_ak_atomic_spin_funcs_8h

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 // AkAtomicSpinFuncs.h
  
 // Helper functions for some simple spin-locks using atomics.
  
 #pragma once
  
 #include <AK/SoundEngine/Common/AkAtomic.h>
 #include <AK/Tools/Common/AkPlatformFuncs.h>
  
 #if defined(AK_MONITORX_SUPPORTED)
  
 #if (defined __clang__ || defined __GNUC__)
 #include <x86intrin.h>
 #elif defined(_MSC_VER)
 #include <intrin.h>
 #endif
  
 #endif // defined(AK_MONITORX_SUPPORTED)
  
 #if !defined(AK_NULL_PLATFORM)
 /// Platform-dependent helpers
 namespace AKPLATFORM
 {
 #if defined(AK_MONITORX_SUPPORTED)
     // monitorx and waitx are available on certain AMD CPUs,
     //  so we can have a custom impl of AkLimitedSpinForZero, and AkLimitedSpinToAcquire,
     // which can slightly improve performance when spinlock is tripped
  
     // Waits for a limited amount of time for in_pVal to hit zero (without yielding the thread)
     inline void AkLimitedSpinForZero(AkAtomic32* in_pVal)
     {
         AkInt64 endSpinTime = 0;
         AkInt64 currentTime = 0;
         PerformanceCounter(&endSpinTime);
         endSpinTime += AkInt64(AK::g_fFreqRatio * 0.01); // only spin for about 10us
         while (true)
         {
             // set up monitorx on pVal
             _mm_monitorx((void*)in_pVal, 0U, 0U);
             // if pval is zero, skip out
             if (AkAtomicLoad32(in_pVal) == 0)
             {
                 break;
             }
             // wait until a store to pVal occurs (or ~1us passes)
             _mm_mwaitx(2U, 0U, 1000U);
  
             // Check if we've hit the deadline for the timeout
             PerformanceCounter(&currentTime);
             if (currentTime > endSpinTime)
             {
                 break;
             }
         }
     }
  
     // Waits for a limited amount of time for in_pVal to get atomically shift from the expected value to the proposed one
     // returns true if acquisition succeeded
     inline bool AkLimitedSpinToAcquire(AkAtomic32* in_pVal, AkInt32 in_proposed, AkInt32 in_expected)
     {
         if (AkAtomicCas32(in_pVal, in_proposed, in_expected))
         {
             return true;
         }
  
         // Cas failed, start the slower evaluation
  
         AkInt64 endSpinTime = 0;
         AkInt64 currentTime = 0;
         PerformanceCounter(&endSpinTime);
         endSpinTime += AkInt64(AK::g_fFreqRatio * 0.01); // only spin for about 10us
         while (true)
         {
             // set up monitorx on pVal
             _mm_monitorx((void*)in_pVal, 0U, 0U);
             // attempt cas to acquire and if successful, skip out
             if (AkAtomicCas32(in_pVal, in_proposed, in_expected))
             {
                 return true;
             }
             // wait until a store to pVal occurs (or ~1us passes)
             _mm_mwaitx(2U, 0U, 1000U);
  
             // Check if we've hit the deadline for the timeout
             PerformanceCounter(&currentTime);
             if (currentTime > endSpinTime)
             {
                 return false;
             }
         }
     }
 #else
     // Waits for a limited amount of time for in_pVal to hit zero (without yielding the thread)
     inline void AkLimitedSpinForZero(AkAtomic32* in_pVal)
     {
         AkInt64 endSpinTime = 0;
         AkInt64 currentTime = 0;
         PerformanceCounter(&endSpinTime);
         endSpinTime += AkInt64(AK::g_fFreqRatio * 0.01); // only spin for about 10us
         while (true)
         {
             // if pval is zero, skip out
             if (AkAtomicLoad32(in_pVal) == 0)
             {
                 break;
             }
             AkSpinHint();
  
             // Check if we've hit the deadline for the timeout
             PerformanceCounter(&currentTime);
             if (currentTime > endSpinTime)
             {
                 break;
             }
         }
     }
  
     // Waits for a limited amount of time for in_pVal to get atomically shift from the expected value to the proposed one
     // returns true if acquisition succeeded
     inline bool AkLimitedSpinToAcquire(AkAtomic32* in_pVal, AkInt32 in_proposed, AkInt32 in_expected)
     {
         if (AkAtomicCas32(in_pVal, in_proposed, in_expected))
         {
             return true;
         }
  
         // Cas failed, start the slower evaluation
         AkInt64 endSpinTime = 0;
         AkInt64 currentTime = 0;
         PerformanceCounter(&endSpinTime);
         endSpinTime += AkInt64(AK::g_fFreqRatio * 0.01); // only spin for about 10us
         while (true)
         {
             // attempt cas to acquire and if successful, skip out
             if (AkAtomicCas32(in_pVal, in_proposed, in_expected))
             {
                 return true;
             }
             AkSpinHint();
  
             // Check if we've hit the deadline for the timeout
             PerformanceCounter(&currentTime);
             if (currentTime > endSpinTime)
             {
                 return false;
             }
         }
     }
 #endif // !defined(AK_MONITORX_SUPPORTED)
  
     inline void AkSpinWaitForZero(AkAtomic32* in_pVal)
     {
         if (AkAtomicLoad32(in_pVal) == 0)
         {
             return;
         }
  
         // do a limited spin on-the-spot until in_pVal hits zero
         AkLimitedSpinForZero(in_pVal);
  
         // if in_pVal is still non-zero, then the other thread is either blocked or waiting for us.  Yield for real.
         while (AkAtomicLoad32(in_pVal))
             AkThreadYield();
     }
  
     // Waits for a limited amount of time for in_pVal to get atomically shift from 0 to 1
     inline void AkSpinToAcquire(AkAtomic32* in_pVal, AkInt32 in_proposed, AkInt32 in_expected)
     {
         // do a limited spin on-the-spot until in_pVal can successfully hit 1
         // or if it fails, then the other thread is either blocked or waiting for us.  Yield for real.
         while (!AkLimitedSpinToAcquire(in_pVal, in_proposed, in_expected))
         {
             AkThreadYield();
         }
     }
 }
 #endif