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 "logging/log.hpp"
  32 #include "oops/oop.inline.hpp"
  33 #include "runtime/atomic.inline.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   No_Safepoint_Verifier 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_trace(gc, stringdedup)(
 158     "   [Queue]\n"
 159     "      [Dropped: " UINTX_FORMAT "]", _queue->_dropped);
 160 }
 161 
 162 void G1StringDedupQueue::verify() {
 163   for (size_t i = 0; i < _queue->_nqueues; i++) {
 164     StackIterator<oop, mtGC> iter(_queue->_queues[i]);
 165     while (!iter.is_empty()) {
 166       oop obj = iter.next();
 167       if (obj != NULL) {
 168         guarantee(G1CollectedHeap::heap()->is_in_reserved(obj), "Object must be on the heap");
 169         guarantee(!obj->is_forwarded(), "Object must not be forwarded");
 170         guarantee(java_lang_String::is_instance(obj), "Object must be a String");
 171       }
 172     }
 173   }
 174 }
--- EOF ---