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