1 /*
   2  * Copyright (c) 2014, 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.hpp"
  27 #include "gc_implementation/g1/g1StringDedupQueue.hpp"
  28 #include "memory/gcLocker.hpp"
  29 #include "runtime/mutexLocker.hpp"
  30 #include "utilities/stack.inline.hpp"
  31 
  32 G1StringDedupQueue* G1StringDedupQueue::_queue = NULL;
  33 const size_t        G1StringDedupQueue::_max_size = 1000000; // Max number of elements per queue
  34 const size_t        G1StringDedupQueue::_max_cache_size = 0; // Max cache size per queue
  35 
  36 G1StringDedupQueue::G1StringDedupQueue() :
  37   _cursor(0),
  38   _cancel(false),
  39   _empty(true),
  40   _dropped(0) {
  41   _nqueues = MAX2(ParallelGCThreads, (size_t)1);
  42   _queues = NEW_C_HEAP_ARRAY(G1StringDedupWorkerQueue, _nqueues, mtGC);
  43   for (size_t i = 0; i < _nqueues; i++) {
  44     new (_queues + i) G1StringDedupWorkerQueue(G1StringDedupWorkerQueue::default_segment_size(), _max_cache_size, _max_size);
  45   }
  46 }
  47 
  48 G1StringDedupQueue::~G1StringDedupQueue() {
  49   ShouldNotReachHere();
  50 }
  51 
  52 void G1StringDedupQueue::create() {
  53   assert(_queue == NULL, "One string deduplication queue allowed");
  54   _queue = new G1StringDedupQueue();
  55 }
  56 
  57 void G1StringDedupQueue::wait() {
  58   MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
  59   while (_queue->_empty && !_queue->_cancel) {
  60     ml.wait(Mutex::_no_safepoint_check_flag);
  61   }
  62 }
  63 
  64 void G1StringDedupQueue::cancel_wait() {
  65   MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
  66   _queue->_cancel = true;
  67   ml.notify();
  68 }
  69 
  70 void G1StringDedupQueue::push(uint worker_id, oop java_string) {
  71   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
  72   assert(worker_id < _queue->_nqueues, "Invalid queue");
  73 
  74   // Push and notify waiter
  75   G1StringDedupWorkerQueue& worker_queue = _queue->_queues[worker_id];
  76   if (!worker_queue.is_full()) {
  77     worker_queue.push(java_string);
  78     if (_queue->_empty) {
  79       MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
  80       if (_queue->_empty) {
  81         // Mark non-empty and notify waiter
  82         _queue->_empty = false;
  83         ml.notify();
  84       }
  85     }
  86   } else {
  87     // Queue is full, drop the string and update the statistics
  88     Atomic::inc_ptr(&_queue->_dropped);
  89   }
  90 }
  91 
  92 oop G1StringDedupQueue::pop() {
  93   assert(!SafepointSynchronize::is_at_safepoint(), "Must not be at safepoint");
  94   No_Safepoint_Verifier nsv;
  95 
  96   // Try all queues before giving up
  97   for (size_t tries = 0; tries < _queue->_nqueues; tries++) {
  98     // The cursor indicates where we left of last time
  99     G1StringDedupWorkerQueue* queue = &_queue->_queues[_queue->_cursor];
 100     while (!queue->is_empty()) {
 101       oop obj = queue->pop();
 102       // The oop we pop can be NULL if it was marked
 103       // dead. Just ignore those and pop the next oop.
 104       if (obj != NULL) {
 105         return obj;
 106       }
 107     }
 108 
 109     // Try next queue
 110     _queue->_cursor = (_queue->_cursor + 1) % _queue->_nqueues;
 111   }
 112 
 113   // Mark empty
 114   _queue->_empty = true;
 115 
 116   return NULL;
 117 }
 118 
 119 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl) {
 120   // A worker thread first claims a queue, which ensures exclusive
 121   // access to that queue, then continues to process it.
 122   for (;;) {
 123     // Grab next queue to scan
 124     size_t queue = cl->claim_queue();
 125     if (queue >= _queue->_nqueues) {
 126       // End of queues
 127       break;
 128     }
 129 
 130     // Scan the queue
 131     unlink_or_oops_do(cl, queue);
 132   }
 133 }
 134 
 135 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) {
 136   assert(queue < _queue->_nqueues, "Invalid queue");
 137   StackIterator<oop, mtGC> iter(_queue->_queues[queue]);
 138   while (!iter.is_empty()) {
 139     oop* p = iter.next_addr();
 140     if (*p != NULL) {
 141       if (cl->is_alive(*p)) {
 142         cl->keep_alive(p);
 143       } else {
 144         // Clear dead reference
 145         *p = NULL;
 146       }
 147     }
 148   }
 149 }
 150 
 151 void G1StringDedupQueue::print_statistics(outputStream* st) {
 152   st->print_cr(
 153     "   [Queue]\n"
 154     "      [Dropped: "UINTX_FORMAT"]", _queue->_dropped);
 155 }
 156 
 157 void G1StringDedupQueue::verify() {
 158   for (size_t i = 0; i < _queue->_nqueues; i++) {
 159     StackIterator<oop, mtGC> iter(_queue->_queues[i]);
 160     while (!iter.is_empty()) {
 161       oop obj = iter.next();
 162       if (obj != NULL) {
 163         guarantee(Universe::heap()->is_in_reserved(obj), "Object must be on the heap");
 164         guarantee(!obj->is_forwarded(), "Object must not be forwarded");
 165         guarantee(java_lang_String::is_instance(obj), "Object must be a String");
 166       }
 167     }
 168   }
 169 }