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Allocate the segment array from native memory and at TryPrepareScatte…
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…rGatherBuffers.
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@teo-tsirpanis
teo-tsirpanis committed Aug 15, 2021
1 parent a160f1d commit 656adf6
Showing 1 changed file with 33 additions and 90 deletions.
123 changes: 33 additions & 90 deletions src/libraries/System.Private.CoreLib/src/System/IO/RandomAccess.Windows.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -433,22 +433,9 @@ private static ValueTask<long> ReadScatterAtOffsetAsync(SafeFileHandle handle, I
}

if (CanUseScatterGatherWindowsAPIs(handle)
&& TryPrepareScatterGatherBuffers(buffers, default(MemoryHandler), out MemoryHandle[]? pinnedBuffers, out int totalBytes))
&& TryPrepareScatterGatherBuffers(buffers, default(MemoryHandler), out MemoryHandle[] handlesToDispose, out IntPtr segmentsPtr, out int totalBytes))
{
try
{
return ReadScatterAtOffsetSingleSyscallAsync(handle, pinnedBuffers, fileOffset, totalBytes,
cancellationToken);
}
catch
{
foreach (MemoryHandle memoryHandle in pinnedBuffers)
{
memoryHandle.Dispose();
}

throw;
}
return ReadScatterAtOffsetSingleSyscallAsync(handle, handlesToDispose, segmentsPtr, fileOffset, totalBytes, cancellationToken);
}

return ReadScatterAtOffsetMultipleSyscallsAsync(handle, buffers, fileOffset, cancellationToken);
Expand Down Expand Up @@ -477,11 +464,6 @@ private struct ReadOnlyMemoryHandler : IMemoryHandler<ReadOnlyMemory<byte>>
public MemoryHandle Pin(in ReadOnlyMemory<byte> memory) => memory.Pin();
}

// GCHandle.AddrOfPinnedObject performs some checks that are not
// necessary since we know we have pinned a specific SZArray.
private static unsafe IntPtr AddrOfPinnedArray<T>(T[] array) =>
(IntPtr) Unsafe.AsPointer(ref MemoryMarshal.GetArrayDataReference(array));

// From https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-readfilescatter:
// "The file handle must be created with [...] the FILE_FLAG_OVERLAPPED and FILE_FLAG_NO_BUFFERING flags."
private static bool CanUseScatterGatherWindowsAPIs(SafeFileHandle handle)
Expand All @@ -497,20 +479,27 @@ private static bool CanUseScatterGatherWindowsAPIs(SafeFileHandle handle)
// 3. not bigger than 2^32 - 1 in total
// This function is also responsible for pinning the buffers if they
// are suitable and they must be unpinned after the I/O operation completes.
// The total size of the buffers is also returned.
private static bool TryPrepareScatterGatherBuffers<T, THandler>(IReadOnlyList<T> buffers,
THandler handler, [NotNullWhen(true)] out MemoryHandle[]? pinnedBuffers, out int totalBytes)
// It also returns a pointer with the segments to be passed to the Windows API and to be
// freed by NativeMemory.Free, and the total size of the buffers that is needed as well.
private static unsafe bool TryPrepareScatterGatherBuffers<T, THandler>(IReadOnlyList<T> buffers,
THandler handler, out MemoryHandle[] handlesToDispose, out IntPtr segmentsPtr, out int totalBytes)
where THandler: struct, IMemoryHandler<T>
{
int pageSize = Environment.SystemPageSize;
Debug.Assert(BitOperations.IsPow2(pageSize), "Page size is not a power of two.");
// We take advantage of the fact that the page size is
// a power of two to avoid an expensive modulo operation.
long alignedAtPageSizeMask = pageSize - 1;

int buffersCount = buffers.Count;
pinnedBuffers = new MemoryHandle[buffersCount];
handlesToDispose = new MemoryHandle[buffersCount];
segmentsPtr = IntPtr.Zero;
totalBytes = 0;

// "The array must contain enough elements to store nNumberOfBytesToWrite bytes of data, and one element for the terminating NULL. "
long* segmentsArray = (long*) NativeMemory.Alloc((nuint)(buffersCount + 1), sizeof(long));
segmentsArray[buffersCount] = 0;

bool success = false;
try
{
Expand All @@ -525,16 +514,15 @@ private static bool TryPrepareScatterGatherBuffers<T, THandler>(IReadOnlyList<T>
return false;
}

MemoryHandle handle = pinnedBuffers[i] = handler.Pin(in buffer);
unsafe
MemoryHandle handle = handlesToDispose[i] = handler.Pin(in buffer);
long ptr = segmentsArray[i] = (long)handle.Pointer;
if ((ptr & alignedAtPageSizeMask) != 0)
{
if (((long)handle.Pointer & alignedAtPageSizeMask) != 0)
{
return false;
}
return false;
}
}

segmentsPtr = (IntPtr)segmentsArray;
totalBytes = (int)totalBytes64;
success = true;
return true;
Expand All @@ -543,47 +531,32 @@ private static bool TryPrepareScatterGatherBuffers<T, THandler>(IReadOnlyList<T>
{
if (!success)
{
foreach (MemoryHandle handle in pinnedBuffers)
foreach (MemoryHandle handle in handlesToDispose)
{
handle.Dispose();
}

