1 /*

     2  * Copyright (c) 2014, 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 "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 "logging/log.hpp"

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

    33 #include "runtime/atomic.hpp"

    34 #include "runtime/mutexLocker.hpp"

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

    36 

    37 G1StringDedupQueue* G1StringDedupQueue::_queue = NULL;

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

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

    40 

    41 G1StringDedupQueue::G1StringDedupQueue() :

    42   _cursor(0),

    43   _cancel(false),

    44   _empty(true),

    45   _dropped(0) {

    46   _nqueues = ParallelGCThreads;

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

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

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

    50   }

    51 }

    52 

    53 G1StringDedupQueue::~G1StringDedupQueue() {

    54   ShouldNotReachHere();

    55 }

    56 

    57 void G1StringDedupQueue::create() {

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

    59   _queue = new G1StringDedupQueue();

    60 }

    61 

    62 void G1StringDedupQueue::wait() {

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

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

    65     ml.wait(Mutex::_no_safepoint_check_flag);

    66   }

    67 }

    68 

    69 void G1StringDedupQueue::cancel_wait() {

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

    71   _queue->_cancel = true;

    72   ml.notify();

    73 }

    74 

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

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

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

    78 

    79   // Push and notify waiter

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

    81   if (!worker_queue.is_full()) {

    82     worker_queue.push(java_string);

    83     if (_queue->_empty) {

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

    85       if (_queue->_empty) {

    86         // Mark non-empty and notify waiter

    87         _queue->_empty = false;

    88         ml.notify();

    89       }

    90     }

    91   } else {

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

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

    94   }

    95 }

    96 

    97 oop G1StringDedupQueue::pop() {

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

    99   NoSafepointVerifier nsv;

   100 

   101   // Try all queues before giving up

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

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

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

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

   106       oop obj = queue->pop();

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

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

   109       if (obj != NULL) {

   110         return obj;

   111       }

   112     }

   113 

   114     // Try next queue

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

   116   }

   117 

   118   // Mark empty

   119   _queue->_empty = true;

   120 

   121   return NULL;

   122 }

   123 

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

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

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

   127   for (;;) {

   128     // Grab next queue to scan

   129     size_t queue = cl->claim_queue();

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

   131       // End of queues

   132       break;

   133     }

   134 

   135     // Scan the queue

   136     unlink_or_oops_do(cl, queue);

   137   }

   138 }

   139 

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

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

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

   143   while (!iter.is_empty()) {

   144     oop* p = iter.next_addr();

   145     if (*p != NULL) {

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

   147         cl->keep_alive(p);

   148       } else {

   149         // Clear dead reference

   150         *p = NULL;

   151       }

   152     }

   153   }

   154 }

   155 

   156 void G1StringDedupQueue::print_statistics() {

   157   log_debug(gc, stringdedup)("  Queue");

   158   log_debug(gc, stringdedup)("    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 }