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 #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 32 class outputStream; 33 34 extern "C" int SpinPause(); 35 36 class 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 46 public: 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. wait()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