL) {

   167         guarantee(G1CollectedHeap::heap()->is_in_reserved(obj), "Object must be on the heap");

   168         guarantee(!obj->is_forwarded(), "Object must not be forwarded");

   169         guarantee(java_lang_String::is_instance(obj), "Object must be a String");

   170       }

   171     }

   172   }

   173 }