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