1 /*
2 * Copyright (c) 2018, 2019, 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 "memory/iterator.hpp"
27 #include "runtime/atomic.hpp"
28 #include "runtime/thread.hpp"
29 #include "runtime/threadSMR.inline.hpp"
30 #include "runtime/vmThread.hpp"
31 #include "utilities/globalCounter.hpp"
32 #include "utilities/spinYield.hpp"
33
34 GlobalCounter::PaddedCounter GlobalCounter::_global_counter;
35
36 class GlobalCounter::CounterThreadCheck : public ThreadClosure {
37 private:
38 uintx _gbl_cnt;
39 public:
CounterThreadCheck(uintx gbl_cnt)40 CounterThreadCheck(uintx gbl_cnt) : _gbl_cnt(gbl_cnt) {}
do_thread(Thread * thread)41 void do_thread(Thread* thread) {
42 SpinYield yield;
43 // Loops on this thread until it has exited the critical read section.
44 while(true) {
45 uintx cnt = Atomic::load_acquire(thread->get_rcu_counter());
46 // This checks if the thread's counter is active. And if so is the counter
47 // for a pre-existing reader (belongs to this grace period). A pre-existing
48 // reader will have a lower counter than the global counter version for this
49 // generation. If the counter is larger than the global counter version this
50 // is a new reader and we can continue.
51 if (((cnt & COUNTER_ACTIVE) != 0) && (cnt - _gbl_cnt) > (max_uintx / 2)) {
52 yield.wait();
53 } else {
54 break;
55 }
56 }
57 }
58 };
59
write_synchronize()60 void GlobalCounter::write_synchronize() {
61 assert((*Thread::current()->get_rcu_counter() & COUNTER_ACTIVE) == 0x0, "must be outside a critcal section");
62 // Atomic::add must provide fence since we have storeload dependency.
63 uintx gbl_cnt = Atomic::add(&_global_counter._counter, COUNTER_INCREMENT);
64
65 // Do all RCU threads.
66 CounterThreadCheck ctc(gbl_cnt);
67 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
68 ctc.do_thread(thread);
69 }
70 for (NonJavaThread::Iterator njti; !njti.end(); njti.step()) {
71 ctc.do_thread(njti.current());
72 }
73 }
74