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.
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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 *
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23 */
24
25#ifndef SHARE_UTILITIES_SPINYIELD_HPP
26#define SHARE_UTILITIES_SPINYIELD_HPP
27
28#include "memory/allocation.hpp"
29#include "utilities/globalDefinitions.hpp"
30#include "utilities/ticks.hpp"
31
32class outputStream;
33
34extern "C" int SpinPause();
35
36class SpinYield : public StackObj {
37 Tickspan _sleep_time;
38 uint _spins;
39 uint _yields;
40 uint _spin_limit;
41 uint _yield_limit;
42 uint _sleep_ns;
43
44 void yield_or_sleep();
45
46public:
47 static const uint default_spin_limit = 4096;
48 static const uint default_yield_limit = 64;
49 static const uint default_sleep_ns = 1000;
50
51 // spin_limit is ignored (treated as zero) when !os::is_MP().
52 explicit SpinYield(uint spin_limit = default_spin_limit,
53 uint yield_limit = default_yield_limit,
54 uint sleep_ns = default_sleep_ns);
55
56 // Perform next round of delay.
57 void wait() {
58 // Simple policy: return immediately (spinning) configured number
59 // of times, then switch to yield/sleep. Future work might
60 // provide other policies, such as (1) always spin if system is
61 // not saturated, or (2) sleeping if yielding is ineffective.
62 if (_spins < _spin_limit) {
63 ++_spins;
64 SpinPause();
65 } else {
66 yield_or_sleep();
67 }
68 }
69
70 // Write information about the wait duration to s.
71 void report(outputStream* s) const;
72};
73
74#endif // SHARE_UTILITIES_SPINYIELD_HPP
75