1 files changed, 160 insertions, 0 deletions
diff --git a/src/Ryujinx.Common/PreciseSleep/Nanosleep.cs b/src/Ryujinx.Common/PreciseSleep/Nanosleep.cs
new file mode 100644
index 00000000..67f067ae
--- /dev/null
+++ b/src/Ryujinx.Common/PreciseSleep/Nanosleep.cs
@@ -0,0 +1,160 @@
+using System;
+using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
+
+namespace Ryujinx.Common.PreciseSleep
+{
+    /// <summary>
+    /// Access to Linux/MacOS nanosleep, with platform specific bias to improve precision.
+    /// </summary>
+    [SupportedOSPlatform("macos")]
+    [SupportedOSPlatform("linux")]
+    [SupportedOSPlatform("android")]
+    [SupportedOSPlatform("ios")]
+    internal static partial class Nanosleep
+    {
+        private const long LinuxBaseNanosleepBias = 50000; // 0.05ms
+
+        // Penalty for max allowed sleep duration
+        private const long LinuxNanosleepAccuracyPenaltyThreshold = 200000; // 0.2ms
+        private const long LinuxNanosleepAccuracyPenalty = 30000; // 0.03ms
+
+        // Penalty for base sleep duration
+        private const long LinuxNanosleepBasePenaltyThreshold = 500000; // 0.5ms
+        private const long LinuxNanosleepBasePenalty = 30000; // 0.03ms
+        private const long LinuxNanosleepPenaltyPerMillisecond = 18000; // 0.018ms
+        private const long LinuxNanosleepPenaltyCap = 18000; // 0.018ms
+
+        private const long LinuxStrictBiasOffset = 150_000; // 0.15ms
+
+        // Nanosleep duration is biased depending on the requested timeout on MacOS.
+        // These match the results when measuring on an M1 processor at AboveNormal priority.
+        private const long MacosBaseNanosleepBias = 5000; // 0.005ms
+        private const long MacosBiasPerMillisecond = 140000; // 0.14ms
+        private const long MacosBiasMaxNanoseconds = 20_000_000; // 20ms
+        private const long MacosStrictBiasOffset = 150_000; // 0.15ms
+
+        public static long Bias { get; }
+
+        /// <summary>
+        /// Get bias for a given nanosecond timeout.
+        /// Some platforms calculate their bias differently, this method can be used to counteract it.
+        /// </summary>
+        /// <param name="timeoutNs">Nanosecond timeout</param>
+        /// <returns>Bias in nanoseconds</returns>
+        public static long GetBias(long timeoutNs)
+        {
+            if (OperatingSystem.IsMacOS() || OperatingSystem.IsIOS())
+            {
+                long biasNs = Math.Min(timeoutNs, MacosBiasMaxNanoseconds);
+                return MacosBaseNanosleepBias + biasNs * MacosBiasPerMillisecond / 1_000_000;
+            }
+            else
+            {
+                long bias = LinuxBaseNanosleepBias;
+
+                if (timeoutNs > LinuxNanosleepBasePenaltyThreshold)
+                {
+                    long penalty = (timeoutNs - LinuxNanosleepBasePenaltyThreshold) * LinuxNanosleepPenaltyPerMillisecond / 1_000_000;
+                    bias += LinuxNanosleepBasePenalty + Math.Min(LinuxNanosleepPenaltyCap, penalty);
+                }
+
+                return bias;
+            }
+        }
+
+        /// <summary>
+        /// Get a stricter bias for a given nanosecond timeout,
+        /// which can improve the chances the sleep completes before the timeout.
+        /// Some platforms calculate their bias differently, this method can be used to counteract it.
+        /// </summary>
+        /// <param name="timeoutNs">Nanosecond timeout</param>
+        /// <returns>Strict bias in nanoseconds</returns>
+        public static long GetStrictBias(long timeoutNs)
+        {
+            if (OperatingSystem.IsMacOS() || OperatingSystem.IsIOS())
+            {
+                return GetBias(timeoutNs) + MacosStrictBiasOffset;
+            }
+            else
+            {
+                long bias = GetBias(timeoutNs) + LinuxStrictBiasOffset;
+
+                if (timeoutNs > LinuxNanosleepAccuracyPenaltyThreshold)
+                {
+                    bias += LinuxNanosleepAccuracyPenalty;
+                }
+
+                return bias;
+            }
+        }
+
+        static Nanosleep()
+        {
+            Bias = GetBias(0);
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct Timespec
+        {
+            public long tv_sec;  // Seconds
+            public long tv_nsec; // Nanoseconds
+        }
+
+        [LibraryImport("libc", SetLastError = true)]
+        private static partial int nanosleep(ref Timespec req, ref Timespec rem);
+
+        /// <summary>
+        /// Convert a timeout in nanoseconds to a timespec for nanosleep.
+        /// </summary>
+        /// <param name="nanoseconds">Timeout in nanoseconds</param>
+        /// <returns>Timespec for nanosleep</returns>
+        private static Timespec GetTimespecFromNanoseconds(ulong nanoseconds)
+        {
+            return new Timespec
+            {
+                tv_sec = (long)(nanoseconds / 1_000_000_000),
+                tv_nsec = (long)(nanoseconds % 1_000_000_000)
+            };
+        }
+
+        /// <summary>
+        /// Sleep for approximately a given time period in nanoseconds.
+        /// </summary>
+        /// <param name="nanoseconds">Time to sleep for in nanoseconds</param>
+        public static void Sleep(long nanoseconds)
+        {
+            nanoseconds -= GetBias(nanoseconds);
+
+            if (nanoseconds >= 0)
+            {
+                Timespec req = GetTimespecFromNanoseconds((ulong)nanoseconds);
+                Timespec rem = new();
+
+                nanosleep(ref req, ref rem);
+            }
+        }
+
+        /// <summary>
+        /// Sleep for at most a given time period in nanoseconds.
+        /// Uses a stricter bias to wake before the requested duration.
+        /// </summary>
+        /// <remarks>
+        /// Due to OS scheduling behaviour, this timeframe may still be missed.
+        /// </remarks>
+        /// <param name="nanoseconds">Maximum allowed time for sleep</param>
+        public static void SleepAtMost(long nanoseconds)
+        {
+            // Stricter bias to ensure we wake before the timepoint.
+            nanoseconds -= GetStrictBias(nanoseconds);
+
+            if (nanoseconds >= 0)
+            {
+                Timespec req = GetTimespecFromNanoseconds((ulong)nanoseconds);
+                Timespec rem = new();
+
+                nanosleep(ref req, ref rem);
+            }
+        }
+    }
+}