1/*
2 * Copyright (c) 2018, 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 "utilities/globalCounter.hpp"
27#include "runtime/orderAccess.hpp"
28#include "runtime/thread.hpp"
29#include "runtime/threadSMR.inline.hpp"
30#include "runtime/vmThread.hpp"
31#include "utilities/spinYield.hpp"
32
33GlobalCounter::PaddedCounter GlobalCounter::_global_counter;
34
35class GlobalCounter::CounterThreadCheck : public ThreadClosure {
36 private:
37 uintx _gbl_cnt;
38 public:
39 CounterThreadCheck(uintx gbl_cnt) : _gbl_cnt(gbl_cnt) {}
40 void do_thread(Thread* thread) {
41 SpinYield yield;
42 // Loops on this thread until it has exited the critical read section.
43 while(true) {
44 uintx cnt = OrderAccess::load_acquire(thread->get_rcu_counter());
45 // This checks if the thread's counter is active. And if so is the counter
46 // for a pre-existing reader (belongs to this grace period). A pre-existing
47 // reader will have a lower counter than the global counter version for this
48 // generation. If the counter is larger than the global counter version this
49 // is a new reader and we can continue.
50 if (((cnt & COUNTER_ACTIVE) != 0) && (cnt - _gbl_cnt) > (max_uintx / 2)) {
51 yield.wait();
52 } else {
53 break;
54 }
55 }
56 }
57};
58
59void GlobalCounter::write_synchronize() {
60 assert((*Thread::current()->get_rcu_counter() & COUNTER_ACTIVE) == 0x0, "must be outside a critcal section");
61 // Atomic::add must provide fence since we have storeload dependency.
62 uintx gbl_cnt = Atomic::add(COUNTER_INCREMENT, &_global_counter._counter);
63
64 // Do all RCU threads.
65 CounterThreadCheck ctc(gbl_cnt);
66 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
67 ctc.do_thread(thread);
68 }
69 for (NonJavaThread::Iterator njti; !njti.end(); njti.step()) {
70 ctc.do_thread(njti.current());
71 }
72}
73