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#include "spin_wait.h"
#include <util/datetime/base.h>
#include <util/system/compiler.h>
#include <atomic>
namespace NYT::NThreading {
////////////////////////////////////////////////////////////////////////////////
static constexpr int SpinIterationCount = 1000;
namespace {
TDuration SuggestSleepDelay(int iteration)
{
static std::atomic<ui64> Rand;
auto rand = Rand.load(std::memory_order::relaxed);
rand = 0x5deece66dLL * rand + 0xb; // numbers from nrand48()
Rand.store(rand, std::memory_order::relaxed);
constexpr ui64 MinDelayUs = 128;
// Double delay every 8 iterations, up to 16x (2ms).
if (iteration > 32) {
iteration = 32;
}
ui64 delayUs = MinDelayUs << (iteration / 8);
// Randomize in delay..2*delay range, for resulting 128us..4ms range.
delayUs = delayUs | ((delayUs - 1) & rand);
return TDuration::MicroSeconds(delayUs);
}
} // namespace
////////////////////////////////////////////////////////////////////////////////
TSpinWait::TSpinWait(
const TSourceLocation& location,
ESpinLockActivityKind activityKind)
: Location_(location)
, ActivityKind_(activityKind)
{ }
TSpinWait::~TSpinWait()
{
if (SlowPathStartInstant_ >= 0) {
auto cpuDelay = GetCpuInstant() - SlowPathStartInstant_;
InvokeSpinWaitSlowPathHooks(cpuDelay, Location_, ActivityKind_);
}
}
void TSpinWait::Wait()
{
if (Y_LIKELY(SpinIteration_++ < SpinIterationCount)) {
return;
}
SpinIteration_ = 0;
if (SlowPathStartInstant_ < 0) {
SlowPathStartInstant_ = GetCpuInstant();
}
Sleep(SuggestSleepDelay(SleepIteration_++));
}
////////////////////////////////////////////////////////////////////////////////
} // namespace NYT::NThreading
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