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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