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 = ParallelGCThreads;
  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 }
--- EOF ---