// When doing IO asynchronously (i.e. _isAsync==true), this callback is
// called by a free thread in the threadpool when the IO operation
// completes.
internal static void IOCallback(uint errorCode, uint numBytes, NativeOverlapped *pOverlapped)
{
// Extract the completion source from the overlapped. The state in the overlapped
// will either be a FileStreamStrategy (in the case where the preallocated overlapped was used),
// in which case the operation being completed is its _currentOverlappedOwner, or it'll
// be directly the FileStreamCompletionSource that's completing (in the case where the preallocated
// overlapped was already in use by another operation).
object?state = ThreadPoolBoundHandle.GetNativeOverlappedState(pOverlapped);
Debug.Assert(state is IFileStreamCompletionSourceStrategy || state is FileStreamCompletionSource);
FileStreamCompletionSource completionSource = state switch
{
IFileStreamCompletionSourceStrategy strategy => strategy.CurrentOverlappedOwner !, // must be owned
_ => (FileStreamCompletionSource)state
};
Debug.Assert(completionSource != null);
Debug.Assert(completionSource._overlapped == pOverlapped, "Overlaps don't match");
// Handle reading from & writing to closed pipes. While I'm not sure
// this is entirely necessary anymore, maybe it's possible for
// an async read on a pipe to be issued and then the pipe is closed,
// returning this error. This may very well be necessary.
ulong packedResult;
if (errorCode != 0 && errorCode != ERROR_BROKEN_PIPE && errorCode != ERROR_NO_DATA)
{
packedResult = ((ulong)ResultError | errorCode);
}
else
{
packedResult = ((ulong)ResultSuccess | numBytes);
}
// Stow the result so that other threads can observe it
// And, if no other thread is registering cancellation, continue
if (NoResult == Interlocked.Exchange(ref completionSource._result, (long)packedResult))
{
// Successfully set the state, attempt to take back the callback
if (Interlocked.Exchange(ref completionSource._result, CompletedCallback) != NoResult)
{
// Successfully got the callback, finish the callback
completionSource.CompleteCallback(packedResult);
}
// else: Some other thread stole the result, so now it is responsible to finish the callback
}
// else: Some other thread is registering a cancellation, so it *must* finish the callback
}
private static void Cancel(object?state)
{
// WARNING: This may potentially be called under a lock (during cancellation registration)
Debug.Assert(state is FileStreamCompletionSource, "Unknown state passed to cancellation");
FileStreamCompletionSource completionSource = (FileStreamCompletionSource)state;
Debug.Assert(completionSource._overlapped != null && !completionSource.Task.IsCompleted, "IO should not have completed yet");
// If the handle is still valid, attempt to cancel the IO
if (!completionSource._strategy.FileHandle.IsInvalid &&
!Interop.Kernel32.CancelIoEx(completionSource._strategy.FileHandle, completionSource._overlapped))
{
int errorCode = Marshal.GetLastWin32Error();
// ERROR_NOT_FOUND is returned if CancelIoEx cannot find the request to cancel.
// This probably means that the IO operation has completed.
if (errorCode != Interop.Errors.ERROR_NOT_FOUND)
{
throw Win32Marshal.GetExceptionForWin32Error(errorCode);
}
}
}
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);
}
