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 

    43   void yield_or_sleep();

    44 

    45 public:

    46   static const uint default_spin_limit = 4096;

    47   static const uint default_yield_limit = 64;

    48 

    49   // spin_limit is ignored (treated as zero) when !os::is_MP().

    50   explicit SpinYield(uint spin_limit = default_spin_limit,

    51                      uint yield_limit = default_yield_limit);

    52 

    53   // Perform next round of delay.

    54   void wait() {

    55     // Simple policy: return immediately (spinning) configured number

    56     // of times, then switch to yield/sleep.  Future work might

    57     // provide other policies, such as (1) always spin if system is

    58     // not saturated, or (2) sleeping if yielding is ineffective.

    59     if (_spins < _spin_limit) {

    60       ++_spins;

    61       SpinPause();

    62     } else {

    63       yield_or_sleep();

    64     }

    65   }

    66 

    67   // Write information about the wait duration to s.

    68   void report(outputStream* s) const;

    69 };

    70 

    71 #endif // SHARE_UTILITIES_SPINYIELD_HPP