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80 lines
2.5 KiB
C#
80 lines
2.5 KiB
C#
using System.Runtime.InteropServices;
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using System.Threading;
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using static Ryujinx.Common.Memory.PartialUnmaps.PartialUnmapHelpers;
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namespace Ryujinx.Common.Memory.PartialUnmaps
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{
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/// <summary>
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/// A simple implementation of a ReaderWriterLock which can be used from native code.
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/// </summary>
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[StructLayout(LayoutKind.Sequential, Pack = 4)]
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public struct NativeReaderWriterLock
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{
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public int WriteLock;
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public int ReaderCount;
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public static int WriteLockOffset;
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public static int ReaderCountOffset;
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/// <summary>
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/// Populates the field offsets for use when emitting native code.
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/// </summary>
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static NativeReaderWriterLock()
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{
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NativeReaderWriterLock instance = new NativeReaderWriterLock();
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WriteLockOffset = OffsetOf(ref instance, ref instance.WriteLock);
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ReaderCountOffset = OffsetOf(ref instance, ref instance.ReaderCount);
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}
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/// <summary>
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/// Acquires the reader lock.
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/// </summary>
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public void AcquireReaderLock()
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{
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// Must take write lock for a very short time to become a reader.
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while (Interlocked.CompareExchange(ref WriteLock, 1, 0) != 0) { }
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Interlocked.Increment(ref ReaderCount);
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Interlocked.Exchange(ref WriteLock, 0);
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}
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/// <summary>
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/// Releases the reader lock.
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/// </summary>
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public void ReleaseReaderLock()
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{
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Interlocked.Decrement(ref ReaderCount);
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}
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/// <summary>
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/// Upgrades to a writer lock. The reader lock is temporarily released while obtaining the writer lock.
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/// </summary>
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public void UpgradeToWriterLock()
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{
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// Prevent any more threads from entering reader.
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// If the write lock is already taken, wait for it to not be taken.
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Interlocked.Decrement(ref ReaderCount);
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while (Interlocked.CompareExchange(ref WriteLock, 1, 0) != 0) { }
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// Wait for reader count to drop to 0, then take the lock again as the only reader.
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while (Interlocked.CompareExchange(ref ReaderCount, 1, 0) != 0) { }
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}
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/// <summary>
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/// Downgrades from a writer lock, back to a reader one.
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/// </summary>
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public void DowngradeFromWriterLock()
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{
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// Release the WriteLock.
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Interlocked.Exchange(ref WriteLock, 0);
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}
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}
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}
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