1/*
2 * Copyright (c) 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 "runtime/atomic.hpp"
27#include "runtime/orderAccess.hpp"
28#include "runtime/os.hpp"
29#include "utilities/waitBarrier_generic.hpp"
30#include "utilities/spinYield.hpp"
31
32void GenericWaitBarrier::arm(int barrier_tag) {
33 assert(_barrier_tag == 0, "Already armed");
34 assert(_waiters == 0, "We left a thread hanging");
35 _barrier_tag = barrier_tag;
36 _waiters = 0;
37 OrderAccess::fence();
38}
39
40int GenericWaitBarrier::wake_if_needed() {
41 assert(_barrier_tag == 0, "Not disarmed");
42 int w = _waiters;
43 if (w == 0) {
44 // Load of _barrier_threads in caller must not pass the load of _waiters.
45 OrderAccess::loadload();
46 return 0;
47 }
48 assert(w > 0, "Bad counting");
49 // We need an exact count which never goes below zero,
50 // otherwise the semaphore may be signalled too many times.
51 if (Atomic::cmpxchg(w - 1, &_waiters, w) == w) {
52 _sem_barrier.signal();
53 return w - 1;
54 }
55 return w;
56}
57
58void GenericWaitBarrier::disarm() {
59 assert(_barrier_tag != 0, "Not armed");
60 _barrier_tag = 0;
61 // Loads of _barrier_threads/_waiters must not float above disarm store and
62 // disarm store must not sink below.
63 OrderAccess::fence();
64 int left;
65 SpinYield sp;
66 do {
67 left = GenericWaitBarrier::wake_if_needed();
68 if (left == 0 && _barrier_threads > 0) {
69 // There is no thread to wake but we still have barrier threads.
70 sp.wait();
71 }
72 // We must loop here until there are no waiters or potential waiters.
73 } while (left > 0 || _barrier_threads > 0);
74 // API specifies disarm() must provide a trailing fence.
75 OrderAccess::fence();
76}
77
78void GenericWaitBarrier::wait(int barrier_tag) {
79 assert(barrier_tag != 0, "Trying to wait on disarmed value");
80 if (barrier_tag != _barrier_tag) {
81 // API specifies wait() must provide a trailing fence.
82 OrderAccess::fence();
83 return;
84 }
85 Atomic::add(1, &_barrier_threads);
86 if (barrier_tag != 0 && barrier_tag == _barrier_tag) {
87 Atomic::add(1, &_waiters);
88 _sem_barrier.wait();
89 // We help out with posting, but we need to do so before we decrement the
90 // _barrier_threads otherwise we might wake threads up in next wait.
91 GenericWaitBarrier::wake_if_needed();
92 }
93 Atomic::add(-1, &_barrier_threads);
94}
95