NativeMemory.Free(segmentsArray);
}
}
}

private static async ValueTask<long> ReadScatterAtOffsetSingleSyscallAsync(SafeFileHandle handle, MemoryHandle[] pinnedBuffers, long fileOffset, int totalBytes, CancellationToken cancellationToken)
private static async ValueTask<long> ReadScatterAtOffsetSingleSyscallAsync(SafeFileHandle handle, MemoryHandle[] handlesToDispose, IntPtr segmentsPtr, long fileOffset, int totalBytes, CancellationToken cancellationToken)
{
int buffersCount = pinnedBuffers.Length;
// "The array must contain enough elements to store nNumberOfBytesToWrite bytes of data, and one element for the terminating NULL. "
long[] fileSegments = new long[buffersCount + 1];
fileSegments[buffersCount] = 0;

GCHandle pinnedSegments = default;

try
{
pinnedSegments = GCHandle.Alloc(fileSegments, GCHandleType.Pinned);

for (int i = 0; i < buffersCount; i++)
{
unsafe // awaits can't be in an unsafe context
{
fileSegments[i] = new IntPtr(pinnedBuffers[i].Pointer).ToInt64();
}
}

return await ReadFileScatterAsync(handle, AddrOfPinnedArray(fileSegments), totalBytes, fileOffset, cancellationToken).ConfigureAwait(false);
return await ReadFileScatterAsync(handle, segmentsPtr, totalBytes, fileOffset, cancellationToken).ConfigureAwait(false);
}
finally
{
foreach (MemoryHandle memoryHandle in pinnedBuffers)
foreach (MemoryHandle memoryHandle in handlesToDispose)
{
memoryHandle.Dispose();
}

if (pinnedSegments.IsAllocated)
unsafe
{
pinnedSegments.Free();
NativeMemory.Free(segmentsPtr.ToPointer());
}
}
}
Expand Down Expand Up @@ -673,22 +646,9 @@ private static ValueTask WriteGatherAtOffsetAsync(SafeFileHandle handle, IReadOn
}

if (CanUseScatterGatherWindowsAPIs(handle)
&& TryPrepareScatterGatherBuffers(buffers, default(ReadOnlyMemoryHandler), out MemoryHandle[]? pinnedBuffers, out int totalBytes))
&& TryPrepareScatterGatherBuffers(buffers, default(ReadOnlyMemoryHandler), out MemoryHandle[] handlesToDispose, out IntPtr segmentsPtr, out int totalBytes))
{
try
{
return WriteGatherAtOffsetSingleSyscallAsync(handle, pinnedBuffers, fileOffset, totalBytes,
cancellationToken);
}
catch
{
foreach (MemoryHandle memoryHandle in pinnedBuffers)
{
memoryHandle.Dispose();
}

throw;
}
return WriteGatherAtOffsetSingleSyscallAsync(handle, handlesToDispose, segmentsPtr, fileOffset, totalBytes, cancellationToken);
}

return WriteGatherAtOffsetMultipleSyscallsAsync(handle, buffers, fileOffset, cancellationToken);
Expand All @@ -706,39 +666,22 @@ private static async ValueTask WriteGatherAtOffsetMultipleSyscallsAsync(SafeFile
}
}

private static async ValueTask WriteGatherAtOffsetSingleSyscallAsync(SafeFileHandle handle, MemoryHandle[] pinnedBuffers, long fileOffset, int totalBytes, CancellationToken cancellationToken)
private static async ValueTask WriteGatherAtOffsetSingleSyscallAsync(SafeFileHandle handle, MemoryHandle[] handlesToDispose, IntPtr segmentsPtr, long fileOffset, int totalBytes, CancellationToken cancellationToken)
{
// "The array must contain enough elements to store nNumberOfBytesToWrite bytes of data, and one element for the terminating NULL. "
int buffersCount = pinnedBuffers.Length;
long[] fileSegments = new long[buffersCount + 1];
fileSegments[buffersCount] = 0;

GCHandle pinnedSegments = default;

try
{
pinnedSegments = GCHandle.Alloc(fileSegments, GCHandleType.Pinned);

for (int i = 0; i < buffersCount; i++)
{
unsafe // awaits can't be in an unsafe context
{
fileSegments[i] = new IntPtr(pinnedBuffers[i].Pointer).ToInt64();
}
}

await WriteFileGatherAsync(handle, AddrOfPinnedArray(fileSegments), totalBytes, fileOffset, cancellationToken).ConfigureAwait(false);
await WriteFileGatherAsync(handle, segmentsPtr, totalBytes, fileOffset, cancellationToken).ConfigureAwait(false);
}
finally
{
foreach (MemoryHandle memoryHandle in pinnedBuffers)
foreach (MemoryHandle memoryHandle in handlesToDispose)
{
memoryHandle.Dispose();
}

if (pinnedSegments.IsAllocated)
unsafe
{
pinnedSegments.Free();
NativeMemory.Free(segmentsPtr.ToPointer());
}
}
}
Expand Down

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