private unsafe Task WriteAsyncInternalCore(ReadOnlyMemory <byte> source, CancellationToken cancellationToken)
{
if (!CanWrite)
{
ThrowHelper.ThrowNotSupportedException_UnwritableStream();
}
Debug.Assert(!_fileHandle.IsClosed, "!_handle.IsClosed");
// Create and store async stream class library specific data in the async result
FileStreamCompletionSource completionSource = FileStreamCompletionSource.Create(this, _preallocatedOverlapped, 0, source);
NativeOverlapped * intOverlapped = completionSource.Overlapped;
long positionBefore = _filePosition;
if (CanSeek)
{
// Now set the position to read from in the NativeOverlapped struct
// For pipes, we should leave the offset fields set to 0.
intOverlapped->OffsetLow = (int)positionBefore;
intOverlapped->OffsetHigh = (int)(positionBefore >> 32);
// When using overlapped IO, the OS is not supposed to
// touch the file pointer location at all. We will adjust it
// ourselves, but only in memory. This isn't threadsafe.
_filePosition += source.Length;
UpdateLengthOnChangePosition();
}
// queue an async WriteFile operation and pass in a packed overlapped
int r = FileStreamHelpers.WriteFileNative(_fileHandle, source.Span, false, intOverlapped, out int errorCode);
// WriteFile, the OS version, will return 0 on failure. But
// my WriteFileNative wrapper returns -1. My wrapper will return
// the following:
// On error, r==-1.
// On async requests that are still pending, r==-1 w/ errorCode==ERROR_IO_PENDING
// On async requests that completed sequentially, r==0
// You will NEVER RELIABLY be able to get the number of bytes
// written back from this call when using overlapped IO! You must
// not pass in a non-null lpNumBytesWritten to WriteFile when using
// overlapped structures! This is ByDesign NT behavior.
if (r == -1)
{
// For pipes, when they are closed on the other side, they will come here.
if (errorCode == ERROR_NO_DATA)
{
// Not an error, but EOF. AsyncFSCallback will NOT be called.
// Completing TCS and return cached task allowing the GC to collect TCS.
completionSource.SetCompletedSynchronously(0);
return(Task.CompletedTask);
}
else if (errorCode != ERROR_IO_PENDING)
{
if (!_fileHandle.IsClosed && CanSeek) // Update Position - It could be anywhere.
{
_filePosition = positionBefore;
}
completionSource.ReleaseNativeResource();
if (errorCode == ERROR_HANDLE_EOF)
{
ThrowHelper.ThrowEndOfFileException();
}
else
{
throw Win32Marshal.GetExceptionForWin32Error(errorCode, _path);
}
}
else if (cancellationToken.CanBeCanceled) // ERROR_IO_PENDING
{
// Only once the IO is pending do we register for cancellation
completionSource.RegisterForCancellation(cancellationToken);
}
}
else
{
// Due to a workaround for a race condition in NT's ReadFile &
// WriteFile routines, we will always be returning 0 from WriteFileNative
// when we do async IO instead of the number of bytes written,
// irregardless of whether the operation completed
// synchronously or asynchronously. We absolutely must not
// set asyncResult._numBytes here, since will never have correct
// results.
}
return(completionSource.Task);
}
private unsafe Task <int> ReadAsyncInternal(Memory <byte> destination, CancellationToken cancellationToken = default)
{
if (!CanRead)
{
ThrowHelper.ThrowNotSupportedException_UnreadableStream();
}
Debug.Assert(!_fileHandle.IsClosed, "!_handle.IsClosed");
// Create and store async stream class library specific data in the async result
FileStreamCompletionSource completionSource = FileStreamCompletionSource.Create(this, _preallocatedOverlapped, 0, destination);
NativeOverlapped * intOverlapped = completionSource.Overlapped;
// Calculate position in the file we should be at after the read is done
long positionBefore = _filePosition;
if (CanSeek)
{
long len = Length;
if (positionBefore + destination.Length > len)
{
if (positionBefore <= len)
{
destination = destination.Slice(0, (int)(len - positionBefore));
}
else
{
destination = default;
}
}
// Now set the position to read from in the NativeOverlapped struct
// For pipes, we should leave the offset fields set to 0.
intOverlapped->OffsetLow = unchecked ((int)positionBefore);
intOverlapped->OffsetHigh = (int)(positionBefore >> 32);
// When using overlapped IO, the OS is not supposed to
// touch the file pointer location at all. We will adjust it
// ourselves, but only in memory. This isn't threadsafe.
_filePosition += destination.Length;
}
// queue an async ReadFile operation and pass in a packed overlapped
int r = FileStreamHelpers.ReadFileNative(_fileHandle, destination.Span, false, intOverlapped, out int errorCode);
// ReadFile, the OS version, will return 0 on failure. But
// my ReadFileNative wrapper returns -1. My wrapper will return
// the following:
// On error, r==-1.
// On async requests that are still pending, r==-1 w/ errorCode==ERROR_IO_PENDING
// on async requests that completed sequentially, r==0
// You will NEVER RELIABLY be able to get the number of bytes
// read back from this call when using overlapped structures! You must
// not pass in a non-null lpNumBytesRead to ReadFile when using
// overlapped structures! This is by design NT behavior.
if (r == -1)
{
// For pipes, when they hit EOF, they will come here.
if (errorCode == ERROR_BROKEN_PIPE)
{
// Not an error, but EOF. AsyncFSCallback will NOT be
// called. Call the user callback here.
// We clear the overlapped status bit for this special case.
// Failure to do so looks like we are freeing a pending overlapped later.
intOverlapped->InternalLow = IntPtr.Zero;
completionSource.SetCompletedSynchronously(0);
}
else if (errorCode != ERROR_IO_PENDING)
{
if (!_fileHandle.IsClosed && CanSeek) // Update Position - It could be anywhere.
{
_filePosition = positionBefore;
}
completionSource.ReleaseNativeResource();
if (errorCode == ERROR_HANDLE_EOF)
{
ThrowHelper.ThrowEndOfFileException();
}
else
{
throw Win32Marshal.GetExceptionForWin32Error(errorCode, _path);
}
}
else if (cancellationToken.CanBeCanceled) // ERROR_IO_PENDING
{
// Only once the IO is pending do we register for cancellation
completionSource.RegisterForCancellation(cancellationToken);
}
}
else
{
// Due to a workaround for a race condition in NT's ReadFile &
// WriteFile routines, we will always be returning 0 from ReadFileNative
// when we do async IO instead of the number of bytes read,
// irregardless of whether the operation completed
// synchronously or asynchronously. We absolutely must not
// set asyncResult._numBytes here, since will never have correct
// results.
}
return(completionSource.Task);
}